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 parts per thousand) at a temperature of 12 +/- 2 degreesC. 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(-1), 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. Crown Copyright (C) 2003 Published by Elsevier Science B.V. All rights reserved.