Nutritional value of soy protein concentrate for larvae of common carp ( Cyprinus carpio) based on growth performance and digestive enzyme activities

Trials were undertaken with first-feeding common carp larvae to determine whether soy protein concentrate (SPC) can be used as a major protein source in larval diets. The effects of supplementation with sulfur amino acid were also studied. A further objective of the study was to determine the effects of soybean trypsin inhibitor (SBTI) on growth performance as well as on the activities of digestive enzymes in common carp larvae. In a series of three trials, common carp larvae were fed experimental diets over 21 days using an automatic feed dispenser. In larvae fed diets containing 20, 60 and 70% SPC, or casein-based diets with purified SBTI (the same or higher level as in the SPC), trypsin and amylase activities were measured on days 8 and 20 after initiation of feeding. Incorporation of SPC levels of up to 40% in the diet did not adversely affect survival or growth of carp larvae. At levels of 60 or 70%, growth retardation was observed which was not improved by sulfur amino acid supplementation. Addition or purified SBTI to casein based diets had no effect on survival and growth. A significant decrease of trypsin specific activity was found in the larvae fed the diets with the highest levels of SPC and of purified SBTI, whereas amylase specific activity was not affected. It is concluded that the growth limitation of carp larvae fed high levels of SPC was not due to SBTI alone but to other antinutritional factors.