Meta-Analysis of Growth for Five North American Catfishes: Effects of Climate, Hydrologic Habitat, and Latitudinal Countergradients
Andrew L. Rypel
Abstract.—Growth rates are a core characteristic of catfish populations that are of increasing research interest. However, few studies have synthesized growth data across catfish populations and species to examine large-scale drivers of catfish growth. Here, a metaanalysis of growth was conducted for channel catfish Ictalurus punctatus, blue catfish I. furcatus, flathead catfish Pylodictis olivaris, brown bullhead Ameiurus nebulosus, and black bullhead A. melas, and relationships were documented between growth and climate variables, hydrologic habitats (lentic versus lotic), and latitudinal countergradients (a tendency for faster subannual growth in the north). Blue catfish, black bullhead, and brown bullhead growth correlated significantly and positively with temperature metrics. Blue catfish, flat-head catfish, and brown bullhead growth also correlated significantly and positively with sunshine fraction, wind speed, and evapotranspiration. Channel catfi sh growth did not correlate to any climate metrics. After removal of growth effects related to climate, blue catfish and brown bullhead had significantly faster growth in lotic than lentic habitats. Channel catfish and black bullhead had faster growth in lentic than lotic habitats. Flathead catfish showed no difference in growth between hydrologic habitat types. After standardizing growth by postsexual maturation age and the thermal opportunity for growth, significant and highly predictive countergradient growth relationships (mean r2 = 0.47) were found for all five species across sites (i.e., faster temperature-standardized growth in more northerly populations). Slopes of these relationships did not differ among species, suggesting similar responses to latitude. There may be a genetic basis for countergradient growth in catfishes that developed over evolutionary scales via selection by a shared environmental factor. Catfish growth is variable within and among species but can be intensely shaped by all three primary factors evaluated in this study.