Effects of dietary κ-carrageenan on growth and resistance to acute salinity stress in the black tiger shrimp Penaeus monodon post larvae

Abstract

Acute salinity stress happens unnoticed in shrimp ponds and there is a need to protect the animals by providing dietary functional ingredients that will elicit resistance to this stress. k-Carrageenan, a sulfated polysaccharide from red seaweed, is reported to trigger innate immunity in vitro and in vivo in shrimps. The present study aims to evaluate its potential as growth-promoter and its immune-enhancement effects against salinity stress. Three separate experiments were done: (a) an attractability test; (b) a 30-day feeding trial to determine optimal inclusion of k-carrageenan, and (3) acute salinity stress test. Results of the attractability tests showed that all the experimental diets did not differ in their attractability to the shrimps. In the feeding trial, 5 groups of post larval shrimp were fed with 5 experimental diets containing various inclusion levels of k-carrageenan, namely, 0.0, 0.15, 0.30, 0.45, and 0.60 g kg-1. Results showed that the final average body weight (FABW), weight gain (WG), and specific growth rate (SGR) and feed conversion efficiency (FCE) values of shrimps in the 0.15 and 0.3 g kg-1 were significantly higher than that of the control group; the values of those in 0.45 and 0.60 g kg-1 groups were not significantly different from those of the control group. Protein efficiency ratio (PER) values, in contrast, were not significantly different from each group. Optimal inclusion level in the diet of k-carrageenan was 0.29 g kg-1. In the acute salinity stress test, 5 groups of shrimps were fed with the same 5 experimental diets as those in the feeding experiment for 2 weeks, transferred them from 21 ppt salinity media to 4 ppt. Results showed that the control group exhibited significantly highest mortality rate while in the 0.6 g kg-1 group the lowest; each group were significantly different from each other. Mortality rate decreased with increased dietary k-carrageenan level in a linear fashion. In conclusion, the study demonstrated that the the diets containing dietary k-carrageenan was equally as attractive as the basal/control diet and that k-carrageenan showed both growth-promoting and immune-stimulating effects against acute salinity stress in the black tiger shrimp P. monodon post larvae.