The effect of endocrine disrupting chemicals on the hepatosomatic index and Gonadosomatic index of Oreochromis mossambicus

Abstract

5 DECLARATION I hereby declare that this work is the product of my own research efforts, undertaken under the supervision of Dr. E. Julies and Mr. A.Faul and has not been presented elsewhere for the award of the degree. All the sources have been duly and appropriately acknowledged. …………………………………………… 6 1. Abstract EDCs (endocrine-disrupting chemicals) have been defined as exogenous substances or mixtures that alter the functions of endocrine systems and consequently cause adverse effects in an intact organism or its progeny, sub-population. EDCs are structurally similar to the endogenous steroid hormone 17β-estradiol, while others may not be seen structurally related to naturally occurring steroids. (Diniz et al. 2005) Thus, many non-steroidal compounds, such as flavonoids, lignins, sterols and fungal metabolites, and synthetic chemicals can interact with sex hormone receptors or can modulate their metabolism and biosynthesis. In this study we investigated the effects of the presence of EDCs in two different water systems namely the Gammams outlet and Goreangab dam on the liver and gonads of the tilapia fish. The focus was on the Oreochromis mossambicus species.72 Juvenile fish were exposed to different water systems to determine the effect of possible endocrine disrupting chemicals present in the waters on the gonadosomatic and hepatosomatic indices of the fish. An ELISA test was performed to detect Vitellogenin and a two sample t-test was performed to test for significant differences. A comparative study to assess the estrogenic potency of treated domestic sewage effluent from a sewage treatment plant in Lisbon (Diniz et al 2005) showed an increase in vitellogenin induction in the exposed fish. The results obtained from the t-test showed that there were no significant differences in the HSI of (a, b, c, & d) except the test between the positive control and negative control in the tank in (a) which showed a significant difference, for the GSI the significant differences were in (a) the positive control against the negative control, in (b) Gammams against Goreangab dam, and in (c) negative control against Goreangab dam. The rest of the treatments in (a, b, c, & d) showed no significant differences in GSI. Detection of VTG in exposed fish was low at 450nm and for this reason could not reveal the presence of the estrogen-inducible protein in the treatment groups. Nonetheless the irregularity seen in this study is less evidence of no effect than a consequence of the difficulty in studying, especially with the lack of histological tests