Growth characteristics:
Under natural and farming conditions
Natural growth rate in North African catfish is best estimated using sectioned otoliths (lapillus), pectoral spines or vertebrae. The use of pectoral spine sections may result in the under-estimation of age, particularly in larger fish (Clay, 1982). Growth of North African catfish has been studied in various localities in South Africa, Namibia, Zimbabwe, Malawi, Egypt and Turkey (van der Waal and Schoonbee, 1975; Willoughby and Tweddle, 1978; Bruton and Allanson, 1980; Clay, 1982; Quick and Bruton, 1984; Marshall, 1990; Yalcin, Solak and Akyurt, 2002; Potts, Hecht and Andrew, 2008). Growth rates within these populations were found to vary widely. Growth increments in both sexes are highest during the first year, and lengths of between 200 and 300 mm TL are attained. In subsequent years, length increments vary between 80 and 150 mm. Based on the findings of these studies, a generalized von Bertalanffy growth equation was calculated. The parameters of the equation were L∞ = 1766 mm TL, K=0.08 and to=-1.70, and the growth curve is illustrated in Figure 5. Table 3 shows the mean length at age and 95 percent confidence intervals. In most populations, there is no significant difference between the growth rates of males and females.
