Prevention of fungal infestation of rainbow trout (Oncorhynchus mykiss) eggs using UV irradiation of the hatching water

Abstract Fungal infestation by water mold Saprolegnia spp. causes great losses in aquaculture and fish egg hatching. To find a safe and effective alternative for the fungal prevention, we studied continuous disinfection of the inlet water by UV irradiation and ozonation combined with low concentration hydrogen peroxide (H 2 O 2 ) treatments in a rainbow trout ( Oncorhynchus mykiss ) egg hatching system. High dose of UV irradiation (400 mWs/cm 2 ) of the inlet water decreased the mortality of rainbow trout eggs from the 77.3% to 14.3% in a 28 day trial. UV irradiation did not modify water quality parameters, while combination of UV irradiation and H 2 O 2 caused up to fivefold increase in the formate levels, and combination of O 3 and H 2 O 2 caused even ten-fold increase in the acetate and formate levels. UV suppressed the gradual increase of the heterotrophic bacterial counts on the fish eggs. Based on the molecular profiling high dose of UV reduced the growth of some of the dominating bacterial groups and combination of UV and H 2 O 2 had a distinctive effect on the overall bacterial community structure on the fish eggs.