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.
Highlights
The increasing intensification of the global aquaculture industry focuses on product quality and profitability, and on the welfare of the farmed fish [1,2,3,4]
Mortalities did not occur during the experimental period, but a strong growth divergence of the fish was observed across all experimental groups
The substitution of fishmeal with Soybean meal (SBM) in the diet groups SBM33, SBM66 and SBM100 resulted in no significant differences in weight gain but influenced the specific growth rates (p = 0.05) and the feed conversion ratio (FCR) (p < 0.05) between the control (SBM0) and SBM100 groups
Summary
The increasing intensification of the global aquaculture industry focuses on product quality and profitability, and on the welfare of the farmed fish [1,2,3,4]. Decades of research have revealed that SBM-based diets reduce the growth of salmonids [25], while provoking mild to severe enteritis and other health complications [26]. These adverse responses are due to the presence of high levels of antinutritional factors, including saponins [27], proteinase inhibitors [28], lectins, oligosaccharides [29], phytoestrogens and antivitamins [27,30]. Unsuitable feed compositions have been reported to impair the immune system [29], and chronic inflammation may have serious consequences for the growth, health and, the well-being of the fish
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