Growth patterns and Fulton’s condition factor of the silver catfish Chrysichthys nigrodigitatus (Actinopterygii: Siluriformes: Claroteidae) from a sanddragged man-made lake of Benin

Abstract

Notwithstanding the nutritional, economic and fisheries importance of Chrysichthys nigrodigitatus, and its relatively high abundance and propagation in Lake Ahozon (South Benin), nothing is known about the well-being of the species in this water body. Thus, this study investigated length and weight frequency distributions, length-weight relationships and condition factors of C. nigrodigitatus. A total of 1020 individuals of C. nigrodigitatus were sampled with seines, cast nets, gill nets and hooks during a 15 month period, from August 2014 to October 2015. Total length (TL) and body weight (W) frequency curves showed a unimodal distribution. The longest TL and highest W recorded were 324 mm and 456.1 g, respectively. In Lake Ahozon, C. nigrodigitatus population exhibited a significant (P≤0.01) isometric growth pattern, indicated by the power function (W = 0.011TL 2.99 ; r=0.96) and the log-transformed linear regression equation (LogW = 2.99 LogTL - 1.94; r=0.96). Growth models varied spatially, sexually, ontogenetically, and seasonally, while corresponding subpopulations showed allometric or isometric growth trends, with slopes b ranging between 2.47 and 3.21. The population showed conditions factors (K) ranging between 0.8 and 3.08 which significantly varied with habitats (F = 7.613, P = 0.006), seasons (F 2,1017 = 29, P = 0.0001) and life stage categories (F 2,1017 1,1018 =5.583, P = 0.004). The active breeding that provided an important stock of offspring for recruitment, the isometric growth model and the relatively high condition factors indicated the perfect establishment of C. nigrodigitatus in the artificial lake of Ahozon. The sustainable exploitation of fisheries in this non-conventional medium-environment requires an integrated approach of lake management.