The Effects of Pollution on the Reproductive System of Fish

The dramatic effects of overfishing on global wild fish stocks have received some attention. However, anthropogenic, or human-made, pollution is also reducing many wild fish species in both freshwater and marine habitats. The harm includes but goes beyond massive fish kills resulting from sudden large releases of raw sewage or toxic chemicals into the water supply. Some pollutants interfere with the ability of diverse fishes to perpetuate their own species.

Fish Reproduction

• Fishes all arise from the combination of male sperm and female egg cells. They otherwise vary widely in their reproductive strategies. With some species, the female releases eggs from her body and the male fertilizes them. With others, he releases his sperm into her body. In viviparous species, the mother carries the young inside her. A few kinds of fish have natural hermaphrodites, individuals with both egg-producing and sperm-producing tissues. However it happens, the reproduction of fish depends on complicated, delicate cycles and sequences of hormones.

Aquatic Pollutants and Sources

• Numerous water pollutants harm aquatic life, including fish. Though long banned from industry, polychlorinated biphenyls, or PCB's, persist in the environment. Heavy metals such as lead, arsenic and mercury originate mostly in mining and other industrial processes. Other industrial toxins include bisphenol A and phthalates. Polycyclic aromatic hydrocarbons, or PAH's, such as naphthalene result from petroleum spills and fossil fuel combustion. Pesticides such as DDT -- still used in some parts of the world -- and Heptachlor enter water through agricultural and even urban runoff.

Pollutant Effects

• PCB's, heavy metals, PAH's, and pesticides are known endocrine disruptors, or EDC's, which mimic natural sex hormones like estrogens. With their very permeable skins and gills, fish highly concentrate EDC's in their bodies, especially the testes and ovaries, their male and female sex organs. Fish embryos or larvae may die from such pollutants, as they lack protective shells. Adult fish may be rendered infertile. Numerous males from species without natural hermaphrodites have become "feminized." Their testes may be abnormally small or slow-growing or contain ovarian tissues. EDC's also thwart reproductive tract development in females.

Significance

• The devastating consequences of EDC's on fish and their reproductive systems have many ecological and ethical implications. Fish are essential to aquatic food chains, which connect with terrestrial or land food chains, including those that nourish humans. Scientific literature increasingly shows that fish are not insensate, but likely can experience emotions such as pain and fear. Thus, there is a growing albeit controversial belief that humans have an ethical responsibility not to harm fish.