Feeding habits of wild and hatchery-reared Pacific threadfin, Polydactylus sexfilis (family polynemidae), in Hawai

As part of a marine restocking study in Hawai, an assessment of the dietary acclimation of hatchery-reared Pacific threadfin, Polydactylus sexfilis, in the natural environment was undertaken. Successful acclimation of cultured threadfin was determined by comparing dietary similarities between stocked and wild threadfin. The diets of both were primarily composed of crustaceans and strongly overlapped (>0.80). Relative prey weights did not differ significantly between cultured and wild threadfin (Mann-Whitney, p > 0.05). Evidence of an ontogenetic shift in diet was apparent where larger prey items such as crabs and fishes became more common, and smaller prey such as amphipods became less common with successively larger threadfin size classes. A trial was carried out to reduce the initial acclimation period of hatchery-reared fish by conditioning them with live shrimp as food for several days before release. Conditioned threadfin had a significantly higher frequency of wild shrimp in the diet up to 5 days post-release than the control group (X(2) = 5.35, p = 0.02). Further research testing the frequency and duration of the treatment period may result in maximizing the initial survival of cultured fish in the field while minimizing the cost of shrimp production.