 Human activities have affected stocks of many species of teleost , through overfishing , pollution and global warming . Among many recorded instances , overfishing caused the complete collapse of the Atlantic cod population off Newfoundland in 1992 , leading to Canada 's indefinite closure of the fishery . Such commercial extinction does not however signify extinction of the species . Pollution , especially in rivers and along coasts , has harmed teleosts as sewage , pesticides and herbicides have entered the water . Many pollutants , such as heavy metals , organochlorines , and <unk> interfere with teleost reproduction , often by disrupting their endocrine systems . In the roach , river pollution has caused the intersex condition , in which an individual 's gonads contain both cells that can make male gametes ( such as spermatogonia ) and cells that can make female gametes ( such as <unk> ) . Since endocrine disruption also affects humans , teleosts are used to indicate the presence of such chemicals in water . Water pollution caused local extinction of teleost populations in many northern European lakes in the second half of the twentieth century . 
