Diet, feeding rate, and assimilation efficiency of American brook lamprey

We examined foods ingested by American brook lamprey larvae from Minnesota streams during spring and summer seasons. The diet was dominated numerically by diatoms, but organic detritus comprised the bulk (>85%) of ingested materials. The organic contents of ingested foods did not differ among streams or between seasons, averaging approximately 70%. Feeding rates based on gut fullness were highest, but most variable, during spring. Assimilation efficiency of the organic fraction of the diet averaged >65% across streams and seasons. Larval American brook lamprey depend on organic detritus to meet most of their nutritional needs and are very efficient at digesting and assimilating these detrital foods. Survival of American brook lamprey populations may be affected by human activities that alter the production and availability of detritus within streams.