Flatfish stock enhancement: Examining conditioning strategies to promote success
Conditioning is the process of providing individuals reared for stock enhancement with some degree of "wild" experience prior to release. Flatfish trained for "wild" conditions may more easily and successfully transition to natural environments. This dissertation identifies strategies that optimize feeding-related performance of flatfish in the hatchery and subsequently post release in the wild. The influence of live feed conditioning on feeding performance of juvenile winter flounder, Pseudopleuronectes americanus, was investigated. In the hatchery, fish reared on live feeds exhibited significantly higher survival (P < 0.0001) and growth (P < 0.01) than those reared on formulated feed. Once released into cages in the wild, amphipodreared fish had higher mean Stomach Contents Index and RNA/DNA of all feed types, including wild fish. Wild and worm-reared fish exhibited the most similar survival, baseline RNA/DNA values, overall stomach fullness, and diet composition profiles over time. Pre-release, experimental cage conditioning was conducted for stocking Japanese flounder, Paralichthys olivaceus, in Wakasa Bay, Japan. Recaptured fish were acquired through a cooperative effort between researchers and local fishermen. More conditioned fish were recaptured than non-conditioned fish. Laboratory experiments revealed that conditioned fish had significantly better burying abilities (p < 0.001) and enhanced feeding abilities compared to non-conditioned fish. Video trials were conducted with Japanese flounder to assess the behavior of reared fish directly from hatchery tanks, cage-conditioned, and released-and-recaptured, compared to wild fish. Wild fish buried and attacked most, followed by conditioned, reared-and-recaptured, and non-conditioned fish. Wild and conditioned fish revealed much lower variation in total movement duration, which corresponded with lower levels and variation in prey vertical movement. All fish exhibited a lower number of attacks and off-bottom swimming events, and a lower movement duration when exposed to a moving predator model. The present research provides information that may promote advances in feeding strategies for flatfish stock enhancement. This work is the first to examine flatfish conditioning strategies using market data and to evaluate the behavior of hatchery-reared flatfish that have been cage-conditioned or released-and-recaptured. In addition, evidence of enhanced performance by cage-conditioned flounder is provided.
Agriculture, Fisheries and Aquaculture, Psychology, Behavioral Sciences, Zoology
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