Effluent Management Using Low Phosphorus Feeds for Spring Chinook

Phosphorus (P) is generally the first limiting nutrient in fresh water for aquatic plant growth. Fish hatcheries effluents are a source of P derived from uneaten and undigested feed and metabolic losses.  Low P feeds are available but meeting the mandated P levels in the effluent can still be difficult. A feeding trial was conducted to investigate the effects of low P feeds on spring Chinook. In addition to the feeds, P leaching from the feces adds to the effluent P.  It can contribute up to 30% of the P produced by a facility.  So the leached P is an important aspect to consider. Diets were formulated to contain 0.6% P, 0.8% CaHPO₄ or 0.8% Na₂HPO₄.  BioDry 1000 low P and BioVita were used in this study for comparison. Spring Chinook (17.7 g initial weight) were used.  The study was conducted in 277.4 L circular tanks, 150 fish/tank, four replicates/treatment for eight weeks.  Well water (12^oC) was provided at a rate of 7.6 L/min/tank. Data collected includes weight gain and survival; level of blood components alkaline phosphatase, P, calcium, total protein and triglycerides; fecal P, leached fecal total and orthophoshorus; whole body P as well as P and calcium digestibility.