Abstract
Filter-feeding invertebrates such as bivalves have been shown to improve the health of aquatic systems by reducing concentrations of bacteria and other harmful suspended organisms, but it remains unknown if microphagous suspension-feeding fishes can provide similar ecosystem services for water quality. Here, we tested whether the presence of the filter-feeding larval ammocoete life-stage of Pacific lamprey (Entosphenus tridentatus) can reduce suspended concentrations of Escherichia coli bacteria. Aquaria containing either filter-feeding ammocoete lamprey larvae (1.5 fish·L−1), lamprey macropthalmia juveniles (1.5 fish·L−1) that do not suspension-feed, or no lamprey (control) were filled with water contaminated with E. coli bacteria and then monitored for 5 d for E. coli concentration changes in the water column. The presence of ammocoete larvae generated a significantly faster decline in E. coli abundance compared to aquaria containing either macropthalmia-stage lamprey or no fish, which showed similar E. coli concentration profiles over that 5 d period. A higher density of ammocoetes (4.3 fish·L−1) resulted in a more rapid decline in E. coli compared to the lower 1.5 fish·L−1 ammocoete density, further implying that ammocoetes augmented bacterial clearance. These observations provide evidence that filter-feeding larval ammocoetes of Pacific lamprey may help promote water-quality enhancement by reducing suspended bacterial concentrations.