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The inclusion of soybean meal and soy concentrates in finfish feeds may introduce endocrine disrupting compounds in the form of phytoestrogens. Genistein, which may dually act as an oestrogen receptor agonist/antagonist, has been shown to elicit both masculinizing and feminizing effects in several teleost species. The objective of this investigation was to examine the effects of dietary genistein administration on reproductive development, growth and survival in southern flounder (Paralichthys lethostigma). Southern flounder received one of three experimental diets which contained varying concentrations of genistein (control - 0, low dose -100 and high dose -1000 mg genistein kg -1 feed) from 84 to 153 days post hatch (DPH). Fish remained in culture until 285 DPH at which time sex ratios were determined. Growth and survival were evaluated at 153 and 285 DPH. Greater numbers of female fish resulted from the low and high dose genistein treatments (98 ± 2% and 78 ± 12% respectively), as compared to the control group (21 ± 10%). Reduced growth at 153 DPH and poor survival (28%) at 285 DPH were also observed for the high dose genistein treatment. Collectively, these results demonstrate the feminizing effects of genistein in southern flounder, but reduced growth and survival with high dietary administration. [ABSTRACT FROM AUTHOR]

Female summer flounder grow considerably faster than males, and rearing temperature has been shown to influence sex differentiation in related species. The present studies were conducted to examine sex differentiation of post-metamorphic juveniles reared at temperatures conducive for commercial production. In experiments 1 and 2, offspring produced from crosses with meiogynogenetic, sex-reversed males and normal females were raised at 14, 16 or 18°C for ≥300 days or 12°C for 30, 60 or 120 days and then transferred to a male-determining temperature (21°C). In all cases, the fish developed predominantly as phenotypic males (≥74%). In a third experiment, offspring produced from crosses with normal males and females were reared at 15, 17 and 19°C for 111, 227 and 278 days and then transferred to 21°C. Most fish (≥92.1%) developed as phenotypic males irrespective of rearing temperature or length of exposure. Several hypotheses are proposed for these findings and further research is necessary to understand the sex-determining mechanisms in this species before the economic advantages associated with sexually dimorphic growth can be realized. [ABSTRACT FROM AUTHOR]

The summer flounder, Paralichthys dentatus L., is a high-value species and considerable research has been conducted to determine practices conducive for its culture. As milt can be limited in this species, experiments were conducted to develop a practical sperm cryopreservation protocol for hatchery use. Two dilution ratios (1:2 and 1:4; sperm:extender), 2 diluents (saline and sucrose-based), 2 cryoprotectants (10% DMSO and 12% glycerol) and 3 freezing rates (−5, −10 and −15°C min−1) were evaluated using differential staining to assess post-thaw sperm survival. Seven combinations of the factors examined reduced post-thaw viability by less than 30%. The average viability of sperm from fresh, pooled flounder milt (67.2 ± 2.9%) was not different from that of thawed milt diluted 1:4 with sucrose diluent (10% DMSO) frozen at −5°C min−1 (38.4 ± 7.7%) and fertilization and hatch success were not different in trials using fresh or thawed, cryopreserved sperm. From these experiments a practical sperm cryopreservation method was developed, but further refinement of the freezing protocol is necessary to optimize results. [ABSTRACT FROM AUTHOR]

Lipid content, lipid class and fatty acid compositions were determined in eggs from wild and captive black sea bass, Centropristis striata L., from northern (New England) and southern (South Carolina) regions to determine the effects of diet on egg composition and fertilization success. The formulated diets fed to the northern captive (NC) fish were higher in total lipids (22%) compared with the cut fish and squid diet fed to the southern fish (SC; 3.3% lipid) and had a higher relative amount of linoleic acid (LA) and lower relative amounts of docosahexaenoic acid (DHA) and arachidonic acid (AA). These dietary differences were broadly reflected in the egg lipid composition. The LA levels were higher in all lipid classes in eggs of NC fish while AA levels were lower. The DHA was higher in the major polar lipids (PL) (phosphatidylcholine and phosphatidylethanolamine) of SC eggs compared with NC. Compared with wild fish, both captive groups produced eggs with PLs richer in LA and lower in DHA and AA. Over all fish groups, fertilization success was directly correlated with levels of DHA and AA in the PLs and was inversely correlated with LA levels. [ABSTRACT FROM AUTHOR]

Black sea bassCentropristis striataL. are protogynous hermaphrodites that develop and spawn as females before changing sex to male. Since all fish eventually become males, determining the relationship between sperm production, sperm quality and seasonal changes in plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) could be useful for identifying appropriate males to maintain as broodstock. Milt and blood samples were collected three times during an 8-week spawning season. Milt volume (3.5±0.76 mL kg−1), sperm density (3.2× 108± 0.31 cells mL−1), sperm production [11× 108±3.4 cells kg−1 body weight (BW)] and sperm motility (80±0.6%) were at their highest during the first sampling interval and coincided with the highest 11-KT levels (1.0± 0.11 ng mL−1). All of the sperm indices decreased to their lowest levels during the final 3 weeks of the study. Sperm viability was highly correlated (adjustedR2=0.84) with sperm motility. Sperm cryopreserved in modified Mounib's extender (MME) had the highest post-thaw motility compared with two other extenders. Post-thaw motility of sperm cryopreserved in MME was not different from fresh after 90 days of storage. There was no difference in fertilization rates between fresh (69±2.4%) and post-thaw (67±4.1%) sperm samples taken from the same male or among males. These results demonstrate that the quality of black sea bass spermatozoa is higher earlier in the spawning season and that acceptable post-thaw fertilization rates can be obtained from cryopreserved sperm. [ABSTRACT FROM AUTHOR]