The effects of naturally occurring or purified deoxynivalenol (DON) on growth performance, nutrient utilization and histopathology of rainbow trout (Oncorhynchus mykiss)

It has been previously established that rainbow trout are extremely sensitive to the ubiquitous Fusarium mycotoxin deoxynivalenol (DON); however, the contribution of co-occurring mycotoxins and/or their potential interactions with DON have not been discounted. Concurrently, there have been few systematic efforts to characterize the pathological basis of the sensitivity of rainbow trout to DON. This study was conducted to investigate these outstanding issues. Triplicate groups of rainbow trout (initial average body weight = 50.3 g/fish) were fed eight diets containing graded levels of purified DON (0, 0.7, 1.4 and 2.1 ppm) or DON from naturally contaminated corn (0, 2.1, 4.1 and 5.9 ppm) for eight weeks. Fish experienced significant linear decreases in weight gain (P < .0001), thermal-unit growth coefficient (TGC; P < .0001) and feed intake (P < .0001) regardless of the source of DON. Similarly, significant linear and/or quadratic decreases (P < .01) in feed efficiency (FE), whole body crude protein (CP) content, retained nitrogen (RN), recovered energy (RE) and nitrogen retention efficiency (NRE) were observed in fish fed the diets containing either purified or naturally occurring DON. There were no significant differences (P > .025) in the above mentioned parameters between fish fed the diets contaminated with the same level of purified or naturally occurring DON (2.1 ppm). In general, bi-weekly sampling (6 fish/treatment/sampling) revealed significant linear or quadratic increases in dead (apoptotic/necrotic) cells in the pyloric caeca and significant linear or quadratic decreases in mitotic cells in the pyloric caeca and liver with increasing dietary levels of purified DON or DON from naturally contaminated corn without any distinct histopathological abnormalities (i.e. lesions). These cellular changes are in agreement with the known ability of DON to activate mitogen-activated protein kinases (MAPKs) indicating that the mechanism of action of DON in rainbow trout is consistent with that described in other species. Comparison of the response of fish fed the diet containing 2.1 ppm purified DON and 2.1 ppm DON from naturally contaminated corn suggested that decreased growth performance and nutrient utilization efficiency of rainbow trout exposed to grains naturally contaminated with Fusarium mycotoxins was most probably associated mainly with DON; however, continued research involving multiple levels of purified and naturally occurring DON is necessary to verify this finding.