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Many fish species exhibit diverse life history strategies that help maintain population viability. An understanding of the relationships among these strategies is crucial for prioritising conservation actions. The Warner sucker, endemic to the Warner Lakes Basin in southern Oregon, USA, is one example of a taxon where a lack of information regarding relationships among life history strategies has hampered conservation efforts. Warner suckers have two distinct life history types: stream-type fish that have a fluvial life history and lake-type fish that have an adfluvial life history. There are advantages and disadvantages associated with each life history, and presently the relationship between life history types is not well understood. Our objectives were to determine the amount of genetic variation within and among tributary populations of Warner suckers and to determine the origins of suckers collected in the Warner Lakes. We collected individuals from four tributary populations, a refugial population, and Hart and Crump lakes and genotyped them at 16 microsatellite loci. Estimates of genetic variation among populations suggested low levels of gene flow ( FST = 0.153) and genetic variation among populations seemed to be influenced by population and habitat characteristics. Nearly all of the individuals collected in Hart and Crump lakes originated in a single tributary, Deep Creek, which likely reflects reduced habitat connectivity between most other tributaries and the Warner Lakes. Data presented in this study are useful for evaluating the status of Warner sucker populations and for prioritising conservation actions such as the removal and modification of barriers. [ABSTRACT FROM AUTHOR]

The objectives of this study were to determine the distribution and abundance of endangered Oregon chub , a small floodplain minnow endemic to the Willamette Valley of western Oregon; to describe the fish communities in current and historic chub habitats; and to establish new populations through introductions. Various sampling gears were used, including seines, minnow traps, dip nets, and a gill net. Oregon chub distribution was found to be restricted in comparison with their historical range, whereas nonnative fishes were widespread in the off-channel habitats preferred by Oregon chub. Oregon chub were absent, or low in abundance, when nonnative fishes were present, and several populations declined or were extirpated when their habitats were invaded by nonnative fishes. Isolated habitats with low connectivity supported larger populations of Oregon chub and were less likely to contain nonnative fish species than were habitats with high connectivity. In habitats that supported abundant Oregon chub populations, chub were often the numerically dominant fish species. Results suggest that increasing the connectivity of floodplain habitats in a system where nonnative fishes are widespread may be detrimental to the conservation and recovery of this species. [ABSTRACT FROM AUTHOR]

Triploid fish hybrids frequently survive better than diploid hybrids. Tiger trout are a sterile hybrid between female brown trout Salmo trutta and male brook trout Salvelinus fontinalis; they have a poor early survival rate but a good growth rate. We produced triploid tiger trout by heat shock treatments of fertilized eggs and examined their survival and growth under hatchery conditions. Triploid tiger trout survived better to the initiation of feeding (34%) than did diploid tiger trout (5%) but had lower survival than brown trout (70%). Triploid tiger trout had similar survival to and better growth than brown trout when the two groups were reared together for 239 d after the initiation of feeding. Analysis of the asymmetry of bilateral meristic traits indicated higher developmental stability in the triploid hybrids than in the diploid hybrids. Expression of both parental alleles of enzyme loci, determined by protein electrophoresis, confirmed the hybrid nature of the offspring. Triploid hybrids could be distinguished reliably from diploid hybrids by differences in relative expression of maternal and paternal alleles at some, but not all, loci. Triploid tiger trout appear to be a vigorous hybrid that could be of particular value in situations where allsterile trout populations are desired for stocking. [ABSTRACT FROM AUTHOR]

The fertilizing capacity of cryopreserved semen of rainbow trout (Oncorhynchus mykiss) was improved when eggs were fertilized in a buffered saline activator solution containing 5 mM theophylline, a caffeine relative that prolongs and intensifies sperm motility. [ABSTRACT FROM PUBLISHER]