Microbial biomass, marine invertebrate meals and feed restriction influence the biological and gut microbiota response of shrimp Penaeus monodon

Abstract

P. monodon juveniles were fed krill meal (KM), krill hydrolysate (KH), whole squid (SQ), and the microbial biomass, Novacq™ (NQ), at 10% inclusion, in practical fishmeal and soybean meal based diets. Diets were fed to apparent satiation as well as restrictively pair-fed (~60% of control diet satiation) for 6 weeks to examine the effects of the test ingredients and feed restriction on shrimp growth, feed efficiency, digestive enzyme activity, nutritional condition, and gut microbiota.All diets when fed to satiety significantly outperformed the control diet, with shrimp fed NQ 87%, SQ 73%, KH 41% and KM 38% larger than shrimp fed the control diet. NQ fed shrimp had the best feed conversion ratio (FCR) and significantly improved retention efficiency (RE) of dietary lipid (RETL), protein (RECP) and gross energy (REGE). SQ significantly promoted feed intake over control and KM fed shrimp, but neither KM, KH nor SQ improved RETL, RECP or REGE. While there was little change in the apparent digestibility (AD) of each diet, the apparent biological value (ABV) of lipid (ABVTL), protein (ABVCP) and gross energy (ABVGE) were significantly improved by inclusion of NQ; and ABVTL and ABVGE were significantly improved by addition of SQ. Feed restriction had a stronger effect on hepatopancreas digestive enzymes and gut microbiota than addition of any feed ingredient. Total protease activity was positively correlated with feed efficiency, including FCR, RETL and REGE. Shrimp fed to satiety tended to have high levels of Vibrio whereas those on the restricted ration tended to have higher levels of bacteria in Rhodobacteracaea, Flavobacteriales and Bacteroidales.We conclude that shrimp are more efficient in using digested dietary macronutrients for growth when whole squid and Novacq™ are provided, due to improvements in feed intake and post-absorptive processes. Feeding restriction was shown to be a useful strategy to improve P. monodon feeding efficiency, digestive capacity and modulate gut microbiota, however it reduced the scope for shrimp growth especially on high performing diets. Novacq™ was more effective than some of the known invertebrate meals and a more environmentally sustainable growth and nutrient utilisation promoter for shrimp.