| Procypris merus,a warm-water fish of Cyprinidae,is cultivated in rice fields and is named after the main rice paddy.Procypris merus originated in Longshui Township,Quanzhou County,Guilin City,and Miaoshan County,Rongshui County,and is now distributed in the northwest and southern mountainous areas of Guangxi for a generation.Procypris merus is omnivorous,fast growing,strong reproductive capacity,delicious meat,soft bones without mud odor,fine leaf scales,its back scales are golden,similar to a golden edge,so it is also known as Golden-edged Grass carp.The purpose of this study was to explore the nutritional needs of Procypris merus larvae and post-larvae under artificial nursery conditions and the development of artifical microdiets.This study could provide theoretical basis for the design and production of feed formula for Procypris merus larvae and post-larvae,and provide scientific and technological support for the development of industry and precise poverty alleviation of Guangxi Procypris merus.The results are summarized as follows.1、The caliber and feeding habits of larvae and post-larvae of Procypris merus were studied in the process of artificial pond culture.The mouth opens on the 3 DAH(day after hatching).3 DAH to 10 DAH is the adaptation phase of gradual acceptance of exogenous nutrient intake,after 12 DAH,the growth rate of Procypris meru began to accelerate.The number of zooplankton rotifers in the nursery pond was the highest,and the number of cladocerans and copepods showed a regular fluctuation.The number and type of phytoplankton in the nursery ponds are variability,which is not only affected by the feeding choice of Hehuan,but also by various factors such as weather and water temperature.In the early stage of larvae,Procypris meru is a omnivorous herbivorous fish.In the post-larvae,the intake of zooplankton increased.The suitable feed size in3-20 DAH is 100-200μm,21-30 21-30 DAH suitable feed size is 200-350μm.The microcystis in the cyanobacteria is a harmful algae.In the nursery pond,the number of the algae is high.The water quality environment should be adjusted in time to achieve the purpose of improving the survival rate of the seedlings.2、The developmental process and histological changes of digestive system in larvae and juveniles of Procypris merus larvae and post-larvae were studied.The histomorphology of digestive system of Procypris merus larvae and post-larvae from 1 to 30 days after hatching was systematically observed and studied by continuous tissue section technique.It was observed that goblet cells appeared in the mouth on the third day after hatching,pharyngeal and dental sacs on the fifth day and striated margins developed in the digestive tract on the sixth day,which indicated that the intestinal function of larvae had gradually improved.In 12 DAH,the contents of nucleus and vacuoles appeared,which indicated that the intestinal cells could drink and digest in cells.The intestine could be distinguished from the anterior and posterior intestines,and the intestinal development was basically completed.Later,with the increase of the fish body,the intestinal tract gradually grows,bends and develops to the 30 DAH,the larvae of Procypris merus have entered the post-larvae stage,and the morphology and function of their digestive system have approached that of adults.3、Several enzymes related to digestion and absorption of acid protease,alkaline protease,amylase,lipase and alkaline phosphatase in different developmental stages of larvae and juveniles of Procypris merus larvae and post-larvae were determined.The larvae have the ability to digest carbohydrates at the beginning of hatching,and sugar metabolism plays an important role in this period.Procypris merus has high amylase activity before opening mouth.High amylase can promote the digestion of algae.Therefore,it is necessary to cultivate not only abundant zooplankton but also a certain amount of phytoplankton in the nursery pond to provide abundant food sources for larvae.The activity of alkaline phosphatase increased significantly on the 4th and 8th day after hatching,which indicated that the intestinal tract developed rapidly on the 4th day.Combining with the observation of digestive system,it can be proved that the intestinal tract developed well on 8 DAH.4、The changes of biochemical composition in the early development stage of larvae and post-larvae of Procypris merus were determined.The protein content of larvae was the highest on the 20 DAH,the dry weight increased first and then decreased.The protein content of larvae and post-larvae of Procypris merus increased first and then decreased,the same as dry weight.Essential amino acids are more important than non-essential amino acids in the absorption and utilization of larvae.The contents of phenylalanine,lysine and arginine in essential amino acids decrease significantly.Therefore,it is necessary to add sufficient nutrition to improve the growth performance and survival rate of larvae.During the period from hatching to 30 DAH,the content of C18 and C20 polyunsaturated fatty acids(PUFA)continued to decrease,while the content of C22 long-chain polyunsaturated fatty acids(LC-PUFA)continued to increase.It is speculated that Procypris merus has the ability to synthesize long-chain polyunsaturated fattyacids.It was found that DHA was preferred to EPA and AA in the retention of these three unsaturated fatty acids in the larvae of Procypris merus,which indicated that DHA was very important for the growth and development of larvae and post-larvae of Procypris merus.5、The effects of 5 protein levels on growth and survival rate of larvae and post-larvae of Procypris merus were studied in 38%(group 1),41%(group 2),44%(group 3),47%(group 4),50%(group 5).From the results of this experiment,the protein efficiency of group 1 and group 4 was the highest.The specific growth rate of group 1,group 2 and group 4 was higher than that of other components,the survival rate of each component had no significant difference,and the fatness of each component had no significant difference.Quadratic regression equation was used to analyze the protein efficiency of larvae and post-larvae of Procypris merus.According to the formula,when the protein content is 40.96%,the protein efficiency is the highest.Using specific growth rate as a dependent variable,it was found that when the protein content was 39.67%,the specific growth rate reached the maximum.Therefore,the optimum protein content of the larvae is between 39.67% and 40.96%.6、In order to study the effects of dietary protein levels on larvae of Procypris merus more systematically,transcriptome sequencing was carried out on three groups that feeding with dietary protein levels of 38%(group A),44%(group B)and 50%(group C).Differential analysis using DEG seq.Over all,there were 226 differentially expressed genes between group A and group C,31 differentially expressed genes in group B and C,87 differentially expressed genes in group A and B,The results of GO annotation of differentially expressed genes showed that different protein levels could cause changes in extracellular area,cell membrane structure and signal transducer activity of larvae.In KEGG enrichment analysis,the significant difference genes were enriched in protein digestion and absorption,carbohydrate digestion and absorption,starch and sucrose metabolism,pancreatic secretion,galactose metabolism,respectively.Significant difference genes include PRSS(trypsin gene),CTRL(chymotrypsin gene),CPA and CPB(carboxypeptidase A,B gene),Amylase(alpha amylase gene),G6PC(glucose 6 phosphatase gene),IMA(oligosaccharide 1,6glucosidase gene),SI(maltase gene)and other genes related to protein metabolism and some transporters,such as PEPT1(oligopeptide 1).A member of the transporter family,SLC6A19(neurotransmitter transporter).The results showed that the larvae and post-larvae of Procypris merus could adapt to the changes of feed protein level through self-regulation,which was closely related to the growth and development of larvae. |
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