Apparent Phosphorus Availabilities of Selected Traditional and Alternative Feedstuffs for Channel Catfish

A digestibility trial with Channel Catfish Ictalurus punctatus was conducted to determine apparent availability coefficients (AACs) of phosphorus for selected common feedstuffs: soybean meal, cottonseed meal, wheat middlings, corn gluten feed (CGF), and corn distillers dried grains with solubles (DDGS). A 32% protein diet containing mostly chemically defined ingredients was used as a reference diet. Test diets were formulated to contain 70% of the reference diet mix and 30% of the test ingredient. Chromic oxide was used at 0.75% of the diet as a marker. Fifteen Channel Catfish of a mean weight of 316 g/fish (SD, 5) were placed into 110-L flow-through aquaria. Water temperature and dissolved oxygen were maintained at approximately 30 degrees C and >= 5 mg/L, respectively. Each diet had three replicated tanks. Apparent availability coefficients of phosphorus were 36, 22, 20, 75, and 77% for soybean meal, cottonseed meal, wheat middlings, CGF, and DDGS, respectively. Corn by-products CGF and DDGS had considerably greater phosphorus AACs than soybean meal, cottonseed meal, and wheat middlings, likely because the wet milling and fermentation processes that result in these by-products degrade the phytate form of phosphorus making it more available to the fish. It appears that phosphorus AACs of these ingredients for Channel Catfish are generally correlated to their nonphytate phosphorus levels. Phosphorus AACs obtained from the present study can be used in formulating commercial Channel Catfish feeds to optimize available phosphorus levels.