Study On The Morphology And Development Of Oplegnathus Punctatus’s Digestive System And The Difference Of Intestinal Flora In Different Diets

To explore the morphological and histological structure characteristics of digestive system for Oplegnathus punctatus,and provide basic data for the artificial culture of Oplegnathus punctatus.We conducted relevant studies on digestive system of Oplegnathus punctatus by using anatomy and paraffin section technology.The digestive tract is composed of six parts,including oropharyngeal cavity,esophagus,stomach,pyloric caecum,small intestine and rectum.Oplegnathus punctatus has a large space inside the oropharyngeal cavity,and its jaw teeth are connected and fused,like a parrot’s beak.Pharyngeal teeth are like flat round shields,distributed inside the jaw teeth.This structure allows Oplegnathus punctatus to crush the shell of the crustacean and eat the meat inside.The esophagus is short and thick,and there are a lot of longitudinal folds on the mucosa layer,and a lot of goblet cells in the mucosa.They help Oplegnathus punctatus swallow food smoothly.The stomach is asymmetrically V-shaped with dense gastric glands under the mucosal layer and the pylorus has the thickest muscle layer of the entire digestive tract.This is where most of the food Oplegnathus punctatus swallows will be digested and broken down.The small intestine can be divided into three parts: foregut,midgut and hindgut.Their pipe diameter decreases in turn.The density and length of intestinal villi in the mucosal layer follow the same rule.It can be inferred from the intestinal structure that the nutrient absorption function of Oplegnathus punctatusis mainly concentrated in the foregut and midgut.The rectum is similar in diameter to the anterior segment of the small intestine,but is only one-seventh the length.The intestinal villi in the rectum are shorter in length and less dense than in the small intestine.The rectum is responsible for the re-absorption of water and trace elements from the residue of food digestion,and then the residue is compressed and excreted.The apparent simplicity of its structure corresponds to a simple function.In order to systematically reveal the changes of organs of Oplegnathus punctatus the early stage of digestive system development,continuous histological sections of Oplegnathus punctatus aged from 1 to 49 days were analyzed.the results showed that the digestive tract of 1-day-old Oplegnathus punctatus was found to be located inside the yolk sac and was only a simple tubular structure.according to the development of the digestive system of Oplegnathus punctatus,it can be roughly divided into three stages:at 1～3 days of age,the digestive system is still in the primitive stage.at this time,the mouth fissure is closed,and only the yolk sac is used as the nutrient source,presenting complete endogenous nutrition.at 4～20 days of age,the digestive system is preliminarily developed,and it is in the transition stage with basic feeding,digestion and absorption capacity.At this stage,the mouth fissure opens,the yolk sac gradually disappears,and the hepatopancreas develops rapidly and gradually has the ability to digest food.the transition to exogenous nutrition began.at 21 to 35 days of age,the digestive system develops further and the gastric glands appear,forming a complete digestive system.After that,the tissues and organs of the digestive system only increase in cell scale,without structural changes.In order to explore the difference of intestinal microbes in Oplegnathus punctatus under different diets,we sampled Oplegnathus punctatus in 5 groups with different diets.HCW＿CK group was 30 days old and jaws teeth are not fused,and its diet was artemia and artificial diet.HCY＿CK group was 60 days old and jaws teeth are fused,and the diet was pure artificial diet.The other four groups were fed artificial diet(EL),oyster(ML),crustacean(JQ)and chilled miscellaneous fish(ZY)for 20 days,respectively.The breeding environment was a glass tank with a side length of60 cm,water temperature of(21±1)℃ and salinity of 29±0.5.After high-throughput sequencing,the bioinformation of each group was analyzed by DADA2 ASV clustering method based on Qiime2.We found that Ruegeria,the dominant bacterium originally existing in the HCW＿CK group,disappeared in the HCY＿CK group and was replaced by Rhodanobacter with great relative abundance.The changes in feeding habits caused by jaws tooth healing or not had significant effects on the intestinal flora of Oplegnathus punctatus.In terms of intestinal microbial diversity,there was no significant difference between HCW＿CK group and HCY＿CK group.However,after only ten days with different diets,there was a significant difference between the groups,after 20 days,the difference was even more significant.This suggests that diet is indeed an important factor affecting gut microbes.Among the four experimental groups,the ZY group and ML group with higher animal protein content showed stronger diversity of intestinal microbes,and the ZY group with higher protein content showed stronger diversity of intestinal microbes earlier than the ML group with feeding time.In the later stage of the experiment,the relative abundance of Microbacterium increased significantly and became the dominant bacterium in JQ group.Microbacterium can secrete multi-antibacterial substances,which can help Oplegnathus punctatus effectively inhibit the proliferation of pathogens in the intestinal tract.