In fl uence of raw polysaccharide extract from mushroom stalk waste on growth and pH perturbation induced-stress in Nile tilapia , Oreochromis niloticus

Article history: Received 20 October 2015 Received in revised form 17 September 2016 Accepted 27 September 2016 Available online 01 October 2016 Fish contributes to half of the total world animal protein produced. In vivo ionic imbalance caused by aqua-environmental pH perturbation makes fish more susceptible to oxidative stress and hence its growth and yield are compromised. Enhancing the antioxidant defense status by supplementing with natural antioxidant rich source is themost convenient alternative to protectfish from stress. Disposal of undesirablemushroompart (mushroom stalk waste, MSW) increases exponentially along with its production. As mushroom is a rich source of polysaccharides and antioxidants, we extracted raw polysaccharide (RP) fromMSW for 2 h (RP2) and 5 h (RP5) respectively and supplemented to fish feed to evaluate the protective effect on stress caused by pH fluctuation. RP5 contained significantly higher amount of beta glucan (P=0.0023) and crude protein (P=0.0000). Phenolic content for the RP5 was 70.67mg GAE/g extract exhibiting significantly better IC50 values for DPPH radical scavenging,metal chelating activity and inhibition of LPO,with values of 0.821 (P=0.0000), 4.48 (P=0.0000) and 1.052 (P=0.0001)mg/mL. The experimental range of supplementation (5 and 10 g RP/kg feed) showed zeromortality for Nile tilapia. Higher amount of SGR was observed in case of diet RP 5 g/kg supplementation, however better WGandHSIwere found for RP 10 g/kg. In in vivo pre and post stress condition, diet RP 5 g/kg feed has significantly improved the activity of SOD (P = 0.0039 and P = 0.0352, respectively for low and high pH) and CAT (P = 0.0006, P = 0.0006 and P = 0.0074, respectively for pH 5.5, pH 8.5 and pH 10.5). Pearson correlation analysis showed TPC and beta glucan has strong correlation respectively with DPPH (1.00 and 0.942), LPO (0.998 and 0.958) and metal chelating activity (0.988 and 0.980). CAT and SOD has shown strong correlation with SGR (0.960 and 0.935), moderate correlation with WG (0.461 and 0.170), respectively. In the principle component analysis, SGR andWGwere observed clustered togetherwith supplemented diet both in pre and post stress condition. In summary, the results suggest that RP5 is a promising antioxidant agent and supplementation of RP5 in fish feed showed the capacity of mitigating pH induced stress in fish, which enhances the growth rate in stress condition. Statement of relevance: This experiment was conducted to improve the growth performance and to enhance the oxidative stress protection capacity of Nile tilapia. Raw polysaccharide of mushroom stalk waste (MSW) was used as supplement in diet which was available, cheap and rich in beta glucan content. This is first report on utilization of MSW as supplement of fish feed to increase the oxidative stress protection in aquatic organism. Nile tilapia, second largest aquatic fish, was used as experimental model fish. Enhancing the antioxidant defense status by supplementingwith natural antioxidant rich source is themost convenient alternative to protect fish from stress. Disposal of undesirable mushroom part (mushroom stalk waste, MSW) increases exponentially along with its production. Asmushroom is a rich source of polysaccharides and antioxidants,we extracted rawpolysaccharide (RP) fromMSW for 2 h (RP2) and 5 h (RP5) respectively and supplemented to fish feed to evaluate the protective effect on stress caused by pH fluctuation. We believe our findings will be of particular interest to the scientific community and very useful in practical to fish feed as supplement. © 2016 Elsevier B.V. All rights reserved.