Sodium chloride (NaCl) as a treatment against trichodiniasis for pike perch (Sander lucioperca) in recirculating aquaculture systems

Pike perch were transferred from an over-wintering net cage into recirculating aquaculture systems (RAS). Within a 21-day period, it was examined whether or not ectoparasites, here specifically a representative of the family of Trichodinidae that were naturally present on the fish, could be reduced or even eliminated from the fish by means of sodium chloride treatment (3 and 6 g NaCl/L). Despite a significant reduction in trichodinid density, the application of 3 g NaCl/L proved to be insufficient to eliminate all trichodinids during the 21-day trial. However, under RAS conditions, a continuous 21-day exposure to 6 g NaCl/L completely eliminated the trichodinids on the fish. Based on the observations of the composition of the trichodinid density, it is recommended to screen fish for ectoparasites on multiple body sites. In conclusion, NaCl can be considered an effective and low-cost therapeutic in pike perch aquaculture against trichodiniasis.