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A 70-day feeding trial was conducted to ascertain the effects of threonine on immune response of juvenile oriental river prawn (Macrobrachium nipponense). Six isonitrogen and isolipidic feeds were formulated according to levels of dietary threonine (0.35%, 0.79%, 1.18%, 1.67%, 2.08% and 2.48% respectively). The juvenile prawns were divided into six groups with four replicates, and stocked into 24 tanks with 50 prawns per tank (initial weight 0.20 ± 0.02 g). The results showed a significant increasing trend of final body weight, specific growth rate, protein efficiency ratio, and weight gain rate when threonine levels increased to 1.67% (P 0.05). However, feed intake, feed conversion ratio, and whole-body lipid composition significantly decreased as threonine levels in the feed increased up to 1.67% (P 0.05). Moreover, haemolymph N-urea content was significantly lowest at 1.67% threonine level (P 0.05), whereas glucose was highest at 0.79% followed by 1.67% of threonine levels in the feeds. Aspartate aminotransferase (AST) enzyme activities were significantly decreased by an imbalance (except 1.67%) of threonine in the feed (P 0.05). Activities of Alanine aminotransferase (ALT) and albumen (ALB) were not significantly affected by threonine in the feed (P 0.05). Excessive dietary threonine level (2.48%) significantly activated haemolymph catalase (CAT) activity (P 0.05), whereas malondialdehyde (MDA) content was significantly affected by deficient (0.35% and 0.79%) dietary threonine levels (P 0.05). Inducible nitric oxide synthase (iNOS) activity and haemolymph complement component 4 (C4) content were significantly decreased by deficient levels of threonine in the feed (P 0.05). Excess threonine concentration significantly down-regulated Toll, Dorsal, Relish, and heat shock protein 60 (Hsp60) gene expressions in the hepatopancreas of M. nipponense (P 0.05), while all genes were significantly up-regulated by the optimal (1.67%) threonine level (P 0.05). The threonine level at which maximum specific growth rate of M. nipponense occurred was estimated by second degree polynomial regression analysis as 1.65% of threonine level, equivalent to 4.44% dry weight bases of protein in the feed. more...