Evaluation of dietary fish oil: soybean oil ratios on growth performance feed utilization, haematological indices and body fatty acid composition of Keeled mullet, Liza carinata fingerlings

Dietary fat is a vital component of fish nutrition. Fish oil (FO) is considered the best source of fat due to its balanced fatty acid content. This prompted nutritionists to consider reducing the reliance on fish oil in fish diets by substituting it for cheaper and more readily available vegetable oils. This study was conducted to investigate the effect of different dietary ratios of fish oil: soybean oil (SO). Four isonitrogenous (30.99% crude protein) and isolipidic (16.92%) diets were formulated to obtain four different dietary ratios of FO: SO. The formulated diets contained the tested oils, either as the sole source of (FO, FO₁₀₀: SO₀ and  SO, FO₀: SO₁₀₀), or various combinations of FO and SO (FO₇₅: SO₂₅ and FO₅₀: SO₅₀). One hundred and eighty Liza carinata fingerlings with an initial weight of 1.54 ± 0.18 g were distributed into 12 plastic tanks (55L each, triplicate per treatment). The experiment was conducted for 60-days. The best significant (P < 0.05) FCR and protein efficiency ratio (PER) values were reported for FO₇₅: SO₂₅ diet, compared to the other experimental treatments. The results observed that the higher FO content (FO₁₀₀: SO₀ andFO₇₅: SO₂₅  diets) had higher n-3 FA content such as 20:5n3 EPA and 22:6n-3 DHA than the diet with higher SO ratios (FO₅₀: SO₅₀ and FO₀: SO₁₀₀). The results of the present study suggested that Liza carinata fingerlings fed diet FO₇₅: SO₂₅ for 60-days enhanced growth performance, diet utilization efficiency, FCR, and hematological indices. The body fatty acid (FA) profile in the experimental fish groups reflected the FA profile of their respective diets.