Nuisance aquatic vegetation (mainly Hydrilla Verticillata ) has become problematic in Lake Conroe, TX. Consequently, triploid grass carp (Ctenopharynogodon idella) were stocked at densities sufficient to completely denude the reservoir of all vegetation (invasive and native plants) within one year. As a result, an assessment was designed to investigate the changes (before and after carp stocking) in the plant assemblage among sampling stations, changes in water quality parameters, length frequency and condition changes of Centrachid species, largemouth diet changes, and changes in the fish assemblages among randomly selected sampling stations between early fall 2007, when grass carp were stocked, and one year later in early fall of 2008. The areas for sampling were based upon aquatic vegetation surveys by Texas Parks and Wildlife during 2007 and 2008, thirteen sampling stations were randomly selected using ArcGIS software and the percentage of water surface covered by vegetation was recorded at each station. Within each station, fish were collected by electrofishing the entire station for five minutes; water samples were also collected. Largemouth bass diet did significantly change for mature (<200 mm-TL) bass as indicated by a chi-square test. Largemouth bass from the samples were shown to consume less sunfish and more shad by the second (post-carp) sample. This is consistent with expected results due to the removal of vegetation consequently eliminating small sunfish habitat. In similar fashion, significant length-frequency changes were seen in the second year as there were fewer smaller (juvenile) Centrachid species found in the sampling sites. Contrary to the Centrachids, length-frequency of gizzard shad significantly decreased in size by the second sampling year. Based upon the aquatic vegetation surveys within the sampling sites of 2007 and 2008, there was an almost complete elimination of all aquatic plants following carp introduction. This result was consistent with what was expected from the carp introductions. Changes in water quality parameters (phosphorous, nitrate, nitrites, orthophosphate, chlorophyll (a)), were generally inconclusive, with the exception of nitrate which significantly increased by the second year. The water quality parameters along with other measured habitat parameters were used in the multivariate analysis.

Hydrilla (Hydrilla verticillata) is an invasive aquatic plant that grows quickly across shallow freshwater habitats. It is a problem for recreational users of lakes and landowners. Grass carp (Ctenopharynogodon idella) is an effective biological control agent that preferentially consumes and can control the spread of hydrilla. However, grass carp also will consume other vegetation, which influences aquatic communities via direct and indirect interactions that can change food and habitat availability and use by various species. Aquatic plants influence habitat and types of prey used by sunfish (Centrarchidae), which must also avoid their own predators. Prey use among sunfish species depends on density and taxonomic identity of both prey and vegetation. This was a one-year analysis of stomach contents from three common species of invertivorous sunfish: bluegill (Lepomis macrochirus), longear sunfish (Lepomis megalotis), and redear sunfish (Lepomis microlophus). Thirteen sampling stations were randomly selected using ArcGIS software. Percentage of water surface covered by vegetation was recorded at each station. A five-minute electrofishing sample was performed within the littoral zone early morning in late September. The stomach contents of all targeted sunfish (N=489) showed high percentages of diet overlap pre- (0.77-0.92) and post- (0.83-0.88) introduction of grass carp. Multivariate analysis showed total explained variation (15.5%) in sunfish diet composition was (P < 0.05) correlated significantly with sunfish species (6.67%), percent surface vegetation coverage (3.97%), and sampling periods pre- versus post-introduction of grass carp (2.13%). Prey-specific abundance showed that all sunfishes displayed a generalized feeding strategy in both sampling periods. Diets of each sunfish species showed differences in abundance (by volume) and occurrence (among individual fish) of prey items between sampling periods. Levin?s standardized index of diet breadth for all sunfish species decreased from pre- (0.12) to post-introduction (0.05). Results imply that vegetation control by grass carp influenced the diets and feeding strategies of three cohabitating sunfish species. These findings may help fisheries biologists to plan future management actions that influence assemblages of aquatic plants and macroinvertebrates, herbivorous fish, invertivorous prey-fish, and piscivorous game fish, to promote a healthy and balanced ecosystem for Lake Conroe stakeholders.