Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2004
Publication Date: 10/1/2004
Citation: Lellis, W.A., F.T. Barrows, and R.W. Hardy. 2004. Effects of phase-feeding dietary phosphorus on survival, growth, and processing characteristics of rainbow trout Oncorhynchus mykiss (Walbaum). Aquaculture. 224; 607-616. Interpretive Summary: In order to reduce the amount of phosphorus leaving hatcheries so that regulatory requirements can be met, we conducted a study to evaluate feeding phosphorus finishing diets. A finishing diet is a type of feed fed for just the last portion of the production cycle. Feeding low levels of phosphorus during this phase of production resulted in more efficient use of dietary phosphorus. The amount of phosphorus retained increased from 22-23% for fish fed the standard level of phosphorus to 88% retention for the groups fed .21% dietary phosphorus. Feeding a low phosphorus finishing diet can reduce the amount opf phosphorus released by a hatchery, but farmers should consult with feed companies regarding the additional cost of the low phosphorus feeds.
Technical Abstract: A factorial experiment involving eight diets and three feeding periods was conducted to determine the minimal level of dietary phosphorus required to maintain survival, growth, and processing characteristics of post-juvenile rainbow trout. Trout were reared to an average size of 200, 300, or 400 g using a commercial feed (1.20% P), then allotted by triplicate groups of nine fish to one of seven experimental diets containing logarithmic increments of dietary phosphorus (0.15%%, 0.21%, 0.30%, 0.42%, 0.60%, 0.85%, and 1.20% P) or a commercial trout feed(1.20%P). At an average weight of 550 g. fish were transported to a commercial processing plant, mechanically filleted, and evaluated for quality. Fish survival and weight gain increased quadratically with increased dietary phosphorus for fish started on treatment at 200 and 300 g, but were similar among all fish started at 400 g. Phosphorus retention decreased with increasing dietary phosphorus level, from approximately 88% in groups fed diets containing 0.21% phosphorus to between 23% and 32% in groups fed diets containing 0.85% phosphorus. Calculated phosphorus losses increased as dietary phosphorus levels increased, from a low of approximately 0.4 g phosphorus kg-1 fish weight gain to between 9.5 and 13 g phosphorus kg-1 fish weight gain at the highest dietary phosphorus level. Dietary phosphorus did not affect carcass moisture, protein, lipid, or ash, but carcass phosphorus