| Lutjanus erythropterus commonly known as crimson snapper belongs to Lutjanidae,Perciformes,Actinopterygii,Osteichthyes.A large number of studies have shown that Lutjanus erythropterus is an important commercial species of aquaculture,which has been introduced into Asia for decades.The fish has the following advantages: rapid growth,high meat quality,and easy to be widely cultivated.Therefore,this species is widely used in aquaculture.Although it is said that the fish circle of deep red snapper has been closed,its rapid development is restricted due to its extremely high mortality and malformation rate.To further improve the production efficiency of this species,this thiesis investigated the ontogenetic development of crimson snapper.In this study,in view of the high death rate and deformity rate of crimson snapper,the ontogenetic development of crimson snapper The larvae are involved in the following three stages of individual development: First,the yolk trophic phase(1-3 DPH),dependenting on yolk sac as a nutrient source,phase II,the mixed vegetative phase(4-14 DPH),from the first intake to the formation of gastric glands.phase III,exogenous nutrition period(15-36 DPH),when you observe the formation of gastric glands,keep moving forward.The three stages of larval development were experimentally studied from three aspects of bone development and malformation rate,digestion and immunophysiology,with a view to provide solutions for production.The following is an overview of the study on the development and induced deformities of the skeletal endoderm after the incubation period of 1-36 days(DPH)of experiment 1.At the age of 3 days,the horny sacrum,the iliac crest,the infrapatellar cartilage appeared in the skull,and four zygomatic arches began to form.On the side of the larvae,it has been observed that trabecular cartilage and sieved cartilage has been formed.At 3 days of age,the spinal cord couldn’t be found,and the chord was an axial suspension structure.An early pectoral fin structure emerged and the spatula began to develop.The jaw bone in the skull began to calcified at 9 DPH.The formation and calcification of the spine and the fins.the nerve arch in the spine began to develop at 10 DPH.At the 11-12 DPH,the vein arch began to develop.The bud shaped structure of the nerve arch extended to the ventral side until it was connected to the pulse arch,forming the spinal structure.Pelvic pterygiophore first appeared in the 9-11 DPH period.At 14 DPH,spines begin to calcify.Most of the jaws(including the anterior jaw,maxilla and dentate bone)have been calcified at 18 DPH.Calcification is complete at 31 DPH.Formation and calcification of vertebrae and fins.Vertebra: At 16 DPH,the nerve arch and venous arch are clearly visible,and the nerve arch begins to calcify;the thoracic arch starts to calcify at 20 DPH;the nerve arch,nerve spine,vascular arch,and vascular spine are completely calcified at 24 DPH;At 16 DPH,the spine begins to develop.At 20 DPH,the spine(V1-V8)begins to calcify,and at 27 DPH,calcification of the spine center is complete.The paired ribs of the abdomen began to form at 24-27 DPH,and was calcified completely at 27-30 DPH.Fins: At 18 DPH,pectoral fins appeared,marking the formation of a intergral structure of the pectoral fins;at 24 DPH,the pectoral fin spines began to calcify;at 36 DPH,hard spines and pectoral fins completed calcification;the pectoral fin cartilage and the fins began to develop at 19 DPH;the fins began to calcify at 24 DPH and completed calcification at 36 DPH.The following overview to the research of experiment 2: to discuss the red fin snapper,the phase of the digestive system development based on digestive enzyme(including amylase,alkaline phosphatase,pepsin,trypsin and lipase)and histological aspects were analyzed.(1)the following is the results of histological study: at the age of 2,the middle of the digestive tract can be observed to expand continuously.When you are 3 days old,you will be able to open your mouth.At the end,the yolk sac can be fully absorbed.At the age of 4,the stomach and swim bladder can be preliminarily formed.At the age of 14,the gastric glands can be formed,and the initial structure of the pyloric cavities can be observed in the front end of the intestine.At the age of 16-17,the stomach gradually divided into three regions: pylorus,cardia and basement.(2)the following is the determination of digestive enzymes(amylase,alkaline phosphatase,pepsin,lipase and trypsin).The total enzyme levels of the above five digestive enzymes were all rising.Among them,the level of lipase,amylase and trypsin was increased,and the level of alkaline phosphatase was increasing,and the total level of the four digestive enzymes increased continuously.The level of lipase and amylase was increased to the highest peak at 4 days and 10 days.The total enzyme levels of the above five types of digestive enzymes were all increasing.At the age of 32,the level of lipase and amylase increased to the highest peak,while the other 3 enzymes increased at the age of 36.The enzyme activity of pepsin was detected for the first time on the 17 th day of age and then showed an upward trend.At the age of 20,the enzyme activity level of trypsin increased to the highest peak,and the alkaline phosphatase activity level increased to the highest peak at 36 days.For experimental 3 research overview of the following: to explore the red fin snapper,the phase of the immune system development based on immune enzyme(catalase,superoxide dismutase(sod),potassium sodium atpase and glutathione peroxidase)and histological aspects were analyzed.The early hepatopancreas started to development at 2 DPH.The renal tubule began to hemopoiesis at 4 DPH.The spleen anlage appeared at 6 DPH.The thymus formed at 14 DPH.The total activities of SOD,CAT,GPX and Na+ K+-ATPase were increase along with the day-post hatch and showed sharply increase after 29 DPH.The specific activities of SOD,CAT,and GPX showed rising rapidly,the highest peak of from hatch to 4 DPH except for Na+ K+-ATPas reached maximum at 10 DPH.The specific activities of these five enzymes showed a gradual decrease after the peak.Experiment 4 investigated the growth,survival,food selection and consumption of crimson snapper larvae under different rotifer densities were examined in this study.Growth and survival of fish larvae were not significantly affected when rotifer density was between 10 and 20 m L-1.Fish larvae grew slower at 1 and 30 rotifers m L-1 than at 10 and 20 rotifers m L-1,and higher fish survival were achieved when fish larvae exposed to 10 and 20 rotifers m L-1.The rotifer density of 1 m L-1 not only reduced food ingestion during the early stage but also delayed diet switch from rotifer to copepod nauplii.Based on the results obtained in the present study,larval crimson snapper is recommended with a feeding density of 10-20 rotifers·m L-1 during the initial feeding stage.This study proposes a management protocol to use appropriate type and quantity of live food to feed crimson snapper larvae in a hatchery rearing condition,which may be applicable to larval culture of other similar marine fish species.Experiment 5 investigated effect of weaning time on the larval performance of crimson snapper Lutjanus erythopterus was studied in the experimental condition.The same weaning regime started on four different days of post hatch(DPH): 13 DPH(W13),16 DPH(W16),19 DPH(W19),and 22 DPH(W22),respectively.Growth,survival,RNA/DNA ratios,and midgut cell height of fish were assessed in each weaning regime over time.Growth and survival rates of fish larvae weaned in the W19 and W22 regimes were significantly higher than those in the W13 and W16 regimes,while no significant differences were found between W19 and W22.Fish showed a low lever of RNA/DNA ratio in W13 and significantly lower than other treatments,and the individuals in W22 was both significantly higher than W16 and W19 group.Weaning time significantly affected the mid-gut cell height in larval crimson snapper.On 22 DPH,the midgut cell height of fish in the W13 and W16 treatments were significantly thinner than those in the W19 and W22 treatments.Based on fish growth,survival,RNA/DNA ratio and midgut cell height,weaning can be started on 13 DPH in crimson snapper larvae,but we recommend that the best weaning window be 16-2 DPH.These results are supported by histological and nutritional evidence and would guide the weaning process for crimson snapper larvae,and offer a useful approach to explore the weaning protocol in larval fish rearing.The results of this study will help researchers in related fields to explore the physiological mechanism of red snapper in a more comprehensive and scientific way in order to effectively improve its seedling work. |
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