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NOTES GALVANONARCOSIS lS defined as the reaction of fish to an uninterrupted direct electric current whereby the fish roll over onto one side, facing the anode and are incapable of movement (Hals- band 1967). Although there is general disagree- ment on the mechanism by which the paralysis occurs (Scheminzhy and Kollensperger 1938; Hartley 1967; Vibert 1963; and C. Volz personal communication), it is generally agreed that gal- vanonarcosis is the safest and least exhausting manner of immobilizing fish with electricity. For this reason, the present study evaluates 1) the usefulness of a steady DC current to immobilize rainbow trout (Salmo gairdnerr) and 2) the effects of the treatment on subsequent fish growth and perception of their environment. Materials and methods -Yearling rainbow trout approximately l2 cm long were obtained from the Arizona Game and Fish Hatchery at Page Springs, Ariz. Prior to testing, fish were held in a large out- door pool for 30 days and were fed daily with Purina Fish Chow. Aerated tap water (temperature 13-21 C; ,specific conductivity 450 µSt/cm) that had been aged for 1 wk was used in all experiments. During treatments, fish were held in a plexiglass aquarium (36 cm X 20 cm X 22 cm). Electrodes of sheet aluminum (20 cm X 22 cm) at each end of the aquarium created a nearly uniform electric field throughout the length of the aquarium. Polarity of the current was reversed every 30 min during experi- ments to prevent alteration of water quality through the electrolysis process. Narcosis was produced when fish were subjected to a minimum of 10 V DC from an EICO Model #1020 power supply. Using DC to produce the field resulted in a 1-V drop at the interface between the negative plate and the water. This resulted in a field intensity of .25 V/cm. To determine the approximate head to tail voltage, which is the primary determinate in galvanonarcosis, we use volts where E is the electric field intensity and L is the length of the fish in centimeters. The experimental fish were approximately 12 cm long which gives a head to tail voltage of 3 V. This agrees closely with the values determined by other investigators (Edwards and Higgins 1973). To determine the effect of electrical treatments on growth, four groups of 30 fish each (15 experimental - 1 S control) were tested at 1, 2, 4, and 6 h of galvanonarcosis on February 26 and 27, 1974. Con- trol fish were held in an equivalent aquarium but were not subjected to an electrical current. Within 48 h after treatment, fish were individually weighed ± 1 g on a split-beam balance. Each of the eight groups was held separately in 1600-liter containers and fed approximately 2% of body weight/day until the cx- 301 periment was terminated after 25 days when the fish were again weighed. The effect of narcosis treatments on rainbow trout growth for the 25-day period was evaluated by t-test. Since there was no difference in initial mean weights between experimental and control fish for each test time, a similar comparison of the final mean weights was performed to reveal any growth difference that resulted from the treatment. The possible effects of narcosis treatment on fish behavior was evaluated by comparing the photo- negative responses of treated and control fish (year- ling rainbow trout are photonegative, McCrimmon and Kwain 1966). The test environment was a pool 2.1 ml with water 50 cm deep. One-half of the pool was shaded by a wooden cover and one-half was ex- posed to direct sunlight. Percent transmittance Of sur- face light at the bottom of the pool was 7°Jo in the shaded area and 91% in the illuminated area. Twenty-four fish were tested after narcosis treat- ment for photonegative response and 24 served as controls. Fish were tested in groups of six with two groups narcotized for l hand two groups for 3 h. After treatment, fish were immediately released into the center of the pool and scored for 1) initial choice of illuminated or shaded areas, and 2) subsequent preference of habitat for 15 min. Preference was recorded as the number of fish in each area at 1-min intervals for 15 min. Chi-square was used to compare the observed and expected frequencies of control and experimental fish. In the l5-min preference tests, the 12 control fish and 12 experimental fish for each test time (1 hand 4 h) were compared using the total number of fish that were counted in each habitat for all 1-min intervals. Results and discussion -Fish were easily im- mobilized using the previously described tech- niques. In achtal practice, the voltage was quickly increased to 20 V to cause immediate paralysis and reduce fright swimming. After 1 min at 20 V, [rout could be field immobile at 10 V except for occasional short bouts of disoriented forced swim- ming. Galvanonarcosis treatments appeared to be safe, with only two fish in the 6-h tests lost to mortality. In general, fish treated for 1 and 2 h recovered instantaneously as indicated by their resumption of swimming and feeding. Fish narcotized for 4 and 6 h had increased difficulty resuming swim- ming activity. Normal swimming activity and feeding were resumed within 12 h even by 6-h narcotized fish. The t-test comparisons of experimental and control fish indicate there was no effect of gal- vanonarcosis on fish growth (Table 1 }. This seems to be the case although an accidental fish kill on March 23 eliminated some of the fish from the evaluation. Similar results for rainbow trout treated with pulsating DC current were obtained by Maxfield et al. (1971) .