The use of ozone in trout hatchery to reduce saprolegniasis incidence.

At present, the prophylactic measures in trout hatchery are based on the use of formaldehyde. The purpose of this work is to set up an alternative system of prevention of saprolegniasis, using ozone. The experiment was carried out in two successive cycles. The first experiment lasted 46 days and five different treatments were applied on every second day on the same number of lots of 250 eggs each, of which three were treated with ozone (O3) in concentrations of 0.01, 0.03 and 0.2 ppm (10 min), one reference treatment with formaldehyde (1-2 ml/l, 15 min) and one as control, without any disinfectants. The second experiment, which lasted 60 days, consisted also of five levels of treatment on the same number of lots of 100 eggs each, to which 0.01 ppm O3 (10 min) was applied on every second day, while 0.01, 0.1 and 0.3 ppm O3 (10 min) were applied daily. The formaldehyde treatment was performed in the same way as the experiment 1 (exp. 1). From the results, it has emerged that the treatment with ozone is effective and the hatching eggs range from 42.6% to 49.1% dose of ozone from 0.01 to 0.2 ppm. As observed in experiment 2 (exp. 2), the dose of 0.3 ppm applied every second day seems to be over the threshold of toxicity.