XENOBIOTICS, XENOESTROGENS AND REPRODUCTION DISTURBANCES IN FISH

Fish maturation and reproduction are complex biological processes that are regulated by endogenous substances (hormones), and synchronized b y exogenous factors (photoperiod and temperature), thus ensuring that reproduction occurs at a time of the year optimal for survival of the offspring. The survival of any fish species is ultimately determined b y the ability of its members to reproduce successfully in a fluctuatin g environment and thereby maintain a viable population. Several report s have documented that many compounds introduced into the environment by human activity either deliberately or unintentionally are capable o f affecting reproductive processes in fish. Zonagenesis and vitellogen esis (eggshell protein and egg yolk precursor production, respectively ) are two estrogen-regulated processes that are integral aspects of fi sh oogenesis. Several in vivo and in vitro studies have reported that some xenobiotics (xenoestrogens) possess the ability to mimic natural estrogens and therefore initiate precocious or unscheduled zonagenesis and vitellogenesis. Aspects of these effects acid other xenobioticall y-induced responses will be discussed here, with special reference to their possible consequences for fish populations.