The actions of in ovo cortisol on egg fertility, embryo development and the expression of growth-related genes in rainbow trout embryos, and the growth performance of juveniles.

Rainbow trout (Oncorhynchus mykiss) oocytes were incubated for 3 hr in ovarian fluid alone (CC), or cortisol-enriched ovarian fluid [100 or 1,000 ng ml(-1) (CL and CH, respectively)], after which they were fertilized; the growth and development of the embryos reared from these oocytes was monitored until first feed, and the juveniles were monitored for 9 months. The hatching rates of the CH group were significantly reduced, but the overall survival as measured at 40-week post-fertilization was similar in the three treatment groups. In addition, significant apparently biphasic changes relative to the CC group were found in the expression of some key growth-related genes in the CL and CH treatment groups, particularly IGF-1, IGF-2, GH1, GH2, GH receptors, and thyroid hormone receptors (TRα and TRβ). Moreover, the juveniles of the CL (but not the CH treatment group) exhibited enhanced growth; the enhanced growth could not be explained on the basis of increased feed conversion efficiency or changes in serum GH levels at the juvenile stage. Additionally, relative growth rates from the three treatment groups were similar, suggesting that the biphasic growth-enhancing effects of cortisol occurred very early in embryogenesis.