In vivo effects of dietary isoflavones in rainbow trout Oncorhynchus mykiss

The increase of consumption of seafood has induced high pressure on traditional fisheries (FAO 2014) and in the main time, traditional fish stocks have been fully exploited limiting the amount of fishmeal, the principle protein component in aquaculture diets. Among vegetable sources, soybean meal (SBM) is frequently used to partially substitute fishmeal because of protein content, good amino acid profile, palatability to fishes, availability and low price (Ng et al. 2006). However, SBM contains also phytoestrogens, known as isoflavones, that are structurally similar to 17-β-estradiol (E2) and exert several estrogen-like biological effects with consequence on health, growth and reproductive development of fish (Latonnelle et al. 2002; Ng et al. 2006). In fish, isoflavones can induce production of vitellogenin (VTG), a complex protein of egg yolk, normally secreted by the liver under induction of estradiol and absorbed by the growing oocytes (Pellissero et al. 2001). The objective of this study was to evaluate the effects of soy isoflavones in rainbow trout in terms of estrogenic activity, health and growth by administration of diet added with different levels of isoflavones simulating the doses that potentially could be found in the commercial fish feed.