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 increasingdemand for proper parasite disinfection methods. It is especially true in cases, when the stocked fishcomes from a natural environment to the RAS for rearing or experimental purposes. Our aim was to testsome 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 arecirculating system with nine aquarium tanks (300 L each) and an overall volume of 4500 L, and inthree separate round tanks (230 L). We used two UV lamps (18 watt each) in series to avoid re-infectionbetween fish tanks. Five fish per group were sampled on the 0.-7th-14tth days. Four treatments werereplicated three times, as follows: 1) Control group, where no treatment was used (the three controlgroups were the three separate round tanks); 2) Continuous 0.5% salt (NaCl) treatment; 3) Combinedbath treatment: 0.5% constant salt concentration along with 2 x 10 minutes, 2% salt short bath. Thiswas 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 saltconcentration. The Detox treatment was used on the first day, and then daily with the concentration of20 mL/m3 (as recommended by manufacturer “ORPC”). The system was shut down for 40 minutes duringthe treatment. During the experiment, three groups of ectoparasites were found: Trichodina sp.Gyrodactylus sp.Ichthyophthirius multifiliis. The Trichodina infection cleared in all three groups, whereasin the control group the infection remained, however it declined. The Gyrodactilus sp. population with theDetox SA's treatment was completely eliminated, while the infection remained in the short bath treatedgroup, again drastically reduced. In the groups of continuous 0.5% salt treatment the stock ofGyrodactilus sp. increased nearly 30 fold, therefore this treatment for this parasite was ineffective. In thecontrol group over the first weekend of the herds it increased and then decreased. SeriousIchthyophthirius multifiliis infection developed only in the control groups, but not in any other group. Thisdemonstrated that use of 0.5% continuous salt treatment alone could inhibit the propagation ofIchthyophthirius multifiliis. As a result of the experiment, the conclusion can be drawn, that a series oftreatments for 10 or 14 days with the three combined methods can be successfully used for disinfectionof f