7133 (2) - Laserfiche WebLink

Home Browse Search

168 1 G~ C~ TECHNICAL NOTES The Progressive Fish-Culturist 51:11/68-169, 1989 ~7~3~ Current and Power Determinations for Electrically Anesthetized Fish MATTHEW L. KOLZ' Bear Creek High School 3490 South Kipling Lakewood, Colorado 80227, USA Abstract.-Goldfish (Carassius auratus) placed across metal electrodes were consistently anesthetized when subjected to continuous direct currents exceeding 3 mA. The corresponding minimum electrical power required for anesthesia was calculated at 20 mW. The measure- ment techniques developed for this study are applicable for other sizes and species of fish. Reports from Alaska (Gunstrom and Bethers 1985; Orsi and Short 1987) describe 12-V DC electrical circuits for handling large salmonids. The method involves the connection of a battery be- tween the head and tail of a fish. As long as the body of the fish conducts current, the fish is im- mobilized. However, when the battery is discon- nected, the fish instantly recovers. This immobi- lization technique is referred to as electrical anesthesia, and there are reports prior to 1954 that describe the effect (Haskell et al. 1954). In this paper, I report electrical measurements taken for goldfish (Carassius auratus) when the fish were placed across two metal electrodes under controlled conditions. The electrodes were driven with limited amounts of current, and reactions of the fish were observed as the magnitude of current was changed. The goal was to determine the elec- trical current and power necessary to keep fish anesthetized. The electrical circuit necessary to perform these tests required a power source, ammeter, and re- sistors of several values. Two pieces of aluminum foil 1 cm apart served as the electrodes across which the goldfish were placed (Figure 1). The placement of the fish on these electrodes was fixed so that the snout of each fish was exactly 3 cm from the gap between the two electrodes. This meant that the head portion of each fish was in contact with 3 cm of the foil on the anode side of the gap, and the rest of the body and tail was in full contact with the second piece of foil. Average total length of the 30 goldfish used in this study was 86 mm (range, 72-109 mm). Their weight averaged 8.0 g (range, 5.3-12.5 g). The circuit required a constant 10-V DC source. Nine resistor values were selected over a range of 0-20,00012 to limit the maximum current passing through the body of the fish. For example, with zero resistance in the circuit, the current was lim- ited only by the resistance of the fish, but with series resistance of 20,000 S2, the current could never exceed 0.5 mA. For each value of series resistance, 10 randomly selected fish were placed one at a time across the electrodes. The fish were observed for about 15 s to note if they were im- mobilized on the electrodes. During this time, the strength of the current passing through the fish was recorded from the ammeter. A fish was judged to be anesthetized if it did not jump off the electrodes within the alloted time period. The number of fish that appeared to be anesthetized during the 15-s period was recorded and converted to a percentage estimate. With only 30 fish, the same fish were tested several times. However, the fish were al- ways rested between tests for at least 1 d. Once the current was measured for a fish, the resistance of the fish was calculated by the for- mula: fish resistance = (10 V/current) - (series resistance). Selected Resistors (0 - 20,000 ohms) Anode Electrode ~' + 0 > - ~T 1 cm 3 cm Cathode Electrode-{-~ /;~;;\ Fish ' Present address: 8520 West Baker Avenue, Lake- wood, Colorado 80227, USA. Ammeter FIGURE l.-Electrical circuit diagram for anesthetiza- tion of fish.