The impact of zinc on the bacterial abundance in the intestinal tract of rainbow trout (Oncorhynchus mykiss) larvae

The paper presents an estimation the effect of zinc (0.13 mg/l, 0.5 mg/l, 2 mg/l and 8 mg/l in water) on the abundance of bacteria in the intestinal tract of rainbow trout (Oncorhynchus mykiss) larvae. Populations of total aerobic heterotrophic bacteria present in the intestinal tract of rainbow trout larvae, estimated using the dilution plate technique, were reduced significantly in comparison with control after exposure to 0.5 mg/l, 2 mg/l and 8 mg/l of zinc. The abundance of total heterotrophic bacteria decreased most significantly after exposure of larvae to 2 mg/l of zinc and was one order of magnitude lower in comparison with control. The same trend was observed for the abundance of proteolytic and total coliform bacteria in the intestinal tract of rainbow trout larvae after exposure of larvae to 2 mg/l of zinc. Zinc is toxic to bacteria in the intestinal tract of rainbow trout larvae, but at significantly higher concentrations in comparison with copper ions.