Quantifying the dietary potassium requirement of subadult grass carp (Ctenopharyngodon idellus)

Abstract

A growth trial lasting for 12 weeks was conducted in a semi flow-through system to determine the dietary potassium requirement of juvenile grass carp (Ctenopharyngodon idellus) with an initial body weight of 4.8 g. Seven isonitrogenous and isoenergetic semi-purified diets were compounded with different dietary potassium levels: 1.50, 2.32, 3.28, 5.30, 7.12, 9.45 and 10.44 g kg(-1) diet. The results showed that specific growth rate and feed efficiency of grass carp were significantly (P 0.05). The Na+-K+ ATPase activity value in the gills varied significantly (P 0.05). Body potassium and moisture contents increased and lipid content decreased with dietary potassium content, while ash content in fish body increased first and then decreased as potassium content increased (P < 0.05). Body protein in the 10.44 g kg(-1) group was significantly lowered (P < 0.05). However, calcium, magnesium, phosphorus and sodium contents in dry matter were not affected by dietary potassium level. When the potassium content of water was 1.86-3.10 mg L-1, judging from the polynomial regression analysis for the specific growth rate of fish and the Na+-K+ ATPase activity in the gill, and the broken-line analysis for body potassium content, the optimal dietary potassium content for juvenile grass carp was 4.65, 7.27 and 5.98 g kg(-1) diet respectively. (C) 2014 Elsevier B.V. All rights reserved.