Branchial arch, Electric fishes, South America, Morphology, Gills, Hypoxia, anoxia, knifefishes
Many tropical aquatic environments worldwide are characterized by intermittent or prolonged hypoxia (low dissolved oxygen). Nevertheless, many tropical freshwater fishes are able to inhabit these challenging environments via a range of morphological, physiological and behavioral adaptations. Brachyhypopomus is a diverse genus of weakly electric fishes represented by 28 known species distributed from Panama to Argentina. 17 species are restricted to permanently normoxic habitats (blackwater rivers and terra firme streams), eight species are restricted to seasonally or perennially hypoxic habitats (whitewater floodplains of large tropical rivers or permanent swampy habitats), and three species are eurytopic (occur in both seasonally hypoxic and normoxic habitats). These habitat distributions offer the opportunity to explore both species- and population-level variation in adaptive responses to hypoxia. Across 25 of the 28 known species in the genus (for which specimens were available), one- and two-way ANOVA was used to correlate total gill filament length (a metric of gill surface area) with lifestyle-divided into four categories: 1) stenotopic species (i.e. species occurring in a narrow range of habitats) restricted to hypoxic habitats; 2) stenotopic species restricted to normoxic habitats; 3) populations of eurytopic species from hypoxic habitats, and; 4) populations of eurytopic species from normoxic habitats. One-way ANOVA revealed that populations of eurytopic species from hypoxic habitats had significantly larger total gill filament lengths than stenotopic species from the same habitat (P = 0.0169). Likewise, populations of eurytopic from normoxic habitats had significantly larger total gill filament lengths than stenotopic species from normoxic habitats (P[less than] 0.005). Two-way ANOVA showed that eurytopic species had significantly larger total gill filament lengths than stenotopic species, independent of the disparity in total gill filament length associated with either hypoxic or normoxic habitats. Results indicate a strong correlation between gill surface area and oxygen-habitat among species and populations, which supports the hypothesis that an enlarged gill surface area increases oxygen uptake and serves as an adaptive response to seasonal hypoxia.
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Crampton, William G. R.
Master of Science (M.S.)
College of Sciences
Length of Campus-only Access
Masters Thesis (Open Access)
Pathak, Leilani B., "Adaptive Responses of Branchial Morphology to Hypoxia in the Neotropical Electric Fish Genus Brachyhypopomus" (2011). Electronic Theses and Dissertations, 2004-2019. 6632.