Use of extruded products from the exotic species Plecostomus punctatus. Part 1: Production of balanced diets based on whole Plecostomus punctatus fishmeal

Abstract

To solve the problem that is presently going on at the Lic. Adolfo López Mateos dam, known as “El Infiernillo”, in Michoacán, Mexico, created by the involuntary introduction of Plecostomus punctatus, known in the area as “Devil Fish”, that has proliferated and dominated on the existing fisheries, this research suggests its use as protein source for extruded feedstuffs for other species with a higher commercial value. The objective was to obtain an extruded balanced feedstuff based on Plecostomus punctatus meal. A lab extruder made in Mexico and an imported lab extruder Wenger X-5 were started and put into operation to obtain the desired feedstuffs considering as protein source a commercial fish meal to evaluate its performance in preliminary experiments. Once the best processing conditions were established, Plecostomus punctatus meal was introduced in the selected diet suggested in the literature for tilapia (Oreochromis spp.) cultivated in aquaculture. A modification of the diet composition was done introducing other carbohydrates (wheat flour instead of finer wheat bran (“afrechillo” in Spanish) and coarse wheat bran instead of rice bran). Conclusions derived from this research were: An acceptable fillet contents was found in big specimens. However, the effort to extract it from the animals is important, and might affect the economic and technical feasibility of the process. If the fish is dried, its manual separation is much easier. There is an initiative to exploit “Devil Fish” fillets for human consumption, and considering that this project were viable, its residues would be adequate as part of the proposed diet, since its protein contents is 27%. The nutritional quality of the dehydrated fillet as well as the meal given by the methodology used make its unit operations satisfactory, since very low mass losses were found. Dried fillets might be used as “surimi” or to be directly sold as dried fish, such as Norway cod but to much lower price. Particle size of the different meals, fish and carbohydrates, play a very important role in the feedstuffs physical characteristics before and after extrusion. Thus, all raw materials were previously pretreated to comply with particle size specifications. Grinding and sieving unit operations are very important for industrial scaling-up and should be optimized to reduce costs. Based on bromatological analyses, “Devil Fish” integral meal has the necessary protein contents for tilapia extruded feedstuffs. Carbohydrates needed in the feed mixture to obtain good physical characteristics (hydrostability, matter losses, and expansion percentage) is 28%, according to this research. It also complies with its protein requirements. Finally, grinding and sieving operations should be optimized with the new materials available in the zone, such as sorghum, to minimize production costs.