Studies On Growth,Development,Feeding Characteristics,Digestive And Endocrine Physiology Of Larval,Juvenile,and Young Thamnaconus Modestus

Knowing the changing law of the growth,development,feeding characteristics,the activity of several major digestion enzymes and the levels of hormone in larval,juvenile,and young Thamnaconus modestus,can be effective to guide the management of water environment and feed fry in the early stage of T.modestus,thus to promote the growth,feeding and survival rate of fry in the process of artificial seedling.We investigated the adoption of experimental ecology methods,changes in growth,development,feeding characteristics,digestive（acid protease,alkaline protease,acid phosphatase,alkaline phosphatase,lipase,amylase）and endocrine（triiodothyronine（T3）,thyroxin（T4）,somatropin（GH）,insulin-like growth factor-I（IGF-I））physiology of larval,juvenile,and young T.modestus under artificial rearing conditions.In addition,samples were taken from normal and abnormal 30-day-old fish fry to analyze the changes of main digestive enzyme activities and hormone content,so as to compare the differences of main digestive enzyme activities and hormone content between 30-day-old normal fish fry and abnormal fish fry.The studies were as follows:1 The Growth Characteristics of larval,juvenile,and young T.modestusIn terms of growth characteristics,the growth indexes of larval,juvenile,and young T.modestus fits into 2 or 3 straight lines,with 1 or 2 inflection points including the total length,body length,body weight,pre-anal length,head length,snout length,body depth（which can be fitted in 3 segments）,and eye diameter（which can be fitted in 2 segments）.Especially at the first inflection point,the growth rate of head length was significantly higher than that of other indexes,.However,the growth rate of head length and body depth declined after the second inflection point,while the growth rates of all other growth indexes accelerated gradually.2 The Feeding Characteristics of larval,juvenile,and young T.modestusIn terms of feeding characteristics,in the“feeding initiation stage”,the feeding incidence and satiation rate of 3dph and 4dph larval were initially lower,but they increased gradually overtime.The feeding incidence and the satiation rate reached 100%at 12dph and 25dph（where the fullness degrees were all of level 3 and 4）.The larval,juvenile,and young T.modestus represented the daytime feeding habit,which accounted for more than 71.6%of daily ration.3 The Digestion Physiology of larval,juvenile,and young T.modestusAll kinds of digestive enzyme can be detected in larval,juvenile,and young T.modestus.The activity of acid protease,alkaline protease,alkaline phosphatase and amylase were lower while the activity of acid phosphatase and lipase were higher in hatching larvae of T.modestus,then the different digestive enzyme have different changing pattern with the development of larvae.The activity of acid phosphatase tends to decrease on the whole while the activity of amylase tends to increase on the whole,the changes of other digestive enzyme activity were fluctuation.4 The Endocrine Physiology of larval,juvenile,and young T.modestusThe contents of the four hormones in hatching larvae were the minimum value.The contents of T₃and T₄ have the same tendency of change,it keep rising and arrive the maximum value at 35 days post hatching.The contents of GH and IGF-I have the same tendency of increase→decline→increase,but the contents of IGF-I decrease significantly（P<0.05）since arrive the maximum value at 20 days post hatching,the contents of GH continued to rise after a short decrease at 25 days post hatching and reached its maximum value at 35 days post hatching.5 The Comparison of Main Digestive Enzyme Activities and Hormone Contents between Normal Fish and Abnormal Fish of T.modestusBy comparing the main digestive enzyme activities and hormone contents of the normal and metamorphosis abnormal fish fry at 30 days post hatching,it found that the digestive enzyme activities and hormone contents of metamorphosis abnormal fish fry were lower than those of normal fish fry,and the contents of T₄ and IGF-I were significantly different（P<0.05）.