Determining the Best Weaning Age to Dry Feeds and the Influence of Phospholipids and Long Chain Polyunsaturated Fatty Acids (LC-PUFAs) on Digestive Enzyme Activity and Growth Performance of African Bony-Tongue (Heterotis niloticus) Fry

Abstract

Limited information exists on the dietary requirements of the African bony-tongue (Heterotis niloticus) fry as well as the suitable age to wean fry from live prey to formulated diets. These have been the major challenges to the commercial culture of the species. This study assessed the optimal weaning age of fry as well as the effect of varying phospholipid (PL) content and long chain polyunsaturated fatty acids (LC-PUFAs) on survival, performance, and digestive enzyme activity of H. niloticus fry. The two weaning diets used were formulated to be isonitrogenous, isolipidic, and isoenergetic (49% CP, 20% CL, and 22.7 MJ/kg). The diets differed only in the content of PLs and LC-PUFAs; eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Soy lecithin (PLs) and Algatrium DHA70 (a glyceride product high in DHA and EPA) were included at two levels. The diets were, respectively, labeled low phospholipid (LPP) (formulated to contain: 3.16% PLs, LC PUFAs: 0.66% DHA 0.10% EPA) and high phospholipid (HPP) (formulated to contain: 12.96% PLs, LC PUFAs: 3.04% DHA, 0.75% EPA). African bony-tongue fry were fed Artemia nauplii until 15, 25, 35, 45, 65, or 85 days after hatching (DAH), respectively, then cofed with Artemia and one of the two weaning diets for an additional 7 days after which Artemia feeding was completely withdrawn. Hereafter, the fry were maintained solely on the experimental diets for 10 days. A control group was kept on Artemia nauplii throughout the experiment. The results showed that the survival rate of fish on the LPP and HPP diets increased significantly (p  < 0.05) with weaning age; from 0% (LPP and HPP) for fry weaned at 15 DAH to a survival rate of 69.4% ± 3.9% (LPP) and 80.0% ± 9.4% (HPP) at 65 and 85 DAH, respectively. This was, however, lower than the survival rate obtained for the control (Artemia) which was 93.3% ± 3.33% at 85 DAH. The final mean weight, weight gain, and survival rate improved significantly (p  < 0.05) for fry fed the HPP diet compared to the LPP diet. All digestive enzyme activity decreased significantly with increasing fish age (p  > 0.05). Based on the results, it is recommended, that H. niloticus fry is maintained on live Artemia nauplii and provided with dry feeds high in LC-PUFAs (33.98 mg g⁻¹ diet) and PLs (12.96 mg g⁻¹ diet) from <65 DAH to obtain higher survival rates.