Are the effects of Deoxynivalenol (DON) on performance, liver and gastrointestinal tract health of rainbow trout (Oncorhynchus mykiss) influenced by dietary composition?

This study investigated if dietary composition influences the effects of Deoxynivalenol (DON) on the health and performance of rainbow trout (Oncorhynchus mykiss). Four experimental diets (2 × 2 factorial design) were formulated which differed in 1) the diet composition; fishmeal (FM) versus soybean meal-based (SBM) and 2) the DON content of wheat; clean versus naturally contaminated wheat. Triplicate groups of n = 30 fish were assigned to each diet: (1) CON-FM; DON= 0 µg/kg feed; (2) DON-FM; DON= 1200 µg/kg feed; (3) CON-SBM; DON= 46 µg/kg feed; (4) DON-SBM; DON= 1300 µg/kg feed. The 8 week experiment was divided into two feeding periods: after 6 weeks of restrictive feeding, fish were fed ad libitum for 2 weeks. Influences on performance were evaluated by determining growth, protein and energy gain metrics, and on health parameters through the determination of histopathological changes in the liver and gastrointestinal tract (GIT). Restrictive feeding showed negative effects of DON and dietary composition on performance but did not show an interaction between DON and diet composition. Similarly, subsequent ad libitum feeding showed effects of DON and/or diet composition on growth, feed efficiency and body biometrics, but no interaction effects. These data confirmed the challenging nature of the SBM-based diet and previously noted negative effects of DON on performance. Only the histopathological assessment of mucosal fold width, enterocyte width and goblet cell density indicated significant interaction effects between DON and diet composition in the midgut. Yet, the differences were generally small and interaction effects were restricted to the midgut and not to the hindgut which is usually challenged by SBM. The combined information on growth performance and health suggests that DON challenges rainbow trout regardless of being fed a FM- or SBM-based diet, allowing more flexible formulations in the aquafeeds.