Respiration Rates, Energy Budgets, and Molting Frequencies of Three Species of Euphausiids Found in the Gulf of St. Lawrence

Respiration rate experiments at different temperatures were conducted on three species of euphausiids, Meganyctiphanes norvegica, Thysanöessa raschii, and T. inermis, found in the Gulf of St. Lawrence. The slopes of the respiration regression lines at different temperatures for the same species were not significantly different. Thysanöessa inermis acclimated to temperature changes with the result that its respiration rates remained relatively stable over most of the temperatures tested.Feeding rates were measured for M. norvegica and T. inermis at different temperatures using Artemia nauplii as food. The number of calories ingested, expressed as a percentage of the total body calories of the euphausiid, decreased with body size and water temperature. Thysanöessa inermis ingested fewer calories than M. norvegica in relation to total body calories at all temperatures. Both species showed a linear relationship between molting frequency and water temperature, T. inermis having a shorter intermolt period than M. norvegica.Results were used to estimate the energy consumption of the natural populations of euphausiids in the upper part of the Gulf of St. Lawrence estuary.