Aqllaculture ELSEVIER Aquaculture 135 (1995) 79-86 Combined application of cortisol and triiodothyronine in the culture of larval marine finfish Christopher L. Brown *, Bong G. Kim Hawaii Institute of Marine Biology, School of Ocean and Earth Science and Technology, University of Hawaii, Box 1346 Coconut Island, Kaneohe, HI 9674, USA Abstract Newly-hatched larvae of Pacific threadfin (or ‘moi’; Polydactj~lus sexfilis) exposed to triiodthyronine (T3; 2.6 p.p.m.) and cortisol (0.1 p.p.m.) by immersion for 1 h exhibited earlier development than untreated controls and larvae exposed to the individual hormones. The onset of initial gut formation and initial somatic pigmentation were accelerated 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 groups as compared with untreated controls. Our ongoing experiments address two working hypotheses: (1) advanced digestive function induced by T3 and cortisol imparts improvements in food utilization during the critical time of first-feeding and (2) uniform growth following hormone treatment leads to reduced rates of cannibalism. These results appear to be consistent with established development-promoting interactions of T3 and cortisol in Japanese flounder, amphibians, and other vertebrates. These observations suggest that hormone therapy may have practical utility in the culture of marine larvae. Keywords: Thyroid; Cortisol; Development; Larval 1. Introduction Although larval husbandry methods have improved steadily over recent years, early mortality remains a primary obstacle to fish farming, especially for marine species that produce small eggs and larvae. Improved larval management and nutrition have brought some desirable marine species to the brink of mass culture, for example milkfish (Kelley and Lee, 199 1) , mullet (Liao and Chao, 199 1) , and red drum (Chamberlain et al., 1990). * Corresponding author: Tel. (808) 236-7445, Fax (808) 236-7423. 0044~8486/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOO44-8486(95)01016-5