Relationships Among Swimming Ability, Habitat use, and Morphology of Freshwater Fishes from Texas and Louisiana




Leavy, Tracy R.

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Relationships between swimming ability and both habitat selection and morphology were assessed for freshwater fishes from Gulf slope, Rio Grande, Red River, and Canadian River drainages in Texas and Louisiana to better understand the influence that flow has on structuring fish assemblages. Swimming ability, relative (body lengths per second, bl·s-1) and absolute speeds (cm·s-1), were determined for 37 species from June through August 2003 in a mobile swim tunnel. Mean absolute (cm·s-1) speeds ranged from 31 to 84 cm·s·1 for Cyprinidae (N of species= 24), 50.9 cm·s-1 for Characidae (N = 1), 70 cm·s-1 for Ictaluridae, 33 cm·s-1 for Cichlidae, 40 cm·s-1 for Percidae, 31 to 43 cm·s1 for Cyprinodontidae (N= 2), 30 cm·s-1 for Atherinidae (N=l), 16 to 19 cm·s-1 for Poeciliidae (N= 2), and 23 to 41 cm·s·1 for Centrarchidae (N= 4). Mean relative (bl·s-1) speeds ranged from 3.4 to 19.6 bl·s-1 for Cyprinidae, 12.6 bl·s-1 for Characidae, 13.7 bl·s·1 for Ictaluridae, 8.7 bl·s-1 for Cichlidae, 11.1 bl·s·1 for Percidae, 5.5 to 12.0 bl·s·1 for Cyprinodontidae, 6.4 bl·s·1 for Atherinidae, 5.5 to 6.8 bl·s-1 for Poeciliidae, and 5.7 to 8.1 bl·s-1 for Centrarchidae. Absolute speeds (cm·s-1) were correlated with habitat current velocity from published and unpublished studies. fu general, swimming ability explained longitudinal distributions of fishes with those having greater absolute speeds inhabiting areas of swifter currents (medium to large rivers) and those with lesser absolute speeds inhabiting areas of slower currents (springs, creeks, and small rivers) (r2 = 0.40; N = 37; P < 0.01 ). Similarly, swimming ability primarily explained spatial (i.e., runs, pools, and riffles) distributions of fishes from Independence Creek (r2 = 0.51, N= 10, P = 0.03), and Banita Creek (r2 = 0. 70, N = 7, P = 0.06) Morphological measurements ( e.g. flatness index, relative body depth) that strongly segregated among families and within the Family Cyprinidae were identified with principle components analysis (PCA) and correlated (Peterson's correlation coefficients) with individual relative (bl·s-1) swimming speed. My results indicated that morphological attributes were a poor indicator of swimming ability among families (PCAl: r=-0.31, N= 412, P <0.01) (PCA 2: r = 0.33, N=412, P <0.01) and within Cyprinidae (PCA 1: r= -0.34, N=317, P <0.01) (PCA 2: r= 0.08, N=317, P= 0.17). Overall, swimming abilities of fishes in part explain species distributions through time and space. However, other attributes ( e.g., benthic orientation) were also deemed important in enabling fishes to persist in flowing environments. Understanding interactions between flow and fish assemblage structure is critical to species conservation and instream flow requirements for fish assemblages, especially obligate riverine specialists.



morphology, Texas, Louisiana, freshwater ecology, fishes


Leavy, T. R. (2004). Relationships among swimming ability, habitat use, and morphology of freshwater fishes from Texas and Louisiana (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.


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