Age and growth of round goby Neogobius melanostomus in the upper Detroit River

The round goby Neogobius melanostomus has quickly become one of the most ab undant benthic fishes in the Lake Huron-Lake Erie corridor of the Laurentia n Great Lakes since it was first discovered in the St. Clair River in 1990. We describe the age, growth, and size structure of the round goby populati on from samples collected in the upper Detroit River. Round gobies were col lected using an otter trawl about every 3 weeks during spring, summer, and autumn 1996. Age-1 fish were found to be the most abundant group in the pop ulation, and fish size within a given age-group was highly variable. Both m ales and females were found to be maturing younger and at smaller sizes tha n in their native range. Marginal increment analysis of otoliths revealed t hat annulus formation occurred in late May-early June. Although mean size o f fish differed significantly with sample date (P < 0.001), there was littl e increase in mean size from May to October. Age-1 fish had a larger growth than age-2 fish. Mean annual growth for age-1 males (37 mm) was greater th an for females (33 mm), but size ranges overlapped. Early maturity and rapi d growth are two factors that may ensure the continued expansion of the rou nd goby throughout the Great Lakes.