The Study Of Ontogeny And Feeding Ecology On Larvae Of Schizothorax Wangchiachii

Schizothorax wangchiachii belongs to the Cypriniformes,Cyprinidae,Schizothoracinae,Schizothorax,mainly distributed in Jingsha River,Dadu River and Wujiang River.The Schizothorax have a rich biological diversity and habital diversity,showing a very strong adaptability to environment.The stock of fish resources have been scarce because of the development of upstream cascade hydropower stations and overfishing.Many studies have been done on the Schizothorax wangchiachii,which mainly focus on embryonic development,behaviourology,and reproduction.In our study,we focus on the ontogenetic process of larvaes and juvenile on Schizothorax wangchiachii,such as the morphology and growth characteristics of ontogeny,the selectivity of different substrates and foods,and the monitoring of environmental factors（water temperature,dissolved oxygen and PH）.The main results are as follows:1.The observation on the development of larvae on S.wangchiachii:The ontogenetic development of larvae on S.wangchiachii experience 66 days.Newly hatched larvae was clear and yellow with a total length of 9.83±0.88mm,the pectoral fin is small,showing a crescent shaped,most larvae lie on the bottom of water;the yolk sac of larvae was absorbed in 20-days-old with total length of 15.18±0.52mm,which full of food in the intestines and only camping exogenous nutrition life;65days-old larvae had a total length of 23.64±0.82mm,with ventral fold disappeared,melanin dense in head,side silver white,white belly and visible abdominal slit.In particular,all fins are already appeared with similar character on adult.2.The growth charactic of S.wangchiachii:The growth of larvae S.wangchiachii shows a S shape,firstly increased rapidly,and then slow down,but then quickly increase again and then slow down.The origin fitting shows that there is a very significant polynomial function relationship between the total length（L_P）and anal length(L_PA).L_P=9.72956+0.55048D-0.02394D²+5.12831E^-4D³-3.44191E^-6D⁴R=0.96665 SD=0.68243 P<0.0001L_PA=2.47334+0.23409D-0.01041D²+2.34049E^-4D3-1.68699E^-6D⁴R=0.93632 SD=0.39217 P<0.0001The specific growth rate（SGR）of larvae S.wangchiachii showed a trend of rapidly increase first and then exponential decline.We found that the day 22.14 and52.35 are the key days for the growth of larvae by using matlab to analyze the relationship between body length and age,the key days are close to the disappearance of the yolk sac（23-days-old）and the high mortality in 52-days-old larvae（close to 20mm）.3.Substrate preference on larvae fish of Schizothorax wangchiachii:Larvae of15-days-old prefered gravel,the percentage of larvae remaining on gravel,sand and mud was 35.69%±6.77%,27.15%±4.50%and 26.94%±3.33%;larvae of both35-days-old and 55-day-old prefered sand and mud,the percentage of 35-days-old and55-day-old larvae remaining on gravel,sand and mud was 22.85%±5.17%,31.53%±3.09%and 34.51%±3.61%;22.43%±7.83%,29.10%±6.98%and 33.96%±8.86%.4:The food selection of the larvae on S.wangchiachii:Laboratory identification shows that larvae food mainly contain Phytoplankton and Periphytic algae,the Cyclotella,Navicula,Cymbella,Stauroneis anceps,Cocconeis placentula and Synedra are the main species in the Phytoplakton.Under the body length of 18cm,the larvae main take the Phytoplankton as the main food,more than 18cm,Phytoplankton and Perphytic algae are the both food in their body.The feeding rhythm of larvae and juveniles on Schizothorax wangchiachii was found to be the highest at 15:00,when the average filling degree reached at 4.20 and 3.60.