James A. Held

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.

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.

Comparative survival, growth, and reproductive development of juvenile walleye and sauger and their hybrids reared under intensive culture conditions.

Abstract Survival and performance characteristics of intensively cultured purebred walleyes (Stizostedion vitreum) and saugers (S. canadense) and hybrids of walleye females × sauger males (W × S) and sauger females × walleye males (S × W) were compared. Among juvenile fishes reared in tanks for 84 d, W × S hybrids had significantly greater (P < 0.05) weight gain, length gain, and condition factors than either purebred walleyes or S × W hybrids, whereas purebred saugers grew slower than the other fishes. The W × S hybrids exhibited less aggressive behavior and were not as negatively affected by routine disturbances and handling as the other fishes. Hybridization had no effect on mean egg survival from fertilization to hatch (78.0% for walleyes, 79.2% for W × S hybrids, 50.3% for saugers, and 48.0% for S × W hybrids). Mean successful habituation of pond-reared fish (40–60 mm total length [TL]) to intensive culture conditions ranged from 67.5 to 91.0% survival after 28 d, but differences between the species ...

Manipulation of Ploidy in Walleyes by Heat Shock and Hydrostatic Pressure Shock

Abstract We evaluated heat shocks and hydrostatic pressure shocks as methods of manipulating ploidy in walleyes Stizostedion vitreum. Hydrostatic pressure shocks of 8,000 psi (1 psi = 6.895 kPa) applied at 4 min postfertilization (i.e., time of initiation, TI) for 30 min produced 100% triploidy in eggs from 18 of 20 females, survival ranging from 50% to 80%. At a preshock incubation temperature of 11°C, heat shocks of 28–31°C applied at a TI of 1–5 min postfertilization for 25 min induced triploidy in 20–50% of the shocked eggs and resulted in embryonic survivals of 20–50%. Hydrostatic pressure shock offered several advantages over heat shock as a method of inducing triploidy in walleyes. Hydrostatic pressure shock of 9,000 psi applied at a TI of 192 min for 8 min was most effective for inducing tetraploidy in walleyes. To date, however, no walleye tetraploids have survived beyond the sac-fry stage.

Production of Monosex Female Populations of Walleye from Intersex Broodstock

Abstract Monosex female populations of walleye Stizostedion vitreum were produced by fertilizing eggs with sperm obtained from intersex genetic female broodstock. To produce these broodstock, groups of walleyes at mean sizes of 50, 70, and 90 mm total length (TL) were fed a diet containing 17α-methyltestosterone at 15 mg/kg of food for 60 consecutive days. At age 2, three masculinized females from the 50-mm TL group were identified by the presence of both ovarian and testicular tissue. Mature spermatozoa were collected from these fish and used to fertilize eggs collected from normal females. Approximately 200 of the resultant progeny were reared to 145 mm TL. Morphological and histological examination of the gonads from a subsample of 35 of these fish confirmed that all were normal females. The potential uses of monosex female populations of walleye and the advantages of this indirect hormonal method of producing monosex female populations are discussed.