Weaning strategies affect larval performance in yellowfin seabream (Acanthopagrus latus)

Abstract

A 30-day study was carried out to determine the influence of different weaning strategies (WS) on growth and survival rates, stress resistance, digestive enzyme activities and whole body fatty acid profiles in yellowfin seabream (Acanthopagrus latus) larvae. Thus, eight WS were designed by combining live foods (LF) (rotifers and Artemia) and a microdiet (MD) (Gemma Micro™, Skretting). In the control group (100 LF), larvae were fed only LF (100%), including enriched rotifers (from 2 to 20 days post hatching, dph) and Artemia (nauplii + enriched metanauplii, from 18 to 30 dph). The other treatments were based on different proportions of LF with the MD: 75LF-25MD, 50LF-50MD, 25LF-75MD and 100 MD in which 25, 50, 75 and 100% of LF that applied in the control group were replaced with a fixed ration of MD, respectively. In addition, for determining the appropriate time of weaning, three WS were applied including: sudden weaning (SW): larvae were weaned on to MD with only rotifer from 2 to 5 days post hatch (dph); early weaning (EW): larvae were weaned on to MD with only rotifer from 2 to 14 dah and late weaning (LW): larvae were weaned on to MD with rotifer (from 2 to 14 dph) and Artemia nauplii (from 12 to 20 dph). Larvae were hand-fed with the MD hourly from 08:00 h to 18:00 h (11 times a day). Results showed that the lowest survival rates were found among larvae from 100MD (1.5%) and SW (1.9%) groups, whereas the highest survival rates were found in larvae from 100LF (31.0 ± 1.7%), 75LF-25MD (34.7 ± 4.5%) and 50LF-50MD (36.2 ± 4.0%). Larvae from the 50LF-50MD group showed the highest resistance against air exposure (70.0%) and osmotic stress (100.0%) challenges. At the end of the trial, larvae from 100LF, 75LF-25MD, 50LF-50MD and LW groups showed higher growth performance than the other groups. At 30 dph, larvae from the LW group had the highest level of alkaline phosphatase to leucine-alanine peptidase ratio, while those from the 100MD, SW and EW treatments showed the lowest ones. The fatty acid profile of larvae reflected that of the diet. In particular, larvae from 100MD and SW groups had generally lower levels of n-3 long chain polyunsaturated fatty acids compared to the other treatments. In conclusion, results of the present study indicated the time of weaning and proportion of LF and MD remarkably affect larvae performance in terms of growth, survival, digestive function and stress tolerance. In addition, the replacement of LF with MD up to 50% after mouth opening of larvae neither have detrimental effects on growth, survival and digestive enzymes activities, meanwhile enhanced stress resistance of A. latus larvae.