Effects of Domestic Pollution on European Brook Lamprey Ammocoetes in a Lowland River: Insights from Microbiological Analysis

This study investigates the impact of water faecal contamination on highly threatened European brook lamprey larvae (Lampetra planeri). Water samples and the midgut contents of lampreys collected from a small lowland river upstream (site 1) and downstream from a wastewater treatment plant (WWTP) discharge (site 2) were analysed to check how the faecal microbial load of the habitat is reflected in the intestines of larval lampreys. The counts of viable mesophiles, psychrophiles, Escherichia coli and faecal streptococci as bacterial indicators of microbial (including faecal) water contamination were estimated. Microbial composition and abundance in larval midgut contents depended on the numbers of various microorganisms in the water environment. At site 2, the water was heavily microbiologically contaminated throughout the year by sewage inflow from the WWTP, and the amounts of studied bacteria were also high in the midgut of lampreys inhabiting site 2 regardless of the season. At site 1, water quality was better, and the levels of tested microbial indicators were lower in the intestines of the lampreys living there. The numbers of bacteria dependent on water temperature were growing in warmer seasons both in water and in intestines. Sewage pollution negatively influenced the condition of lampreys in site 2, where they exhibited lower body condition than in site 1.