Embryonic Mortality, Bioassay Derived 2,3,7,8-tetrachlorodibenzo- p-dioxin Equivalents, and Organochlorine Contaminants in Pacific Salmon from Lake Ontario

Abstract

While large numbers of hatchery reared salmonids have been stocked into the Great Lakes, few of these introduced populations have become self-substaining. Many salmonid populations are contaminated by organochlorine chemicals, and some experience embryonic and fry mortality when reared in hatcheries, which might reduce the survival of naturally deposited embryos and thereby compromise natural recruitment. Embryos from two such populations inhabiting Lake Ontario, coho salmon (Oncorhynchus kisutch) and chinook salmon (Oncorhynchus tshawytscha), were reared under hatchery conditions in 1990, experiencing mean mortality rates of 46% and 24% respectively. This mortality occurred both prior to eye-up and from eye-up to hatch, was female specific, and did not correlate with either muscle or egg levels of total PCB, mirex, octachlorostyrene, or DDT. The levels of 2,3,7,8-tetra-chlorodibenzo-p-dioxin equivalent concentrations (TEC) determined with the H41IE rat hepatoma bioassay ranged from 88 to 320 ppt in the eggs, and while they correlated with organochlorine residues, TEC did not correlate with embryonic mortality. Further investigations of fish-specific TEC bioassays and chemical or biotic influences on gonadal maturation and quality appear necessary to confirm the suggestion that embryonic mortality in these species is not related to organochlorines such as PCBs or dioxins.