This study examined the effect of endosulfan upon the health of Cyprinus carpio caught from a cotton-growing region. Contextually, a decline in the health was referred to as any impairment of the physiological, biochemical and reproductive processes that may potentially limit the growth, survivorship and reproductive success of C. carpio.

To facilitate this and other aquatic toxicological studies, a framework for assessing the health of aquatic organisms was developed from an extensive review of literature. This framework was designed to incorporate the specific physio-chemical properties of the contaminant, as well as enabling the health of fish to be assessed by the examination of three major biological components: the biochemistry and metabolism; reproductive status; and endocrine system. It was envisaged that the framework’s design would not only assess the health of fish, but also provide enough sensitivity to illustrate comparative differences in their health, and the relationships between the three major biological components.

The environmental concentrations of endosulfan were determined from submerged sediment samples, whilst the livers of carp were used to assess the accumulation of the pesticide in the fish. A variety of biochemical measurements from the blood plasma of C. carpio were employed to identify differences in the metabolic status of fish exposed to endosulfan. In addition, the activities of three enzymes, g-glutamyltransferase, alkaline phosphatase and creatine kinase were measured to provide tissue and organ specific information. Changes to both the morphology of oocytes and the process of oogenesis were used to assess ovarian development. Two assays, the Gonadosomatic Index and concentrations of plasma 17b-oestradiol were incorporated as a preliminary means for identifying possible endocrine disruption.

Although endosulfan was not detected in sediments, liver samples clearly demonstrated that the toxic metabolite endosulfan sulphate was continually being absorbed by C. carpio. Consequently, the effects of the metabolite were reflected in the biochemistry and ovaries of the fish. Evidence from this study indicates that endosulfan sulphate induced a state of hypermetabolic activity and an increase in the relative proportion of necrotic and atretic oocytes. Although no permanent changes in the production of sex steroids or in the size of the gonads were evident, peripheral evidence from the biochemical measurements suggests that the endocrine system was being subjected to additional stress in order to maintain homeostasis of the central nervous system.

A greater decline in the health of fish in one of the two populations exposed to endosulfan was observed. As both of the exposed populations had identical pesticide residue concentrations, other factors may have contributed to the observed differences. Consequently, refinements to the framework are suggested to permit the identification of any possible confounding factors. In summary, this study provides a template for the design and implementation of future studies into the effects of contaminants on aquatic organisms.