Dietary phosphorus requirement of juvenile haddock (Melanogrammus aeglefinus L.)

A study was conducted to determine the quantitative requirement, excretion, availability and deficiency signs of phosphorus in haddock. Triplicate groups of haddock (4.2±0.01 g) were fed diets containing 0.42, 0.62, 0.82, 1.02 and 1.22% P and 19 MJ digestible energy (DE) per g of diet to satiation for 12 weeks. The basal diet, containing 0.42% P (0.08 g available P per MJ DE), was supplemented with graded levels of calcium phosphate, Ca(H2PO4)2. H2O, to formulate the five experimental diets. The fish were reared in seawater (salinity, 32‰) at a temperature of 12±2 °C. The growth, feed conversion ratio, vertebrae and opercula ash and urinary phosphate excretion were positively correlated with dietary phosphorus levels. Vertebrae ash increased from 44.5% to 56.6±0.47% and operculum ash from 31.4% to 48.2±0.56% of fat free dry matter with increasing dietary phosphorus content. Phosphorus requirement was estimated by using a quadratic equation for vertebrae ash. The data suggest that a diet of 0.96% total phosphorus, or 0.72% available phosphorus or 0.34 g available phosphorus per MJ DE, is required for haddock fingerlings. Plasma and urinary phosphate excretion increased with increasing dietary phosphorus levels and ranged from 0.4–1.5±0.03 to 0.1–7.9±0.2 mmol−l, respectively. The availability of organic phosphorus was 43.2±0.86%, however, inorganic phosphorus was highly available (99±1.23%). Signs of phosphorus deficiency were characterized by poor growth, loss of appetite, poor bone mineralization, deformed vertebrae and an increase in body lipid content.