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To determine the effects of Cordyceps militaris mycelia and leftover of Cordyceps militaris grain on diease resistance of Pengze Crucian Carp（Carassius auratus） xSeap Carp （Cyprinus acutidorsalis）, the whole experiment is divided into two parts.the firtst part is that fish were fed diets containing 0 （control）, 0.1%, 0.2%, 0.3% Cordyceps militaris mycelia and 1%, 2%, 3% leftover of Cordyceps militaris grain for 30days, and at the 40th day, fish were fed basal diets. The lysozyme activity, the antibacterial activity and antiprotease activity in mucous and serum, the ACP activity in serum, gill, hepatopancreas and spleen, kidney, SOD activity, GSH-Px activity in hepatopancreas , MDA concentration in gill and hepatopancreas, protease activity and amylase activity in intestine were studied at the 0, 10, 20, 30, 40 days of post-feeding.The second part is that fish were fed diets containing 0（control）, 0.1%, 0.2%, 0.3% Cordyceps militaris mycelia and 1%, 2%, 3% leftover of Cordyceps militaris grain for 40days, were injected with Aeromonas caviae CSS-4-2（5.0×l08CFU/ml） at the 40th day. The specific growth rate and mortality rate were studied.The results showed that Cordyceps militaris mycelia significantly increased the lysozyme activity , the antibacterial activity and antiprotease activity in mucous and serum, the ACP activity in serum, gill, hepatopancreas and spleen, kidney, SOD activity, GSH-Px activity in hepatopancreas , and decreased MDA concentration in gill and hepatopancreas. 3% leftover of Cordyceps militaris grain significantly increased the lysozyme activity, antiprotease activity and ACP activity in serum, GSH-Px activity in hepatopancreas, and decreased MDA concentration in gill. 2% leftover of Cordyceps militaris grain significantly increased antiprotease activity in mucous, ACP activity in gill and kidney, GSH-Px activity in hepatopancreas. But no significant differences were observed between experiment and control groups for specific growgh rate , protease activity and amylase activity in intestine. The infection experiments show that all additive except 0.1% Cordycepsmilitaris mycelia and 1%, 2% leftover of Cordyceps militaris grain decreased the death rate challenged by Aeromonas caviae CSS-4-2.The experiment also showed that the function of non-specific immune system and antioxidant system were builduped with the increase of dosage and time, and keeped up for 10 days.Based the experiment, it is induced that Cordyceps militaris mycelia and leftover of Cordyceps militaris grain can increased the resistance of Pengze Crucian Carp （ Carassius auratus ） ×Seap Carp （ Cyprinus acutidorsalis） on diease. 0.1% Cordyceps militaris mycelia and 2-3% leftover of Cordyceps militaris grain were feasible as the additive for anti-disesase food, the additive should be stopped using for 10 days after having been used for 30days.
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