EMBRYONIC MORTALITY, BIOASSAY DERIVED 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN EQUIVALENTS, AND ORGANOCHLORINE CONTAMINANTS IN PACIFIC SALMON FROM LAKE-ONTARIO

While large numbers of hatchery reared salmonids have been stocked int o the Great Lakes, few of these introduced populations have become sel f-substaining. Many salmonid populations are contaminated by organochl orine chemicals, and some experience embryonic and fry mortality when reared in hatcheries, which might reduce the survival of naturally dep osited embryos and thereby compromise natural recruitment. Embryos fro m two such populations inhabiting Lake Ontario, coho salmon (Oncorhync hus kisutch) and chinook salmon (Oncorhynchus tshawytscha), were reare d under hatchery conditions in 1990, experiencing mean mortality rates of 46% and 24% respectively. This mortality occurred both prior to ey e-up and from eye-up to hatch, was female specific, and did not correl ate with either muscle or egg levels of total PCB, mirex, octachlorost yrene, or DDT. The levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin equiv alent concentrations (TEC) determined with the H4IIE rat hepatoma bioa ssay ranged from 88 to 320 ppt in the eggs, and while they correlated with organochlorine residues, TEC did not correlate with embryonic mor tality. Further investigations of fish-specific TEC bioassays and chem ical or biotic influences on gonadal maturation and quality appear nec essary to confirm the suggestion that embryonic mortality in these spe cies is not related to organochlorines such as PCBs or dioxins.