饲料中添加水飞蓟素对低盐度下凡纳滨对虾生长、免疫、肝胰腺组织结构及肠道菌群的影响

为研究投喂策略对牛蛙蝌蚪生长发育的影响，建立科学的投喂标准，实验分别设置了4种投喂频率(1 、2 、3 和4 次/d)与4个投喂水平(4%、6%、8%和10%)饲养牛蛙蝌蚪，以探究牛蛙蝌蚪合适的投喂策略。投喂频率实验表明，投喂3 次/d或4 次/d的牛蛙蝌蚪在实验周期内的变态率显著高于投喂1 次/d或2 次/d的牛蛙蝌蚪，且投喂3 次/d的牛蛙蝌蚪增重率最大。变态率与投喂量的比值(MFR)随投喂频率增加而上升，2、3或4 次/d显著高于1 次/d。投喂频率对已变态牛蛙蝌蚪的肝脏组织结构及肠道蛋白酶、脂肪酶、淀粉酶活性无显著影响。投喂水产实验结果显示，实验周期内牛蛙蝌蚪变态率随投喂水平增加而上升，且8%与10%组已变态牛蛙蝌蚪的均重显著高于4%与6%组，但已变态牛蛙蝌蚪肠道蛋白酶活性随投喂水平升高而降低。8%与10%组已变态牛蛙蝌蚪肝细胞脂滴含量明显增多，脂肪沉积现象明显。8%投喂水平组有益菌属暖绳菌属(绿弯菌门)与鲸杆菌属(梭杆菌门)相对丰度较高，一定程度改善了肠道微生物结构。研究表明，牛蛙蝌蚪每日投喂3次，综合投喂水平8%左右，蝌蚪的生长发育性能较优，兼顾了牛蛙养殖生产效益与蝌蚪肝肠健康，促进了牛蛙产业健康发展。

Effects of feeding frequency on growth,feed utilization,digestive enzyme activity and body composition of Litopenaeus vannamei in biofloc-based zero-exchange intensive systems

Bullfrog (Lithobates catesbeiana) tadpole culture technology is still in a vulnerable stage, and metamorphosis rate is an important index of L. catesbeiana tadpole culture. Traditional empirical feeding strategy may lead to insufficient or excessive feeding of L. catesbeiana tadpoles, affecting the digestion and absorption of nutrients and the development of internal organs. Eventually, it leads to slow growth and development, light weight after metamorphosis, poor immunity and it is easy to corrupt water body and cause other problems. The feeding strategy has a significant effect on the growth and development of tadpoles, but no scientific feeding standard has been established. Therefore, four feeding frequencies (1, 2, 3, 4 times/d) and four feeding levels (4%, 6%, 8% and 10%) were set to feed L. catesbeiana tadpoles to explore the appropriate feeding strategy for tadpoles. The feeding frequency experiment showed that the metamorphosis rate of tadpoles fed 3 times/d or 4 times/d was significantly higher than that of tadpoles fed once or twice/d, and the weight gain rate of 3 times/d was the highest (P>0.05). The metamorphosis to feeding ratio (MFR) increased with the increase of feeding frequency and was significantly higher for 2, 3, and 4 times/d than once/d. Feeding frequency had no significant effects on liver structure and intestinal protease, lipase, and amylase activities of froglets. The feeding level experiment showed that the metamorphosis rate increased with the feeding level increasing, and the average weight of metamorphosed tadpoles in 8% and 10% groups was significantly higher than that in 4% and 6% groups, but the intestinal protease activity of metamorphosed tadpoles decreased with the feeding level increasing. The content of lipid droplets in hepatocytes of metamorphosis tadpoles increased significantly in 8% and 10% groups, and fat deposition was obvious. The feeding level of 8% increased the relative abundance of Caldilinea (Chloroflexi) and Cetobacterium (Fusobacterium), and improved the intestinal microbial structure to a certain extent. In conclusion, it is recommended to feed L. catesbeiana tadpoles 3 times a day at a feeding level of 8%. Research on the scientific feeding strategy of L. catesbeiana tadpoles can improve the L. catesbeiana research system and increase the production efficiency of L. catesbeiana.