Studies On The Early Development And Body Composition Of Polydon Spathula

Paddlefish(Polyodon spathula) populations is now threatened,and it is listed in the AppendixⅡof the Convention on International Trade in Endangered Specied of Wild Fauna and Flora(CITES).P.spathula was introduced into China from America in 1990. At present,there are only several reports about culture technology of P.spathula,and sporadic reports about early life history and nutritional studies on P.spathula.This experiment was conducted to observe the early development and body composition of larvae and juvenile P.spathula.The main results were generalized as follows:1.The fertilized eggs of P.spathula was megalecithal,and the cleavage of eggs was the speical spokewise cleavage.The whole embryonic development of paddlefish can be divided into nine periods:fertilized eggs periods,cleavage periods,blastula periods, gastrula periods,yolk plug periods,neurula periods,heat beating periods,pre-hatching periods and hatching periods.Under water temperature of 18～22℃(Average 20℃),the embryonic development lasted for 119～138 hrs.The total accumulated temperature was 2266℃·h～2617℃·h.The total length of newly hatched larvae was 7.38 mm.2.When water temperature was 18～22℃(Average 20℃),In the early-larvae stage the yolk sac of the larvae was absorbed completely at the 8^th DAH(day afer hatching),the total length of larvae was 15.50 mm.In the late-larvae stage(8～22 DAH),the snout of the larvae protruded forward and became dark gradually due to pigmentation,the fins began development,the average length of larvae was 7.38～15.50 mm;In the juvenile stage(22～71 DAH) the average length of larvae was 230 mm,all fins completed their development and the caudal fin completed bifurcation.3.Starvation will result in the stunt growth and organ differentiation.Starved larvae was thin,the posterior cerebral caved,the body unbalanced,and swam slowly.When water temperature was 19～23℃(Average 21℃),the starved larvae reached their PNR (the point-of-no return) at 17.5 DAH.At 17^th DAH,the total mortality of starved larvae was up to 85.71%and its instantaneous mortality was up to 49.25%.At 19^th DAH,both total and instantaneous mortalities of starved larvae were up to 100%.4.As the juvenile paddlefish grow,its protein content and fat content in the muscle increase significantly while water content decrease.When the body weight is 50 g,150 g, 300 g and 600 g,the protein content in its muscle is 13.17±0.54%,15.71±0.23%, 16.77±0.39%and 17.09±0.28%,respectively,and fat content,1.75±0.14%,2.21±0.30%, 2.72±0.24%and 3.10±0.13%,respectively.The amino acid content has the same tendency as protein content,increasing with the increase of body weight.The content of Glu,Lys, Leu,Asp,Gly and Ala was high in the muscle of paddlefish.