Effect of replacement of fish meal by fermented soybean meal in the diet for Japanese eel (Anguill japonica) on growth performance and content of mineral elements in muscle and skin

We investigated the effects of replacement of fish meal (FM) by fermented soybean meal (FSBM) in the diet for Japanese eel (Anguill japonica) on growth performance and content of mineral elements in muscle and skin. 0, 50 gkg-1, 100 gkg-1, 150 gkg-1 and 200 gkg-1 FSBM were substituted for 0.5%, 10%, 15% and 20% FM in the basal diet respectively. Experiments were carried out in 15 net cages, each was stocked with 50 elvers (37.620.16)g. The results show that curves of weight gain rate (WGR) and specific growth rate (SGR) present a parabola shape as the proportion of replacement increases, in which 15% replacement group is a turning point. The feed coefficient of fish fed with 15% FSBM is significantly lower than other groups (P0.05). 15% may be the best ratio of FSBM alternative to FM, that is150 kg FSBM could be used for every ton of eel feed. In addition, the replacement changes mineral elements amount in diet such as Al, K, Cu, B, Ca, Na, P and Fe. Concretely, the level of constant elements such as K, Ca, and P in fish muscle have no significant difference between all groups, while trace element Cu in muscle and skin of fish fed with FM is significantly different with that fed with FSBM (P0.05). Therefore, when replacing FM with FSMB, we should adjust the amount of mineral elements in feed.