Sodium chloride against Dawestrema cycloancistrium in juvenile Arapaima gigas

Abstract

Abstract The aim of the present study was to assess the use of sodium chloride (NaCl) against monogenoid infestations in pirarucu (Arapaima gigas). Two assays were conducted with pirarucu juveniles, the first comprising an in vitro exposure to 8; 9; 10 and 11 g.L− 1 NaCl and comparison to controls not exposed to NaCl, and the second, an in vivo exposure to NaCl at the same concentrations applied in the in vitro exposure. The best in vitro results were observed for one hour exposures at 9, 10 and 11 g.L− 1 NaCl, resulting in 60% and 100% parasite mortality, respectively. In vivo exposures to 8 and 10 g.L− 1 NaCl were 36 and 22% efficient, respectively, following two hours of exposure, with no mortality. Some dose-dependent changes were observed in exposed fish, such as decreased hemoglobin and HCM values at the highest NaCl concentration compared to the other NaCl concentrations and the control group. More frequent gill tissue alterations were observed compared to the control group at the highest NaCl concentrations (10 and 11 g.L− 1). Decreased mean (p < 0.05) water pH values and increased mean electrical conductivity were noted compared to the control group. Our findings suggest that NaCl exhibits low toxicity towards pirarucu and anthelmintic activity to the monogenoid Dawestrema cycloancistrium, directly influenced by exposure time and concentration.