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MAXFIELD ET AL.-PULSATING DIRECT CURRENT EFFECT ON TROUT 547 Survival, Growth, and Fecundity of Hatchery-Reared Rainbow Trout after Exposure to Pulsating Direct Current GALEN H. MAXFIELD, ROBERT H. LANDER, AND KENNETH L. LISCOM National Marine Fisheries Service, Biological Laboratory 2725 Montlake Boulevard East Seattle, ?Fashington 98102 ABSTRACT Control (or unshocked) 1 land shocked (or test) rainbow trout (Salmo gairdneri) were held through spawning to determine the effects of electrical shock on the survival, growth, and fecundity of two year classes-young of the year of the 1953 year class and yearlings of the 1952 year class-and on the survival of the eggs and of the fry of the exposed fish. The test groups were exposed for 30 sec to one of two sets of electrical conditions-the young of the year to a pulse frequency of 8 pulses/sec, a pulse duration of 40 milliseconds, and a voltage gradient of 1 volt/cm ; and the yearlings to a pulse frequency of 5 pulses/sec, a pulse duration of 60 milliseconds, and a voltage gradient of 0.75 volt/cm. The exposure was longer than that usually encountered by fish during either electrical fish guiding or collection with a pubating4direct-current shocker. The slr ival, growth, and fecundity of the fish apparently were not affected by the electrical shock, nod were the survival and development of their offspring. w INTRODUCTION t The electr attic response of fish toward the positive ei trode (anode) in a continuous, direct-current field was well known by 1950 from electrofishing in freshwaters of Europe and North (see bibliography by Applegate, M ryerica and Harris, 1954). Advances in eronics after World War II resulted in improvements in the control of pulse shapes, Jrequencies, and durations of direct current.] These improvements attracted the interest of fishery workers in the use of unidirectional' pulsed fields in freshwater streams and lakes in: (1) qualitative and quantitative population studies (Burnet, 1959; Smith, Franklin, and Kramer, 1959; Miller, 1965; Lowry, 1966; Klein, 1967; Moore, 1968; Klein and Finnell, 1969) ; (2) control of unwanted species (Sharpe, 1964; Maxfield, Monan, and Garrett, 1969) ; (3) collection of fish for transport and planting (Giguere, 1954; Horak and Klein, 1967) ; and (4) energizing of screens (electrode arrays) to frighten or divert fish away from dangerous environments (McLain and Nielsen, 1953; McLain, 1957; Kuroki, 1959). Collection of mature trout by the electric shocker is a com- mon hatchery practice in North America and in Europe. Experiments in the use of pulsating direct current for guiding migrant juvenile salmon (Oncorhynchus spp.) and tibut (Salmo spp.) away from turbine intakes at dams, irrigation canals, and other dangerous areas were begun in 1952 by the BCF (Bureau of Commercial Fisheries), now NMFS (National Marine Fish- eries Service), Biological Laboratory, Seattle, and in 1953 by the University of Washington College of Fisheries and the IPSFC (Inter- national Pacific Salmon Fisheries Commis- sion). The potential utility of the stimulus was demonstrated in laboratory studies and with small-scale field installations by scientists of these agencies, but some of the useful elec- trical conditions were found by BCF scientists to be injurious or lethal to the young fish (Collins, Volz, and Trefethen, 1954). Three IPSFC scientists tried large-scale installations in the field, designed to guide juvenile salmon downstream migrants to safe passage facilities at dams. They demonstrated no alarming mortalities, but they did not achieve fully their purpose (Andrew, Kersey, and Johnson, 1955; and Andrew, Johnson, and Kersey, 1956). At the time of BCF's laboratory work in 1952, the authors suggested the need for ex- ploring the possibility of nonvisible injurious effects of electricity on the well-being of young fish, on their growth to maturity, and on their reproductive ability. The question had been raised to some extent by McMillan (1928) in his experiments with the electric screen and by Delov and Tomashevskii (1933) in connection 546 TABLE 1.-]Pater and electrical conditions to which test lots of rainbow trout from the 1952 and 1953 year classes were exposed, 9-10 June 1953 Electrical conditionsr Exposure Water conditions Pulse Pulse Voltage Year Duration frequency duration gradient Temperature Resistivity class Date Number (secs) (pulse/sec) (.see) (volts/cm) (C) (ohm-cm) 1952 June 9, 1953 825 30 5 80 0.75 10.5-13.2 5,800-7,000 1953 June 9-10, 1953 954 - 30 8 40 1.00 9.1-11.3 7,550-8,750 'Pulse shape used was called pulse shape "B" by Collins, Volz, and Lander (1953); it has an exponential (capacitor charge) leading edge and a rectangular trailing edge. with electrofishing; Meyer-Waarden (1953) and Riedel (1954) investigated the effects of electrical shock on some species, but the sur- vival, growth, and fecundity of salmon and trout that had been shocked, and the survival and development of their offspring, have not been studied. This paper describes a study of the survival, growth, and fecundity of two successive year classes of hatchery-reared rainbow trout (S. gairdneri) after they were shocked with pulsat- ing direct current (p.d.c.), and of the survival and the development of their eggs through hatching and of the resulting fry to the feeding stage._ MATERIALS AND METHODS Yearling and young-of-the-year rainbow trout were selected at random in May 1953 from fry hatched in January 1952 and 1953, respectively, at the Bureau of Sport Fisheries and Wildlife National Fish Hatchery, Win- throp, Washington. Test and control groups of each year class were anesthetized with chloro- butanol, weighed, measured, and finclipped for identification on 26-27 May 1953. Test and control young of the year (1953 year class) were kept in a divided hatchery trough and test and control yearlings (1952 year class) in a divided outdoor pond until electroshocking. Test fish were exposed to pulsating d.c. in lots of about 25 (1952 year class; total of 825 fish) and 100 (1953 year class; total of 954 fish), on 9-10 June 1953 (Table 1). The test chamber was between two flat, vertical elec. trodes of hardware cloth placed 71 cm apart in a long, wooden trough with a top screen of plastic mesh. A special electronic switch and shaper circuit interrupted the output of a portable d.c. unit to produce pulse frequencies, pulse durations, and a pulse shape' known to guide young coho salmon (O. kisutch) effec- tively under laboratory conditions (Collins, Volz, and Lander, 1953). Voltage was read on a calibrated oscilloscope, and the pulse shape was monitored on a special, synchro- nized oscilloscope. Temperature and resis- tivity of water in the test chamber were mea- sured and recorded before and after each test lot was exposed. Water and electrical condi- tions are summarized in Table 1. From 4 to 84% of the fish in test lots of the 1952 year class were narcotized, but all fish revived immediately. None of the fish of the 1953 year class suffered electronarcosis. All test and control fish were alive 2 days after exposure. Test lots were combined with the respective controls and held under the age- specific conditions of handling and feeding at the station. Samples of the fish were examined for determination of growth and mortalities on several dates from 15 July 1953 to spawn- ing time. Because of the high rate of survival of the test fish of both year classes, numbers of test fish were reduced by random elimina- tion throughout the experiment, mainly to conform with hatchery requirements at spawn- ing time. The experimental fish of the 1952 year class were spawned between 28 December 1954 and 23 February 1955; those of the 1953 year class were spawned between 9 January and 21 March 1956. Low water temperatures during the winter of 1955-56 delayed the onset of maturity and extended the spawning season of the 1953 year class. Spawning procedures ' Pulse shape was called pulse shape "B" by Collins, Vohs, and Lander (1953) ; it has an exponential (capacitor charge) leading edge and a rectangular trailing edge.