Palm oil-laden spent bleaching clay as a substitute for marine fish oil in the diets of Nile tilapia, Oreochromis niloticus

A 8-week feeding trial was conducted to determine the effect of substituting fish oil with palm oil-laden spent bleaching clay (SBC), a by-product from crude palm oil (CPO) refining, on growth, feed utilization, fatty acid composition and heavy metal accumulation in the muscle of Nile tilapia, Oreochromis niloticus. Four isonitrogenous and isolipidic practical diets were formulated to contain 0, 100, 200 or 300 g kg⁻¹ SBC. Growth performance of Nile tilapia was significantly better in fish fed the 100 g kg⁻¹ SBC diet compared with fish fed the 0, 200 or 300 g kg⁻¹ SBC diet. Growth and feed utilization efficiency of fish fed 200 or 300 g kg⁻¹ SBC were similar to fish fed the control diet without added SBC. Whole-body composition, body-organ indices and haematocrit of tilapia were not affected by dietary treatments. Fatty acid compositions in the muscle lipid of Nile tilapia were strongly influenced by dietary treatments with progressively elevated levels of total saturates and n-6 PUFA because of the dietary influence of these fatty acids from residual CPO adsorbed onto SBC. A gradual decrease in total n-3 PUFA concentrations were also observed with the ratio of n-3 to n-6 fatty acids in muscle lipids decreasing from 4.75 to 4.41, 3.23 or 2.37 after 8 weeks on the 0, 100, 200 or 300 g kg⁻¹ SBC diet, respectively. The arsenic, cadmium and lead concentrations in the experimental diets increased with increasing dietary levels of SBC but the concentrations of these heavy metals in the whole body and bone of Nile tilapia were not significantly different among fish fed the various diets. The present 8-week study showed that in fishmeal-based diets for Nile tilapia, palm oil-laden SBC can totally replace added fish oil. The use of this presently discarded waste product from palm oil refining in tilapia diets will greatly contribute to reducing the impact of rising feed costs in the culture of tilapia in many tropical countries. Other potential benefits may include acting as a feed binder, removal of mycotoxins in fish feeds as well as adsorbing toxic substances present in the culture water.