Crowding reduces feeding rate, effectiveness of diet selection, and efficiency of digestion by Northern Brook Lamprey ammocetes (Ichthyomyzon fossor)

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© 2018, Springer Nature B.V. We studied the effect of larval density on food utilization by sediment-dwelling northern brook lamprey (Ichthyomyzon fossor) larvae in the Otter River, Baraga County, MI, USA using field surveys and in situ cage experiments. Field surveys found that food utilization was inversely proportional to density across the range of 1 to 10 larvae/m2. Compared to 1 larvae/m2, values at 10 larvae/m2 were lower by an average of 36% for gut fullness, by 32% for selective ingestion of organic matter, and by 71% and 58% for assimilation of diet organic matter and diet amino acids, respectively. In situ cage experiments and additional field studies in other nearby rivers revealed the same relationships. We hypothesize that physical disturbance of the sediment by adjacent larvae interferes with food utilization with the frequency of disturbance proportional to density. Condition factors were not correlated with density and indicate that individual larvae minimize the effect of crowding by moving away from higher density patches. We conclude that these findings are generalizable to other lamprey species in similar environments in which lower rates of growth, maturation, and survivorship of lamprey larvae at higher densities have been reported by other researchers.

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Environmental Biology of Fishes