Information on the effects of stocking density, especially on later life stages of the African catfish (Clarias gariepinus), is lacking. Therefore, the purpose of this study was to assess the influence of density on the welfare of juvenile African catfish in a growth stage of 100–1500 g. Furthermore, the changing impact of stocking density on welfare indicators at different stages throughout the growth cycle (from 10–1500 g) of African catfish is discussed. In Phase 2a, 15 groups of African catfish (102.1 ± 3.49 g) were assigned to one of five final densities (67, 133, 267, 533, and 1067 fish/m3). In Phase 2b, 12 groups of African catfish (1044.6 ± 31.6 g) were assigned to one of four final densities (67, 155, 244, and 333 fish/m3). Welfare was studied by recording both growth, physiological and behavioural parameters. A combination of univariate and multivariate analysis was applied in order to acquire an integrated and objective reflection of the effects of stocking density on a range of welfare indicators. Within the size and density ranges used, welfare was not impacted negatively by increasing density. In Phase 2a, fish welfare improved with increasing density while in Phase 2b no effects of stocking density were found. These results also show that the effects of stocking density are not uniform throughout the growth cycle. These differences need to be taken into account by husbandry practices to assure that high welfare standards are maintained throughout the life cycle of the fish being cultured.