In this study, we analyzed contents of phytoestrogens (genistein, daidzein, equol, and coumestrol) in two commercial fish diets [a diet for trout (TD) and a diet for ornamental carp (CD)] using Liquid Chromatography-Mass Spectroscopy/Mass Spectroscopy (LC-MS/MS), and these contents were compared with that of a casein-based formulated fish diet (FD) which does not contain soya bean or fish meal. We also analyzed phytoestrogen contents in commercial infant casein-and soya bean-based diets. The contents of phytoestorogens were generally high in CD, TD, and soya milk, and low or non-detectable in FD and casein-based milks. Among these samples, CD showed the highest phytoestrogen contents: genistein, 390800 ng/g; daidzein, 416800 ng/g; coumestrol, 1325 ng/g; equol, 6.4 ng/ g. We also determined the estrogenic activity of the fish diets using male goldfish by measuring plasma vitellogenin (VTG) levels as a biomarker of estrogen exposure. When male goldfish were fed one of these diets for 31 days, plasma VTG was detected in CD-fed fish (78.01 ± 48.18 µg/ml) and TD-fed fish (3.51 ± 3.83 µg/ml), whereas plasma VTG was not detected in FD-fed fish (less than 0.040 µg/ml). These results indicate that the commercial fish diets examined contain a large amount of phytoestrogens and showed estrogenic activity that were strong enough to induce VTG production in male goldfish. It is necessary to eliminate estrogenic substances other than test chemicals in the screening test system for estrogenic endocrine-disrupting chemicals (EDCs). Since the formulated diet developed in the present study contain less phytoestrogens than the commercial fish diets and has low estrogenic activity, it is suggested that VTG production using male goldfish in combination with the low estrogen fish diet is a good in vivo system for evaluation of estrogenic effects of EDCs.

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Taste is an important trait of sea urchin quality. Highly contained alanine in gonads of the sea urchin Mesocentrotus nudus results in desirable taste. Past studies hypothesized that high levels of glutamic acid and/or alanine in feed increase the alanine content in the gonads. To identify the amino acids in feed that increase the alanine content in the gonads, the free amino acid content in the gonads of M. nudus of the following five treatment groups were compared at the start and end of the feeding experiment during May-July: sea urchins fed one of four experimental diets, in which glutamic acid (Glu S), alanine (Ala S), aspartic acid (Asp S), or glycine (Gly S) was supplemented, or a control diet without supplementation (Control). The alanine content in the gonads of Ala S increased significantly from the start. The content in the gonads of Glu S increased without significance. There was no significant difference in the alanine content in the gonads between Ala S and Glu S. The content in the gonads of Ala S was significantly higher than that of Asp S, Gly S, and Control. There were no significant differences in the aspartic acid and glutamic acid contents in the gonads among treatments at the end of the experiment. The higher alanine content in the gonads of Ala S than that in Glu S indicates that direct accumulation of alanine from the feed is effective. This study first identified the amino acids in feed that are closely associated with improvement in the taste of sea urchin gonad.

For developing sustainable fish feed in aquaculture industry, it has been indicated that minimizing fish-derived ingredient in aquaculture feed is important (Naylor et al., 2009). Plant protein and lipid sources are recommended as more stable and sustainable alternative feed ingredient than fish meal and oil; however, they are well-known for its demerits such as anti-nutritional factors, lack of indispensable amino acids and essential fatty acids for fish, low digestibility and palatability issues, poor growth performance in rearing trial (J.