The effects of dietary fumonisin B1 on growth and physiology of rainbow trout (Oncorhynchus mykiss)

Traditionally, fish meal and fish oil have been used as main sources of proteins and energy in the commercial fish feeds. Nowadays these ingredients have been partially substituted with materials of plant-origin (e.g. maize, wheat and soy) due to their more inexpensive price and easier availability. If contaminated plant material is used in the making of fish feed, the finished product can contain harmful substances called mycotoxins. Mycotoxins are the secondary metabolite products of moulds that are produced mainly for competition against other moulds. Feed mycotoxins have been observed to suppress growth and cause diseases on several domestic animals, but their effects on fish have been studied scarcely. One of the most common mycotoxins is fumonisin B1 (FB1) produced by fungus Fusarium moniliforme. FB1 contaminates mainly maize and maize products. In this 8-week study, the effects of dietary FB1 on the growth and physiology of juvenile rainbow trout (Oncorhynchus mykiss) were examined. The fish were divided randomly into treatment groups that were fed with graded concentrations of FB1: 0, 1, 5, 10 or 20 mg/kg. The growth of the fish and the feed consumption was monitored during the trial. After the trial, the blood samples of the fish were analysed for haematocrit, glucose and plasma chloride, and hepatosomatic index and liver water content were measured. Samples were taken from livers to examine possible histopathological abnormalities. The results indicate that FB1 does not affect growth, haematology or livers of rainbow trout at tested concentrations. Rainbow trout is known to be sensitive towards mycotoxins deoxynivalenol and aflatoxin, but appears more resistant towards FB1. This is maybe due to different metabolic pathways at cellular level and differences in biotransformation between different toxins. However, a longer experiment and/or increased amounts of FB1, may be needed to track possible adverse effects of FB1 on rainbow trout.