SEASONAL-CHANGES IN THE TOTAL LIPID-CONTENT OF THE OPOSSUM SHRIMP, MYSIS-RELICTA (MALACOSTRACA, MYSIDACEA)

Seasonal changes in the percent total lipid content of Mysis relicta were investigated in four lakes in southern Ontario. Stony and Twelve Mile lakes contain populations of Mysis with a l-yr life cycle, while Crystal and Boshkung lakes have populations with a 2-yr life cycle. Mature female and male mysids have a lipid content between 15 and 33% and between 14 and 25%, respectively, while juvenile mysids have approximately 10% less total lipids than adults. The relationship between total lipid and lipid-free dry weight is best described by the power curve Y = aX(b) and is the same (ANCOVA, p < 0.05) in all four mysid populations. Lipid content accumulates steadily with time as the mysid grows, and lipid reserves do not appear to influence mysid time to maturity. For studies on the transfer of energy and lipophilic organic contaminants through the food web, the results imply that seasonal and body size differences of organisms are important considerations.