Effects of formulation and processing variables on dry fish feed pellets containing fish waste

A low-cost preparation process starting from fish waste, pregelatinised wheat flour and soya flour was optimised with regard to the physical properties of the pellets, by using response surface modelling. Independent variables were the ratio of wheat flour to soya flour, quantity of added water, temperature of added water, and mixing time. Pellet quality attributes measured for each set of variables were bulk density, water absorption index, sinking velocity, residual moisture, and structural integrity in water. Mixing time played the most important role among the input variables in defining pellet quality. The results suggest that a dry fish feed pellet of good quality can be manufactured by a simple pressing method using a mixture of 50% fish waste, 30–35% pregelatinised wheat flour, and 15–20% soya meal mixed with water (30-35% of the sum of other ingredients) of 60–65°C for 4–5 min. A method for determining structural integrity of pellets in turbulent water is presented.