Substitution of fish meal by soybean meal in diets for juvenile marbled spinefoot Siganus rivulatus -

Abstract

The challenge of replacing fish meal protein with alternative plant protein sources in aquafeeds for cultured species is an important aspect of modern aquaculture. The present study was conducted to assess the extent to which fish meal could be replaced with soybean meal as a source of dietary protein for marine herbivore Siganus rivulatus. Five iso-nitrogenous (40percent CP) and iso-energetic (14MJ-Kg) diets were prepared with SBM replacing fish meal at 0, 25, 50, 75, and 100percent levels of dietary protein. An 8-week feeding trial was performed with 240 juvenile S. rivulatus (mean weights 1.74 ± 0.03 g) size-sorted and stocked into 15 tanks randomly assigned in triplicates to each of the five treatments. The effect of SBM on survival, growth, condition, feed efficiency, protein efficiency and protein utilization in marbled spinefoot was assessed. A 3-week follow-up feeding trial using fish from the first experiment was performed to assess the effect of SBM in the diets on hematological parameters in S. rivulatus. Growth correlated negatively with increase in SBM inclusion, with best fit regression analysis of final body weights (g) resulting in a straight line with R20.91. Inclusion of SBM at high levels in the diet negatively affected SGR, FE, PER and GPU, with 100percent SBM in diet resulting in smallest K and least values in all growth parameters among treatments. No significant effect on VSI, whole body protein and body ash was observed while HSI and body lipid decreased significantly with increased SBM inclusion. There was no observed immediate effect on total or differential blood counts, hemoglobin, or plasma protein, except for a statistically non-significant increase in neutrophils with increase in SBM inclusion. Hematocrit expressed a negative correlation with SBM and decreased significantly when 100percent SBM was supplied in the diet. The results of the present study suggest that SBM is unsuitable for use as alternative to fish meal in diets for juvenile marbled spinefoot, and further investigations are necessary