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Alternating current is easier to generate than Direct current and the simplest way to produce PDC for electrofishing is to modify the AC. Half wave rectification removes the negative half of the cycle and full wave rectification turns the negative half-cycle into a positive one. Quarter-sine current has not only the negative half-cycle removed but also the leading portion of the positive half-cycle. This is the simplest form of PDC used for electrofishing and it works well as fish tend to respond best to a rapid rise in current flow and a slow fall.
The European and British Standard for electrofishing prohibit the use of AC (Anon., 2003). AC can result in high fish mortality, does not attract fish from cover and also tends to be a greater health and safety hazard than DC. Consequently AC should not be used for electrofishing and will not be covered in the remainder of this document.
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Fishing using Direct Current (DC) tires the fish the least and Alternating Current (AC) the most. This is reflected in the recovery times, and risk of injury to the fish, which increase from smooth DC through pulsed DC to AC.
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Smooth DC has the lowest tetanising effect, therefore resulting in less injury to fish. It also is better at stimulating fish to swim towards the anode and has the ability to attract fish from hiding places. However the higher power demand to provide smooth DC compared to pulsed DC may limit its use, for instance in high conductivity waters, unless a large generator can be used. Pulsed DC can be used in these situations where smooth DC is not effective, as fish tend to exhibit a greater reaction to pulsed DC compared to the same voltage of smooth DC and the power demand is lower.
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Species Pulse frequency (Hz)
Salmonids 40-60
Cyprininds 30-50
Percids 10-40
Pike 30-50
Eels 10-40
Table 1. Pulse frequencies for different fish species based on the optimum combinations of attraction, immobilisation and welfare.
INTRODUCTORY ELECTROFISHING
TRAINING MANUAL
http://www.scotland.gov.uk/resource/doc ... 096725.pdf
romurallye kirjoitti:Mielenkiinnolla testituloksia odottaen.
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