Year: 2018, Issue: June
Toxicological impacts of cadmium on a fresh water fish Oreochromis mossambicus, Peters and its ecological implications.
Pradeep Kumar Behera and A. K. Panigrahi
Cadmium, Fresh water fish, Toxicity, Fish behavior, Tilapia.
All the exposed fish appeared lethargic after exposure to cadmium chloride. The major clinical symptoms such as inappetance and ataxia appeared after 24-48 hours of exposure. At higher concentration of the cadmium chloride, the exposed fish showed erratic movements. The other signs of toxicity such as loss of equilibrium, gradual onset of inactivity, periodic erratic swimming with irregular collision to the inner lining of glass walls of the aquarium. Feeding of the exposed fish significantly reduced in the first week of exposure and slowly the exposed fishes took normal feed. The exposed fish shed fins after 21st days of exposure onwards and huge destruction of dermal mucous layer was marked. At higher exposure periods, profuse bleeding was marked in the gills. Infection of eyes was marked in the exposed fish when compared to control fish. Heavy oxygenation can help to around 65% exposed fishes to survive but the rest of the excited fish die instantly and never recover from the shock. The MAC value of cadmium chloride was found to be 1.325 mg l-1 for 30th days and to be on the safe side 1.30 mg l-1 was considered for 28th days of the exposure for sub-lethal toxicological studies. No mortality of fish was recorded in the control set through out the period of toxicity testing. Body weight of the control fish increased during exposure and recovery periods. Whereas the body weight of the exposed fish gradually decreased during the exposure period and no recovery in body weight was noted during recovery period. Autopsy studies revealed that the liver and brain of exposed fish were congested and tender. The brain somatic index decreased gradually, with the increase in exposure period. No recovery in BSI was observed in 28d exposed fishes. The Hepato Somatic Index (HSI) remained almost at the same level in the control fish throughout the experimental period. The HSI gradually and significantly decreased with the increase in exposure period. When the exposed fish were transferred to toxicant free tap water, no significant recovery in their activity was observed. Exposed fish could not regain their pre-exposed activity after transferring the exposed fish to cadmium free water in recovery studies.