Nutrition of red drum, Sciaenops ocellatus L.: An additional evaluation of the effects of soya-based diets and supplemental prebiotic

We assessed the effects of a fishmeal (FM)- and two soya-based diets [without or with prebiotic (GroBiotic((R)) -A; GBA) supplementation] on the production performance, non-specific immunity, blood parameters and gut microbiota diversity of red drum, Sciaenops ocellatus. All diets were formulated to contain 450g/kg crude protein (CP) and 120g/kg lipid. A combination of soya bean meal and soya protein concentrate (SP) was used to replace 88% of the FM in the FM-based diet (REF) originating the first soya-based diet (SOY). The second soya-based diet (SOY+GBA) was designed identically to SOY except for the supplementation of GBA (20g/kg) substituting for wheat flour. After feeding the experimental diets to triplicate groups of 25 (similar to 3.4g/fish) and 90 (similar to 4.1g/fish) red drum juveniles for 9 (Trial I) and 16weeks (Trial II), our results showed that (i) red drum was highly sensitive to the soya-based diets in the first week of feeding; (ii) replacing 88% of FM with SP reduced the production performance of red drum without affecting intestinal micromorphology; (iii) whole-blood leucocyte oxidative radical production was unaffected while lower haematocrit and higher plasma lysozyme activity were found in fish fed REF; (iv) plasma osmolality was unaffected while lower glucose and higher lactate levels were observed in fish fed SOY and SOY+GBA; (v) 16S rRNA gene-based diversity of fish gut microbiota was affected both by SP and by GBA. This study expands the information on red drum responses to soya-based diets and prebiotic supplementation.