The potential for using the anabolic hormones 17α-methyltestosterone and (or) 3,5,3′-triiodo-L-thyronine in the fresh water rearing of coho salmon (Oncorhynchus kisutch) and the effects on subsequent seawater performance

Abstract

Juvenile coho salmon (Oncorhynchus kisutch) held in 11 °C fresh water (FW) were fed Oregon moist pellets supplemented with 3,5,3′-triiodo-L-thyronine at 4 ppm (T34) or 20 ppm(T320) and (or) 17α-methyltestosterone at 0.2 ppm (MT0.2) or 1 ppm (MT1) until early or normal seawater (SW) transfer.During FW residency all hormonal treatments improved growth, appetite, and food utilization. In February, fish fed T320 singly or with MT had increased degranulation of somatotrop cytoplasm. Thyroid epithelial cell height of fish fed T34 or T320 was either suppressed or enhanced. MT1 singly or combined with T3 induced androgenic side effects in males. Proximate body composition was affected only by MT. T320 induced morphological anomalies and treatment was discontinued. In May, thyroid activity and number of putative gonadotrops of fish fed MT1 were increased. Androgenic effects of all groups given MT1 were greater in May than in February.After SW transfer in February growth, appetite, and food utilization were depressed but fish fed T34 performed better than controls. Performance of all groups improved after May but, in general, mortality increased slightly. After transfer in May, T3-fed fish had increased growth in length.It is concluded that MT and T3 effectively enhance growth in FW but only T3 facilitates SW transfer.