Hormonal responses of the fish, Cyprinus carpio, to environmental lead exposure

Abstract

The present study reports the acute and sublethal toxicity of lead nitrate on plasma cortisol and prolactin level of a freshwater fish, Cyprinus carpio. The median lethal concentration of lead nitrate to fish for 24 h was found to be 4.10 ppm. 1/10th of the LC50 concentration of the lead nitrate (0.41 ppm) was taken for sublethal concentration. During acute and sublethal treatment the plasma cortisol level increased throughout the study period showing a direct relationship with exposure period. Similarly, plasma prolactin level was increased during acute treatment. However during sublethal treatment plasma prolactin level was increased up to 14th day and then declined. The significant increase of plasma cortisol level might have resulted from the release of cortisol from the interrenal tissue as a mechanism of coping up with stress or impaired immune function. The elevated level of plasma prolactin may be a step to reestablish ionic equilibrium due to the disturbances caused by the metal. Whereas the decline in plasma prolactin level indicate the destruction of prolactin cells due to metal toxicity. The alterations of the hormonal levels may be used as a potential biomarker and also can establish the ability of endocrine tissues to respond to their appropriate releasing factors.