Abstract
Rainbow trout, Oncorhynchus mykiss, were reared in flowing deep seawater (DSW) pumped from a depth of 687 m in Suruga Bay. One hundred and eleven alive fishes (8.6 cm in fork length (FL) in average), cultured in freshwater (FW) for 9 months, were used for this experiment. These fishes were moved to 100% DSW on the 3rd day after acclimated in mixed waters (1/2 and 3/4 in DSW/FW ratios, 16.5°C) by adding DSW every day. They were reared at a temperature of 14.7°C for 330 days by feeding sufficient amounts of formula food daily. The survival rate of fish decreased from the 2nd to 6th day (particularly on the 4th day) but thereafter became stable (27.9% on the 7th day). The fishes were considered to be successfully acclimated to DSW after 7days because of their stability of survival, silver to white (smolting) body color and good appetite. The survival rates after initial depletion in three size classes (< 8 cm, 8-11 cm and ≥ 11 cm in FL) were 0, 39.7 and 100%, respectively. Of the 31 acclimated fishes, 9 fishes (29%) survived 330 (323) days after the start (completion) of acclimation. At the end of culture, alive fishes attained an average FL of 32.9 cm, which was larger than the commercial size in FW culture. Their body colour was silver to white, which was different from those obtained in FW culture. Although some techniques should be revised, these data and the estimated growth and survival patterns in the cases of acclimating larger juveniles (11 and 15 cm in FL) demonstrated the possibility of rainbow trout aquaculture using DSW. Because of its clean, cold and stable nature, use of DSW will support the health of cultured fish (i.e., decrease of pharmaceuticals against fish diseases) and in turn the safety as food.
