Assessment of the toxicity of radiographic developer effluent on catfish (<i>Heterobranchus longifilis</i>)

Abstract

Toxicity of radiographic developer effluent on catfish juveniles (H. longfilis) from the Institute of Oceanography fish farm, University of Calabar was assessed. Seventy five (75) juveniles of H. longifilis were acclimated in about 5 litres of habitat water for 48 hours with minimum feeding. Range finding test was conducted at effluent concentration of 100%, 50%, 25%, 12.5%, 6.25%, 3.125%, 1.0% and control (0%) in 200ml of habitat water. After, the acclimated juveniles were introduced into the standard solution. They were observed for behavioural changes and/or mortality. Behavioural changes such as hyperactivity, increased number and length of gills on the anterior fontenelle, restlessness and loss of balance of test organisms occurred at 100%, 50% and 25% effluent concentration. Mortality of organisms occurred at 5, 8, 15, 25 and 51 minutes respectively in the test solutions. The control contained only habitat water. The test solution which resulted in 100% mortality within 96 hours (1.0%) was taken as highest test dose for toxicity testing. Other concentration used for toxicity testing were 0.8%, 0.6%, 0.4%, 0.4%, 0.2%m 0% (control) respectively. Toxicity testing showed that there was increased death of catfishes as effluent concentration increased from 0.8% to 1.0% with increased duration of the exposure. Nine (9) juveniles of average length 36cm each were exposed to the test solutions. Maximum exposure time was 96 hours while estimated 96 hours LD50 is 0.32 of which safe disposal of 1 limit (approximate is 0.032 (1/10 or 10% of LD50). Resultantly, considering the importance of
catfishes as a source of food (protein), sporting tools for anglers; and a vital part of the ecosystem (tertiary consumers), it is pertinent therefore, that legislations, policies and sanctions be put in place to ensure safe disposal limit and adherence to laws on radiographic developer effluent disposal in Nigeria.