Total replacement of dietary fish oil with vegetable lipid sources influenced growth performance, whole body composition, and protein retention in Nile tilapia (Oreochromis niloticus) fingerlings

ABSTRACT Several reports show that aquaculture is the fastest food-producing sector globally, contributing nearly half of global fish production from all sectors. However, there has been a steady decline in production of fish oil (FO), which supports intensive aquaculture production. This has resulted in variable but generally increasing prices of FO. Finding suitable alternatives to scarce FO is essential for aquaculture sustainability. Therefore an experiment was carried out to investigate the influence of complete FO substitution with vegetable oil (VO) in the diet of Oreochromis niloticus fingerlings on growth performance, whole-body composition, and protein retention. Four isonitrogenous (30% crude protein), isolipidic (8% crude lipid), and isocalorific (17 MJ kg−1gross energy) basal diets were formulated as follows: a control diet was formulated to contain 5% FO and labeled FOD (fish oil diet), and three other diets were formulated and labeled SOD (soya oil diet), GOD (groundnut oil diet), and POD (palm oil diet); they contained soya oil (SO), groundnut oil (GO), and palm oil (PO) respectively as total replacements for FO. Triplicate O. niloticus fingerlings (N = 120, n = 10, 1.20 ± 0.03 g, mean weight ± SD) were randomly allocated to one of four experimental diets. Fish were hand-fed to apparent satiation twice daily for 63 days. The result obtained from the experiment revealed that dietary lipids significantly influenced growth performance and nutrient utilization of O. niloticus (P < 0.05). The fish fed POD had the least weight gain (WG) and highest feed conversion ratio (FCR) compared with fish fed FOD, SOD, and GOD from days 7–28 (P < 0.05). At day 35 the fish fed SOD had the highest WG (P < 0.05); fish fed GOD had the least WG. The best weekly overall growth at the end of day 56 was observed in fish fed FOD; fish fed POD had the least WG. At day 63, WG of fish fed FOD declined significantly compared to fish fed GOD, POD, and SOD, which had the best growth. At the end of the trial, the best cumulative growth in fish was observed for fish fed FO; however, there were no significant differences (P < 0.05) in WG and FCR between fish fed FOD and SOD. Survival was 100% for all treatments. Fish fed POD exhibited significantly lower levels of whole-body protein compared to fish fed FOD, SOD, and GOD. Fish fed a diet containing FO had the highest (P < 0.05) whole protein compared to diets with VO. However, no significant difference (P < 0.05) between whole-body protein of fish fed FOD and SOD was observed. Fish fed SOD had the highest (P < 0.5) body lipid compared with fish fed the FO, GO, and PO diets. In conclusion, the study has demonstrated that VO can completely replace FO in Nile tilapia diet without affecting growth performance of O. niloticus and that tilapia diet containing SO is a better alternative to FO compared to GO and PO. These findings are useful in dietary formulation to reduce feed costs without compromising tilapia fish growth.