Abstract
Two feeding trials were conducted to examine the replacement of fishmeal (FM) by hydrolyzed feather meal (HFM) in the diet of juvenile gilthead sea bream (Sparus aurata). In trial I (100 days), three isonitrogenous (500 g kg−1 crude protein) and isoenergetic (21 kJ kg−1) diets were formulated, where FM protein was replaced by HFM at 50% (HFM50) and 100% (HFM100), while in trial II (110 days) four diets were formulated using the same FM control diet but FM was replaced at lower levels: 25% (HFM25), and 25% (HFM25+) and 50% (HFM50+) supplemented with lysine and methionine. Juveniles were allocated in quadruplicate and triplicate groups, respectively for trial I and II and fed to satiation 2 times day−1. HFM can successfully replace FM protein at 25% without compromising the feed intake, growth performance, feed utilization and proximate composition of juvenile gilthead seabream. Higher FM replacement levels down-regulated the liver gene expression of the GH/IGF axis and thus reduced the growth performance and nutrient metabolism, although the digestive protease activities and several haematological parameters were unaffected.
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