The prebiotic effect of agavin inclusion levels in low fishmeal diets for Totoaba macdonaldi juveniles

The prebiotic effects of dietary agavin on growth performance, feed efficiency and digestibility, digestive enzyme activity, and distal intestine integrity in low fishmeal diets for Totoaba macdonaldi juveniles were evaluated in the present study. For this purpose, totoaba juveniles with a mean initial weight of 29 ± 1 g were fed for 56 days with four experiential diets formulated to replace fishmeal (FM) and poultry by-product meal (PBM) with soybean meal (SBM). The reference diet (RD) contained FM and PBM solely as the primary protein source. The following three diets contained SBM included at 240 g kg−1 with graded levels of agavin; 10, 20, and 30 g kg−1, in order to determine if a lower or higher quantity of the prebiotic in the diet would maximize growth parameters and fish intestinal integrity and reduce putative adverse effects of SBM in the diet. The inclusion of agavin in the diet, independently of the inclusion level, resulted in higher growth performance without significant differences in feed utilization and nutrient digestibility compared with the RD. Acid proteases (i.e., pepsin-like), trypsin, and total alkaline proteases activities resulted in significant differences among treatments but were not correlated with growth improvements. In terms of the intestinal health, significant differences in the number of mucosal folds and brush border height were found among dietary treatments and the light microscopy images and our semi-quantitative scoring revealed that agavin prevented the typical alterations in the distal intestine morphology associated with SBM induced enteritis in totoaba juveniles after 56 days of feeding. Thus, based on the results from the present study a 1 % agavin is recommended as the minimum dietary inclusion level in a low fishmeal diet (18 % FM) containing 24 % SBM to prevent typical symptoms of enteritis in totoaba juveniles under culture conditions.