Replacement of Fishmeal with Plant Feedstuffs in the Diet of Red Drum Sciaenops ocellatus: An Assessment of Nutritional Value

The expansion of aquaculture has increased demand for fishmeal supplies around the world; this, in turn, has resulted in dramatic increases in the cost of fishmeal, which has sparked interest in alternative feedstuffs. The development of new processing technologies, as well as the expanding generation of by-products from ethanol production has resulted in the development of novel protein sources that have the potential for replacing fishmeal in aquafeeds. The present study assessed the nutritional value of soy protein concentrate (SoyPC), barley protein concentrate (BarPC) and corn protein concentrate (CornPC) in the diet of red drum. Three sequential feeding trials were conducted; in these 50%, 75%, or 90% of the protein provided by Special SelectTM menhaden fishmeal in the reference diet was replaced with either SoyPC, BarPC, or CornPC in isonitrogenous (40% CP), isoenergetic (3.1kcal g-1) diets. Red drum with an average weight of 2.5 g, 1.6 g, and 1.5 g for trials 1, 2, and 3, respectively, were stocked in a recirculating system and fed twice daily at a rate approaching apparent satiation for 6 to 8 weeks. Along with the substitution of the selected plant feedstuffs, supplementation of DL-methionine and L-lysine was provided to exceed the established requirements of red drum for lysine and methionine, and glycine was added for palatability. Performance parameters of weight gain, feed efficiency, survival, hepatosomatic index, intraperitoneal fat ratio, and apparent digestibility coefficients for protein along with proximate composition of whole-body tissues were determined in the various trials. Results showed that 50% replacement of fishmeal protein by each of the protein concentrates produced fish performance, condition indices, and whole-body composition similar to those produced by the reference diet. However, replacing 75% and 90% of fishmeal protein with each of the plant protein concentrates reduced fish performance but not as severely as replacing all of the fishmeal protein with equal (33%) contributions from SoyPC, BarPC, and CornPC. Contrarily, these dietary substitutions did not reduce the apparent protein digestibility of the experimental diets. Based on the various results of this study, SoyPC, BarPC, and CornPC can readily replace 50% of the protein provided by menhaden fishmeal without adversely affecting the performance of cultured red drum.