Dietary isoflavone intake and tissue concentration in cultured sturgeons

Abstract

A common global trend in modern aquaculture is to reduce or replace fishmeal in fish diets with alternative protein sources, mainly from protein‐rich plants such as soybean; however, plant‐based aquafeeds are a source of substantial amounts of phytoestrogens. Phytoestrogens belong to endocrine‐disrupting chemicals (EDCs) which can negatively interfere with fish reproduction; thus, they should be avoided in sturgeon diet. Therefore, the aim of the study was to evaluate concentrations and the profile of dietary isoflavone phytoestrogens in the two commercial sturgeon diets. A substantial amount of isoflavones, reaching in total from 1.5 to 50 mg/kg of feed, were found in analysed diets. Genistein and daidzein, which are typical constituents of soybean, were the most abundant phytoestrogens in the analysed feeds. Equol, the third most abundant phytoestrogen in the tested samples, was originated most probably from animal components. Additionally, the accumulation of dietary isoflavones in the liver, blood and gonads of two commonly farmed sturgeon species (Acipenser gueldenstaedtii and Acipenser baerii) after long‐term dietary exposure was also assessed. Significant concentrations of isoflavones were found in liver and blood samples of both sturgeon species at 600th and 800th dph, indicating high accumulation of these compounds, which may lead to endocrine disturbance.

Isoflavones in Animals: Metabolism and Effects in Livestock and Occurrence in Feed

“…However, it cannot be concluded from these results that sturgeons are in fact EQ producers as EQ was also present in feed. Additionally, the ISF profile detected in the serum indicates that sturgeons did not produce EQ in this experiment [159].…”

“…Considering that there is little data on the metabolism of ISF in fish, it is also inconclusive whether fish can produce EQ or not. For example, no EQ was detected in the bile of rainbow trout fed with DAI (up to 49 mg/kg feed) [158], whereas EQ could be detected in the tissue of sturgeons (EQ intake up to 432.3 mg) [159]. However, it cannot be concluded from these results that sturgeons are in fact EQ producers as EQ was also present in feed.…”

Histological Evaluation of Gonad Impairments in Russian Sturgeon (Acipenser gueldenstaedtii) Reared in Recirculating Aquatic System (RAS)

“…The presence of soybean phytoestrogens—namely, genistein, daidzein and the highly estrogenic phytoestrogen metabolite equol—was previously detected in the livers and blood of sturgeon originating from the analyzed sturgeon stock. The same phytoestrogens were also detected in substantial amounts in fish feeds, indicating that diet is an important source of sturgeon exposure to EDCs [ 29 ]. However, to date, there has been a striking lack of knowledge on the effects of dietary phytoestrogens on sturgeon gonad differentiation.…”

“…Phytoestrogens are considered the main source of EDCs in sturgeon feeds [53]. These compounds occur in high concentrations in legumes, especially in the soybean [56], and therefore, they are commonly found in high concentrations in fish feeds [57], including sturgeon commercial diets [29]. Phytoestrogens, due to their ability to bind and interact with estrogen receptors, mimic endogenic estrogens [58], and therefore, they may interfere with fish sex differentiation [59][60][61].…”

“…The feeds were administered by automatic feeders: from the 30th to the 35th dph in ten, from the 35th to the 60th dph in seven, from the 60th and the 200th dph in five and from the 200th to 1600th dph in four equal doses per day. More detailed information on the feeds is provided in Rzepkowska et al [ 29 ]. The survival rate over the first 30 dph was 70.7%; at the 800th dph, mortality was below 5%.…”