What is the definition or description of: avoiding fish high in mercury?

Esp if pregnant: Mercury is a metal that can interfere with cell growth. It is esp toxic for growing embryos or babies. The developing nervous system, lungs and kidneys can be adversely affected by high levels of mercury. Babies who are exposed to mercury in the womb can have visual or hearing problems.

Fish: avoid & limit: Avoid eating fish that are high on the predatory food chain as they have the highest mercury levels. Fish with very high potential mercury levels include: shark, swordfish, marlin, king mackerel, big eye & ahi tuna, orange roughy & tilefish. Limit intake of yellow fin and white albacore tuna, spanish & gulf maceral, group, bluefish & chilean sea bass.