A Multidisciplinary Approach Evaluating Soybean Meal-Induced Enteritis in Rainbow Trout Oncorhynchus mykiss

Abstract

This study evaluated a diverse range of markers of feeding stress to obtain a more precise assessment of the welfare of rainbow trout in relation to inadequate husbandry conditions. A feeding stress model based on dietary soybean meal was employed to identify suitable minimally invasive “classical” stress markers, together with molecular signatures. In a 56-day feeding experiment, rainbow trout were fed diets containing different levels of soybean meal. The impact of these different soybean meal diets on rainbow trout was assessed by water quality analyses, clinical health observations, classic growth and performance parameters, gut histopathology, blood-parameter measurements and multigene-expression profiling in RNA from whole blood. Soybean meal-induced enteritis was manifested phenotypically by an inflammatory reaction in the posterior section of the intestine and by diarrhoea in some trout. These inflammatory changes were associated with decreased supranuclear vacuolation. The haematocrit values and the levels of plasma cortisol and circulating lymphocytes in the blood were increased in trout that had consumed high amounts of SBM. Notably, the increased haematocrit depended significantly on the bodyweight of the individual trout. The transcript levels of certain genes (e.g., MAP3K1, LYG, NOD1, STAT1 and HSP90AB) emerged as potentially useful indicators in the blood of rainbow trout providing valuable information about inadequate nutrition. The expression-profiling findings provide a basis for improved, minimally invasive monitoring of feeding regimens in trout farming and may stimulate the development of practical detection devices for innovative aquaculture operations.

Growth and Welfare of Rainbow Trout (Oncorhynchus mykiss) in Response to Graded Levels of Insect and Poultry By-Product Meals in Fishmeal-Free Diets

“…The novelty of the present study was a paradigm shift in that it evaluated the response of fish to graded levels of PBM and BSFM, either singly or in combination, to replace the protein from vegetable sources in fishmeal-free diets, including substantial levels of soybean meal (SBM). It is well known that in salmonids, feeding diets high in vegetable protein sources, particularly SBM, can result in impaired growth performance and gut disorders [33,[65][66][67]. This has recently also been confirmed in this research, as previously reported by Randazzo et al [11].…”

“…Moreover, the knowledge on the involvement of dietary protein/amino acids in modulating the primary and secondary stress response is still quite unexplored [27,98,99]. Previous studies have shown that plant-based diets induce chronic stress or reduced stress tolerance in rainbow trout [33,100,101], but little or no information is available on the stress response to diets containing insect or poultry by-product meals. In this study, the serum cortisol level did not differ among dietary treatments and was close to the basal levels reported for rainbow trout, indicating no primary stress response [102].…”

“…Other indicators, such as the gross anatomy of the external and internal organs, the organosomatic indices, and the histopathological markers, are useful to complement the information resulting from blood screening and to provide an integrated diagnosis of fish welfare [30,31]. The concomitant monitoring of these parameters was suitable for the evaluation of the effects of fishmeal replacement with vegetable meal [32,33], insect meal [34][35][36], or a blend of plant, insect, and rendered animal proteins [11,[37][38][39] on the physiology, health, and welfare of rainbow trout. In this study, these different types of parameters were integrated to assess the welfare of rainbow trout in response to novel dietary formulations.…”

Red blood cells in proliferative kidney disease—rainbow trout (Oncorhynchus mykiss) infected by Tetracapsuloides bryosalmonae harbor IgM+ red blood cells

“…The presence of leukocyte and thrombocyte markers was also evaluated by real-time quantitative PCR (RT-qPCR) using the LightCycler 96 System (Roche, Germany) in combination with the SensiFAST SYBR No-ROX Kit (Bioline, London, UK). We profiled the marker genes encoding sptb in RBCs (5’-CACGCATCAAAACCCTAACAGAT-3’, sense; 5’-TGATGAGCATGCGTCCATCCC-3’, antisense), cd8 on cytotoxic T cells (5’-TTTTGTCAAGAAACTCTCCAACTGA-3’, sense; 5’-AATCACCATGTTGCTCTTAGTCTT-3’, antisense), cd4 on T-helper cells (5’-ATCTCCTCAACAGGGGCTGAAG-3’, sense; 5’-CTGTCTTTCCACTCTGGATCTAT-3’, antisense), igm on B cells ( 54 ), and cd41 on thrombocytes ( 54 ). Eef1a1 and rps5 served as reference genes to normalize the expression data.…”

Partial and total replacement of soybean meal with a corn‐fermented protein product in Rainbow Trout feeds

“…Soybean meal has a high protein concentration relative to other plant sources (~40% dry weight [DW]), has a relatively good balance of essential amino acids, and is typically inexpensive (Booman et al 2018;Agboola et al 2022). While soybean meal has already been incorporated into many commercial fish diets, high inclusion rates (above 25%) in carnivorous finfish feeds are associated with reduced protein digestibility, intestinal inflammation (enteritis), and reduced growth efficiency (Seibel et al 2022). Conventional soybean meal contains anti-nutritional factors, such as saponins, protease inhibitors, and lectins, which cause proximal intestine inflammation and reduce the overall efficiency of nutrient digestion and absorption from feeds (Agboola et al 2022).…”