Standard weight equations of two sub-/tropic nonnative freshwater fish, Clarias gariepinus and Oreochromis niloticus, in the Sakarya River Basin (NW Turkey)

Abstract

Clarias gariepinus and Oreochromis niloticus are two hot-water fish species of African origin that have been recently reportedto occur unnaturally in hot-water resources and springs in the Sakarya River Basin (northwestern Turkey). Within effective planningstrategies to maintain native biodiversity, monitoring fishes’ well-being can be useful to evaluate the status of nonnative fish populationsand their degree of adaptation to new environments. Relative weight (Wr) is a condition index widely used to estimate the well-being offish by comparing the actual weight of a specimen with a standard weight (Ws) that is the ideal weight of that fish at that length. In thisstudy, length and weight data of C. gariepinus and O. niloticus, collected throughout the Sakarya River Basin, were used to estimate Wsequations. The resulting Ws equations were log10Ws = –3.668 + 1.885 log10TL + 0.2087 (log10TL)2 (TL range: 18–45 cm) for C. gariepinusand log10Ws = –8.796 + 6.751 log10TL – 0.8479 (log10TL)2 (TL range: 8–28 cm) for O. niloticus. The use of these Ws equations to estimatethe fishes’ condition is suggested as a monitoring tool to assess the status and the best management actions of these two nonnativespecies populations throughout the Sakarya River Basin.