Vitellogenin (VTG ) is a precursor of egg yolk proteins and like in all oviparous species, it is present also in fish. It is synthesized in the liver and is transported to the ovary via the bloodstream. VTG suggests the maturity level of female individuals but its gene is also present in male fish. Exogenous factors such as isoflavones (ISFs) present in the plant-derived raw materials used for aquafeeds, can exert estrogenic effects on vitellogenesis. The aim of the present study was to estimate the effects of dietary isoflavones on the vitellogenin levels of gilthead sea bream (Sparus aurata) , one of the most commercially important species in the Mediterranean aquaculture. This work was part of “Estrofish” project, that was co-financed by Greece and EU, under the “Operational Programme Competitiveness, Entrepreneurship and Innovation - EPAnEK 2014-2020” (MIS: 5052097, Code: T6YBP-00536).
Two isonitrogenous and isoenergetic diets, A and B, with similar fatty acid profile but different ISF content, were used for sea bream rearing. The ISF content of feeds was rich in isoflavones such as genistein (diet A: 9.45 μg/g, diet B: 2.47 μg/g) and daidzein (diet A: 3.41 μg/g, diet B: 2.25 μg/g). Two fish groups, L (initial size 101.4±0.8 g) and S (initial size: 55.58±0,55g) were fed on both diets ( 4 treatments: LA, LB, SA, SB) at satiation in Recirculating Aquaculture Systems (3 tanks per treatment). After 12 weeks, blood samples were collected . For the determination of plasma VTG a semi-quantitative ELISA method and the polyclonal anti-Rabbit Sole VTG were used. Blood parameters were measured by colorimetric assays. T he fatty acid profile of fish (liver and fillet ) and diets were estimated by gas chromatography (GC-FID).
OD values of VTG, were significantly higher (P <0.05) in LA than in LB treatment . No significant differences were observed in the VTG levels between S treatments. B oth fish groups showed significantly higher n-3 LC PUFA levels (% of total fatty acids) in liver, while the opposite in fillet, when fed on diet A compared to B. On the contrary, saturated fatty acids of fillet were significantly higher in fish fed on diet A compared to B, either in group S (mainly 16:0) or group L (mainly very long- chain saturates). In addition, the levels of 18:1n-9 were lower in LA than in LB treatment, especially in the liver . Moreover, in group L the levels of liver lipid content and hepatosomatic index, as well as plasma LDH, GPT, TG, LDL and total cholesterol were lower in LA compared to LB treatment .
M easurement of vitellogenin levels is an important biomarker of estrogenic activity in farmed fish. In this study, it has been shown that ISFs , have the potential to induce hepatic VTG production combined with antilipogenic effect on the liver of sea bream. T he increased content of diet A in isoflavones and especially in genistein seems to have estrogenic effect only on larger individuals, whereas smaller individuals remain unaffected. This could be attributed to the degree of sexual maturation of larger individuals, the higher consumption of ISFs via feed or the activation of biochemical pathways related to lipid metabolism. To elucidate this hypothesis further study on mRNA levels is needed.