Rainbow Trout Rearing Performance, Intestinal Morphology, and Immune Response after Long‐term Feeding of High Levels of Fermented Soybean Meal

Abstract

The incorporation of PepSoyGen (PSG), a commercially produced fermented soybean meal product, was evaluated in a 205‐d feeding trial. Three isonitrogenous and isocaloric experimental diets containing 0, 35, or 50% PSG and 40, 15, and 0% fish meal, respectively, were fed to Rainbow Trout Oncorhynchus mykiss. The diets containing either 0% or 35% PSG produced similar total tank weight gains, percent gains, and feed conversion ratios and were significantly different from the diets containing 50% PSG at the end of the trial. Mean individual fish lengths and weights were significantly greater in the fish receiving 35% PSG than either of the other two diets. Specific growth rate (SGR) was significantly lower in the 50% PSG treatment, but there was no significant difference in SGR between the other two diets. Viscerosomatic index was significantly lower in the fish fed 35% PSG. Hepatosomatic index was not significantly different among the diets, but fish receiving 50% PSG had a significantly poorer liver condition scores. No other significant differences were observed in health assessments of fat, fin condition, gills, pseudobranchs, opercles, eyes, guts, kidneys, or spleens. Significant differences were observed in distal intestine morphology among the diets at day 94, but no differences were observed at the end of the trial on day 205. Splenosomatic index, macrophage activity, and respiratory burst activity were not significantly different among the dietary treatments. Based on these results, PSG can safely constitute 35% of Rainbow Trout diets without any decrease in rearing performance compared with a reference blend containing fish meal.

An Evaluation of Vertically Suspended Environmental Enrichment Structures during Rainbow Trout Rearing

“…The relatively low SSI values reported in this study, compared with those in Barnes et al. () and Parker and Barnes (), are surprising because fish in all of the tanks showed symptoms of bacterial coldwater disease (Neiger et al. ), and the causative agent of the disease, Flavobacterium psychrophilum , was isolated.…”

“…Similar SSI values also indicate no overt effects on the immune response (Hadidi et al 2008;Wiens et al 2014) resulting from spheres or rods in the tanks. The relatively low SSI values reported in this study, compared with those in Barnes et al (2014) and Parker and Barnes (2015), are surprising because fish in all of the tanks showed symptoms of bacterial coldwater disease (Neiger et al 2016), and the causative agent of the disease, Flavobacterium psychrophilum, was isolated. It is possible that relative spleen sizes were low because the trout had ample time to recover after the bacterial coldwater disease infection before being sampled at the end of the study.…”

Gut histology, immunology and the intestinal microbiota of rainbow trout, Oncorhynchus mykiss (Walbaum), fed process variants of soybean meal

“…A total of 72 slides were processed, 24 from each of the three sampling time points. Slides were examined using 100× magnification (Nikon E‐200, Melville, NY, USA) and the segments were evaluated using previously reported methodology (Barnes, Brown, Bruce, Sindelar & Neiger, ; Table ). Two separate reviewers independently analysed all slides at random and assigned a ranking to each slide, based on the overall intestinal appearance and composition.…”

Comparative performance of two rainbow trout strains fed fermented soybean meal

“…An approximately 2-mm-wide section of the distal intestine was removed from each fish, fixed in 10 % buffered formalin, and stained with hematoxylin and eosin using standard histological techniques (Burrells et al 1999). Intestinal morphology was assessed using an ordinal scoring system based on lamina propria thickness and cellularity, submucosal connective tissue width, and the number of large vacuole, adapted from Knudsen et al (2007) and Colburn et al (2012) as described in Barnes et al (2014).…”