Synergistic toxicity of dietary aflatoxin B1 (AFB1) and zearalenone (ZEN) in rainbow trout (Oncorhynchus mykiss) is attenuated by anabolic effects

Although several studies have reported co-occurrence of mycotoxins in fish feed limited information is available on the physiological effects. In the current study, the single and combined effect of added dietary AFB1 and ZEN in various concentrations for 60 days was tested in rainbow trout on growth parameters, mortality, intestinal digestive enzymes activity and on serum and intestinal oxidative stress and immunological parameters and on intestinal histopathology, versus untreated controls. Both mycotoxins groups irrespective of concentration, showed a significant deterioration of SGR and FCR as compared to control, whereas no consistent differences in mortality were present. The small intestinal enzyme activity was significantly reduced by ZEN in particular at the higher mycotoxin concentrations and when combined with AFB1. Serum and intestinal immunological parameters were significantly affected largely consistent with additive and synergistic negative effects on the (innate) immune system, in particular enhanced inflammation. The latter was also reflected in the serum and intestinal oxidative stress parameters. Histopathological examination showed decreasing villus length and Goblet cell density with increasing mycotoxin load. It is concluded that the combination of AFB1 and ZEN clearly increased the toxic effect on the fish as far as the serum and intestinal parameters are concerned. This is in some cases merely additive, but clear synergistic toxicity was seen too, in particular at the higher mycotoxin concentrations. Surprisingly, the increasing intestinal impairment did not translate into increased growth retardation and mortality since those were similar in all non-control groups. This may be consistent with anabolic effects of mycotoxin (metabolites) as has been described before.

Automated summary

The study found that the combination of AFB1 and ZEN in fish feed led to deterioration in growth, feed conversion rate, immune system, and intestinal tissue. Despite increased intestinal damage, there were no significant changes in growth and mortality rates.