Search

This research, which is part of a larger study designed to assess the feasibility of winter flounder, Pseudopleuronectes americanus, stock enhancement in New Hampshire, identifies hatchery feeds that optimize feeding-related performance of fish once released in the wild. Fish reared on post-nauplii of brine shrimp, Artemia sp., white worms, Enchytraeus albidus, common burrower amphipods, Leptocheirus plumulosus, and formulated pellets were evaluated post-release from in situ cages using survival, growth rate, feeding onset and incidence, stomach fullness, diet composition, and nucleic acid-based condition as indicators of hatchery diet suitability. Amphipod-reared fish had the highest mean stomach content index of all feed types, including wild fish. Wild and worm-reared fish exhibited the most similar survival, overall stomach fullness, and diet composition profiles over time. Amphipod-reared fish ranked highest in overall performance; however, if wild fish performance is viewed as the ideal for a stocked fish, worm-reared fish performed optimally. This study describes hatchery feeding strategies that may ease the transition of flatfish released into the wild for stock enhancement.

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

Flatfish reared for stock enhancement often exhibit irregular behavioral patterns compared with wild conspecifics. These “deficits”, mostly attributed to the unnatural characteristics of the hatchery environment, are assumed to translate to increased predation risk. Initially releasing fish in predator-free conditioning cages may help flatfish adjust to the wild environment, establish burial skills, begin pigment change, recover from transport stress, and experience natural (live) food sources before full release into the wild. However, the impact of cage conditioning on the performance and behavior of flatfish has yet to be fully assessed. We conducted video trials with 10-cm, hatchery-reared Japanese flounder, Paralichthys olivaceus , in sand-bottomed aquaria to assess four treatments of flounder: (1) reared fish cage conditioned for 7 d in the shallow coast, (2) reared fish directly from hatchery tanks, (3) wild fish, and (4) reared fish released directly from hatchery tanks into the wild and then recaptured after 6 d at large. Burying ability, predation, and threat response to a model predator were examined. Wild fish buried most, followed by cage conditioned, and released-then-recaptured and non-conditioned (directly from tank) fish. Wild and conditioned fish revealed much lower variation in total movement duration, which corresponded with lower levels and variation in prey vertical movement. Fish of all condition types exhibited a lower number of attacks and off-bottom swimming events, and a lower movement duration when the model predator was in motion versus when it was still. This study is the first to evaluate the behavioral mechanisms of hatchery-reared flatfish that have been cage-conditioned or released-then-recaptured. In addition, we provide evidence that cage conditioning can enhance the performance of released flatfish.

Conditioning is the process of providing individuals reared for stock enhancement with some degree of “natural” experience prior to release. Conditioning flatfish in predator-free cages may help adjustment to the wild. From 2008–2010, the Obama Laboratory conducted pre-release, experimental cage conditioning for Japanese flounder in both the Takahama and Obama portions of Wakasa Bay, Japan. Recaptured fish were acquired through a cooperative effort between researchers and local fishermen. The objectives were to describe how characteristics of released flounder changed with cage exposure and to determine how recapture rates compared between conditioned and non-conditioned fish. Significantly more conditioned fish were recaptured than non-conditioned fish in Obama Bay in 2010 (p < 0.05). In 2008 and 2009, recapture rates of conditioned and non-conditioned flounder followed the same trend, although these were not significantly different. Laboratory experiments revealed that conditioned fish had significantly...