Field Observations on Reproductive and Developmental Dysfunction in Introduced and Native Salmonids from the Great Lakes

Abstract

The paper summarizes the available evidence of reproductive and developmental problems that have been identified in populations and stocks of Great Lakes salmonid fish, and explores the arguments for and against the hypothesis that these problems are caused by toxicants in the food chain. Most studies have focused on introduced species, and a variety of problems has been identified including thyroid enlargement, lowered egg thyroid hormone content, high prevalence of premature sexual maturation in males, loss of secondary sexual characteristics, reduced plasma gonadotropin and gonadal steroid hormone content, low egg fertility, and high embryo mortality and deformity. Some of these conditions are related (e.g., dysfunctional reproductive syndrome), and limited to specific stocks, whereas others (e.g., thyroid enlargement) are widespread throughout the Great Lakes. Although the evidence for an etiology based on the presence of toxic compounds is not as clear as that for fish-eating birds and mammals, when taken together, there is strong evidence for environmentally-related impairment of endocrine and reproductive function, and ontogenic processes of Great Lakes salmonid fish.