Electrofishing

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West Country River Trust electro fishing on the main river Dart at Newbridge Dartmoor Devon Photo credit Paul Glendell www.glendell.co.uk. Mobile 07802480710

Electrofishing is an effective tool for fishery scientists because most aquatic organisms become motionless when the body voltage exceeds a certain value from nose to tail. Early methods were only applied to freshwater streams and small pools; this was due to limited knowledge of fish reaction.

Gear Requirements and Reactions:

Commonly the gear requirements for electrofishing consist of three main pieces of apparatus. Firstly the power unit, this can produce a 2 or 3-phase alternating current; the energy produced by this device will ultimately be determined by the conductivity of the water. It is usual to convert this to direct current through a transformer and this can be at different voltages plus the shape, length, and frequency of the pulse will also be determined at this stage. The final section consists of the electrodes, and the shape of these will influence the field strength.

The electrodes consist of two types, the anode (positive) and the cathode (negative). The choice of material and size of an electrode can influence fishing efficiency; ultimately this will determine the field strength (voltage gradient). Essentially an increase in electrode size will increase the electrical field size, decrease the resistance of the electrodes and most importantly reduce harm to the fish.

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