Growth, Production, and Community Composition of Fishes Inhabiting a First‐, Second‐, and Third‐Order Stream of Eastern Kentucky

Fish populations in a first—order, a second—order, and a third—order stream were studied during the summers of 1967—68. The primary food of each fish species was determined. Available food sources included terrestrial invertebrates, aquatic primary production, aquatic invertebrates, aquatic vertebrates, and detritus. Average daily growth rates showed that age—group I fish of most species grew faster in early than in late summer. The growth rate of most age—group II fish varied little between these seasons. Total numbers, total standing crop, and gross production were estimated for each species in each order. Total production was compared among stream orders on a per linear meter basis. Production values were nearly equal in first (2.35 g dry weight per linear meter) and second order (2.36), but increased in third order (3.29). The relative importance of terrestrial invertebrates as an energy source decreased with increasing stream order. Aquatic primary production and aquatic invertebrates began to be utilized as energy sources in second order. The aquatic vertebrates and detritus began to be utilized in third order. The relative importance of aquatic primary production utilization increased in third order, but the relative importance of aquatic invertebrate utilization was approximately the same as in second order. The community structure of the fish populations of each pool was analyzed the information theory and the ratio H/Hₘ ₐ ₓ. Community structure differed between third—order and second—order pools even when the same species complement was present. It is postulated that stream order in most cases represents a biological unit which can be subdivided into microhabitats based on riffle, pool, type of substrate, etc., and addition in most cases proceeds by discrete units of stream order.