养殖密度对投喂模式下网箱养殖刺参生长、消化酶及肠道菌群的影响

Effect of culture density on growth, digestive enzymes, and intestinal flora of net-cage culture of sea cucumber (Apostichopus japonicus) under feeding mode

中文关键词: 海参  网箱养殖  养殖密度  酶活  菌群结构

英文关键词: Sea cucumber  Net-cage culture  Stocking density  Enzyme activity  Gut microbial structure

中文摘要:

      为评估养殖密度对投喂模式下浅海网箱养殖刺参(Apostichopus japonicus)的影响，本研究在辽宁省大连刺参网箱养殖核心区开展了为期42 d的养殖实验，分析了不同养殖密度条件下(10、20、30 kg/箱，标记为F10、F20和F30)刺参的生长、消化酶及肠道菌群结构的差异。结果显示，F10、F20和F30组增重率(WGR)分别为(51.63±4.27)%、(33.21±8.58)%和(23.08±0.24)%。随着养殖密度的增大，刺参的WGR和特定生长率(SGR)显著降低，净产量增加，饵料系数(FCR)升高。F10组的FCR(0.76±0.06)显著低于F30组(1.72±0.03) (P<0.05)。随着养殖密度的增大，刺参肠道胰蛋白酶、淀粉酶和脂肪酶等消化酶活性均呈下降的趋势，F30组的消化酶活性显著低于F10组和F20组(P<0.05)。F10组与F20组的菌群相似性较高，其ACE、Chao1、Shannon和Simpson等多样性指数均显著高于F30组(P<0.05)。优势菌属随着养殖密度的不同存在差异，F10组、F20组和F30组分别显著富集于链球菌属(Streptococcus)、瘤胃球菌UCG_005属和Alkanindiges等菌属。Pearson相关性分析显示，链球菌属、Muribaculaceae和UCG_005属与消化酶活性呈显著正相关。效益估算显示，F20组与F30组养殖效益相差不大，较F10组有大幅提高。研究表明，养殖密度在20~30 kg/箱时，可提高养殖净产量，但养殖密度达30 kg/箱时，刺参生长、肠道消化酶活性和微生物多样性显著降低，现有小网箱投喂模式下养殖密度宜提高至20 kg/箱。研究结果可为刺参浅海网箱的科学养殖和提质增效提供参考。

英文摘要:

      The shallow-sea net-cage culture of sea cucumber (Apostichopus japonicus) has been developing rapidly in recent years, and the culture mode of feeding formula feed has been accepted by farmers. However, the optimal culture density under the feeding mode is still unknown. To evaluate the influence of culture density on the shallow sea net-cage culture of sea cucumber under a feeding mode, this study examined the growth, digestive enzymes, and gut bacterial community structure of sea cucumber at different culture densities. The culture density was set to 10 kg/cage, 20 kg/cage and 30 kg/cage, marked as F10, F20 and F30, respectively. Sea cucumber seedlings with an initial body weight of (75.11±2.99) g were randomly assigned into 9 cages (3 replicates of each density level) according to the density settings. The net cage is cuboidal and its length, width and height were 4 m, 4 m, and 3 m, respectively. After a 42-day experimental period, the total weight of sea cucumber in each cage was weighted and 20~30 individuals in each cage were randomly sampled for individual weight and body wall weight. Then, intestines from 3 individuals were sampled and preserved at –80 ℃ freezer. Digestive enzyme (Trypsin, Amylase, and Lipase) activities were determined spectrophotometrically using enzyme activity assay kits (Nanjing Jiancheng Bioengineering Institute, China) following the manufacturer’s instructions. Gut microbial DNA was extracted, and the V3～V4 region of the prokaryotic ribosomal RNA gene (16S rDNA) was amplified and sequenced on an Illumina Novaseq platform. Sequence data were then analyzed on the platform BMKCloud (www.biocloud.net). The results showed that as culture density increased, the weight gain rate of sea cucumbers in net-cage culture significantly decreased, and both the F20 and F30 groups had significantly lower weight gain rates compared to the F10 group (P<0.05). In addition, increasing culture density resulted in a significant increase in net production and body wall production rates, although none of the differences were significant (P<0.05). The feed conversion ratio of the F10 group was the lowest and not significantly different from that of the F20 group, but significantly lower than that of the F30 group (P<0.05). The enzyme activities of all three digestive enzymes showed a decreasing trend with the culture density increase. The digestive enzyme activity of F30 was significantly lower than that of F10 and F20 (P<0.05). The similarity of the bacterial community structure between the F10 group and F20 group was relatively high. The ACE index of F10 group was significantly lower than that of the F20 group (P<0.05), while the Chao1 index, Shannon's index and Simpson's index showed no significant difference from that of the F20 group (P>0.05). All the microbial diversity indices of the F30 group were significantly lower than those of the other density groups (P<0.05). The relative abundance of dominant organisms varied with culture density. The relative abundance of Firmicutes and Actinobacteria tended to decrease with increasing density, while the opposite was true for Bacteroidota and Proteobacteria. The relative abundance of Actinobacteria in group F10 was significantly higher than that of group F30 (P<0.05). The relative abundance of Lachnospiraceae, Bifidobacteria and Streptococcus was significantly higher in group F10 than in groups F20 and F30 (P<0.05), and the relative abundance of Oscillospiraceae and Rikenellaceae was significantly higher in the F20 group than in the F10 and F30 groups (P<0.05). LEfSe analysis showed that F10, F20, and F30 were mainly significantly enriched in Streptococcus, Ruminococcus UCG_005 and Alkanindiges, respectively. Pearson's correlation analysis showed that three gut bacteria genera were significantly positively correlated with digestive enzyme activities, including Streptococcus, unclassified_ Muribaculaceae and UCG_005. According to the benefit estimation, there was little difference in culture benefit between the F20 and F30 groups, both of which were significantly higher than the F10 group. The results indicate that higher culture densities can improve the net-cage culture production of sea cucumber, thus increasing the overall benefit. However, too high culture density could negatively affect the growth, digestive enzymes, and the gut microbial balance of the sea cucumber. Therefore, to improve the overall benefit, it is better to increase the culture density to 20 kg/cage in the current small net-cage feeding mode. These results provide references for the scientific culture of sea cucumbers in shallow-sea net-cage systems, leading to improvements in both quality and culture efficiency.