Diel Feeding by Larval Northern Brook Lampreys in Two Northern Michigan Streams
Trent M. Sutton and Stephen H. Bowen
Abstract.—Larval lampreys are burrowing suspension feeders in streams that efficiently use organic detritus as their primary nutrient source. Although larval lampreys often exhibit daily patterns in activity (being most active at night), diel variations in food habits and feeding behavior have not been investigated. The objective of this study was to determine whether larval northern brook lampreys Ichthyomyzon fossor exhibit diel periodicity in diet composition, assimilation efficiency, or gut fullness. Larvae were collected at 4-h intervals over a 24-h period from the Pike and Pilgrim rivers, Michigan. Organic detritus composed most of the diet ash-free-dry-mass (AFDM) for each sampling period, and averaged 94.7% and 97.4% for the Pike and Pilgrim rivers, respectively. Assimilation efficiency of AFDM averaged 61.3% (range, 55.7–68.9%) for the Pike River and 87.5% (range, 80.8–94.3%) for the Pilgrim River. Gut fullness in the Pike and Pilgrim rivers was low, averaging 0.23 (range, 0.18–0.30) and 0.20 (0.14–0.25) mg diet AFDM per grams larvae, respectively. Although gut fullness did vary slightly on a diel basis, larval northern brook lampreys feed continuously but slowly in order to achieve a high rate of assimilation from a low-quality food resource.