The use of permitted ectoparasite disinfection methods on young pike-perch (Sander lucioperca) after transition from over-wintering lake to RAS.

With the growing importance of recirculating aquaculture systems there is an increasing demand for proper parasite disinfection methods. It is especially true in cases, when the stocked fish comes from a natural environment to the RAS for rearing or experimental purposes. Our aim was to test some parasite disinfection methods on pike-perch (Sander lucioperca) stock (14.25 + 0.45 cm, 20.57 + 2.03 g), from a farm, where they were kept in over-wintering ponds. The experiment was conducted in a recirculating system with nine aquarium tanks (300 L each) and an overall volume of 4500 L, and in three separate round tanks (230 L). We used two UV lamps (18 watt each) in series to avoid re-infection between fish tanks. Five fish per group were sampled on the 0.-7-14 days. Four treatments were replicated three times, as follows: 1) Control group, where no treatment was used (the three control groups were the three separate round tanks); 2) Continuous 0.5% salt (NaCl) treatment; 3) Combined bath treatment: 0.5% constant salt concentration along with 2 x 10 minutes, 2% salt short bath. This was applied directly after the first and the second sampling; 4) “Detox SA” treatment (active ingredients: 4.5% peracetic acid, 10% acetic acid, and 20% hydrogen peroxide), plus 0.5% constant salt concentration. The Detox treatment was used on the first day, and then daily with the concentration of 20 mL/m (as recommended by manufacturer “ORPC”). The system was shut down for 40 minutes during the treatment. During the experiment, three groups of ectoparasites were found: Trichodina sp. Gyrodactylus sp. Ichthyophthirius multifiliis. The Trichodina infection cleared in all three groups, whereas in the control group the infection remained, however it declined. The Gyrodactilus sp. population with the Detox SA's treatment was completely eliminated, while the infection remained in the short bath treated group, again drastically reduced. In the groups of continuous 0.5% salt treatment the stock of Gyrodactilus sp. increased nearly 30 fold, therefore this treatment for this parasite was ineffective. In the control group over the first weekend of the herds it increased and then decreased. Serious Ichthyophthirius multifiliis infection developed only in the control groups, but not in any other group. This demonstrated that use of 0.5% continuous salt treatment alone could inhibit the propagation of Ichthyophthirius multifiliis. As a result of the experiment, the conclusion can be drawn, that a series of treatments for 10 or 14 days with the three combined methods can be successfully used for disinfection of fish originating from ponds.