Fish assemblage and reproductive condition and food habits of ribbon shiner and blackstripe topminnow as influenced by road crossings in Ayish Bayou watershed, in eastern Texas.

摘要

Previous studies of water quality and fish community composition in the Ayish Bayou watershed, San Augustine, Texas, have typically focused upon individual streams, without consideration of the watershed as a whole. This research focused upon first and second order streams throughout the watershed to examine water quality, stream structural habitat, and stream fish assemblage structure as influenced by road crossings and seasons. Twelve streams (ten first order, two second order) were sampled seasonally (winter, spring, summer, and fall) either upstream (six study streams) or downstream (six study streams) of a road crossing (16 February 2007--9 November 2007). Temperature ( P 0.001) and dissolved oxygen (P 0.001) varied among seasons but were similar between upstream and downstream locations. All other water quality parameters: conductivity (P = 0.691), total dissolved solutes (P = 0.788), salinity (P = 0.866) and pH (P = 0.511) were similar among seasons and between upstream and downstream locations. Stream habitats (i.e., depth, width, and flow of pools, runs, and riffles) were also consistent over time and between upstream and downstream locations. Thirty-seven fish species (10 families, 21 genera) were captured, where all metrics of diversity and richness were consistent among seasons and between upstream and downstream locations. Overall, relatively consistent stream habitats tended to support a generalist-tolerant fish assemblage, where few individuals of only three intolerant species were captured during this study.;Reproductive condition and food habits of ribbon shiner (Lythrurus fumeus) and blackstripe topminnow (Fundulus notatus) were also quantified throughout the watershed. Ribbon shiners began gonadal development during late winter and continued through spring, where sexual maturity may occur when individuals attain 55--65 mm. Blackstripe topminnow experienced gonadal development somewhat later, but also appear to attain sexual maturity when individuals attain 50--90 mm. Both species are invertivore-generalist, where food habits tended to reflect assumed invertebrate prey availability. Body condition for both species varied over time, but appears to be related to a combination of morphology and reproductive status. Although ribbon shiners tended to be larger, longer, and in better condition in upstream locations, blackstripe topminnow also followed this general pattern with the sole exception of male blackstripe topminnows, which tended to be longer in upstream locations, but were heavier in downstream locations. Both species appear to be seasonal breeders. Due to the relatively stable habitat and stream water quality conditions throughout the annual cycle in study site streams, there seems to be little evidence to suggest that either species responds to unpredictable environmental conditions to cue reproduction.