The Piebald Madtom, Noturus gladiator, is found in tributaries of the Mississippi River from the Obion River in northern Tennessee to the Big Black River in central Mississippi. The species is currently petitioned for listing under the federal Endangered Species Act of 1973, and is of conservation concern in both Mississippi and Tennessee. Yet little is known about the feeding ecology of the species. To this end, diets were extracted from stomachs and intestinal tracts from available formalin-preserved museum specimens (n = 57). These specimens came from the Hatchie River, Wolf River, Yazoo River, and Big Black River of Mississippi or Tennessee. All diet items were identified to the lowest possible taxonomic level, and contribution characterized as percent composition by number, total number of prey items, proportion of diets containing a prey item, frequency of occurrence, and prey-specific abundance. Twenty-one different diet items included larval trichopterans with sand cases, teleost scales, ostracods, and larval odonates (primarily Macromiidae). The relationship between prey-specific abundance and frequency of occurrence was described using an Amundsen plot, and revealed that trichopteran larvae and larval odonates are of high importance, and suggesting the species may forages on both sandy substrates and leaf packs.

The Mobile Basin has undergone extensive channel modification with corresponding declines in the distribution and abundance of native aquatic fauna. However, many of the declining aquatic species of the Mobile Basin may persist within unmodified sub-basins. The Noxubee River is a sub-basin of the Mobile Basin that is relatively unaltered throughout its watershed, and we hypothesized that the system could serve as a refugium for declining riverine species of the Mobile Basin. We characterized species richness and assemblage structure of fishes in the Noxubee River and its tributaries to determine whether or not contemporary fish assemblages resembled the historical assemblages as described before construction of the Tennessee-Tombigbee Waterway. We found that fish assemblages of the contemporary river are similar to those of the historical river, and many species now absent from another portion of the Mobile Basin are still present and maintain similar distribution and abundance patterns. Our results are informative because there is little existing information available regarding fish assemblages in the Noxubee River since major alterations were imposed upon the Mobile Basin through construction of the waterway. These results are discussed relative to findings from another Mobile Basin tributary that exhibited a marked change in many fish assemblage properties following construction of the waterway. Variable resiliency among tributaries to altered main-channel rivers illustrates the need for predictive tools that can be employed to prioritize conservation efforts.

The Mississippi silverside (Menidia audens), now common throughout the Tennessee-Tombigbee Waterway (TTW) in Mississippi, apparently invaded this highly modified system from the Tennessee River, concurrent with TTW construction (1972-1985). Subsequent decline in distribution and abundance of the native brook silverside (Labidesthes sicculus) led to speculation that dietary competition with M. audens might be occurring. Therefore, diet data from sympatric and allopatric collections of the two silversides at several sites in TTW were analyzed using multivariate statistics and null models to test for significant dietary differences, overlap and niche shifts potentially attributable to habitat alteration. Diet overlap between the two silversides at sites of co-occurrence was greater than expected under the null model. Moreover, intraspecific food habits did not differ between individuals occurring in sympatry and those occurring in allopatry for either silverside. Thus, significant portions of their diet overlapped and neither species has exhibited dietary shifts that would facilitate coexistence. The two species differed significantly along stream size and current velocity gradients, with M. audens preferring the larger, slower moving habitats of the waterway. Unlike L. sicculus, M. audens included the exotic daphnid Daphnia lumholtzi in its diet. Because M. audens capitalized on a wider variety of prey items in the modified TTW environment and because of their previous interactions in other systems, we conclude that the native silverside, L. sicculus, is likely to be replaced by M. audens in lentic TTW habitats.

The upper Tombigbee River in northeastern Mississippi now exists as a fragment, confluencing with and fed by an extensively modified aquatic landscape now called the Tennessee‐Tombigbee Waterway (TTW). We examined the changes to fish assemblages and flow regime after waterway construction based on contemporary comparisons to historical fish collections and discharge data. The river's flow regime has changed markedly since TTW construction. Analysis of discharge data from two stations for 15 years, pre‐ and post‐waterway, indicated significant differences in flow regime including increased minimum and base flows, lower spring and higher late summer‐autumn flows, and lower high flow durations, post‐TTW. These changes corresponded to significantly reduced regional and local species richness, and strong shifts in fish assemblage structure across a 20 yr time span. Post‐waterway fish assemblages were related strongly to measured environmental variables characterizing local habitats. Several lentic‐adapted species increased their abundances in lower reaches of the river, including a recent invader to the TTW system, the Mississippi silverside Menidia audens. Fragmentation of river ecosystems via disruption to hydrologic regimes is a major threat to aquatic biodiversity worldwide. Because the flow regime of this fragmented river is in part controlled by waterway operations via five minimum flow control structures, adaptive conservation and management efforts could be implemented in order to maintain and potentially restore the natural flow regime and the ecological integrity of the system.

Non-parametric, multivariate analyses commonly used to characterize spatial and temporal patterns in the taxonomic composition of ecological communities can likewise be useful when applied to data generated from the examination of gut contents. A suite of analyses including non-metric multidimensional scaling (NMS), multi-response permutation procedures (MRPP), and indicator species analysis (ISA) revealed interesting dietary shifts that Occurred across individuals of emerald shiner (Notropis atherinoides) collected from among different habitats and two different time periods (pre- and post-impoundment of the upper Tombigbee River). These patterns were delineated from data that exhibited non-linear distribution and that incorporated measurements made at different scales, two factors that confound traditional parametric analyses. NMS ordination provided clear, graphic representation of the separation that occurred when N. atherinoides diets were viewed across space and time. MRPP analysis validated that the observed separation was statistically significant, and ISA complemented these other two analyses by identifying diet contributors that were indicative of each grouping.

The crystal darter, Crystallaria asprella (Jordan), is a benthic, riverine specialist, rare throughout its range and critically imperiled in the state of Mississippi. Construction of the Tennessee-Tombigbee Waterway has fragmented a once continuous population of this species into several subpopulations in remaining, free-flowing tributaries of the system. In spite of this fragmentation and population subdivision, we collected numerous individuals from the waterway during summer 2004 and 2005. Because of the lentic conditions in the waterway, we questioned whether a dietary shift accompanied darters occupying this new environment. We also obtained museum specimens from the Tombigbee River before waterway construction and quantified and compared diets among the historical, tributary (contemporary) and waterway specimens. We hypothesised that waterway specimens would differ significantly in diet from both historical and tributary specimens, and that the latter two groups would have similar diets. Multiresponse permutation procedures indicated that all three groups were significantly different from each other and indicator species analysis identified significant indicator taxa for waterway and tributary specimens. Using a null model approach, dietary overlap was significantly greater than expected for tributary and waterway specimens, and significantly less than expected for waterway and historical specimens. Dietary plasticity was evident for crystal darters across space and time, but it remains unknown whether waterway individuals represent a population sink or are actively dispersing from nearby population sources.