The systematic status of whitefishes endemic to Bear lake, Utah-Idaho, has remained tenuous since their original description. Clarification of this problem was the major objective of the present study. The general approach was an integrated one, including examination of morphological, biochemical and ecological parameters; artificial hybrids were produced and compared with questionable groups from the natural population. Morphological analysis revealed five forms of Bear Lake whitefishes Prosopium gemmiferum (Bonneville cisco) and P. abyssicola (Bear lake whitefish) were well differentiated from other forms and were treated as originally described. The P. spilonotus (Bonneville whitefish) group, however, was found to be made up of two morphologically distinct populations, referred to as P. spilonotus (small form) and P. spilonotus (large form). The fifth group referred to as P. gemmiferum-like (represented by only five specimens) was intermediate between P. gemmiferum and either P. spilonotus (small form) or P. abyssicola and was hypothesized to be of hybrid origin. Multiple discriminant function analysis of the four major groups and P. williamsoni (mountain whitefish) (Logan River) confirmed morphological differentiation between forms. Hybridization studies among Bear Lake Prosopium and P. williamsoni involved 50 homo - and heterospecific crosses (17 combinations). Of 12 experimental hybrid combinations attempted, all those involving simultaneously ripe specimens of two groups (five crosses) showed maximum fertilization success equalling that of pure crosses. no evidence that interspecific crosses are less successful than conspecific crosses, with the possible exception of P. williamsoni ♀ x P. gemmiferum ♂ (W x G), was obtained. Culture methods were developed and morphological comparisons made. Origin of P. gemmiferum-like hybrids in the lake population was not consistently explained by morphological comparison of known P. spilonotus (small form) ♀ x P. gemmiferum ♂ (S x G) hybrids or P abyssicola ♀ x P. gemmiferum ♂ (A x G) hybrids; morphometric characters were more like S x G hybrids while meristic characters were more closely associated with A x G hybrids. Based on evidence available, no definitive statement could be made concerning the origin of P. gemmiferum-like hybrids except that they are hybrids among combinations of P. gemmiferum and either P. spilonotus (small form) or P. abyssicola. no known hybrid explained the origin of either group of P. spilonotus. Electrophoretic analysis of general proteins and several enzyme systems of various tissues showed much similarity among Bear Lake Prosopium; only P. williamsoni was totally unique. Biochemical evidence did not support or refute separate consideration of the two forms of P. spilonotus but did establish that neither were phenotypic variants of P. williamsoni. Ecological characteristics of Bear Lake Prosopium revealed important distinctions between forms. Growth histories of P. abyssicola, P. spilonotus (small form) and P. spilonotus (large form) showed pronounced differences. Distinct differences in growth and in age and size at maturity of forms of P.. spilonotus provided further evidence supporting their separate consideration. Spatial overlap of spawning activities was marked between forms of P. spilonotus and P. gemmiferum; P. abyssicola was well separated spatially. Temporally, slight overlap was observed between ripe females of one group and ripe males of the succeeding group to spawn. the only observation of the simultaneous occurrence of ripe females of two forms was between P. spilonotus (large form) and P. spilonotus (small form); in this instance, the number of ripe females of each form was extremely small. No evidence of mass hybridization among forms was observed. A combination of temporal, spatial and ethological premating isolating mechanisms are thought to be important in reproductive isolation of Bear lake whitefishes while postmating mechanisms are nonfunctional with the possible exception of hybrid sterility. Morphological and ecological analyses, combined with results of experimental hybridization, provided abundant evidence supporting separate recognition of the two forms of P,. spilonotus. Karyotypes of P. gemmiferum, P abyssicola and P. spilonotus (small form) have been determined (Booke, 1974) and are unique for each species. If the karyotype of P. spilonotus (large form) is found to also be unique, there should be no question that the two forms of P. spilonotus represent distinct species. Final clarification of the taxanomic status of these forms will not come until karyotype data is available; however, based upon present evidence, tentative recognition of a new species is recommended.

Spatial patterns in parasite communities of freshwater fish are often characterized as low in diversity and unpredictable. Whether or not his view is a true reflection of community patterns is unclear, in particular when comparing studies of parasite communities of fish occuring in man-altered ecosystems. To understand the structure of a fish parasite community, I first described the parasite fauna of 13 species of freshwater fish from 19 isolated lakes on the Caribou Mountains plateau in northern Alberta. After my initial broad-scale survey, I selected the diverse and complex community of parasites in whitefish, (Coregonus clupeaformis) for further analysis. This host had the most diverse parasite community of any species of fish on the plateau and was disproportionally important in the dissemination of parasites to the other species of fish. Ten parasite species infected whitefish in the 7 large lakes on the plateau; 7 were core species (i.e found in every lake) and 9 were salmonid specialists. Parasite intensities were much higher (>100 per host) in the Caribou Mountains than elsewhere in Canada, as was community similarity (>70%). Ordination analyses showed that 48% of the variation in parasite intensities between lakes could be explained by factors associated with aquatic productivity (e.g. chlorophyll-a and total phosphorus). Low-intensity lakes were characterized by low productivity and high colour and high-intensity lakes were characterized by low productivity and high colour and high-intensity lakes had high prductivity and low colour. Patterns of high similarity between lakes, together with the association between aquatic productivity and community structure shows that the spatial structure of parasite communities can be predicted on the basis of a common suite of specialist, core species. / vii, 147 leaves : ill. ; 28 cm.