Performance Characteristics of Nile Tilapia and Channel Catfish Fed Diets Containing Graded Levels of Dried Distillers Grain with Solubles

Travis W. Schaeffer

            Feed costs account for over 50% of the total cost in fish production, with the protein constituent marine fish meal (currently $1,100 ton^-1) composing the most expensive diet ingredient (Coyle et al. 2004). Plant-based proteins, such as dried distiller’s grains with solubles (DDGS, currently $155-185 ton^-1), are readily available and would provide a relatively inexpensive alternative protein source. Several feeding trials will investigate levels of inexpensive DDGS used as a supplemental protein source in the diets of juvenile Nile tilapia Oreochromis niloticus and channel catfish Ictalurus punctatus. Initially, six isocaloric and isonitrogenous diets will be formulated using graded levels of DDGS to allow performance comparisons for Nile tilapia and channel catfish; DDGS levels were estimated from a pilot study and peer reviewed literature. Complete diets will be formulated using known ingredient composition values from literature sources (e.g., National Research Council 1993). Twenty-four 132-L glass aquaria, connected in parallel to a recirculating culture system, will be stocked with 10 Nile tilapia (initial weight = 20 g) or 10 channel catfish (initial weight = 25 g) with four replicate aquaria randomly assigned to each diet. Fish will be fed three times per day to apparent satiation for 60 days. Primary performance metrics to be compared include: weight gain, food conversion ratios, protein efficiency ratios, and condition factors. Three randomly selected fish per aquarium will be sacrificed at the end of each feeding trial to allow organosomatic comparisons (e.g., hepatosomatic index and muscle ratio). Apparent digestibility of DDGS feeds will be determined using both total protein and chromic oxide marker assays. Bomb calorimetry will be used to determine the amount of combustible energy. Treatment responses will be analyzed using one-way analysis of variance. If significant treatment effects exist, least significant difference (LSD; α = 0.05) tests will be applied to determine differences among treatment means. Additional feeding trials may be required, but study results should provide dietary DDGS levels that will best support performance of cultured Nile tilapia and channel catfish.

References:

Coyle, S. D., G. J. Mengel, J. H. Tidwell, and C. D. Webster. 2004. Evaluation of growth, feed utilization, and economics of hybrid tilapia, Oreochromis niloticus × Oreochromis aureus, fed diets containing different protein sources in combination with distillers dried grains with solubles. Aquaculture Research 35:365-370.

National Research Council. 1993. Nutrient requirements of fish. National Academy Press, Washington D.C.