Change in energy density of the sea lamprey (Petromyzon marinus) during its parasitic phase: Implications for modeling food consumption and growth

Previous energetics-based models of feeding and growth by sea lampreys (Petromyzon marinus) have included the assumption that the wet energy density of sea lamprey tissue is constant. It was hypothesized that a seasonal or body-size related increase in wet energy density of sea lamprey tissue contributed to a tendency for model predictions to overestimate growth in wet mass by large sea lampreys late in the year. Bomb calorimetry of parasitic-phase sea lampreys collected in northern Lake Huron during 1996 and 1997 revealed that wet energy density increased with wet body mass. Seasonal effects were not significant once the effects of body mass were taken into account. Increased wet energy density resulted both from a decrease in percentage water content and an increase in energy density of dry tissue with increased body mass. Statistical comparisons failed to reveal significant differences between sexes or years. Although the overall mean wet energy density for sea lampreys sampled in the present study was similar to the empirically-derived constant value used in previous models, incorporating a relationship between wet energy density and wet body mass into our sea lamprey feeding model improved its ability to predict instantaneous growth.