Abstract
An eight-week feeding trial was conducted to evaluate the effects of soy isoflavone and soy saponin on growth performance, intestinal structure, intestinal immunity and gut microbiota community of rice field eel Monopterus albus (initial weight 20.12 ± 0.15 g). Six isonitrogenous and isolipidic experimental feeds were formulated, including a positive control (55% fish meal, FM), a negative control (28.6% fish meal, 37.2% soybean meal, SBM) and basic diet group (28.6% fish meal, 22.6% soy protein concentrate, SPC), the rest was supplemented with soy isoflavone (40%, 2.5 g / kg, SI), soy saponin (≥98%, 2 g / kg, SS) and their mixed in basic diet (SI + SS). Compared with FM, growth performance, intestinal immune indices (acid phosphatase, alkaline phosphatase, complement 3, complement 4 and immunoglobulin M), intestinal villus height and intestinal muscular thickness and mRNA (occludin-like, claudin 12, tight junction protein ZO-1-like, tight junction protein ZO-2-like, interleukin-10, transforming growth factor beta 1, transforming growth factor beta 2) expression intestine of M. albus fed SBM diet were significantly decreased (P < 0.05). Growth performance of M. albus in SPC group was better than that in SBM. Compared with SPC, dietary soy isoflavone and soy saponin and their mixed (SI, SS, SI + SS) decreased growth of M. albus, serum alkaline phosphatase in SI significantly increased (P < 0.05), and intestinal immunoglobulin M in SS remarkably declined (P < 0.05), intestinal complement 3, complement 4 and immunoglobulin M, amounts of intestinal goblet cells per root, gut shannon were significantly decreased in SI + SS (P < 0.05). Based on the current results, there has the trend that dietary soy isoflavone and soy saponin damaged the intestinal structure and changed gut bacteria community of M. albus, and destroyed the intestinal barrier, eventually induced intestinal inflammatory, soy isoflavone and soy saponin mixed feed has more serious effects than they single supplemented.
Highlights
Fish meal (FM) is a high-quality protein source for aquatic feed because of its balance of amino acids, high fatty acid content and low carbohydrate content
Various anti-nutritional factors like trypsin inhibitors, antivitamins, lectins, soy antigens, isoflavone, saponins, phytic acid, phytoestrogens and oligosaccharides are major shortcoming of soybean products used in aquatic feeds [3]
Trypsin inhibitors and antivitamins are heat labile factors could be destroyed by high temperature and extruded treatment, and phytates and antigenic compounds in aquatic feeds containing commercially available soybean protein sources did not affect growth performance and immunity of fish [4]
Summary
Fish meal (FM) is a high-quality protein source for aquatic feed because of its balance of amino acids, high fatty acid content and low carbohydrate content. The aquatic feed industry rapidly expanded, soybean protein is widely used to replace FM in aquatic feed [2]. Various anti-nutritional factors like trypsin inhibitors, antivitamins, lectins, soy antigens, isoflavone, saponins, phytic acid, phytoestrogens and oligosaccharides are major shortcoming of soybean products used in aquatic feeds [3]. Trypsin inhibitors and antivitamins are heat labile factors could be destroyed by high temperature and extruded treatment, and phytates and antigenic compounds in aquatic feeds containing commercially available soybean protein sources did not affect growth performance and immunity of fish [4]. Soy isoflavone and soy saponin are heat-stable glycosides present in soybean meal, which is the major factor restrict soy protein using in aquatic feed. This study is aimed to conduct that dietary soy isoflavone and soy saponin on growth performance, intestinal structure, intestinal immunity and gut microbiota community on rice field eel (Monopterus albus), and revealed its mechanism
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