This experiment was conducted to investigate the effects of excessive dietary chromium on growth performance, glucose metabolism, oxidative stress and immune responses in juvenile shrimps of Macrobrachium rosenbergii.Four isonitrogenous and isoenergetic diets were designed with chromium picolinate (Cr-Pic) at lev-els of 0 (Cr0),20 (Cr20),40 (Cr40),and 50 (Cr50) mg/kg.A total of 240 shrimps with an average body weight of (3.48±0.12) g were randomly distributed into four groups with four replicates of 25 shrimps per a-quarium and fed experimental diets for 28 days.Crowding stress was conducted in each group with ten shrimps (40 g/L)after 24 h starvation.The results showed as follows: (1) compared with the Cr0 group, excessive chromium supplementation significantly depressed the terminal length, final weight, and survival rate (SR) of shrimps.The shrimps fed a diet containing 50 mg/kg chromium exhibited lower specific growth rate (SGR) and condition factor(CF) declines.The cumulative death rate in each group increased with increasing chromi-um concentrations under the sustained crowding stress for 96 h.(2) In the hepatopancreas,the glucose metabo-lizing enzymes showed a declining tendency with the elevation of dietary chromium concentration.The hexoki-nase (HK) and pyruvate kinase (PK) activities both in the Cr40 group and Cr50 group were significantly low-er than those of the Cr0 group at 14 d, and the phosphofructokinase (PFK) activity of the Cr50 group was significantly lower than the other groups at 28 d.Lactic dehydrogenase (LDH) and succinate dehydrogenase (SDH) activities in excessive chromium supplementation groups also significantly decreased at 14 d.The phos-phoenolpyruvate carboxykinase (PEPCK) activity decreased as chromium concentration increased,and the PEPCK activities of the Cr40 and Cr50 groups were significantly lower than those of the Cr0 group at 28 d.In muscle, the glucose metabolizing enzymes increased with the increasing concentration of chromium at 14 d, while suppression of enzymes appeared at 28 d.(3) The catalase (CAT) activity in the Cr20 group and CAT and glutathione peroxidase (GSH-PX) activities in the Cr40 group also significantly decreased at 28 d.How-ever, the activities of CAT, GSH-PX and superoxide dismutase (SOD) in the Cr50 group significantly de-creased in this trial.The malondialdehyde (MDA) contents in the Cr20 and Cr40 groups were significantly higher than those in the Cr0 group.In addition, the acetylcholinesterase (AChE) activity decreased with the increasing chromium concentration and was significantly lower than that of the Cr0 group at 28 d.(4) The ly-sozyme (LZM) activity at 14 d, alkaline phosphatase (AKP) and acid phosphatase (ACP) activities at 28 d of the Cr50 group were significantly lower than those of the Cr0 group.Consequently, it is suggested that ex-cessive chromium inclusion in diet may lead to obvious suppression of glucose metabolism, antioxidant capaci-ty, and the immune system, thus inhibiting the growth performance and survival rate of M.rosenbergii.
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