Effect of formalin treatment on saltwater tolerance in Caspian roach (Rutilus rutilus caspicus)

Abstract:The effect of formalin exposure on subsequent saltwater tolerance was investigated in Caspian roach (Rutilus rutilus caspicus). Fish were subjected to 0 (control), 10, 15 and 25 ppm formalin over 0 (control), 12, 24 and 168 h (4×4 treatments; 6 tanks per treatment) as well as 25, 50, 100 and 150 ppm formalin over 0.5 and 1 h (4×2 treatments; 6 tanks per treatment). Thereafter, half of each treatmentʹs tanks (3 tanks) were subjected to formalin-free freshwater and the rests were subjected to formalin-free saltwater (12 ppt NaCl) and mortality was recorded at 0, 72 and 168 h exposure. Results showed decrease in saltwater-induced mortality with increase in formalin exposure from 12 to 168 h, particularly in fish exposed to 25 ppm formalin. However, increment in formalin exposure from 0.5 to 1 h caused increase in saltwater-induced mortality, particularly in formalin concentrations of 100 and 150 ppm. Increase in saltwater tolerance after 168 h formalin exposure might be due to adaptation mechanisms development or suppression in stress induced by formalin exposure. Decrease in saltwater tolerance after 1 h, compared to 0.5 h, formalin exposure might be due to cumulative effect of the two stressors (formalin and saltwater exposure).