More specifically, ingredient nutri

More specifically, ingredient nutritional properties and compositions have been reported to play significant roles in the physical qualities of feed pellets. High lipid and fibre contents of ingredients are generally known to negatively affect pellet physical properties (Rumpf, 1962, Thomas et al., 1998 and Kaliyan and Morey, 2009). The high fibre and residual lipid contents of the copra and palm kernel meals used in this trial may have negatively affected pellet structural integrity and nutrient retentions of their respective diets. Proteins can also induce binding functionalities in an ingredient (Thomas et al., 1998). Soy protein for example is known to generally improve the quality and stability of feed pellets (Sørensen et al., 2009). The adhesiveness of soy protein is caused by intermolecular forces (electrostatic and covalent disulphide bonding) in unfolded proteins (Kumar et al., 2002). The pellet nutrient retention capacities of the different experimental feeds were directly related to their respective water stabilities. The selective retention of lipid in the residual dry matter of the different feeds is comparable to the findings of Baeverfjord et al. (2006) although in their study retention was slightly higher for low water-stable diets than in high water-stable diets. Although after half-an-hour, there were significant pellet dry matter loss and nutrient leaching for all the experimental diets, tilapias are adapted to picking up feed pellets from the water surface or within the water column immediately after feed administration. It is thus unlikely that the feed pellets used in this study will significantly leach out the nutrients intended for the target species before ingestion since the sinking velocities of all the different feed pellets were well-suited to the feeding habits of Nile tilapia.