FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

In this study, we investigated the acute toxicity of formalin (a 37% formaldehyde solution) and formaldehyde residue in the muscle of common carp (Cyprinus carpio) exposed to different formalin concentrations for various periods. The effects on some hematological parameters of the carp were also examined. The acute toxicity test revealed that the 96-h LC50 values of formalin for carp reared at 20 and 30 °C were 126.44 and 101.69 ppm, respectively. The practical therapy of formalin for fish was considered in the formaldehyde residue study; therefore, carp reared at 30 or 20 °C were treated with 250 ppm formalin for 1 h, 100 ppm for 2 h, and 25 ppm for long-term exposure. Fish with no formalin treatment served as the control group. Formaldehyde in the muscle was analyzed after 1 h for the 250-ppm group and 2 h for the other three groups, and the analysis continued every 24 h after the first sampling. Results showed that formaldehyde in the muscle increased in the first samples after being exposed to various formalin treatments, and the level of formalin in treated fish was significantly higher than that of the control group. Furthermore, formaldehyde in the muscle of fish at 30 and 20 °C treated with 25 ppm for the long-term exposure reached a peak at 24 and 48 h, respectively. However, the formaldehyde concentrations of treated fish gradually decreased before returning to the background level after 144 h in each group. Hematocrit, hemoglobin, and total plasma protein did not significantly differ among any groups after various formalin treatments. However, plasma glucose levels in fish treated with formalin at 250 ppm for 1 h and at 100 ppm for 2 h were significantly higher than those of the control fish. Interestingly, this hyperglycemic condition was also found in fish treated with 25 ppm formalin for the long-term exposure after 24 h. It was also found that the hematocrit level of fish treated with 250 ppm formalin after 24 h was markedly higher than that of the control fish. The results of this study showed that the formaldehyde concentrations of all formalin-treated fish returned to the background level after 144 h, and non-significant changes in hemoglobin and total plasma protein among treatments were also observed during the period of formalin exposure.