Effect of fishmeal replacement by hydrolyzed feather meal on growth performance, proximate composition, digestive enzyme activity, haematological parameters and growth-related gene expression of gilthead seabream (Sparus aurata)

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.