Jeffrey A. Malison

Effects of rearing density on the stress response and growth of rainbow trout.

Abstract One-year-old rainbow trout Oncorhynchus mykiss were reared for 8 weeks at a density of either 56 or 267 g fish/L (based on the volume of net-pens), equivalent to density indexes of 2.3 and 11.1 g fish/L-cm total fish length), respectively. The fish were held in 0.6 × 0.3-m netpens submerged to a depth of 0.15 m. Two net-pens for each fish density were suspended in each of three 3,040-L circular tanks provided with sufficient flow to maintain loading rates in the tanks at less than 800 g/(L-min). The fish were then subjected to an acute handling stress by being removed from the water for 60 s. No differences in the time course of changes in serum cortisol levels or hematocrits were observed over a 12-h period between fish in the two density groups. There were also no differences between the two groups of fish in weight, length, body condition factor (weight/length3), interrenal nuclear diameter, or the percentage of the anterior stomach that was mucosa. These results indicate that if high water qu...

Validation of a microtitre plate ELISA for measuring cortisol in fish and comparison of stress responses of rainbow trout (Oncorhynchus mykiss) and lake trout (Salvelinus namaycush)

A microtitre plate enzyme-linked immunoassay (ELISA) was validated for measuring serum cortisol in rainbow trout (Oncorhynchus mykiss) and lake trout (Salvelinus namaycush). The ELISA uses a highly specific rabbit antibody raised against cortisol-3-carboxymethyloxime (CMO)/bovine serum albumin (BSA), and a conjugate of horseradish peroxidase (HRP) also linked to cortisol in the 3-position by a CMO bridge. The chromatogenic substrate is 3,3′,5,5′-tetramethylbenzidine (TMB). The standard curve was linear (logit/log) from the lower limit of sensitivity of the assay (2 pg/well = approx. 100 pg/ml serum) to approximately 1000 pg/well. The ELISA satisfied the strictest criteria of specificity, reproducibility (interassay coefficient of variation 98%). Changes in serum cortisol, glucose and chloride were measured in rainbow trout and lake trout following an acute 1-min handling stressor. In both species, cortisol levels rose rapidly to peaks of approximately 300 ng/ml by 1 h post-stress, and slowly returned to baseline over the next 48 h. Glucose levels rose faster in rainbow trout than in lake trout but reached similar peak levels of approximately 135 mg/dl at 6 h post-stress in both species. Chloride levels declined between 1 and 3 h in both species, although rainbow trout showed a greater and more prolonged hypochloremia than lake trout. Within 1 week following administration of the stressors, 19 rainbow trout ( ∼ 17% of the fish in the experiment) and 2 lake trout ( ∼ 2%) died. Most of the fish which died had been sampled when their serum chloride levels were low, suggesting that the survival rates of stocked trout may be increased if they are rehandled and stocked before or after this period of hypochloremia.

Endocrine and gonadal changes during the annual reproductive cycle of the freshwater teleost,Stizostedion vitreum.

The annual reproductive cycle of walleye (Stizostedion vitreum) was characterized by documenting changes in gonadal development and serum levels of estradiol-17β (E2), testosterone (T), 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P), and 11-ketotestosterone (11-KT) in wild fish captured from upper midwestern lakes and rivers throughout the year. Fish from the populations used in this study spawn annually in early- to mid-April. Walleye showed group synchronous ovarian development with exogenous vitellogenesis beginning in autumn. Oocyte diameters increased rapidly from ∼ 200 μm in October to ∼ 1,000 μm in November, and reached a maximum of 1,500 μm just prior to spawning. Changes in gonadosomatic indices (GSIs) paralleled changes in oocyte diameters. Serum E2 levels in females increased rapidly from low values in October (< 0.1 ng ml−1) to peak levels of 3.7 ng ml−1 in November, coinciding with the period of the most rapid ovarian growth. Subsequently, E2 levels decreased from December through spawning. Serum T levels exhibited a bimodal pattern, increasing to 1.6 ng ml−1 in November, and peaking again at 3.3 ng ml−1 just prior to spawning. We detected 11-KT in the serum of some females at concentrations up to 5.6 ng ml−1, but no seasonal pattern was apparent. In this study (unlike our results in a related study) 17,20-P was not detected. In males, differentiation of spermatogonia began in late August, and by January the testes were filled (> 95% of germ cells) with spermatozoa. Mature spermatozoa could be expressed from males from January through April. GSIs ranged from 0.2% (post-spawn) to 3.2% (pre-spawn). Serum T levels rose from undetectable levels in post-spawn males to 1.6 ng ml−1 by November, remained elevated throughout the winter, and peaked at 2.8 ng ml−1 I prior to spawning. Levels of 11-KT in males remained low (< 10 ng ml−1, from post-spawning through January, then increased significantly by March and peaked just prior to spawning at 39.7 ng ml−1. Our results indicate that vitellogenesis and spermatogenesis are complete or nearly so, in walleye by early winter, and suggest that it may be possible to induce spawning in this species several months prior to the normal spawning season by subjecting fish to relatively simple environmental and hormonal treatments.

Habituation to Captivity and Controlled Spawning of White Bass

Abstract We successfully spawned white bass Morone chrysops that had been habituated to captivity in indoor tanks for over 1 year and whose cycles were entrained by simulated temperature and light regimes. In summer (1990) 300 white bass (300–600 g) of an approximately even sex ratio were distributed into three 10,000-L water-recycle systems. One system was maintained under an ambient photoperiod and temperature regime, one was maintained under a regime that simulated a 9-month (compressed) annual cycle of changing photoperiod and temperature, and one was held at a temperature range at or above spawning temperature (15–25°C) and constant photoperiod (14 h light: 10 h darkness). By human chorionic gonadotropin (hCG) injections (1,100 IU/kg for female fish; 275 IU/kg for males), we induced the compressed-cycle fish to spawn in March 1991 and the ambient-cycle and constant-cycle fish to spawn in May 1991. Constant-cycle fish injected with hCG in March 1991 failed to spawn. Male white bass continuously held a...

The influence of triploidy and heat and hydrostatic pressure shocks on the growth and reproductive development of juvenile yellow perch (Perca jlavescens)

Abstract We evaluated triploidy induction as a means to sterilize yellow perch (Perca flavescens) and reduce the diminution of growth associated with the onset of sexual maturation. Treatment of perch eggs with heat shocks (28–30°C, for durations of 10–25 min, beginning at 2–5 min post-fertilization) or hydrostatic pressure shocks (9000 or 11 000 psi, for durations of 8 or 12 min, beginning at 5 min post-fertilization) resulted in triploidy induction rates of 30–70%. In one experiment, juvenile heatshocked triploid perch grew faster than heat-shocked diploids. In a second experiment, heat-shocked triploid perch grew slower than unshocked diploids up to 25 g, but subsequent growth of fish from the two groups was not different. In a third experiment, unshocked diploids grew faster than fish subjected to either heat or pressure shocks, and among shocked fish, triploids outgrew diploids. Histological inspections revealed that gonadal development of juvenile triploid perch of both sexes was retarded compared to that of diploids. These findings show that heat and pressure shocks exert a negative influence on growth that is independent of changes in ploidy, and that triploid perch may have the potential to outgrow diploids if the negative effects of such shocks can be avoided.

Effects of fish size at harvest, initial stocking density and tank lighting conditions on the habituation of pond-reared yellow perch (Perca flavescens) to intensive culture conditions

Abstract Groups of age-0 pond-reared yellow perch ( Perca flavescens ) fingerlings were harvested and habituated to intensive culture conditions and formulated feeds under various treatment regimes. The habituation intervals for the different fish groups lasted from 19 to 51 days, until the number of dead fish recovered daily for each group became insignificant and all remaining fish were actively feeding. End points measured included (1) habituation, defined as the percentage of fish that survived the transition to intensive culture conditions; (2) starvation, defined as the percentage of fish that died and were recovered; and (3) cannibalism, defined as the percentage of fish that could not be accounted for at the end of the habituation intervals. The habituation of perch harvested at mean total lengths (TLs) of 16.9, 32.5, or 42.6 mm did not differ (53.3 ± 5.5, 68.3 ± 6.3, and 55.7 ± 4.5%, respectively), but habituation occurred faster and over a shorter interval in smaller perch. Perch harvested at 16.9 mm TL grew to a larger ultimate size than those harvested at 42.6 mm TL. Fingerlings harvested at 16–20 mm TL and initially stocked into 750-l tanks at 13.7 fish/l had improved habituation (53.3 ± 5.5%) and reduced cannibalism (20.3 ± 11.0%) compared to those stocked at 37.4 fish/l (28.0 ± 3.2 and 50.5 ± 3.2%, respectively). Perch reared using internal tank lighting had improved habituation compared to those reared overhead lighting (54.5 ± 3.2 vs. 42.7 ± 2.2%). Our results show that pond-reared perch fingerlings can be successfully habituated to intensive culture conditions at a mean size as small as 16.9 mm TL, and that fingerling production can be greatly improved by using a strategy of early pond harvest in combination with appropriate tank stocking densities and internal tank lighting.

Fast growth in rainbow trout is correlated with a rapid decrease in post-stress cortisol concentrations

Abstract Growth rates of rainbow trout (Oncorhynchus mykiss) were assessed with respect to serum concentrations of cortisol, glucose, and chloride following exposure to a standardized handling stressor. Individually tagged rainbow trout (N=400, 90–250 g) were reared for 10 months and the handling stressor was administered three times at approximately 3-month intervals. Fish were bled at either 1-, 3-, or 6-h post-stress for measurement of serum cortisol, glucose, and chloride, with individuals always being bled at the same time post-stress. For cortisol, 42% of the fish had a consistent response, defined as being ranked in the upper or lower 50th percentile for all three samples collected, whereas for glucose and chloride, 35% and 37% had consistent responses. Among all the fish, growth was best correlated (P

Manipulation of ploidy in yellow perch (Perca flavescens) by heat shock, hydrostatic pressure shock, and spermatozoa inactivation

Abstract Heat shocks, hydrostatic pressure shocks, and ultraviolet radiation were evaluated for their efficacy as methods of manipulating ploidy in yellow perch (Perca flavescens). The most effective methods of inducing triploidy were heat shocks of 28–30°C applied at a time of initiation (TI) of 5 min postfertilization for durations of 10 or 25 min, and hydrostatic pressure shocks of 9000 or 11 000 psi applied at a TI of 5 min for a duration of 12 min. These treatments resulted in triploidy induction rates that ranged from 54–100%, and embryonic survival rates of 16–80%. Cold shocks of 0°C had no effect on the ploidy or survival of embryos. For perch, hydrostatic pressure shock offered several advantages over heat shock as a method of manipulating ploidy. The most effective methods of inducing tetraploidy were hydrostatic pressure shocks of 9000 psi applied at a TI of 192 min for durations of 16 or 24 min. Ultraviolet radiation of perch sperm with doses of 3240–6480 ergs/mm2 resulted in 100% inactivation of paternal chromosomes, and perch eggs fertilized with inactivated sperm had survival rates of > 50%, thereby establishing methods for producing gynogenetic perch. Studies comparing the growth and performance of diploid vs. triploid perch are underway. Tetraploid perch are being reared to sexual maturity to evaluate their potential as brood fish.

Induction of out-of-season spawning in walleye (Stizostedion vitreum)

Abstract Simple environmental and hormonal treatments were used to induce out-of-season spawning in walleye Stizostedion vitreum up to 10 weeks prior to the normal reproductive season. Wild walleye were captured in the autumn, held in earthen ponds, and in late January, February, and March (approximately 10, 6, and 3 weeks prior to natural spawning), 16–20 female and 4–8 male walleye were recaptured and transferred to indoor tanks. Water temperature was raised from 2°C to 10°C over a one week period, and photoperiod held at 12 h light: 12 h dark. The females were injected with either human chorionic gonadotropin (hCG), des-Gly 10 [ d -Ala 6 ] LHRH-ethylamide (LHRHa), hCG and 17 α ,20 β -dihydroxy-4-pregnen-3-one (17,20-P), or saline as a control. Each month, at least some females in each treatment group were successfully induced to ovulate. No control fish ovulated at any time. In January, hCG was the most effective treatment at inducing ovulation (3/5 fish). In February and March, all but one hormone-injected fish ovulated. In general, the eggs collected from fish treated with either hCG or LHRHa were of good quality with overall survival highest in hCG-treated fish. Eggs collected from 17,20-P-treated fish were small and had very low survival. In February and March, serum levels of estradiol-17 β and testosterone were different between fish treated with 17,20-P and those treated with either hCG or LHRHa. Out-of-season spawning could be used to provide walleye fry for intensive culture systems at multiple times of the year, thereby facilitating research on indoor fry culture. In addition, walleye fingerling production could be initiated as early as January, allowing public and private hatcheries to produce larger age-0 walleye fingerlings for stocking than would otherwise be possible.

Effects of selected hormones and male cohorts on final oocyte maturation, ovulation, and steroid production in walleye (Stizostedion vitreum)

Abstract A series of in vivo and in vitro experiments were conducted to evaluate the effects of selected hormones and male cohorts on oocyte maturation and ovulation in walleye captured from the wild. In one experiment conducted 2 weeks prior to the normal spawning season, single intramuscular injections of human chorionic gonadotropin (hCG, 500 IU kg −1 ) and des-Gly 10 [D-Ala 6 ] LHRH-ethylamide (LHRHa, 100 μg kg −1 ) stimulated final oocyte maturation and ovulation. LHRHa induced oocyte maturation faster than hCG. The presence of spermiating males had a slight stimulatory effect on oocyte maturation in non-injected fish, but did not potentiate the effects of LHRHa. In a second experiment conducted 3 weeks prior to normal spawning, hCG (500 IU kg −1 ), LHRHa (100 μg kg −1 ), and 17,20-P (100 μg kg −1 ) all induced final oocyte maturation. In this experiment, however, hCG was more effective than LHRHa, and there was no male cohort effect. In maturing females, oestradiol-17β levels declined, and testosterone levels increased transiently prior to final oocyte maturation and ovulation. Levels of 17α,20β-dihydroxy-4-pregnen-3-one (17,20-P) were significantly elevated 2 and 3 days prior to ovulation. Cortisol levels were high (50–100 ng ml −1 ) in newly captured fish and remained elevated during the experimental period. No control fish in either experiment underwent final oocyte maturation. These findings suggest that capture and confinement stress may inhibit oocyte maturation in walleye. In vitro, human chorionic gonadotropin (hCG) was a potent inducer of final oocyte maturation whereas LHRHa had no effect. Of various steroids tested in vitro, 17,20-P and 17α,20β,21 -trihydroxy-4-pregnen-3-one were the two most effective inducers of final oocyte maturation and ovulation, and the lowest dose of 17,20-P tested (0.01 ng ml −1 ) was a consistent and potent inducer of final oocyte maturation. These data, together with our in vivo results, support the hypothesis that 17,20-P may be the maturation-inducing steroid in walleye. Cortisol, alone or in combination with hCG, had no effect on oocyte maturation or ovulation in vitro, indicating that any negative effects of cortisol on oocyte maturation in walleye probably occurs at higher levels of the hypothalamic-pituitary-gonadal axis.