投喂频率对池塘循环水养殖大口黑鲈消化酶、组织结构及脂代谢酶基因表达的影响

为研究池塘工程化循环水养殖模式下投喂频率(2 次/d、3 次/d、4 次/d)对大口黑鲈(Micropterus salmoides)体成分、肠道消化和肝脏组织结构及脂蛋白酯酶(LPL)和肝脂酶(HL)基因相对表达丰度的影响, 选用平均体重为 (5.0±0.4) g 的大口黑鲈为研究对象, 在池塘工程循环水养殖系统中进行为期 120 d 的养殖实验。结果表明, 投喂频率对鱼体全鱼的粗脂肪和灰分含量影响显著(P<0.05); 投喂频率 2 次/d 组的灰分含量显著高于其他两组, 而 2 次/d 组体脂肪含量低于投喂 3 次/d、4 次/d 组, 体水分和粗蛋白含量均不受投喂频率的影响(P>0.05); 投喂频率 2 次/d 组肠道淀粉酶和脂肪酶活性显著高于 4 次/d 投喂组(P<0.05); 投喂频率对大口黑鲈肠道绒毛高度和宽度影响不显著 (P>0.05), 4 次/d 组肠道绒毛排列整齐度下降且肌层厚度显著低于 2 次/d 和 3 次/d 组(P<0.05)。肝脏组织学显示, 投喂频率越高肝脏脂肪堆积加重, 相对于 2 次/d 和 3 次/d 组, 4 次/d 组肝细胞偏移、空泡化的现象较明显。在第 60 天和 90 天, 2 次/d 组 LPL 基因相对表达量显著高于 4 次/d 组(P<0.05); 而在第 120 天时, LPL 的相对表达量在各组间差异不显著(P>0.05)。2 次/d 组 HL 基因相对表达量显著高于 4 次/d 组(P<0.05)。综合分析, 在饱饲投喂条件下, 池塘循环水养殖大口黑鲈的适宜投喂频率为 2 次/d。

Effects of feeding frequency on digestive enzymes, histomorphology, and gene expression of lipid metabolic enzymes of largemouth bass (Micropterus salmoides) reared in in-pond raceway culture systems

A 120-day growth trial was conducted to evaluate the effects of different feeding frequencies on intestinal and liver tissues, and the expression of HL and LPL mRNA in largemouth bass (Micropterus salmoides) reared in in-pond raceway culture systems (IPRS). Largemouth bass is with an initial average body weight of (5.0±0.4) g were randomly divided into three groups (fed two, three, and four times day). The results showed that fish fed twice a day had significantly higher ash rate (P<0.05), but the crude protein was not significantly different (P> 0.05). The crude lipid content in fish fed twice a day was significantly higher than that in the other groups (P< 0.05), while the moisture content did not significantly differ among the three groups (P>0.05). The feeding frequency had a significant effect on intestinal amylase and lipase activity (P<0.05). Fish fed twice a day had higher intestinal amylase and lipase activity than those fed four times/d on days 90 and 120 (P<0.05). The intestinal tissue of fish fed four times/d appeared to have a thinner muscular layer while the villi integrity decreased. Fish fed two times/d had a thicker muscle layer than those fed four times/d. From liver histological observations, more severe liver fat accumulation leads to more serious liver damage with increasing feeding frequency. Fish fed four times/d had much higher occurrence rates of the hepatocyte vacuolization and nuclei shifting to the cellular periphery than fish fed at other frequencies. Feed frequency had a significant effect on HL and LPL mRNA expression in M. salmoides. Fish fed two times/d exhibited higher LPL mRNA expression on days 60 and 90 (P<0.05), while no significant difference was found on day 120. Fish fed two times/d exhibited higher HL mRNA expression than those fed three times/d and four times/d at a fixed feeding rate (P<0.05). Based on growth, intestinal and liver tissues, and HL and LPL expression levels, the optimal feeding frequency of M. salmoides reared in IPRS is twice a day. These data are necessary for optimizing the culture conditions and feeding management strategy in IPRS culture operations.