7710 - Laserfiche WebLink

Home Browse Search

\ 1298 J. FISH. RES. BOARD CAN., VOL. 35, 1978 purpose of this study was to investigate the effects of extended galvanonarcosis on selected aspects of the be- havior of rainbow trout, Salmo gairdneri, and channel catfish, /ctalurus punctatus, to evaluate the feasibility of long-term immobilization of fish. Materials and Methods Yearling rainbow trout 50-87 mm standard length were obtained from the National Fish Hatchery, Alchesay- Williams Creek, Arizona. Channel catfish 45-80 mm stand- ard length were obtained from the Arizona Game and Fish Department. Fish were held in 1600-L holding tanks for 2 wk and fed Purina Fish Chow before any experimentation. Tap water used in all experiments was aged and aerated for at least 2 d. Conductivity was 1100-1375 mhos/ cm and temperature was n.0-I8.0oC in the water used during elec- trical trealments, Experimental and control fish were marked for individual recognition by cold branding (Fujihara and Nakatani 1967) and held for 72 h to check mortalities and appearance of brands. Test fish were narcotized using the procedures and apparatus described by Kynard and Lonsdale (I 975). V o]t- age was slowly increased until 100% of the treatment group were immobilized and resting on one side. The voltage was decreased until 80% of the group remained in narcosis. Field intensities that narcotized 80% of the test fish ranged from 0.42 to 0.56 V /cm. Approximate head to tail voltages (V}{ _ T) were 2.1-4.9 V as determined by the formula V 11 _ T = E X L V where E is the electric field intensity and L is the fish length (Edwards and Higgins 1973; Kynard and Lonsdale 1975). Fish were narcotized for either 30 min or 3 h and then evaluated for effects on their behavior. Swimming activity is a partial reflection of the general activity and motivation of a fish. The effect of galvano- narcosis on individual activity, defined as upright, horizontal swimming activity, was investigated immediately after treat- ment and again after 24 h. In each test, three fish were exposed to electricity and then were individually evaluated for activity after placement in a tank (60 X 45 X 45 cm; water depth 30 cm) that had a grid of 7.5-cm squares marked on the glass cover. After a 5-min acclimation period, the number of squares each fish passed through in 3 min was recorded. Control fish were treated similarly ex- cept for exposure to electricity. Student's t-test was used to compare mean activity for immediate and 24-h results be- tween experimental and control groups. The effect of galvanonarcosis on groups of fish was also evaluated. General group activity was defined as the num- ber of fish in a group (n = 5) displaying directed upright swimming. Groups were simultaneously evaluated for ac- tivity and photonegative response in circular tanks (58 cm diam; water depth 30 cm). One half of each tank was shaded by a cover and the other half was illuminated by a 130-W overhead flood light. The number of fish from each group in the shaded half represented the photonegative re- sponse. Percent of surface light at the bottom of the tank was 42% in the lighted area and 0% in the shade. Treatment and control groups were released in identical tanks at the shade-light interface and the initial habitat preference noted. After 3 min, both groups were observed for 15 min. A score was kept of the number of fish moving and the number of fish in the shade at the end of each minute. Then, fish were left in the experimental tanks for 1 h and observed again for 5 min. Treated and untreated groups for each test were then placed together in a tank (60 X 45 X 45 cm) and separated for evaluation after 24 h. The null hypothesis that experimental and control groups did not differ in group activity or photonegative behavior was tested using chi-square analysis. Data from each test were compared individually and were pooled for each treat- ment category. Comparisons were made by chi-square analysis at the individual and pooled levels and a hetero- geneity chi-square test was done for each treatment category to evaluate the trend of the individual test results (Sokal and Rohlf 1969). Vulnerability of electrically treated trout to predation was examined by exposing equal numbers of treated and un- treated fish to two largemouth bass, Micropterus salmoides, which were 30-35 cm total length. Predators were starved for 48 h before each test. After an electrical treatment, five test and five control fish were mixed in an 18.9-L container. The container was covered by a net and placed on the bot- tom of the circular predator tank (165 cm diam; water 60 cm deep). Test fish were exposed to predation 1-5 min after introduction by removing the net from the container and then removing the container from the tank. Experiments were terminated when 50% of the total group had been eaten or at the end of 0.5 h (Barns 1967; Coutant 1973). A record was kept of the number of test and control fish that remained. Results of individual tests were pooled for each treatment category since the expected frequency was less than five in each test (Sakal and Rohlf 1969). The hypothesis of no difference in vulnerability was tested on the pooled data using chi-square analysis. TABLE 1. Individual activity of channel catfish and rainbow trout immediately after extended galvanonarcosis and after 24 h of recovery. *Significant at 0.05 probability level. Immediate 24-h Species and group Test Control Test Control Immediate 24-h 2.890* o . 360b 2.191b* 0.084 2.162 1.204 2.546b* 1.133 Channel catfish 0.5 h Channel catfish 3 h Rainbow trout 0.5 h Rainbow trout 3 h 30.7:t 13.8 (19)R 29 .2 :t 11 .4 (16) 37.6 :!::14.0 (18) 36.7:t13.0(18) 96.6:t 18.2 (19) 78.0:t19.2(16) 83 .9 :t 16.2 (18) 98 .6 :t 21 . 1 (18) 69.0:t9.7 (19) 62.3:t15.9 (19) 54.8:tl4.1(5) 57.1:tl2.9(5) 45.l:t14.2(8) 75.0:t20.4(8) 80.5:tl5.J (17) 108.6:t19.1 (18) &Represented by the mean number of squares that individual fish passed through in 3 min :t SE. Number of fish evaluated in parentheses. bt-test of means with unequal variances (Steel and Torrie 1960).