Protein and energy utilization and the requirements for maintenance in juvenile mulloway (<Emphasis Type="Italic">Argyrosomus japonicus</Emphasis>) |
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Authors: | Igor Pirozzi Mark A Booth Geoff L Allan |
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Institution: | (1) NSW Department of Primary Industries and Aquafin Cooperative Research Centre, Port Stephens Fisheries Institute, Taylors Beach, NSW, 2316, Australia;(2) School of Marine Biology and Aquaculture, James Cook University, Townsville, QLD, Australia |
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Abstract: | This study describes the digestible protein (DP) and digestible energy (DE) utilization in juvenile mulloway, and determined
the requirements for maintenance. This was achieved by feeding triplicate groups of fish weighing 40 or 129 g held at two
temperatures (20 or 26°C), on a commercial diet (21.4 g DP mJ DE−1) at four different ration levels ranging from 0.25% of its initial body weight to apparent satiation over 8 weeks. Weight
gain and protein and energy retention increased linearly with increasing feed intake. However, energy retention efficiency
(ERE) and protein retention efficiency (PRE) responses were curvilinear with optimal values, depending on fish size, approaching
or occurring at satiated feeding levels. Maximum predicted PRE was affected by body size, but not temperature; PRE values
were 0.50 and 0.50 for small mulloway, and 0.41 and 0.43 for large mulloway, at 20 and 26°C respectively. ERE demonstrated
a similar response, with values of 0.42 and 0.43 for small, and 0.32 and 0.34 for large mulloway at 20 and 26°C respectively.
Utilization efficiencies for growth based on linear regression for DP (0.58) and DE (0.60) were independent of fish size and
temperature. The partial utilization efficiencies of DE for protein (k
p) and lipid (k
l) deposition estimated using a factorial multiple regression approach were 0.49 and 0.75 respectively. Maintenance requirements
estimated using linear regression were independent of temperature for DP (0.47 g DP kg−0.7 day−1) while maintenance requirements for DE increased with increasing temperature (44.2–49.6 kJ DE kg−0.8 day−1). Relative feed intake was greatest for small mulloway fed to satiation at 26°C and this corresponded to a greater increase
in growth. Large mulloway fed to satiation ate significantly more at 26°C, but did not perform better than the corresponding
satiated group held at 20°C. Mulloway should be fed to satiation to maximize growth potential if diets contain 21.4 g DP mJ DE−1. |
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