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Table 3. Oxygen capacity of blood of different fish (Sternin et al. 1976). Species Percent of total volume of blood Pike Cod 5.4 - 7.8 Trout 6.5 - 7.8 Eel 9.5 - 13.4 Carp 10.2 - 15.6 11.5 - 16.8 Pike have relatively low amounts of oxygen in the blood, carp have high amounts and trout are somewhere in between. These individual variances in oxygen content will affect the ability of fish to recover from electrofishing. Sternin et al. (1976) examined what happens to oxygen levels in the blood of rainbow trout that were shocked for 20 seconds with ac, dc, and pulsed do currents (Figure 6). With ac (line 3), the initial consumption of oxygen at shock was a 150% increase over what the body would normally consume, and it took 120 minutes to recover to preshock conditions. When shocking with ac, a fish exerts-much more energy because its body is receiving the total swing of current from negative to positive poles (a sine wave). With ac, a fish assumes a position perpendicular to the electrical current produced between the two electrodes in an effort to minimize the voltage gradient received by its body. The fish undulates in rhythm with the ac cycle contracting its muscles as many times per second as the cycle until tetany occurs. Fish do not swim toward the electrodes when shocked with ac. Unmodified ac is most damaging and can be very traumatic to fish. 0 7 `~ Time (Minutes) Figure 6. Time of restoration of oxygen metabolism in trout after 20-second exposure to different kinds ,of current; 1) pulsating, 2) direct, and 3) alternating (.Sternin et al. 1976). With do (line 2), the initial consumptive of oxygen at shock was 130% and recovery occurred i'n 80 minutes. With pulsed do (line 1), the increase in oxygen consumption was 110 at shook, and the fish recovered to preshock conditions in 30 minutes. GAL.-N6VA ~IIL.DL.IFE TRANSACTIQNS 1984 66 ~u zu 3u ~40 50 60 70 80 90 100 110 120 130 140 150 160170 180