Effects of the timing of initial feeding on growth and survival of loach (Misgurnus anguillicaudatus) larvae

Abstract

The effects of delayed first feeding on growth and survival and starvation on the point-of-no-return of loach Misgurnus anguillicaudatus larvae were studied by evaluating morphometric characteristics under controlled conditions. Larvae began to feed exogenously at 3 days after hatching (DAH) and the PNR occurred between 9 and 10 DAH at 23 ± 1.0°C. The experimental design included a conventional feeding regime with initial feeding from 3 DAH as a control, delayed first feeding for 4, 5 and 6 DAH. Morphometric characteristics (head depth, body depth, eye diameter, mouth diameter, musculature height, total length and yolk sac volume) were evaluated under different initial feeding time (3, 4, 5 and 6 days after hatching). Loach larvae initiated first feeding at 4, 5 and 6 days after hatching achieved comparatively lesser growth performance in all morphometric characteristics than that of 3 days at the end of the experiment. By day 6, significant differences were observed between 3 and 6 days initial feeding larvae for all morphometric characteristics except eye diameter and mouth diameter. Similarly, significant differences were noticed between 3 and 5 days initial feeding. However, there were no significant differences in head depth, body depth, eye diameter, mouth diameter, and total length between 3 and 4 days initial feeding until 12 DAH. After 15 days rearing, significant differences in all morphometric characteristics appeared between 3 and 4 days 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 days irrespective of the differences in the initial feeding. The yolk volume of 4 and 5 DAH larvae initiated first feeding at 3 days (0.0125 ± 0.0015; 0.0077 ± 0.0009 mm3) had significant differences compared with yolk volume of larvae initiated first feeding at 4 days (0.0081 ± 0.0011; 0.0039 ± 0.0004 mm3), 5 days (0.0079 ± 0.0010; 0.0017 ± 0.0002 mm3) and 6 days (0.0082 ± 0.0011; 0.0016 ± 0.0001 mm3). Survival rates of four treatments were estimated daily for 30 days and significant differences were observed between the treatments at the end of the experiment. The final survival rate was higher when the loach larvae initiated feeding at 3 days (75.9%) when compared with 4 days (31.8%), 5 days (14.5%) and 6 days (6.4%). The present study suggests that the first feeding of loach larvae should be initiated at 3 DAH for achieving better growth and survival or else bad growth performance will engender if the first feeding is delayed.