No abstract

Winter flounder, Pseudopleuronectes americanus, are capable of releasing hundreds of thousands of eggs annually, but because of the vulnerability of the small, early life stages, there is high natural mortality, and few survive to maturity. Captively spawning, rearing, and releasing animals at a size or age beyond this period of high mortality may enhance stocks. The objectives of this research were to determine how different diets (both live and formulated) influenced hatchery survival and growth of juvenile winter flounder. Live feeds included post-nauplii of brine shrimp, Artemia salina; white worms, Enchytraeus albidus; and common burrower amphipods, Leptocheirus plumulosus. Fish reared on live feeds exhibited significantly higher survival (P < 0.0001) and growth (P < 0.01) than those reared on formulated feed, with fish fed white worms exhibiting the highest growth rates. This study provides hatchery feeding strategies that may ease the transition of flatfish released into the wild for stock enhancement.

No abstract

No abstract

Winter flounder, Pseudopleuronectes americanus, is currently being evaluated as a stock enhancement candidate in New Hampshire, USA; however, little is known about the gonadal development or the sex ratio of cultured juveniles. To determine the size at gonadal differentiation, 327 cultured fish ranging from <20 to 110 mm total length (TL), in 10‐mm‐TL size classes, were examined histologically. Gonads had differentiated into testes and ovaries in fish ≥41 mm TL (98%), whereas the majority of fish (81%) smaller than 40 mm TL possessed undifferentiated gonads. A total of 313 cultured fish >40 mm TL were analyzed for sex ratio. In 2003, 67 females and 164 males were identified, yielding a sex ratio that was significantly skewed toward male (χ2= 40.7, df = 1, P < 0.001). This trend held true when cultured fish were sorted by age and length, with the exception of those fish 61–70 mm TL. This aberration probably was because of a small sample size in this length category. However, in both the 2004 and the 2005 cultured populations, flounder sex did not deviate from a 1:1 ratio (2004 χ2= 0.12, df = 1, P= 0.724 and 2005 χ2= 0.02, df = 1, P= 0.881). The 2003 data suggest that environmental or genetic factors may affect winter flounder sex determination; rearing manipulation studies in the hatchery are needed to confirm this hypothesis.