FEEDING AND GROWTH OF <I>SINIPERCA SCHERZERI</I> LARVAE REARED IN CIRCULAR RACY WAY

Abstract

Feeding and Growth of Siniperca scherzeri larvae were studied in function morphology and ecology,and the growth model of larvae was established,which could provide biological and ecological data for Siniperca scherzeri larvae rearing.Experiments were performed in the Hubei Qichun Chidonghu Seed Stock Farm from 3rd May to 6th June,2007.Adult fish,Siniperca scherzeri,were caught in the Zhelin Lake of Jiangxi Province.44 adult fish Siniperca scherzeri(♀: 34,♂: 10)whose gonads reached full development were chosen to obtain larvae by artificial propagation at 17:00 on 4th May.The eggs were collected in a circular-racy-way to hatch with slow flow.The hatchery circular-racy-way was maintained at temperatures of(24±2)℃,DO(6.51±1.32) mg/L,COD(4.88±0.94) mg/L,pH 7.54±0.31,TN(0.63±0.27) mg/L and TP(0.08±0.01) mg/L.82 percentage collected eggs were hatched at 6:00 on 11th May.The newly-hatched larvae were cultivated in a circular-racy-way for feeding tests.From 17:00 to 20:00 on 12th May,16000 newly-hatched larvae were collected,placed and cultivated in the other circular-racy-way for starvation tests to measure point-of-no-return(PNR).At least 10 larvae were picked from feeding tests in 8:00-10:00 everyday to observe their growth by anatomy microscope(NIKON SMZ2800),and the total length(TL) and volume of the yolk sac of larvae were measured in the process of observation.When the larvae started exogenous feeding and established exogenous nutrition,the growth was observed every 5-6h.At last,the daily rate of growth,the volume of the yolk sac and the consuming rate of yolk sac of larvae were figured out,and the growth model of larvae was established.The initially feeding rates of larvae were calculated in the feeding tests.The point of no return(PNR) was defined as a critical time at which the initially preying larvae could tolerate starvation.The PNR was measured as follows: the initially feeding rate of larvae was daily measured and the maximum feeding rate was estimated.It was PNR when the initially feeding rate decreased to half of the maximum feeding rate,namely,50% of the starved larvae were too weak to re-gain taking food.Therefore,PNR was represented as the number of days(day-old) after hatched out.The volume of the larva's yolk sac was calculated as: 4/3π·R/2·(r/2)2,where,R was the long diameter of yolk sac,r was short diameter of yolk sac.As observed,the total length(TL),volume of the yolk sac and diameter of oil globules of the newly-hatched larvae of Siniperca scherzeri were(4.87±0.10) mm(n=50),(1.461±0.172) mm3(n=50) and(0.47±0.04) mm(n=50),respectively,which were reared in a circular-racy-way with slow flow at water temperature of(24±2)℃.12 hours post hatching larvae could swim flatly fitfully and its pectoral fins had become large markedly.A freely swimming mode was established at one day post hatching(dph).2 dph larvae started exogenous feeding and came in the stage of the mixed nutrition.3 dph larvae established exogenous nutrition relationships completely.The yolk sac and oil globules of larvae at 5 dph vanished,and the total length of larvae at 15 dph was(13.72±0.76) mm(n=12).In period of growth of 15 days,the larvae grew rapidly in both the stages of endogenous and exogenous nutrition,but slowly in the stage of mixed nutrition.Length increments averaged 0.59 mm/d.The relationship between increment in TL and age in days(D) was described as: TL =-0.0004D3 + 0.0283D2 + 0.2159D + 4.9335(R 2 = 0.985,n=261).Mouth width of larvae increased with its TL from 2 to 15 dph.The growth of larvae reached the point-of-no-return on the fifth day or the sixth day.To avoid potential starvation mortality,the larvae had to establish successful initial feeding within 4 days.