PATTERNS AND DETERMINANTS OF HELMINTH COMMUNITIES IN THE ACIPENSERIDAE (ACTINOPTERYGII, CHONDROSTEI), WITH SPECIAL REFERENCE TO THE LAKE STURGEON, ACIPENSER-FULVESCENS

Patterns. processes, and some hypotheses regarding the structure of he lminth communities in freshwater fishes have been investigated using s turgeons (Acipenseridae), a widely distributed group of basal actinopt erygian fishes. Analyses at the infracommunity and component-community levels for one species, Acipenser-fulvescens, indicated occasionally dense, but isolationist, gut helminth communities with moderate specie s richness and a high degree of predictability conferred by host-speci fic helminths that dominated the communities. Largely predictable helm inth communities are also characteristic of acipenserids from Siberian and Ponto-Caspian drainages and basins. Although host specificity was the major determinant of helminth community diversity in most acipens erids, exceptions were found in sturgeons of the Aral Sea drainages, w here non-host-specific parasites dominated the helminth communities. G ut complexity and evolutionary age were both found to be poor predicto rs of community richness in sturgeons and other basal actinopterygians . The stochastic component of the gut helminth fauna is determined by shared trophic category and sympatry with other major benthivorous fis hes, mainly benthic coregonines in Holarctic drainages and benthic ost ariophysans (e.g., cypriniforms) elsewhere. Although some predictions of ''evolutionarily mature'' communities are partially fulfilled, the authors of this study caution that owing to differences in the biology and history of individual species and groups and the diversity of fis hes in general, broad generalizations about the factors shaping fish p arasite communities will be difficult to make.