Electro fishing is being successfully used in the many countries of the world. Commercial electric fishing is common in these countries both for river and sea fishing. Electro fishing is an unconventional method of fish collection and used to catch fishes through saving time, labor, money and man-power. Also, this method does not affect the growth, the viability and the reproductive capacity of the fishes; moreover, food of fishes present in the water does not influenced by the electric field created during fishing by this method.
Fishing:
Fishing is the activity of trying to catch fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping.
The term fishing may be applied to catching other aquatic animals such as molluscs, cephalopods, crustaceans, and echinoderms. The term is not normally applied to catching farmed fish, or to aquatic mammals, such as whales, where the term whaling is more appropriate.According to FAO statistics, the total number of commercial fishermen and fish farmers is estimated to be 38 million. Fisheries and aquaculture provide direct and indirect employment to over 500 million people.In 2005, the worldwide per capita consumption of fish captured from wild fisheries was 14.4 kilograms, with an additional 7.4 kilograms harvested from fish farms.In addition to providing food, modern fishing is also a recreational pastime.
Electrofishing:
Electrofishing uses electricity to stun fish before they are caught. Electrofishing is a common scientific survey method used to sample fish populations to determine abundance, density, and species composition. When performed correctly, electrofishing results in no permanent harm to 
fish, which return to their natural state in as little as 2 minutes after being stunned.
Types: There are three types of electrofishers: backpack models, tote barge models, and boat mounted models, sometimes called a stunboat.
Backpack electrofisher generators are either battery or gas powered. They employ a transformer to pulse the current before it is delivered into the water. The anode is located at the end of a long, 2 meter pole and is usually in the form of a ring. The cathode is a long, 3 meter braided steel cable that trails behind the operator. The electrofisher is operated by a deadman's switch on the anode pole. There are a number of safety features built into newer backpack models, such as audible speakers that sound when the unit is operating, tilt-switches that incapacitate the electrofisher if the backpack is tilted more than 45 degrees, and quick-release straps to enable the user to quickly remove the electrofisher in the event of some emergency.
Tote barge electrofishers operate similarly to backpack electrofishers, with the exception that the generator is located on a floating barge instead of on a backpack. Often the barge can be left stationary on the shore and longer cathodes and anodes allow the crew to sample large areas. Barge electrofishers often employ gas-powered generators since a user does not have to carry the extra weight on his or her back.
When boat electro fishing, the boat itself is the cathode, and the anode(s) are generally mounted off the bow. The stunned fish swim toward the anode, where they are caught alive using a dip net.
Electro fishing and its mechanism:
In brief, electro fishing is a quick method of harvesting large number of fish by affecting them through creating electric field in the water. During fishing, an electric field is created in water between two electrodes. These electrodes are called anode and cathode. When fishes became affected by the electricity produced by the field, they are collected by netting or fish pumping. Generally 3 types of electric current are used in this process, i.e. direct current (D.C.), alternative current (A.C.) and interrupted current (I.C.). Fishes show different types of reaction depending on types of electricity produced in the field.
Reaction of fishes to direct current (D.C.):
At first, when electric field starts to produce electricity and if the voltage is low, the target fishes are will not be affected or influenced by the electric field and they may escape from the field area.
When voltage increases and crosses a certain threshold value, electrotaxis reaction will be shown by the affected fishes. During this time, if the fish will remain in transverse position to the current direction, it will turn parallel to it and the fish-head will be directed towards the anode. The body of fishes will be vibrated if the fishes remain in a parallel position to the current direction.
Then, with a fresh pulse application, all affected fishes will turn parallel to the current direction and begin swimming towards the anode which is called galvanotaxis. Before reaching anode by swimming, the fishes will be stupefied and will loose locomotion ability and may turn upside down which is called galvanonarcosis. It the electric current is switched off at this level, the narcotized fish will be able to recover completely.
Reaction of fishes to alternative current (A.C.):
If certain threshold value of voltage is produced by the field, the affected fish will show oszilloiaxis reaction. In this reaction, all fishes between anode and cathode will take up a position transverse to the direction of the current. Fishes will cease to swim and will narcotized with fading of body color as a consequence of concentration of the pigments.
If the current source will turn off, the fish do not recover immediately and for several minutes, they remain in a state of hypnosis, unable to recover. During this period, the fish body stays in lateral or dorsal position.
After hypnosis period, the affected fish will return to their normal swimming posture and may be escaped from the field.
Reaction of fishes to the interrupted current (I.C.):
When fishes affects by a pulse threshold voltage and show electrotaxis, they undergo heavy vibrations and starts swimming towards the anode. If the electric voltage increased gradually and then decreased abruptly this time, the fish will turn about and swim towards the cathode. Galvanonarcosis will follow in the same way as it occurs in case of direct current.
When the affected fishes in an electric field receive electric current, the free nerve endings in the fish skin become stimulated which produces excitation in the central nervous system and this excitation leads to tetanic contractions of the muscles resulting in the stoppage of locomotion of fishes. During this time it becomes easy to catch the affected fishes.
In commercial fishing both A.C. and D.C. are used in freshwater habitats whereas I.C. is used to harvest fish in sea water. The attracting anodic effect and the blocking effects are used to advantage of fishery.
Attracting anodic effects:
Attracting anodic effects is generally produced to capture fish on commercial scale in both freshwater and sea water environments. In freshwater, two electrodes (anode and cathode) are immersed in water and 2:3 (anode:cathode) size ratio of electrodes are maintained. They electrodes are operated on batteries and anode carries a hoop net at its base. The narcotized fish assembled at the anode are removed by the hoop net and the entire operation is conducted from a boat.
Blocking effect:
In this method, affected fishes are frightened or forced to move towards a particular zone or area. The effects when produced in freshwater shows following facts-
v Fishes are forced to enter new river systems, bays catching areas for easy fishing.
v Unwanted fishes are frightened so that they leave the specific water area for harvesting target species only.
v Fishes are prevents from entering the turbines or pumps of hydro-electric plants and dams.
Disadvantages of electro fishing:
Electro fishing is becoming something like an art and skilled fishermen or fish catcher can caught large amount of fishes but this method has some disadvantages too. These are as follows-
Ø Extensive electricity current may damage the fish population.
Ø Turbid water and excessive vegetation restrict visibility and reduce the value of immobilizing capability of A.C. electro fishing.
Ø High conductivity bottom materials tend to “short circuit” the current out of the water into the bottom material reducing the electro fishing effectiveness.
Ø There is always a great risk of scaring away the fishes at the hands of untrained catchers.
Ø Other fish population (except target fish species) may also be damaged by the electric field.
Ø Comparatively high-tech for the fishermen of developing countries like Bangladesh.
Though electro fishing is being practicing successfully in foreign countries, but in Bangladesh
Electrofishing Guidelines: (Training)
Field supervisors and crew members must have appropriate training and experience with electro fishing
techniques. Training for field supervisors can be acquired from programs such as those offered from the U.S. Fish and Wildlife Service - National Conservation Training Center
Conclusion:
Electrofishing - is another recently developed technique, primarily used in freshwater by fisheries scientists. Electrofishing uses electricity to stun fish so they can be caught. It is commonly used in scientific surveys, sampling fish populations for abundance, density, and species composition. When performed correctly, electrofishing results in no permanent harm to fish, which return to their natural state a few minutes after being stunned.
Reference:
1. www.wikipedia.org
2. www.encyclopediacenter.com
3. www.fisheriesmanagement.co.uk/electrofishing.htm
4. www.rickly.com/as/electrofishing.htm
5. www.rickly.com/as/electrofishing.htm
6. www.halltechaquatic.com
Fishing:Fishing is the activity of trying to catch fish. Fish are normally caught in the wild. Techniques for catching fish include hand gathering, spearing, netting, angling and trapping.
The term fishing may be applied to catching other aquatic animals such as molluscs, cephalopods, crustaceans, and echinoderms. The term is not normally applied to catching farmed fish, or to aquatic mammals, such as whales, where the term whaling is more appropriate.According to FAO statistics, the total number of commercial fishermen and fish farmers is estimated to be 38 million. Fisheries and aquaculture provide direct and indirect employment to over 500 million people.In 2005, the worldwide per capita consumption of fish captured from wild fisheries was 14.4 kilograms, with an additional 7.4 kilograms harvested from fish farms.In addition to providing food, modern fishing is also a recreational pastime.
Electrofishing:
Electrofishing uses electricity to stun fish before they are caught. Electrofishing is a common scientific survey method used to sample fish populations to determine abundance, density, and species composition. When performed correctly, electrofishing results in no permanent harm to fish, which return to their natural state in as little as 2 minutes after being stunned.
fish, which return to their natural state in as little as 2 minutes after being stunned.Types: There are three types of electrofishers: backpack models, tote barge models, and boat mounted models, sometimes called a stunboat.
Backpack electrofisher generators are either battery or gas powered. They employ a transformer to pulse the current before it is delivered into the water. The anode is located at the end of a long, 2 meter pole and is usually in the form of a ring. The cathode is a long, 3 meter braided steel cable that trails behind the operator. The electrofisher is operated by a deadman's switch on the anode pole. There are a number of safety features built into newer backpack models, such as audible speakers that sound when the unit is operating, tilt-switches that incapacitate the electrofisher if the backpack is tilted more than 45 degrees, and quick-release straps to enable the user to quickly remove the electrofisher in the event of some emergency.
Tote barge electrofishers operate similarly to backpack electrofishers, with the exception that the generator is located on a floating barge instead of on a backpack. Often the barge can be left stationary on the shore and longer cathodes and anodes allow the crew to sample large areas. Barge electrofishers often employ gas-powered generators since a user does not have to carry the extra weight on his or her back.
When boat electro fishing, the boat itself is the cathode, and the anode(s) are generally mounted off the bow. The stunned fish swim toward the anode, where they are caught alive using a dip net.
Electro fishing and its mechanism:
In brief, electro fishing is a quick method of harvesting large number of fish by affecting them through creating electric field in the water. During fishing, an electric field is created in water between two electrodes. These electrodes are called anode and cathode. When fishes became affected by the electricity produced by the field, they are collected by netting or fish pumping. Generally 3 types of electric current are used in this process, i.e. direct current (D.C.), alternative current (A.C.) and interrupted current (I.C.). Fishes show different types of reaction depending on types of electricity produced in the field.
Reaction of fishes to direct current (D.C.):
At first, when electric field starts to produce electricity and if the voltage is low, the target fishes are will not be affected or influenced by the electric field and they may escape from the field area.
When voltage increases and crosses a certain threshold value, electrotaxis reaction will be shown by the affected fishes. During this time, if the fish will remain in transverse position to the current direction, it will turn parallel to it and the fish-head will be directed towards the anode. The body of fishes will be vibrated if the fishes remain in a parallel position to the current direction.
Then, with a fresh pulse application, all affected fishes will turn parallel to the current direction and begin swimming towards the anode which is called galvanotaxis. Before reaching anode by swimming, the fishes will be stupefied and will loose locomotion ability and may turn upside down which is called galvanonarcosis. It the electric current is switched off at this level, the narcotized fish will be able to recover completely.
Reaction of fishes to alternative current (A.C.):
If certain threshold value of voltage is produced by the field, the affected fish will show oszilloiaxis reaction. In this reaction, all fishes between anode and cathode will take up a position transverse to the direction of the current. Fishes will cease to swim and will narcotized with fading of body color as a consequence of concentration of the pigments.
If the current source will turn off, the fish do not recover immediately and for several minutes, they remain in a state of hypnosis, unable to recover. During this period, the fish body stays in lateral or dorsal position.
After hypnosis period, the affected fish will return to their normal swimming posture and may be escaped from the field.
Reaction of fishes to the interrupted current (I.C.):
When fishes affects by a pulse threshold voltage and show electrotaxis, they undergo heavy vibrations and starts swimming towards the anode. If the electric voltage increased gradually and then decreased abruptly this time, the fish will turn about and swim towards the cathode. Galvanonarcosis will follow in the same way as it occurs in case of direct current.
When the affected fishes in an electric field receive electric current, the free nerve endings in the fish skin become stimulated which produces excitation in the central nervous system and this excitation leads to tetanic contractions of the muscles resulting in the stoppage of locomotion of fishes. During this time it becomes easy to catch the affected fishes.
In commercial fishing both A.C. and D.C. are used in freshwater habitats whereas I.C. is used to harvest fish in sea water. The attracting anodic effect and the blocking effects are used to advantage of fishery.
Attracting anodic effects:
Attracting anodic effects is generally produced to capture fish on commercial scale in both freshwater and sea water environments. In freshwater, two electrodes (anode and cathode) are immersed in water and 2:3 (anode:cathode) size ratio of electrodes are maintained. They electrodes are operated on batteries and anode carries a hoop net at its base. The narcotized fish assembled at the anode are removed by the hoop net and the entire operation is conducted from a boat.
Blocking effect:
In this method, affected fishes are frightened or forced to move towards a particular zone or area. The effects when produced in freshwater shows following facts-
v Fishes are forced to enter new river systems, bays catching areas for easy fishing.
v Unwanted fishes are frightened so that they leave the specific water area for harvesting target species only.
v Fishes are prevents from entering the turbines or pumps of hydro-electric plants and dams.
Disadvantages of electro fishing:
Electro fishing is becoming something like an art and skilled fishermen or fish catcher can caught large amount of fishes but this method has some disadvantages too. These are as follows-
Ø Extensive electricity current may damage the fish population.
Ø Turbid water and excessive vegetation restrict visibility and reduce the value of immobilizing capability of A.C. electro fishing.
Ø High conductivity bottom materials tend to “short circuit” the current out of the water into the bottom material reducing the electro fishing effectiveness.
Ø There is always a great risk of scaring away the fishes at the hands of untrained catchers.
Ø Other fish population (except target fish species) may also be damaged by the electric field.
Ø Comparatively high-tech for the fishermen of developing countries like Bangladesh.
Though electro fishing is being practicing successfully in foreign countries, but in Bangladesh
Electro-Fishing Unit - Model 2000: The Model 2000 Electro-Fishing Unit is a 2000 watt electro-fisher that features variable voltage and frequency mounted on a non-conductive nylon pack frame with quick release shoulder straps and hip belt. It is a lightweight, noise free unit with electronic digital timer and waterproof case. The Model 2000 is completely portable
and comes with an aluminum field case for easy storage, traveling and carrying that will house all parts for the electro-fisher.
Electrofishing Guidelines: (Training)
Field supervisors and crew members must have appropriate training and experience with electro fishing
techniques. Training for field supervisors can be acquired from programs such as those offered from the U.S. Fish and Wildlife Service - National Conservation Training Center
1) A review of these guidelines and the equipment manufacturer’s recommendations, including basic
2) gear maintenance.
3) Definitions of basic terminology (e.g. galvanotaxis, narcosis, and tetany) and an explanation of how
4) electrofishing attracts fish.
5) A demonstration of the proper use of electrofishing equipment (including an explanation of how
6) gear can injure fish and how to recognize signs of injury) and of the role each crew member 3 performs.
7) A demonstration of proper fish handling, anesthetization, and resuscitation techniques.
8) A field session where new individuals actually perform each role on the electrofishing crew.
Conclusion:
Electrofishing - is another recently developed technique, primarily used in freshwater by fisheries scientists. Electrofishing uses electricity to stun fish so they can be caught. It is commonly used in scientific surveys, sampling fish populations for abundance, density, and species composition. When performed correctly, electrofishing results in no permanent harm to fish, which return to their natural state a few minutes after being stunned.
Reference:
1. www.wikipedia.org
2. www.encyclopediacenter.com
3. www.fisheriesmanagement.co.uk/electrofishing.htm
4. www.rickly.com/as/electrofishing.htm
5. www.rickly.com/as/electrofishing.htm
6. www.halltechaquatic.com
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