Mercury is toxic in tiny concentrations and can be found around the home in thermostats, thermometers, fluorescent bulbs, button batteries (like those used in watches and hearing aids), fire-alarm switches, and, of course, your refrigerator. Pregnant women know to avoid eating too much fish so that they don't accumulate mercury in their system, but that advice may extend to those trying to get pregnant as well—and for both halves of the couple.
Mercury is so well known for its toxic effects on neurodevelopment that it seems almost beside the point to consider how it might impact conception in the first place. But according to at least one case study among in vitro fertilization (IVF) patients, however, there does seem to be a link. Infertile couples tended to have higher concentrations of mercury in their blood and had consumed more seafood. There was also a correlation between infertile men with abnormal semen and high mercury concentrations in the bloodstream.
Source: "Infertility, blood mercury concentrations and dietary seafood consumption: a case-control study," BJOG: an international journal of obstetrics and gynecology