Patterns of habitat use among vegetation-dwelling littoral fishes in the Atchafalaya River Basin, Louisiana

Information regarding the relative value of different aquatic macrophytes as fish habitat is lacking for large floodplain river systems, such as the Atchafalaya River basin in south-central Louisiana. We made seasonal comparisons of fish (total length, <100 mm) density, diversity, and biomass and physicochemistry among submersed hydrilla Hydrilla verticillata, emergent bulltongue Sagittaria lancifolia, and floating water hyacinth Eichhornia crassipes. In addition, we examined the influence of habitat structure and physicochemistry on fish assemblage composition and density. Although there were no seasonal differences in fish biomass among plant types, hydrilla consistently supported the greatest fish density and diversity across seasons. While hydrilla and water hyacinth fish density changed little among seasons, density in bulltongue was higher during tow water. Of the 12 most common fish species, the pirate perch Aphredoderus sayanus and yellow bullhead Ameiurus natalis showed no consistent pattern of habitat use. However, the densities of golden topminnow Fundulus chrysotus, bluegill Lepomis macrochirus, warmouth L. gulosus, redear sunfish L. microlophus, and pugnose minnow Opsopoeodus emiliae were highest in hydrilla, whereas the density of bantam sunfish L. symmetricus was highest in water hyacinth. A seasonally variable pattern was found for western mosquitofish Gambusia affinis, redspotted sunfish L. miniatus, sailfin molly Poecilia latipinna (higher in bulltongue), and least killifish Heterandria formosa (lower in water hyacinth). Overall, littoral fish distributions reflected responses to several spatially and temporally variable environmental factors (e.g., water quality, plant complexity, and seasonal depth changes). We suggest that the consistently high fish density and diversity in hydrilla across seasons were related to an optimization of favorable water quality (particularly dissolved oxygen [DO]), architectural complexity, and biovolume. However, during low water, as hydrilla and water hyacinth canopies became very dense and water hyacinth DO levels remained low, bulltongue was more heavily used by several species, presumably because of a more favorable combination of DO, complexity, and particularly depth.