Serum biochemical characteristics of Carassius auratus (L) following short-term formalin or NaCl treatment

Goldfish (Carassius auratus) were subjected to either formalin (250 ppm) or NaCl (10 ppt), over a 0.5-h period followed by 24-h freshwater exposure. Serum biochemistry was monitored before exposure (0), immediately after (0.5) plus 3 and 24 h after exposure. Results showed that both formalin and NaCl treatments caused rapid increase in cortisol with a peak at 3 h, which did not recover until 24 h. Likewise, glucose showed similar patterns, however, returned to initial levels at 24 h after exposure. Formalin caused significant decrease in sodium and chloride levels which returned to initial levels at 24 h after exposure. Both formalin and NaCl caused calcium and total protein elevation at 3 and 24 h after exposure. Albumin and globulin levels were significantly affected by formalin and NaCl at 3 and 24 h after exposure. It is suggested that formalin and NaCl at the therapeutic concentrations cause rapid stress in goldfish which is eliminated after 24 h in freshwater. In addition, formalin causes slightly osmotic disturbance which is eliminated after 24 h recovery in freshwater. Both formalin and NaCl cause serum calcium and protein alteration after a while, which lasts until, at least, 24 h. More studies are needed to explain underlying mechanisms. Formalin and NaCl treatment, although advantageous in ecto-parasite removal, are stressful in goldfish, which should be considered if they are going to be used. Since formalin causes osmotic disturbance and more stress response, NaCl treatment is suggested as an alternative.