活饵与饲料投喂对幼鳜肠肽酶活力及小肽转运、吸收的影响

FEEDING LIVE BAIT AND FEED ON THE PEPTIDASE ACTIVITY, TRANSPORT AND ABSORPTION OF SMALL PEPTIDES IN JUVENILE MANDARIN FISH

  • 摘要: 以初始体重(6.77±0.64) g的鳜(Siniperca chuatsi)为实验对象, 从消化道肠肽酶活力和小肽转运吸收方面比较研究鳜对活饵与饲料消化吸收能力的差异。实验采用3种分组投食策略, 将鳜分活饵组(仅投喂活饵鱼)、饲料组(仅投喂饲料)、复投活饵组(以下简称复投组, 先投喂饲料后活饵鱼)。活饵组、饲料组分别饲养22d, 复投组经5d驯饲、15d饲料和2d活饵喂养。饲养结束时在各组进食0.5h、1h、2h、3h、6h、12h、16h时分别取样肠和幽门盲囊, 测定氨肽酶和羧肽酶含量与活力, 小肽转运载体基因Pept1a、Pept1bPept2 mRNA表达水平, 及进食12h后肠内容物及粪便中残余小肽含量。结果表明: 各组羧肽酶、氨肽酶含量变化无显著性规律, 酶活力总体呈先升后降趋势; 活饵组肽酶活力峰值显著高于复投组高于饲料组(P<0.01), 复投组由饲料转喂活饵后, 肠道肠肽酶活力显著上升; 各组前肠、中肠及幽门盲囊Pept1a、Pept1b mRNA表达显著高于后肠(P<0.01), 后肠则以Pept2 mRNA高表达(P<0.01)。在复投组摄食活饵后, 小肽转运载体基因表达水平较饲料组迅速回升(P<0.01); 摄食12h, 复投组肠内容物小肽含量显著高于活饵组和饲料组, 小肽吸收效率随消化时间延长而上升。饲料组粪便中小肽含量显著高于活饵组与复投组, 未转运的小肽中含必需氨基酸居高。综上所述, 投喂鳜配合饲料, 对肠肽酶活力、小肽转运载体基因表达和小肽吸收速率均产生不利影响, 鳜对饲料蛋白的分解和小肽转运吸收效率显著低于活饵鱼。

     

    Abstract: In this study, we examined Siniperca chuatsi with an initial weight of (6.77±0.64) g to explore the difference of digestive and absorption ability between live bait and feed from the aspects of digestive tract peptidase activity and small peptide transport and absorption. Overall, fish were divided into three groups by random: live bait group (the following group was fed with live bait only for 22d), feeding group (the following group was fed with feed only for 22d) and re-feeding group (the following group was fed with 5d of domestication, 15d of feed and 2d of live bait). At 22d post feeding, the isolated intestinal and pyloric caecum sampled at 0.5h, 1h, 2h, 3h, 6h, 12h and 16h after eating were used to measure activities of aminopeptidase and carboxypeptidase and gene expression of mall peptide transport vector genes: Pept1a, Pept1b and Pept2. Besides, the content of residual small peptides in intestinal contents and feces 12h after eating were measured. The results showed that there was no significant change in the contents of carboxypeptidase and aminopeptidase in each group, and the enzyme activity increased first and then decreased; The peak value of peptidase activity in the live bait group was significantly higher than that in the re-feeding group (P<0.01); In foregut, midgut and pyloric caecum, the mRNA expression of Pept1a and Pept1b was significantly higher while that of Pept2 was comparatively lower than those in hindgut (P<0.01); After feeding live bait, the gene expression level of small peptide transport vector in the re-feeding group increased rapidly compared with that in the feed group (P<0.01); At 12h post feeding, the content of small peptides in intestinal contents in the re-feeding group was significantly higher than that in the live bait group and feed group, and the absorption efficiency of small peptides increased with the extension of digestion time. However, the content of small peptides in feces of feed group was significantly higher than that of live bait group and re-feeding group, and the content of essential amino acids in small peptides not transported was higher. In conclusion, feeding S. chuatsi compound feed has adverse effects on the activity of intestinal peptidase, small peptide transporter gene expression and small peptide absorption rate. The decomposition of protein and the efficiency of small peptide transport and absorption of mandarin fish which intake artificial feed are significantly lower than those that intake live bait.

     

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