Abstract

The production of floating fish feed for the African catfish, Clarias gariepinus, in sub-Saharan African countries is challenged by a lack of affordable equipment and processing know-how. The present study aimed at defining the operating conditions for a locally built single-screw extruder. The effects of main ingredients and their particle size on the extrusion outcome were assessed. Moisture contents of 200 to 250 g kg-1 (wet basis) led to jamming during the extrusion process and low yields of extrudates. However, the ideal starch source for the production of the floating feed consisted of Cassava (Manihot esculenta) chips. Extrusion without oil in the blend favoured the production of extrudate with increased floatability-moisture contents of 350 g kg-1 allowed smooth extrusion with high yields of extrudate albeit with lower floatability. The optimum moisture content for extrusion of floating extrudate was between 275 and 300 g kg. The particle size of the blend significantly affected the physical qualities of granules. Extrusion of blends of 1 mm particle size without oil addition favoured the production of granules with a low density (≈ 0.45 kg l-1) and high floatability (≈ 94%). The required oil was added as a coating of the extrudate.

Key words: Cassava, fish feed, floatability, low-cost single-screw extrusion, oil, particle size.