EXPERIMENTAL STARVATION ON HUCHO TAIMEN AND DEFINITION OF THE POINT OF NO RETURN

As the experimental animal,Hucho taimen larvaes,with rupture of membrane by artificial spawning and hatching,were experimented by direct observation,data measurement,Motic Image Plus 2.0 and SPSS 13.0.Under the water temperature of 10-1-℃,the effects of starvation on growth,morphology and behavior were researched.The study determined the point of no return(PNR) for the larvae of Hucho taimen and the best time of initial feeding.The results showed that the total length and length before anus of Hucho taimen increased straightly in 02-4d.The total length of 30d larvae was 2.97±0.30cm,of which the length before anus was 2.09±0.13cm.After 30d,the increase of the total length and length before anus stopped,while the total length generally maintained constant.But the fatness unceasingly decreased,and the weight changed obviously that increased negatively after 24d,while there was close relation between the yolk sac and growth changes.At the beginning of incubation,the volume of yolk sac was 0.087cm3.In the first 15d,the volume of yolk sac decreased quickly,which was 0.029cm3 in 15d and stepped down later.The yolk sac absorbed completely at 30-33d after rupture of membrane.From 21d to 45d,there were significant differences in body weight of the starvation group and the control group by using the correlation analysis with spss13.0,p=0.001,p﹤0.01.The starvated larvae were black and thin,which had bigger head and slender body.The high of body were lower than that of control group,and the total length were shorter than that of control group.The melanin in stomach intestine was thickness remarkably.The hindbrain was sagged by starvation for long time;the gregariousness and ability of initial feeding had negative correlation with the starvation time.The behavioral response of starvated Hucho taimen larvae contained three stages:(1) The high assembly stage in the surface layer of water body.In this stage,the larvae swam rapidly,and this was the foraging stage.There were a great quantity of self-mutilation larvae.(2) The stage of distributing in mesopelagic zone of water body.In this stage,there were 40% larvae that began to away from the group,while larvaes showed head up and tail down and swam torpidity.It showed the change of exterior shape,and the torpidity of reaction.(3) At the anaphase of starvation,larvae distributed on the bottom of water,while the body of the larvae swam like "V",the reactiveness was low,the irritant reaction to the outside was dull,and the self-mutilation was disappeared.The self-mutilation appeared in individual larvaes in 25d and increased obviously in 27d.The individuals of self-mutilation increased with the days of starvation,of which the maximum rate was 14.5% in 30d.The rate of self-mutilation decreased in 35d,and only a few individuals showed self-mutilation in 41d.The initial feeding time of Hucho taimen was in -1d,and the initial feeding rate was 100% in 29d.The point of no return(PNR) was in 39d to 40d,while the initial feeding rate was 50%.The best time of initial feeding of the larval appeared in 25d when the fourth day after swimming up.In 45d,the larvaes of the starvation group died completely.This experiment not only provided the reciprocal theory base for the artificial propagation of Hucho taimen and artificial domestication of the initial feeding larvae,but also made the study of morning life history of fish plentiful.