COMBINED APPLICATION OF CORTISOL AND TRIIODOTHYRONINE IN THE CULTURE OF LARVAL MARINE FINFISH

Newly-hatched larvae of Pacific threadfin (or 'moi'; Polydactylus sexf ilis) exposed to triiodthyronine (T-3; 2.6 p.p.m.) and cortisol (0.1 p .p.m.) by immersion for 1 h exhibited earlier development than untreat ed controls and larvae exposed to the individual hormones. The onset o f initial gut formation and initial somatic pigmentation were accelera ted by this treatment. Survival to 29 days of age was also improved (P <0.05, Experiment 1; P<0.005, Experiment 2) in hormone-treatment group s as compared with untreated controls. Our ongoing experiments address two working hypotheses: (1) advanced digestive function induced by T- 3 and cortisol imparts improvements in food utilization during the cri tical time of first-feeding and (2) uniform growth following hormone t reatment leads to reduced rates of cannibalism. These results appear t o be consistent with established development-promoting interactions of T-3 and cortisol in Japanese flounder, amphibians, and other vertebra tes. These observations suggest that hormone therapy may have practica l utility in the culture of marine larvae.