Comparison of fish intestinal histology in offshore aquaculture net pen

Large offshore net pen aquaculture is one of the most important modes for the development of deep-sea aquaculture. Precise feeding is the key to ensureing efficient farming, nutrient digestion and absorption for farming fish. Intestine is the main area for digesting and absorbing nutrients. Thus, investigating its structure will provide a theoretical basis for accurate feeding in captivity. The intestinal tissue of five marine fishes (Verasper variegatus, Paralichthys olivaceus, Oplegnathus punctatus, Thamnaconus modestus, Mugil soiuy) reared in offshore aquaculture net pen were detected via tissue sectioning, hematoxylin-eosin (H.E) staining and optical microscope observing in this study. Meanwhile, the relative intestinal length, the height, width, the number of intestinal folds, the thickness of the circular muscle, the longitudinal muscle, the number of goblet cells, the morphological differences of different intestinal segments and correlations were evaluated. The results showed that M. soiuy had the most significant relative with intestinal length, followed by T. modestus and O. punctatus, and Verasper and P. olivaceus were the least significant relationship. The intestinal fold number, height and width of five fishes decreased from anterior intestine to posterior intestine, and the degree of intestinal fold developed M. soiuy>Verasper>O. punctatus>P. solivaceus>T. modestus. At the same time, the muscle thickness of O. punctatus intestinal tract was the largest, significantly higher than that of the other four fishes (P<0.05). While P. olivaceus and O. punctatus had the smallest, significantly lower than that of the other three fishes (P<0.05), M. soiuy and T. modestus had no significant difference (P>0.05). There were substantial differences in the number and distribution of intestinal goblet cells in the five fishes. The number of intestinal goblet cells in the five fishes was showed as sphyraenus>O. punctatus>P. olivaceus>Verasper>T. modestus. M. soiuy goblet cells were mainly distributed in the foregut and middle intestine, Verasper, P. solivaceus and O. punctatus intestinal goblet cells were mainly distributed in the foregut and posterior, and T. modestus intestine goblet cells were mainly distributed in the posterior. Correlations analysis results showed that the intestinal muscular layer of Verasper, P. olivaceus, O. punctatus, T. modestus was significantly negatively correlated with intestinal folds, and was significantly positively correlated with the number of intestinal goblet cells. M. soiuy had a significant positive correlation among intestinal parameters. In summary, the relative intestinal length, the number, height, width of intestinal folds, the thickness of the circular and the longitudinal muscles, and the distribution of goblet cells in different intestinal segments of the five fishes which were breeding suitably by offshore aquaculture net pen have significant differences among species. The aforementioned parameters indicated that five fish reared in the offshore net pen adopts different digestion and absorption strategies due to species specific. Therefore, these results provided basic data for the designing of precise feeding and feeding strategies in offshore aquaculture net pen.