Effect of pelleted diets with different protein levels on the growth and survival of the African bony-tongue (Heterotis niloticus) fry

• Feeding live Artemia increases the survival. • Weaning fry onto dry diets decreases survival. • Fry have a conservative feeding habit. A major challenge to the commercial culture of African bony-tongue ( Heterotis niloticus ) is the low larval survival rates owing to the lack of suitable weaning diets. This study evaluated the survival and growth performance of H. niloticus fry weaned at 40 days after hatching to three formulated pelleted diets of different crude protein (CP) contents, namely, CP-41 %, CP-43 % and CP-45 %, and a commercial fry feed CP-40 %, with a control group maintained on live Artemia nauplii. Eight hundred and ten H. niloticus fry (0.60 ± 0.17 g) raised on Artemia nauplii before the start of the experiment were randomly distributed into (15) tanks with 54 individuals per tank. The trial lasted for 21 days, with each larval group co-fed with Artemia nauplii and dry feeds for 7 days, followed by 14 days fed solely on their respective dry diets. Dry feeds were administered at ∼ 10 % of fry biomass/tank daily, and when co-fed, the fry were supplied with 1–2 nauplii per mL. The final mean weights of fish (g ± SD) were the following: 1.0 ± 0.2, 1.75 ± 1.10 and 2.00 ± 0.20 for the three test diets and 1.80 ± 0.20 and 3.60 ± 0.20 for the commercial diet and the Artemia control, respectively. The survival rate differed significantly between treatments (p < 0.0001), with the highest for the control (88.3 %), followed by the commercially extruded diet (21.6 %). The formulated pelleted diets had poor survival rates (0.6 %, 4.9 % and 3.0 %). When co-feeding with Artemia nauplii during the weaning period, the mortality was very low (<8%). However, mortality increased sharply from the second week when the fish were solely on their respective test diets. Results indicate that the fry of H. niloticus require a longer adaptation period to dry feeds. More knowledge on the optimal dry feed formulation is needed to enhance growth and survival.