Determination of phosphorus composition and availability from various feedstuffs to channel catfish (Ictalurus punctatus)

Abstract

The availability of phosphorus in fish diets is an raphics. important consideration in aquaculture because phosphorus excretion by fish may influence eutrophication of the culture system or receiving water, as phosphorus is a primary nutrient stimulating phytoplankton growth. This study was conducted to determine the phosphorus (P) composition and availability from the following feedstuffs to channel catfish (Ictalurus punctatus): devilled, solvent-extracted soybean meal, cottonseed meal, wheat, wheat middlings, rice bran, sorghum, corn, fish meal analog, meat-bone meal and menhaden fish meal. Test diets consisting of a 70:30 mixture of reference diet to test ingredient were utilized with chromic oxide as the non-digestible marker. The various test diets were fed to channel catfish weighing approximately 100-150 g and the feed samples were obtained by stripping approximately 12 h after feeding. Feed and fecal samples were analyzed for total phosphorus (TP), soluble reactive phosphorus (SIRP), fractionations of phosphorus, total nitrogen (TN), ammonia [], nitrate [], and nitrite [] from which apparent digestibility coefficients were computed. Fecal samples contained relatively [] Concentrations but rather high [] concentrations. The TP concentrations in fecal material from fish fed the different diets ranged from feedstuffs. The major part of this decrease could be accounted for by uptake of calcium phosphate and organic phosphorus from the feed ingredients. Approximately 25 % of the TP in feedstuffs was readily labile but this fraction increased to 35 % in fecal material. Fecal material from fish fed diet ingredients of plant origin had lower concentrations than samples from fish fed ingredients of animal origin. Phosphorus availability from animal products was variable, with a low of 47 % for menhaden fish meal and a high of 92 % for fish meal analog. Plant products also had variable phosphorus availability values which generally ranged from 33% to 83%. The phosphorus availability values obtained for the various feedstuffs may allow formulation of diets that are better utilized by channel catfish and also reduce phosphorus excretion.