Age and growth of sharptooth catfish, Clarias gariepinus (Burchell, 1822) (Clariidae), in the Lower Okavango Delta, Botswana

Abstract

Managing any inland fishery requires reliable age data and accurate estimates of growth rate. Clarias gariepinus, the largest catfish species in most tropical African floodplain river systems, is an important constituent of subsistence fishery catches. We used otolith-derived age estimates to describe patterns of age and growth for C. gariepinus from the Lower Okavango Delta in northern Botswana. Edge analysis of sectioned sagittal otoliths showed that growth zone deposition occurred during the annual flood peak between July and September. The maximum recorded age was 8 years. Growth was best described by the von Bertalanffy Growth Model of the form E[L|age] = 528.70(1–e–0.72(age+1.35)). A comparison of growth parameters from this study with those from previous studies suggests two distinct populations of C. gariepinus between the Upper and Lower Okavango Delta, emphasising the importance of regional stock assessment for key fishery species. The fairly short life span and high variability in growth of C. gariepinus are important indicators that it is imperative to maintain natural habitat and flow regime for sustainable management of fishery resources in the Lower Okavango Delta.

Dynamics of the Seasonal Floodplain Fishery of the Okavango Delta, Botswana

“…Dudley [56] also observed that growth of floodplain fish differed significantly among years driven by flooding and temperature. While some studies have observed no size differences for Clarias gariepinus in the Delta, upper Delta populations follow K life histories while lower Delta populations are more r selected [77], [80]. The feeding ecology of most floodplain fish species is flood-pulse driven [46].…”

“…Serranochromis macrocephalus and C. rendalli) was significantly associated with water temperature , which agrees with van der Waals [72]observations. Growth and Feeding: Floodplain fish growth is fastest during increasing water levels [78]- [80] and peaks at maximum flooded area to take advantage of the available food in the floodplains [57], [80]. During the low flood season intra-specific competition for food [46] decreases fish growth rates [56], [81].…”

“…They are characterized by multi-species assemblages, of different sizes exploited by diverse fishing gears and methods [3], [84], [85]. In the Okavango Delta, the hydrological regime is a major driver of change in the biology and ecology of the fish species in these systems [43], [46], [58], [67], [80], [86]. Like other floodplains the fisheries are dynamic due to environmental variability.…”

“…It makes biological sense to exploit populations in proportion to their natural productivity, as suggested by the concept of "Balanced harvest" [104], [105]. Similar species from different habitats in the Delta have different life history strategies [15], [80], [92] where lower Delta species are generally r selected while upper Delta species are K selected [106]. While O. andersonii from lower Delta has slower growth than those from upper Delta, O. macrochir and C. rendalli from the lower Delta grow faster than their upper Delta counterparts.…”

Gillnet selectivity for the north African catfish, Clarias gariepinus (Actinopterygii: Siluriformes: Clariidae), from the Upper Okavango Delta, Botswana

“…This is also an indication of a healthy stock that is under exploited thus agreeing with Mosepele (unpublished) who found that Maximum Sustainable Yield could not be reached for C. gariepinus in the Okavango Delta. Future studies should aim to conduct fi shery dependent selectivity studies in the Lower Okavango Delta to see if selectivity changes with location, gear or target species (Baremore et al 2012), particularly because recently, studies have suggested the possibility of two distinct populations of C. gariepinus between the Upper and Lower Okavango Delta (Bokhutlo et al 2015).…”