The piscicides rotenone and antimycin have been used for more than 70 years to manage fish populations by eliminating undesirable fish species. The effects of piscicides on aquatic invertebrate assemblages are considered negligible by some and significant by others. This difference of opinion has created contentious situations and delayed native fish restoration projects. We review the scientific evidence and report that short-term (< 3 months) impacts of piscicides to invertebrate assemblages varied from minor to substantial and long-term (> 1 year) impacts are largely unknown. Recovery of invertebrate assemblages following treatments ranged from a few months for abundances of common taxa to several years for rarer taxa. Variation in reported effects was primarily due to natural variation among species and habitats and a lack of adequate pre-and post-treatment sampling which prevents determining the true impacts to invertebrate assemblages. The factors most likely to influence impacts and recovery of aquatic invertebrate assemblages following piscicide treatments are: (1) concentration, duration, and breadth of the piscicide treatment; (2) invertebrate morphology and life history characteristics, including surface area to volume ratios, type of respiration organs, generation time, and propensity to disperse; (3) refugia presence; and (4) distance from colonization sources.

Glass microscope slides were placed to span a range of temperatures in and around a warm spring in the Portneuf River, Idaho in the winter of 1987. Diatoms were allowed to colonize these slides for 8 weeks. Analysis of slides revealed that maximum species diversity and species richness were reached between 25' and 30 "C. Analysis also showed that certain diatom taxa were stenothermal, showing distinct preferences for various temperatures while others were eurythermal.