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

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 (H2O2) treatments in a rainbow trout (Oncorhynchus mykiss) egg hatching system. High dose of UV irradiation (400 mWs/cm2) 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 H2O2 caused up to fivefold increase in the formate levels, and combination of O3 and H2O2 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 H2O2 had a distinctive effect on the overall bacterial community structure on the fish eggs.

► UV irradiation decreased mortality of rainbow trout eggs from 77.3% to 14.3%.
► UV irradiation decreased number of operationally taxonomic units on eggs.
► UV + H2O2 inlet water treatment modified microbial epibiota of rainbow trout eggs.
► O3 + H2O2 and UV + H2O2 treatments modified acetate and formate levels of water.