Studies On The Morphology?Histology And Activity Of Digestive Enzmye During The Early Development On Yellowtail Kingfish(Seriola Aureovittata)

1.In order to understand the characteristics of postembryonic development of yellowtail kingfish,morphological observation was carried out on larvae and juvenile,and describe the temporal sequence and morphological characteristics.The embryonic development requires 72 hours and 30 minutes under the following condition in the sea water at 20.5-22.5? and salinity at 28-30.The total length of the newly hatched larvae was(4.26±0.15)mm and with long oval yolk sac;The larvae opened their mouths at 3 days after hatching(DAH)with a TL of(4.65±0.11)mm.Larvae at 4DAH were 4.67±0.15 mm in TL,at the time anus communicated with the outside world,the larvae began to feed on rotifers and entered into the mixed nutrition stage.The total length of 5 DAH larvae was(4.69 +0.14)mm,and the yolk sac was completely consumed.The oil globule was absorbed at 9 DAH,the larvae were(5.13±0.25)mm and completely entered the exogenous nutritional stage.The total length of 25 DAH larvae was(8.22±1.24)mm,fin membrane of fish disappear and fish grow fast.45 DAH juvenile were(22.51±2.34)mm,the whole body of fish was covered with scales,completing the metamorphosis and was similar adult fish.According to the characteristics of yolk sac and oil globule absorption,fin development and scales,the early developmental stages of yellow stripe were divided into larval stage,juvenile stage and young stage.2.In order to study histology of digestive system in early stage of yellowtail kingfish,observe the structural changes of digestive system from newly hatched larvae to 50 days after hatching by using continual section cutting technique.The results showed that the fertilized eggs hatched after72 hours at water temperature20-22?.The digestive tract of newly hatched larvae was only an undifferentiated simple closed tube.At 5 DAH,the yolk sac was completely absorbed,the digestive tract consists of clearly oropharyngeal,oesophagus,stomach and intestine,liver and pancreas appeared,nutritional requirements of the larvae gradually transitioned fromendogenous to exogenous.At 9 DAH,intestinal circles were formed and goblet cells were found in the intestines of larvae.Gastric glands appeared at 16 days after hatching,and goblet cell was abundant in intestine.Pyloric caecum formed at 18 days after hatching,which indicates the beginning of digesting exogenous protein,gastrointestinal epithelial cells increased and muscle thickened,digestive and absorption efficiency increased with the development of digestive system function and structure.The ontogeny of liver started from newly hatched stage,and the differentiation of liver was prior to pancreas.The pancreas spread along the stomcah and intestine at 7 DAH.In conclusion,the development of digestive system are in accordance with their physiological and the understand of larval and juvenile digestion physiology will be useful in design of artifical food.3.To clarify the digestive and physiological characteristics in the early developmental stage of Seriola aureovittata,the activity of different digestive enzymes(lipase,amylase,trypsin,and alkaline phosphatase)were studied.Fertilized eggs and 1-to 60-day-old larvae and juveniles of S.aureovittata were selected as the research objects.The results indicated that lipase,amylase,and alkaline phosphatase were detectable during the embryonic stage;trypsin was detected in newly hatched larvae,which indicated that S.aureovittata can digest lipid,carbohydrate,and proteins before feeding.The specific activities of lipase and alkaline phosphatase increased rapidly after hatching(P < 0.05),reached a peak at 5.88 ± 0.45 U/mg and5.56 ± 0.41 U/mg,respectively at first feeding;the amylase activity reached its peak at 1.59 ± 0.02 U/mg on day 7;the specific activity of trypsin increased slowly after hatching,and reached a maximum at 1098.67 ± 24.03 U/mg on day 15(P < 0.05).Lipase,alkaline phosphatase,and trypsin were basically stable in the visceral mass of juvenile fish,and the activity of lipase,alkaline phosphatase,and trypsin increased the development of S.aureovittata.The amylase activity in the visceral mass of juvenile fish showed a downward trend and was basically stable at a lower specific activity level.The results of this study showed significant changes in various digestive enzyme activities during the development of larvae and juveniles,which were closely related to the development stage and feeding habits.The digestive enzymes were detected in early larvae that had not yet eaten food;it was considered that the digestive enzymes were maternal in origin and not from exogenous food.The lipase,alkaline phosphatase,and trypsin activities in juveniles significantly increased,which reflect the improvement of intestinal structure and digestive function and theincreasing demand for fat and protein.