| The loach(Misgurnus anguillicaudatus),an autochthonous fish of Asia,has recently shown a great potential in the aquaculture of China.However,the early culture techniques and methods of loach are becoming the bottleneck of loach culture on a large scale.The main reason is that feeding ecology of loach in early life stage has not been investigated distinctly.This study was conducted to investigate the diel feeding rhythm,the optimal first feeding time and effects of different diets on growth and survival in early life stage of loach in order to supply some scientific criterions for loach culture and early cultivation.The main contents are as following:1.Feeding rhythm of loach in early life stageThe diel feeding rhythm and ontogenesis during early life stage of loach were investigated under experimental conditions(light:L 06:00-18:00,D 18:00-06:00 hours). Morphological and behavioural developments of loach from newly hatched to 40 DAH were observed.Larvae were able to prey on daphnia 3-4 DAH at 23±0.5℃.As the larvae grew,they showed an increasing feeding capacity and a distinct feeding rhythm. Feeding intensity and incidence for day-4 larvae were highest at 10:00 and 16:00 hours. The highest levels of feeding intensity for day-12 larvae occurred at 08:00,12:00 and 18:00 hours as did feeding incidence.By day 20,when the larvae metamorphosed,the highest levels of feeding intensity occurred at 06:00,18:00 and 24:00 hours and were concurrent with the highest feeding incidence.After metamorphosis,feeding capacity had again increased considerably and,in contrast to the earlier stages before day-20,feeding intensity for day-30 juveniles peaked at 05:00 and 20:00 hours,about 1-2 h after the maximum feeding incidence.The feeding rhythm of loach juveniles at day-40 was almost the same to the day-30 juveniles.The estimated maximum daily feeding rates were 43.1%, 33.4%,19.0%,12.8%and 5.8%of body weight on days 4,12,20,30 and 40,respectively. Thus,loach was found to have different feeding rhythms in the pre- and post-metamorphosis stages,with the highest feeding activity in daytime during the larval planktonic stage before metamorphosis,and intensely nocturnal feeding behaviour during the juvenile benthic stage after metamorphosis.2.Effects of different diets on growth and survival of loach larvaeCulture performance beyond metamorphosis of larval loach was examined in feeding experiment of early development stage(20 days after hatch).Total length,dry weight, length- and weight-specific growth rate(SGR) and survival were monitored in different diet regimes.During 20 days,diet treatments included:microparticle diets(A);live daphnia(Moina micrura)(B);live daphnia plus live chlorella(Chlorella pyrenoidosa)(C); live daphnia plus microparticle diets(D).Fish survival rates during 20 days were 21.23±4.2%(A),73.19±2.8%(B),90.76±3%(C) and 91.46±3.1%(D),respectively.Length-and weight-specific growth rate after 20 DAH(final mean SGR;%·day-1) were 5.36±0.44 and 15.75±1.52(A),9.29±1.25 and 23.47±2.23(B),9.42±1.55 and 24.88±2.9 (C) and 9.55±1.23 and 24.40±2.75(D),respectively.Fish in treatment B,C and D displayed higher growth rates which were significantly longer and heavier than fish in treatment A by the end of the experiment(P＜0.05).Fish in treatment A had highly significantly greater(P＜0.001) mortalities than in treatment B,C and D.There were no significant differences in any growth parameter between Fish in treatment B,C and D,but the survivals in treatment C and D(90.76%and 91.46%) were significantly higher than that in treatment B(73.19%,P＜0.05).The results demonstrated that enriched prey and co-feeding may serve as a potential feeding strategy for loach larvae and the form of co-feeding reduces the costs and dependence on live foods to a certain extent.We concluded that larval loach should be reared over metamorphosis using either of the following methods:feed with live daphnia supplemented with microparticle diets or live chlorella.3.Effects of delayed first feeding on growth and survival of loach in early stageThe effects of delayed first feeding on growth and survival and starvation on the point-of-no-return(PNR) of loach larvae were studied by evaluating morphometric characteristics under controlled conditions.Larvae began to feed exogenously at 3 DAH and the PNR occurred between 9 and 10 DAH at 23±1.0℃.The experimental design included a conventional feeding regime with initial feeding from 3 days after hatching (DAH) as a control,delayed first feeding for 4,5 and 6 DAH.Morphometric characteristics(total length,head depth,body depth,eye diameter,musculature height, mouth diameter,yolk sac volume) were evaluated under different initial feeding time(3 d, 4 d,5 d and 6 d after hatching).Loach larvae initiated first feeding at 4 d,5 d and 6 d after hatching achieved comparatively lesser growth performance in all morphometric characteristics than that of 3 d at the end of the experiment.By day 6,significant differences were observed between 3 d and 6 d initial feeding larvae for all morphometric characteristics except eye diameter and mouth diameter(P＜0.05).Similarly,significant differences were noticed between 3 d and 5 d initial feeding.However,there were no significant differences in total length,head depth,body depth,mouth diameter,and eye diameter between 3 d and 4 d initial feeding until 12 DAH.After 15 days rearing, significant differences in all morphometric characteristics appeared between 3 d and 4 d initial feeding and followed to the end of the experiment.It was also observed that the yolk absorption in loach larvae was completed by 6 d irrespective of the differences in the initial feeding.There was no significant difference in the yolk sac volume of 1 DAH, 2 DAH and 3 DAH larvae among different treatments.The yolk volume of 4 and 5 DAH larvae initiated first feeding at 3 d(0.0125±0.0015 mm3;0.0077±0.0009 mm3) had significant differences with yolk volume of larvae initiated first feeding at 4 d (0.0081±0.0011 mm3;0.0039±0.0004 mm3),5 d(0.0079±0.0010 mm3;0.0017±0.0002 mm3) and 6 d(0.0082±0.0011 mm3;0.0016±0.0001 mm3)(P＜0.05).Survival rates of four treatments were estimated after 30 days rearing and significant differences were observed between the treatments.The final survival rate was higher when the loach larvae initiated first feeding at 3 d(75.85%) when compared to 4 d(31.76%) and 5 d (14.50%) and 6 d(6.43%).The present study suggests that the first feeding of loach larvae should be initiated at 3 d after hatching for achieving better growth and survival or else bad growth performance will engender if the first feeding is delayed.
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