A Gut-Marker and Food Entrainment Device for Evaluating Food Consumption by Net-Spinning Caddisflies

A filter-feeding entrainment device was used for saturating small areas of a fast-flowing river with gut marker composed of DAY-GLO® red fluorescent pigment with Wayne® dog food used as the carrier. In water less than 30 cm deep, the entrainment device effectively concentrated the gut marker into a defined area of stream bottom. The gut marker was readily consumed by Hydropsyche venularis, H. morosa, H. sparna and the mayfly Isonychia bicolor, and was easily distinguishable from the brown and black colored natural food. Consumption of the gut marker began almost immediately, with 60% of H. venularis larvae having marker in their gut after 2 min. It may be possible to use the natural food of lotic filter-feeders (e.g., detritus) as the carrier rather than dog food.