Zooplankton is a categorization spanning a range of organism sizes including small protozoans and large metazoans. It includes holoplanktonic organisms whose complete life cycle lies within the plankton, as well as meroplanktonic organisms that spend part of their lives in the plankton before graduating to either the nekton or a sessile, benthic existence. Researchers found at least 12 species of zooplankton in Mezquital Valley. Though deet is not expected to bioaccumulate, it has been found to have a slight toxicity for fresh-water fish and it also has been shown to be toxic for some species of freshwater zooplankton.