Factors such as nutrition, water temperature and rapid growth play a key role in bone development of Atlantic salmon.
Novel research shows that the naturally occurring level of vitamin K present in fish feed given to Atlantic salmon juveniles is sufficient for good growth and bone health from the start of feeding until smoltification.
Norway produced more than 700 000 tons of salmon in 2007. The development of bone deformities presents a challenge to the aquaculture industry. The cause is unknown, but the composition of the feed for various stages of the salmon’s lifecycle is probably a key factor.
– One theory is that vitamin K deficiencies in fish can have negative effects on bone mineralisation. Although research shows that farmed salmon get enough vitamin K through the feed from the start of feeding until they weigh around 100 grams, says Robin Ørnsrud, researcher in the seafood safety research group at the National Institute of Nutrition and Seafood research (NIFES).
New method of measuring vitamin K in feed
The vitamin K content in fish feed can vary, depending on the raw materials, and is not well documented. Synthetic vitamin K is therefore added to the fish feed, but it is unstable and can leak out in the process. After implementing a new method which few other laboratories have, NIFES is able to measure the vitamin K content in fish feed. It is common practice to state the amount of vitamin K added to commercial feed rather than document the actual amount of vitamin K present.
Substantial loss of vitamin K in the feed process
During a feeding trial extending over six months from the start of feeding, Atlantic salmon juveniles in fresh water were given a feed to which between 0 and 50 mg of synthetic vitamin K per kg of feed had been added.
– All the fish in the trial showed good growth and health. Neither X-rays nor strength tests of the spine revealed any difference among the different fish groups. In other words, even the fish that had not been given the synthetic additive received sufficient amounts of vitamin K. This indicates that salmon juveniles need a low level of vitamin K, and that the naturally occurring content of vitamin K in fish feed ingredients may be enough to maintain good fish growth and bone health, says Ørnsrud.
– There was a surprisingly substantial loss of synthetic vitamin K after the feed production process and storage. This shows how important it is to be able to analyse the vitamin level in the feed that is consumed by the Atlantic salmon, and not just state the amount of the additive. In view of the large loss of vitamin K in the process, it is difficult to conclude how much vitamin K should be added to the diet in order to meet the Atlantic salmon’s requirements, says Ørnsrud.
At present, it is recommended adding 10 mg of vitamin K per kilo of feed for salmon. By comparison, the recommended amount of vitamin K to be added for other production animals varies from 0.05 to 1.5 mg per kilo of feed.
– This trial examined the vitamin K requirement of Atlantic salmon juveniles. What the requirement is during smoltification and in the seawater phase until harvesting size is still uncertain, says Ørnsrud.
Collaborating partner: Institute of Marine Research, Norway
Norway: NIFES has analysed the content of drug residues and other undesirable substances in farmed fish. No residues of illegal drugs were found in samples of farmed fish, and the level of approved drugs and other undesirable substances was below internationally accepted limits in all species of farmed fish investigated.
NIFES`s surveillance activities document good seafood safety with respect to drug residues and other undesirable s in farmed fish.
On behalf of the Norwegian Food Safety Authority, the National Institute for Nutrition and Seafood Research (NIFES) has, under its surveillance programme for monitoring undesirable substances in farmed fish, examined the level of illegal drug residues, legally used veterinary medicines and other undesirable substances in Norwegian farmed fish. The following species were included in the surveillance programme: salmon, trout, rainbow trout, Arctic char, turbot, halibut, cod and pollack. The analyses were done on individual or pooled samples of a total of 12676 farmed fish harvested in 2009. The Norwegian Food Safety Authority was responsible for the sampling plan and the collection of samples. Samples harvested in 2009 from an extended monitoring of delousing agents in farmed fish are also included in this report.
No findings of illegal drug residues
Samples of fillets of farmed fish were taken on site by official inspectors and analysed for residues of illegal drugs. As in previous years, there were no findings of illegal drug residues in the samples of farmed fish analysed.
Approved veterinary drugs
Use of delousing agents in fish farming has recently gained much attention, and NIFES has previously published preliminary data from these analyses.
To determine the levels of approved veterinary drugs, analyses were carried out on samples of fillets taken from fish in harvesting or packing plants. As in previous years, the levels of approved veterinary drugs were below internationally established Maximum Residue Limits (MRL) in all samples examined.
A number of approved substances can be used to treat sea lice infection in farmed fish. In 2009 sample material taken from 910 fish (salmon, rainbow trout, trout, halibut and cod) was analysed for six different delousing agents: cypermethrin, deltamethrin, diflubenzuron, emamectin benzoate, ivermectin and teflubenzuron. Recently, the two delousing agents diflubenzuron and teflubenzuron have gained attention. Sample material taken from a total of 330 fish, mainly salmon, was analysed for these two delousing agents. No residues of diflubenzuron or teflubenzuron were found in any of the samples examined using methods that can identify very small concentrations, i.e. 1% of internationally accepted MRL values. Nor were there any detection of residues of the delousing agents cypermethrin, deltamethrin or ivermectin.
Emamectin benzoate is a delousing agent that is added to the fish feed. Residues of emamectin benzoate was found in 1 out of 79 samples analysed, but the concentration was low (approximately 13 μg/kilo wet weight), corresponding to 13% of the applicable EU MRL value of 100 μg/kilo wet weight for fillets. Residues of emamectin benzoate were also found in some samples of farmed salmon in 2008, but the concentrations were found to be low, the highest being 9.1 μg/kilo wet weight, corresponding to less than 10% of the applicable MRL value.
Undesirable substances
To a great extent, the level of contaminants in farmed fish fillets reflects the feed that is given to the fish. EU and Norway has set upper limit values for a number of undesirable substances in fish. Samples of farmed fish have been analysed for organic and inorganic undesirable substances, and also for selected additives which are added to fish feeds.
The figures for 2009 show that the levels of contaminants in farmed fish fillets are low compared with the EU’s upper limits for these contaminants where such limits exist. Dioxins and dioxin-like PCBs are fat soluble environmental pollutants which are found in fatty fish. Mercury is an environmental pollutant which is absorbed and stored in both fatty and low fat fish. In order to maintain food safety, it is important to monitor the level of these substances in fish for consumption. None of the samples analysed contained levels of dioxins, dioxin-like PCBs or mercury close to the EU’s upper limit values for these substances. The average level of mercury in all of the samples analysed was slightly less than 1/10 of the EU’s upper limit for mercury in fish filets, while the total content of dioxins and dioxin-like PCBs was slightly above 1/10 of the EU’s upper limit for these compounds.
In nature, environmental pollutants usually exist in mixtures, and not individually. Recent research shows that the toxicity of the environmental pollutants non-dioxin-like PCB and dioxins are altered when they appear in mixtures rather than individually.
Novel substances and products are continuously being produced and new environmental pollutants are released in nature, adding to those that already exist. Animals and humans are commonly exposed to the combined effects of these pollutants through food, air and water, and in order to protect us against environmental pollutants in food they are subject to risk assessments.
Dioxins and dioxin-like PCBs are environmental pollutants which break down slowly in nature and may have detrimental effects. Over the last 20 years attempts to combat pollution have greatly reduced the level of these substances in food products (see related information at the Norwegian Institute of Publich Health, www.folkehelseinstituttet.no).
Dioxins exist in 210 different chemical forms, with different degrees of toxicity. For some of these substances the toxicity is measured using Toxic Equivalent Factors (TEFs). TEFs gives an indication of the relative toxicity of a dioxin-like environmental pollutants compared to the dioxin compound 2,3,7,8 -TCDD, which is known to be most toxic. When mixtures of several dioxin-like environmental toxins are assessed, the concentration of each substance is multiplied by its TEF- value and the sum of these values is used as a measure of how potentially toxic the mixture is, given as the toxic equivalent (TEQ).
– The toxicity of mixtures of environmental pollutants is known to differ from the toxicity of the individual substances. Little is known about why and how dioxins and non-dioxin-like PCBs affect each other’s toxicity. We wanted to investigate this further, says researcher Pål A. Olsvik at the National Institute of Nutrition and Seafood Research (NIFES).
– Our studies showed that two specific chemical forms of dioxin were less toxic together than they were individually, while non-dioxin-like PCB and dioxin were more toxic together than they were individually.
Environmental pollutants tested on liver cells from salmon
Fact box:
What is meant by gene expression?
All cells in the body have a cell nucleus which contains DNA. The DNA contains genetic sequences which define the structure of different proteins with different functions. For a protein to be created, the DNA must undergo a process whereby the genetic sequences are transcribed to mRNA, which is transported out of the cell nucleus. The term “gene expression” means the amount of mRNA in a cell or a tissue at a given time. When mRNA is transported from the cell nucleus the transcription unit is translated to a protein. When we say that a gene is up-regulated, more of a specific mRNA that codes for a protein is produced. More of this protein will be produced, such as an intake protein, a transport protein or an enzyme. This, in turn, can affect processes in the cell and otherwise in the body.
Environmental pollutants can accumulate in fish and other animals. The liver is the fish’s main detoxification organ and the gene expression in liver cells can indicate which cellular mechanisms are affected. Liver cells from Atlantic salmon were exposed to a medium containing either non-dioxin-like PCB (PCB 138), or the dioxins pentachlorodibenzo-p-dioxin(1,2,3,7,8-PeCDD) and tetrachlorodibenzofuran (2,3,7,8,-TCDF), singularly or in a mixture. The gene expression of eight different genes involved in detoxification processes were examined (see fact box for an explanation of “gene expression”).
– Expression of the genes CYP1A and UDPGT showed that PeCDD and TCDF were less toxic at high concentrations and cells were exposed to the two substances simultaneously. Conversely, the toxicity of PCB 138 and PeCDD was greater when cells were exposed simultaneously rather than singularly.
– PCB 138 has not been assigned a TEF-value since it is not a dioxin-like PCB. The study therefore shows that in some situations the TEQ may underestimate the toxicity of compounds when they are present in a mixture.
As the study was carried out on liver cells the results are not necessarily representative for the whole fish. Likewise, changes at the mRNA level do not necessarily reflect effects on proteins in the cells. Nevertheless, the results give some indication of which mechanisms are affected in the liver cells, and in this respect cells can be used as a tool to identify possible effects before conducting studies with live animals.
– Studies which examine several environmental pollutants simultaneously are demanding and complex and more research is needed in this field of research, says Olsvik.
UK: The Institute of Aquaculture in Stirling is leading research to develop a user friendly genetic tool to monitor the health and performance of Atlantic salmon.
The project, which is described in the Institute’s latest newsletter, aims to identify the genetic basis of commercially important traits in salmon, and to develop DNA microarrays or“chips”, to monitor indicators of health and performance.
‘TRAITS’ (TRanscriptome Analysis of Important Traits in Salmon) is a four-year, collaborative research project between the Universities of Stirling, Aberdeen and Cardiff, the Roslin Institute and the Norwegian School of Veterinary Science, coordinated by Alan Teale, Professor of Molecular Genetics in the Institute,
Different aspects of the biology of salmon that are relevant in terms of the constraints on salmon aquaculture, including supply of contaminant-free oils for the salmon diet, protein growth efficiency, infectious disease, and a long and complex lifecycle, were studied.
In the last year, a preliminary chip was produced based on expressed sequence tag (EST) collections.
In essence, DNA chips enable a ‘snapshot’ of indicator biological processes within the fish to be assessed from small tissue samples. Initial results indicate that it will prove a valuable research tool, but could also benefit the salmon farming industry and restocking of wild salmon populations, the report said.
Norway: Pharmaq and the Norwegian School of Veterinary Science have identified the Pharmaq and the Norwegian School of Veterinary Science have identified the virus causing CMS of salmon.
Through this discovery more tools will become available that will make it possible to control the disease and limit the spread and the impact of the disease. PHARMAQ will explore the possibilities for developing a vaccine against CMS, a disease which currently results in significant losses for the aquaculture industry.
Cardiomyopathy syndrome of Atlantic salmon was first recorded in the mid 80’s in Norway. Economic losses are high since primarily fish at slaughter size die.
The virus was discovered through a close research collaboration between Pharmaq with project manager Marit Rode, and Professor Øystein Evensen and his research group at the Norwegian School of Veterinary Science.
– This is a result of a close and productive collaboration over many years, say the two scientists. The research program was partly funded by the Research Council of Norway.
Pål Nilsen and Dr Karine Lindmo were the main scientists at Pharmaq while Drs. Øyvind Haugland and Aase B. Mikalsen were the two scientists with strongest involvement at the Norwegian School of Veterinary Science. The focus has been to characterize the virus and study the host-pathogen interaction and development of disease.
– We have identified a new and until now unknown virus of fish and part of the genome show resemblance with viruses of the family Totiviridae, says Øyvind Haugland, and he continues: The fact that such a virus has not been described in fish before is by itself interesting, but also challenging scientifically. A related virus has earlier been identified as the cause of myonecrosis of white shrimp, but no virus of this family has been isolated from a vertebrate species before.
– Experimental challenge based on virus grown in cell culture results in pathological changes of the heart typical of CMS. Fish injected with the virus as well as cohabiting fish (with those injected) develop typical CMS changes, say Drs. Marit Rode and Øystein Evensen. The virus can be detected in the heart of clinically diseased fish and the amount of virus correlates with heart lesions.
Additional CMS research is carried out as part of a large CMS-consortium where academic and commercial partners have joined forces, including partners like Marine Harvest, AquaGen, Pharmaq, Lerøy Seafood, the National Veterinary Institute, Nofima Marine, the Norwegian School of Veterinary Science, NIFES, and Ewos Innovation. This work is co-funded by the Research Council of Norway, and the Fisheries Research Fund. The result from this collaboration will also provide applied knowledge to the aquaculture industry.
CMS has been recorded along the entire Norwegian coast, and the disease was reported from 79 different locations in 2009, close to what has been reported from previous years. The disease shows clinical manifestation throughout the year, peaking in the late fall and late winter/early spring. Accumulated mortality (by site) has been reported at 6%. CMS has also been recorded in the Faroe Islands and in Scotland.
NIFES has been monitoring the content of undesirable substances in Norwegian farmed fish since 1994. The status of samples collected in the course of 2009 shows low levels of these substances in various species of farmed fish, and a decline in total dioxins and dioxin-like PCB in farmed salmon. Monitoring thus provides documentation that farmed salmon conforms to regulations on seafood safety.
Status report on the levels of undesirable substances and drug residues in farmed fish
Chemical pollutants in farmed fish
The levels of contaminants in farmed fish fillets largely reflects the feed the fish has consumed. Commercial fish feed is regulated by EU directives which Norway also implement. Thus the EU and Norway have established maximum levels in feed for several pollutants, such as dioxins and dioxin-like PCBs and heavy metals. The Norwegian Food Safety Authority has a programme for monitoring the levels of undesirable substances in fish feed, which also covers feed ingredients, as well as a monitoring programme on drug residues and the levels of certain environmental pollutants in farmed fish.
Farmed salmon
Pollutants such as PCB7 and heavy metals in salmon fillets have been monitored for more than 10 years, while dioxins and dioxin-like PCB have been included since 2004. Documentation of the levels undesirable substances in salmon comes from two sources; one is NIFES’s surveillance programme which examines individual fish and these results can be accessed in NIFES’s searchable database (http://www.nifes.no/seafooddata), while the other is the Norwegian Food Safety Authority’s surveillance programme linked to EU Directive 96/23 (these reports can be accessed on the websites of both the Norwegian Food Safety Authority and NIFES).
The levels of pollutants in salmon fillets in 2009 were low compared with the EU’s upper limits for those pollutants where such values have been established. The level of dioxins and dioxin-like PCBs in salmon fillet is approximately 1/8 of the limit set by the EU and Norway for the legal sale of seafood, and is comparable to the levels found in oily fish species such as mackerel, spring-spawning herring and North Sea herring. As yet, no upper limit has been set for PCB7 in the Codex or by the EU or Norway, but the levels are low and largely comparable with the levels found in mackerel, spring-spawning herring and North Sea herring. As regards the presence of the heavy metals from 2009, The levels of mercury, cadmium and lead in farmed salmon, stated as a percentage of the EU’s upper limit are 6%, 4% and 3%, respectively. The levels of dioxins and dioxin-like PCBs and PCB7 have declined in recent years, while the heavy metal concentrations are low and show a stable trend.
Farmed trout
Farmed trout is included in the Norwegian Food Safety Authority’s surveillance programme and the results found for pollutants in this species are comparable with those reported above for farmed salmon.
Farmed cod
Farmed cod is a lean species with a low fat content and the levels of organic pollutants such as dioxins and PCB in the fillet are about 1/10 of the concentrations found in oily fish species , but are comparable with the levels found in wild cod. Similarly the levels of heavy metals in farmed cod are similar to those measured in wild cod.
Drug residues in farmed fish
In order to ensure that farmed fish for human consumption do not contain remnants of approved drugs, including anti-lice agents, in quantities that represent a health risk, or residues of unauthorised drugs, Norway has a system of controls that is in complete conformity with international guidelines. The system was introduced in Norway at the end of the 90s and is based on the control and registration of drug use, the establishment of retention periods which ensure that the fish cannot be harvested until a specified period has elapsed after drug treatment, and analytical controls to determine any presence of drug residues in farmed fish. Analyses of samples taken in 2009 and previous years have not shown any remnants of unauthorised drugs, or remnants of authorised drugs above internationally accepted levels. (See previous published article: Monitoring of drugs in farmed fish in 2009).
Surveillance system
Under international regulations, Norway is committed to monitor the level of certain drugs and environmental pollutants in farmed fish. These regulations also apply to all other food-producing livestock and products of animal origin. The Norwegian Food Safety Authority is responsible for sampling, wheras NIFES carries out the analyses and is responsible for reporting on issues related to farmed fish. The system is monitored by the EFTA Surveillance Authority (ESA) which ensures that EU law is correctly enforced in EFTA states. The samples taken in 2009 were from approximately 9000 farmed fish. The surveillance results are published in publicly available reports which can be accessed at www.nifes.no
Contact person:
Kåre Julshamn
Head of Research, Surveillance Research Programme
Norway: The tropical island of Mauritius in the Indian Ocean aims at increasing its fish farming activities. The National Institute of Nutrition and Seafood Research (NIFES) contributes with scientific advice in order for Mauritius to establish appropriate legislation and monitoring of both fish and feed.
Mauritius is an island of 2000 sq. km. with a population of about one million and an economic zone for sea territories covering a vast 1.9 million sq. km. The island currently has one sea bass farm and licenses have been granted for a further six farms. In 2008, Norad started a 3-year programme of co-operation between the Centre for Development Co-operation in Fisheries, the Norwegian Institute of Marine Research, the Directorate of Fisheries and the National Institute of Nutrition and Seafood Research (NIFES) on the Norwegian side, and the Ministry of Agro Industry and Fisheries (MAIF) in Mauritius. The aim of the project is to share expertise on management of fisheries and fish farming activities.
– Through several workshops NIFES will contribute with expertise within monitoring systems to assist public management in Mauritius and the establishment of monitoring systems for the island’s fish farming activities. This includes the production of fish feed, the use of therapeutics and control of residual therapeutics in fish, says researcher Bjørn Tore Lunestad, at NIFES.
Fish feed legislation
Fish from a number of countries is landed and processed in Mauritius, thus providing a stable supply of fish cuttings. NIFES and the Norwegian Institute of Marine Research have completed a workshop in Mauritius in May this year which aimed to address how to apply this raw material, which legislation to adopt and which monitoring system is the most appropriate.
– Since undesirable substances in fish feed can affect fish health and food safety, it is important to have stringent control and surveillance, and appropriate regulations, says Lunestad.
– It is also important that the fish receive good quality feed. The workshop in May also addressed the topics on fish nutrition, types of feed and feed regulations. Subsequent workshops will focus on control systems for the sale and use of therapeutic agent for aquaculture, as well as monitoring drug residues in fish.
The Norwegian Institute of Marine Research and the Directorate of Fisheries will focus on the legislative framework for the island’s fishery resources.
Seafood is naturally rich in selenium, but it may also contain the environmental pollutant methylmercury. New research indicates that methylmercury is less toxic to mice if they are simultaneously exposed to selenium.
Mercury is known to have detrimental effects on the nervous system, especially in the early phases of development of the foetus. In a study carried out by the National Institute for Nutrition and Seafood Research (NIFES) pregnant mice were fed a diet which was spiked with either methylmercury or the mineral selenium, or both. The level of methylmercury in the feed was around 100 times higher than is normally present in seafood. The results from the study showed that the mice which had been exposed to both selenium and methylmercury through the mother had a better balance than the mice that had not been given the selenium supplement. The results indicate that selenium may counteract some of the negative effects of methylmercury on the nervous system.
Selenium and methylmercury in seafood Seafood is a natural source of the mineral selenium which is important for a number of metabolic processes in the body. Mercury occurs naturally in several different chemical forms, and methlymercury is known to be one of the most toxic forms. Seafood may contain methlymercury, but usually in concentrations that are considerably lower than the EU’s upper limit for mercury. The limit is 0.5 mg per kilo of fillet for most species and 1 mg per kilo for some predatory fish species, such as tuna and Atlantic halibut. Comprehensive knowledge about the effects of environmental pollutants and is important to enable public authorities to assess seafood safety.
Based on the scientific article:
Does selenium modify neurobehavioural impacts of developmental methylmercury exposure in mice? by K. I. Folven, C. N. Glover, M. K. Malde and A.-K. Lundebye and published in “Environmental Toxicology and Pharmacology” 2009.
To successfully develop commercial diets for marine fish larvae, knowledge about how various constituents of the feed e.g. smell and taste will affect their feeding behavior is essential.
This article identifies the feed-related substances that Atlantic cod and halibut can taste and smell.
Most marine fish larvae for which attempts at intensive rearing have been made require live prey as an initial diet. Large-scale culturing of such prey is time-consuming and expensive, and this greatly increases production costs. Further, marine fishes typically exhibit low appetite to formulated feeds, resulting in slow growth rate and feed wastage. Addition of attractants and/or stimulants in feeds may motivate them to actively feed in optimum quantities. Thus, development of formulated feeds that are effectively consumed by marine fish larvae is widely considered an essential step towards cost-effective exploitation of marine fish farming. Despite significant effort on several continents, there has been limited success in producing such formulated feeds.
In order to develop a successful commercial diet for marine fish larvae, knowledge about how various constituents of the feed will affect their feeding behavior is of central importance. Certain substances might attract larvae, and motivate the feeding response. Such odors could be added to a formulated diet. Other substances might serve as repellents, and demotivate the feeding response. Such odors should be avoided in a formulated diet. Very little is known about the olfactory responses of marine fish larvae to odors. Recent reports strongly indicate that permeating formulated feeds with specific chemical odors can dramatically increase the growth rate of fish larvae. Thus, identifying substances that can motivate the feeding response of marine fish larvae holds promise for the rapid improvement of formulated feeds.
Results The project gives a lot of information which can be used to decide what substances should be included in formulated feeds in order to ensure that cod and halibut can smell and taste them.
There’s no mistake about it! Winter comes every year and to fishermen that means a couple of things.
First, the summer heat is fading away and many species of fish will be pretty active prior to the real cold temps of winter during the fall months. Secondly; it’s time to consider winterizing your boat and this includes things beyond just the batteries and fluids. It also means taking care of your electronics such as fish finders and even trolling motors.
Why take a chance on ruining a high dollar investment such as your fish finder to the cold temps and harsh weather depending on where you live? For that matter, even if you purchased a budget piece of electronics you should still want to protect it as well.
I can make this article real short by simply stating that you should follow the directions in your user manuals when it comes to winterizing. But to be honest, how many of us keep those little booklets?
Table of Contents
Isn’t my Fish Finder Weather Resistant?
For the most part the answer to the question is yes. For the sake of argument the majority of fishing electronics are built to withstand the elements when you are out on the water. A summer storm, late afternoon shower, drizzle, and fog.
Even air temperatures are taken into consideration. The problem is that those elements only last for a few minutes or hours and the actual exposure time is relatively low when you consider finding cover and wiping things down when the rain ends.
In the winter time a boat on a trailer parked in the driveway with a loose cover will face the elements for an extended period of time. Those cold and dry winter days can be mixed with moist and drizzle filled days. Think about those mornings on the lake or river when it took a second or two longer for your fish finder to seem like it was performing at a hundred percent.
That happened when you were fishing all of the time and using your equipment on a regular basis. The moisture in the air and temperature on that cool morning affected the performance of your equipment.
Now think about those conditions happening daily only you’re not in the boat to check on things and keep everything maintained. So yes, your fish finder may be weather resistant but why take a chance.
Winterizing
First, let me say that I know not every person that owns a bass boat stores it haphazardly in the driveway with loose fitting covers. Some do, some don’t, some have heated garages, some store the boats covered and protected in storage facilities at the marina. So please excuse these general guidelines. I’m just asking that when you winterize your boat’s fluids and starting batteries that you take this into consideration.
It’s a good idea to remove electronic equipment such as your fish finder from your kayak or boat and store them properly inside during long periods of time when not in use such as winter. The same goes for items such as your battery operated items, and even smaller trolling motors.
Electronics that you choose to leave on a boat that operate on batteries should have the batteries removed. This includes everything from emergency handheld radios to flashlights. Avoid the corrosion! Portable electronics should be removed and stored in their protective cases indoors as well.
There is some good news for those that don’t want to take the time to remove electronics that are tough to get to. You can store in place! If you have items that are permanently mounted, or installed and difficult to remove, it’s fine to leave them in place. Just make sure you take a minute to be sure that they are dry. You could also consider covering them with a thermal protector like you would a battery.
Don’t use plastic or like materials that could capture moisture in the air and cause condensation. I had a friend that used pieces of foam as insulation and rubber bands. He would wrap the entire console and electronics as best as possible with the foam and use rubber bands and tape to hold things in place. He would then toss a couple of moth balls in a plastic butter dish and set it in the middle of the boat before covering.
A couple of years ago he upgraded his foam insulation. “Hey Wes, I like the purple foam you’re using this year,” I said while I watched him winterize his boat. “Yep, it’s my wife’s old yoga mat!” You guessed it – he ended up buying a brand new yoga mat for his wife!
Bottom Line and Sinker!
The bottom line is that a boat and all of the electronics on it are more than just a hobby item for people that love to fish. It’s an investment and it should be properly taken care of during the winter months or when not in use for a long period of time.
When you start winterizing your boat in the traditional manner you should consider the vast number of electronics that boats are adorned with these days.
A few minutes of effort in the late fall will equal less frustration, and possibly hits to your wallet, in the spring when the fish start biting again!
Fish finders (sometimes also referred to as sounders) are great ways to help you find the right spot when out on the water in your fishing boat. They consist of two parts: a main unit (with a display) that you keep with you on the deck of the boat, and a transducer, which is connected to the main unit and is mounted on the hull.
Fish finders use sonar technology which was developed during the second world war to show what is directly below your boat. They also borrow some of their technology from fathometers, which are devices used by marine vessels to figure out how deep the water is and what potential hazards(like large rocks and corals) are below. This helps them navigate safely.
When you turn your fishfinder on, the transducer that you have mounted on the hull of your boat sends out sonar waves. These waves, like sonar waves in a radar, bump into objects in the water, as well as the waterbed, and bounce back up towards the transducer, which receives them again.
The transducer then sends the received waves up to a component in the main unit called transmitters, which measure the new sonar waves, and sends those measurements up through a wire into the main unit. The main unit then displays the readings on a screen.
Depending on how advanced your fish finder unit is, these readings are displayed either as spikes on a graph, where flat areas represent the sea bed and spikes represent objects. These objects could be fish, rocks, or conceivably anything solid somewhere in the water.
More advanced units have more sensitive transducers that are able to pick up signals and display little fish icons on the screen. They differentiate between fish and other objects by measuring how the sonar waves bounce off of the contours of the fish’s body.
Using a fishfinder can really help take a lot of the guesswork out of where to take your boat. Whether you are a professional fisherman or fish for sport and hobby, using a fish finder can really help turn a calm day out on the water into an exciting day that ends with a few trophies and a huge barbeque!
The transducer is the device that sends out and receives the echoes that your fish finder displays on its screen. It uses the same technology as SONAR. The transducer sends out waves in a cone shape underneath your boat(from wherever it is mounted). As the waves bounce back, the transducer picks them up, sends them via wire to the main fish finder unit, and the unit shows the readings in a visual form on its display.
When you buy a fish finder for the first time, a transom mount transducer is usually included. Remember: if you buy a new transducer, it has to be from the same brand, otherwise the plugs wont fit! You also need to match the transducer frequency/wattage to the finder units frequency and wattage.
The general set up for a fish finder on any boat is like this:
Transom Mount Transducers
Transom mount transducers are the transducers that usually come in the box with most of the fish finder units that we stock at Fish Finder Source. These are fitted on the boat’s transom, at a place that sits completely submerged in the water, and where it will stick a little below the hull. Transom mounts are made of plastic and are usually cheaper than other mount types.
This type of transducer is recommended for planing hulls that are less than 27 feet(8 meters). Examples of such vessels are personal craft and powerboats with outboard, inboard-outboard and jet drives.
Using them on larger or twin screw inboard boats is not a good idea because the bubbly water from the props will interrupt the signals. They don’t work too well at very high speeds, either.
This mount is ideal for trailered boats, and is very easy to install and mount.
In-Hull Mount Transducers
Transducers that have In-Hull mounts are mounted(glued or epoxied) on the inside of the hull, at a position that’s outside is always underwater.
In-hull mounts can only be used in fiberglass hulls. They will not work with metal or wood hulls as they disrupt the sonar waves. Additionally, the fiberglass hulls must be solid and have no pores or air pockets – this will further disrupt the signal.
The great part about in-hull mounts is that they can be installed AND serviced while the vessel is in the water. Since they don’t stick out of the hull, they don’t cause any extra drag in the water, they don’t accumulate marine plants and growth, and are very easy to maintain, as the unit won’t be damaged when the boat is trailered.
In hull mounts give great readings at high speeds, don’t need any holes drilled in the hull to install. The main disadvantage is that it can only be used for fiberglass hulls, and that slight disturbance can sometimes mess up the reading. Some fiberglass hulls are reinforced with balsa or some other material – this will again interrupt the signal. It is best to use a spot where there is no such reinforcement.
Through-Hull Mount Transducers
Through Hull mounts are of two kinds: flush mounts and external mounts. Flush mounts sit flush with the boat hull, and are best for smaller boats that have a minimum deadrise angle. They are used on sailing boats because they produce minimal drag.
External mounts stick out of the hull surface and normally need a fairing block to aim the SONAR beam correctly. These are generally used for larger vessels that are always in the water and not trailered. It also has to be mounted in front of the propeller and any moving gear to produce the most effective signal.
Is it always a good idea to go cheap when buying a fish finder? One side of the argument is to say “No!” You already spent a good chunk of money on a boat and it’s accessories, and you want the best of the best for your pride of the sea, right? So there’s no point skimping now. After all, how else will you reel in that trophy?
Some of you might be saying “Yes!” And for the same reason, too. You’ve already spent a good load of money on a boat, so should you spend another $1000 or more on a fish finder?
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The advantages of going cheap
In my opinion(and not just because I own this store, but because I know fish finders), the only upside to going cheap when you are buying a fish finder is that you will have a little bit more cash in your wallet than otherwise.
It’s not like a cheap fish finder will be of lesser quality than the expensive one. Humminbird, Garmin, and Lowrance take pride in their stuff and don’t (usually) make inferior fish finders.
Your fish finder, however, will be nothing special. Some of the cheapest fish finders, like the Garmin Echo 100 and the Lowrance X-4 are really, really basic.
Here’s what to expect at the most from a cheap unit:
A 3.5 inch screen (that’s just a little smaller than the screen of an iPhone 8)
A grayscale display
Basic fish finding to depths of about 100 feet
If this much is good enough for you, then by all means, go for the cheap one. However, if you need a little more oomph, you will need to shell out a little more cash.
The advantages of spending a little more
As your need for features increases, your budget will have to increase a little more, too. Let’s take a look at what additional features you can get and what their advantages are.
Color screen
A color screen is a great feature to have, for obvious reasons. If you are using traditional SONAR(arches and blobs), a color screen will give you better readings on the hardness of whatever is showing up on the screen. Darker, stronger colors usually mean harder objects, and lighter, softer colors mean softer objects.
Bigger screen sizes
If you ask me, 3.5 inches is pretty tiny, especially if you have to fit 40-50 feet of SONAR data into it. The larger your screen is, the clearer your picture will be. It’ll also be easier on your eyes. Lenny Rudow, a marine electronics pro once mentioned to me that he finds even 5 inch screens a little small. He prefers screens that are even bigger.
GPS capability
GPS is another useful feature to have. At the most basic level, GPS capability will get you the ability to set tracks and waypoints. This is a useful way to create fishing “routes” and “spots” based on SONAR data that you collect.
Getting more advanced, some units have really robust mapping packages that can stand in for any decent standalone chartplotter out on the market right now.
3D SONAR
3D SONAR is known as Down Imaging in Humminbird models and DownScan or StructureScan in Lowrance models. 3D SONAR is very useful if your style is structure fishing. While you can’t really tell what kind of structure you are seeing on traditional SONAR, with 3D SONAR, you pretty much get a picture of exactly what’s below your boat.
Networking
In really high end units, such as the Lowrance HDS and Humminbird 800 and 900 series, there are lots of networking options available. You can hook up two or more units together to share data(if you have one on the bow and one on the stern), or you can add radar, external GPS, connect your engine to see fuel data, and even control your audio system and VHF radio from the one screen. All fish finders use NMEA 2000 for data sharing, so as long as your existing peripherals support it, they should work fine.
Fishing is an exciting experience and there are so many ways through which you can catch fish. Using a cast net is one of the common methods used by most fishermen. The success of using a cast net for fishing highly depends on the way you throw the cast net.
Ideally, there are a number of ways to throw a cast net. While there is not a right or wrong way to throw a cast net, this guide will help you make the most of the fishing experience.
We have put some instructions and tips that will help you get a big catch with your cast net. There are some people who prefer to use the teeth while others use the net over the hand.
Each of these methods will work as long as you understand the basics of throwing a cast net. In this guide, we have included some instructional videos to make you understand every stage of the process.
Just like any other skill, throwing a cast net requires practice and the more you do it, the better you become. If you have tried to throw a cast net and failed, it means that you have practiced enough or lacked some basic skills.
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Essential Tips on Throwing a Cast Net
The main objective of learning how to throw a cast net is to ensure that the net opens up properly. There are so many guides on the internet, but some of them overlook the basics and at the end of it all, most people give up on this technique. Here are some tips to keep in mind, even as you are learning how to throw a cast net:
The main focus is on how you throw the net and not how hard you throw it.
Preparation of the cast net makes it easier to throw the cast net.
The setup process is as critical as the throw itself; with a good set up, the throwing will be accurate.
When throwing the net, you need to do it in a smooth motion.
Do not attempt to open the net when throwing it, the proper throw allows the net to open itself.
Your body movement is vital in making the cast net open. You will twist the upper body, while the lower body remains intact.
The more you practice, the better you become at throwing a cast net.
Steps on How to Throw a Cast Net
While these instructions are meant for right-handers, if you are left-handed, you will just need to reverse the hands. We will break this into 2 sections:
Preparing and setting up the cast net
Throwing the cast net
Preparing and Setting Up the Cast Net
Step 1
Most of the cast nets have an adjustable hand loop, which you need attach to the wrist of your left hand. This is critical as it will ensure your throw is productive.
Ensure that it is tightly secured. You should hold the cast net up in the air while it is fully extended. Shake the net so as to make the lead line around the bottom part untangled. This is essential as it will determine if the net will open completely.
Step 2
The second step is to release everything and have the hand loop on your hand only. You should not have anything else attached to the net beside the loop of the hand line.
Once this done grab the net in half and this is critical as you should not grab it too low as it may prevent it from opening as it ought to. You should find the ideal spot at the middle, which is neither too low nor too high.
Step 3
Pick the hand line and make a number of small coils of about 30 to 40 cm in your left hand. The size of the coils will depend on the size of the cast net. If you have a smaller net, then you will have fewer coils.
Take the horn of your cast net and place it on your left hand and ensure that your palm is facing upward. Make another coil using the net that is beneath the horn.
Step 4
Coil up the net over the left hand, this should be done under your left hand in the backward motion. You need to be careful with this step since the net will not open if you fail to roll it in the right manner. In order to do this perfectly, you should have the lead line at the bottom split.
Ultimately, you will have half of the net rolled over your left hand while the other half hanging down. When doing this, you should keep checking the net so as to ensure that it does not get tangled in the process. If the lead line is tangled, take the time to untangle and straighten it.
Step 5
Take the other half of the cast net and split it with your right hand. You should keep untwisting it as you pass it on to the right hand. Get hold of the net halfway, between the end of the coil and the leaded weights.
To confirm if you have done this in the right manner, you should have half of the leaded weights resting on the end of the net, which is in your right hand.
Step 6
Take the half that is on your right hand and roll it over the left thumb until all the net is on the left hand. Do not let go of the initial coils that you have made at the beginning as this would mess up the whole process. The two sets of the net should not intersect when you are transferring it.
To check if this has been done correctly, ensure that the skirt bottom of the net has two different piles of the net. They should be at different heights, with the pile that you have rolled over your left thumb being higher.
Step 7
Place the lead line in your teeth, just the rope part of it and not the weights. If you choose to throw your cast net without using teeth, then you should have the lead line over the top of your left hand.
When putting the line on your teeth, you would need to locate the skirt bottom where the pile has transitions from the high to the low place and put it in your teeth.
Alternatively, throw the lead line over the left shoulder and in this case, you need to use more of the skirt bottom if you are not using your teeth. Ensure that it is resting comfortably on your shoulder and does not slip.
Step 8
Using your right hand, grab the part that is swinging from the teeth. Grab this part with the right palm facing upward and left it be between the ring and pinky finger.
At this point, you will be getting hold of the lead line and top pile that was resting on your left thumb as indicated in the previous step. This is the part of the line that is facing away from you and makes sure you grab the lowest point, without necessarily bending over.
Step 9
Once you have the lead line in your hand, you should roll the part of the net that is on your left arm onto the palm of the right hand and hold it in a firm manner.
When all these steps are followed correctly, you will have accomplished the first, and most important step; the setting up and preparing the cast net. As long as you can get this process correctly, you will have an easier time throwing your cast net.
As discussed in the tips above, it is not how hard you will throw the net that will determine your success, but instead, it is how you throw it. The weight of the net and the motion of your body is what will determine if the net will open or not.
It is important to try and keep the lower body as still as you can and allow the motion to come from the upper body only. Ensure that you have a perfect balance before attempting to throw the net.
You can try to rotate your upper body without letting go of the net so that you can have a feel of what to expect.
As you attempt to twist your upper body, the net should swing open, away from you. While practicing, do not let go of the other parts of the cast net that you have in your hands.
Twist your body at the waistline, while keeping the toes pointing to the front and unleash the cast net to throw it. You should release the net like a coil and rotate to the right, which your entire body facing the same direction as the toes.
Release the net and every other component of the nets. Some important things to note:
You should allow the centrifugal force to open the net. You should not use too much power to cast your net, just think of this as a golf swing and make it as natural and smooth as possible. This is the only way that you will be able to get a great outcome.
While uncoiling the net, you should ensure that your arm remains outstretched. Just open up your arm and release the net without extending the arm like one who is throwing a Frisbee.
Do not make the mistake of rotating your body and lob the net out. You should allow the net to open itself and use the right hand to help to open the net. When using your teeth, you should not forget to open your mouth so as to release the net from your teeth.
Let the net flow in a clockwise direction and lay on the water and watch as it starts to sink to the bottom of the fishing source.
When it is at the bottom, pull it by the hand line and get the rewards of the bait fish that you will catch.
Conclusion
With these simple, yet practical steps, you will be able to throw your cast net effectively and have a remarkable outcome. You will reap a great deal of fish if you learn how to throw the cast net as required.
Please keep practicing so as to become better at it. Feel free to share this guide with your friends and family and also leave a comment. All the best in your fishing expedition.
This is a guest post by Jason Dirks of Mystery Tackle Box
For an angler, there’s nothing like the suspense of seeing your line twitch, or waiting for that slight tug that alerts you to set the hook hard and fast. The suspense keens your senses, slowing the pace of nature to a subtle stir. One of the best aspects of fishing is the surprise of the unknown tugging on your line, actually similar to being afraid. Maybe because both fear and fishing share a common element: the unknown.
The unknown can be exciting on the water, but it can be a bit daunting when it comes to lure selection. With endless aisles of crankbaits, soft plastics, spinnerbaits, etc. finding your next confidence bait takes a bit of research and trial and error.
Your current confidence bait might be a trusty old green pumpkin stick bait which isn’t a bad thing, although it can prevent you from finding that next favorite and adding it to your fishing arsenal.
Anglers need to get out of their comfort zone to become more versatile fisherman. Becoming a versatile fisherman means trying new lures, new colors, and new techniques so you can apply those learnings to attacking new waters and fishing conditions.
So, how do you get out of your comfort zone and find that next confidence bait? Try this, we call it the CAST method…4 simple steps to help you identify that next confidence bait and improve your fishing skills.
Compare: Look at the baits you’re currently using, your favorites, and compare those to the new baits you see in the market. Finding something similar with an added feature or innovation is a great option to try first.
Ask: This is simple, talk to the experts. Any local tackle shop or fisherman out on the water is a perfect candidate to ask for tips and see what they suggest.
Sample: Sampling products is a great way to find your next favorite bait and one company’s mission is just that. Mystery Tackle Box will send you a box each month filled with different lures and baits for less than the cost of a dinner. Anglers tout that discovering these new baits and brands not only makes them better fishermen, but it’s like Christmas once a month.
Throw: Get out and throw your line into the water to see what works for you. You won’t catch them if you don’t try and throwing your line in the water is the key to finding your next confidence bait.
Following one or all of these steps will help you find your next confident bait so give it a try. And remember, “if fishing was easy, they would’ve called it catching” so don’t get discouraged and have fun on the water.
Fish Finder/GPS Combos come with a large variety of charting packages pre-installed. Making the right choice can sometimes be intimidating. Here is a list of some of the more common packages and ther features.
A Basemap is Lowrance’s version of a very basic chart(as the name suggests). Basemaps do not have contour data, depth data, or any other extra data such as lighthouses and marine services.
Expect to see a big brown/green area for land, and a big blue area for water. You can plot tracks and mark waypoints on a Basemap without any problem, so if that’s all you want your GPS for, this should serve your purpose.
Lowrance Lake Insight:
These charts have incredibly detailed views of 650 lakes from the Midwest(Texas, Oklahoma, Kansas, Missouri, Illinois, Iowa, North Dakota, South Dakota, Nebraska, Michigan, Minnesota and Wisconsin, plus Lake of the Woods and Rainy Lake), with contour data as small as 3 feet. There are also crowdsourced fishing hotspots on certain lakes, as well as contour and relief data for over 5,000 U.S. lakes.
Lowrance Nautic Insight:
Nautic Insight charts are the coastal version of Lake Insight charts. It has detailed coverage of the shoreline, marinas, fishing hotspots, and lake and river data up to 100 miles inland.
It also shows tides, currents, and navigation aids.
ContourXD:
ContourXD charts are Humminbird’s advanced maps. ContourXD charts cover 3,000 U.S. lakes and they show depth contour lines, U.S. lights/markers, and interstate highways.
Humminbird ships this mapping package pre-loaded on many of their 1100, 900, 800, and 700 series models.
Humminbird Unimap:
Humminbird’s UniMap covers the continental US Coastline, major lakes and rivers, and shows chart data at a resolution of 30 meters per pixel.
If your fish finder is 5 inches and has a resolution of 640×480, on the whole screen, the most you can zoom will be about 19 km x 14 km or 12 mi by 9 mi.
It is a very basic mapping system and as one user put it, it’ll only tell you whether you are in the water or not!
Navionics Gold:
The “big daddy of charts”, Navionics gold charts can cover an entire continent, and still be able to zoom in down to 3 meters.
They show tides and currents, port plans, depth contours, marine services contact information, and marsh areas.
BlueChart g2 Vision:
This is Garmin’s answer to Navionics – BlueChart g2 Vision features auto-guidance technology, where you enter a waypoint and the charts will automatically search for the safest and fastest route customized to your boat size.
You can also view satellite images of the bigger ports and shorelines, as well as a 3D view of the land and an underwater view as would be seen from the waterline.
This type of transducer is recommended for planing hulls that are less than 27 feet(8 meters). Examples of such vessels are personal craft and powerboats with outboard, inboard-outboard and jet drives.
The great part about in-hull mounts is that they can be installed AND serviced while the vessel is in the water. Since they don’t stick out of the hull, they don’t cause any extra drag in the water, they don’t accumulate marine plants and growth, and are very easy to maintain, as the unit won’t be damaged when the boat is trailered.
External mounts stick out of the hull surface and normally need a fairing block to aim the SONAR beam correctly. These are generally used for larger vessels that are always in the water and not trailered. It also has to be mounted in front of the propeller and any moving gear to produce the most effective signal.
