After grass carps Ctenopharyngodon idellus were injected with cortisol, with (CBC) and without (C) a cocoa butter carrier, the effects of both slowly and rapidly acting exogenous cortisol on their non-specific immune functions were investigated. On the one hand, after injection with CBC, the cortisol concentration and lysozyme activity in fish serum were enhanced and were sustained at high levels for a long period (30 days). The killing activity in the serum declined with time, and phagocytosis of head kidney macrophages diminished significantly (P < 0Á05 or P < 0Á01). The leukocrit values in the high dose group (31Á8 mg cortisol fish À1) increased over time, however, with the maximum average being 5Á6% at day 30. The spleen mass index in the high dose group was 0Á93 Â 10 À3 after 30 days, notably lower (P < 0Á05) than that in the control group. In addition, a decrease in resistance to Aeromonas hydrophila infection in cortisol-treated fish was shown, with the final cumulative mortalities being 54Á5 and 66Á7% in the low and high dose groups, respectively. On the other hand, there was a decrease in both serum cortisol concentration and lysozyme activity of the experimental fish within 2 weeks after injection with C, where plasma bactericidal activities in the high dose group (31Á8 mg cortisol fish À1 ) were remarkably lower (P < 0Á01) than those in the control group at each sampling, but were increased slightly over time. The results of which were different from those in the CBC trial. Phagocytic activity of head kidney macrophages and spleen mass index decreased significantly (P < 0Á05), while there were increases in leukocrit value and cumulative mortality due to A. hydrophila. The results of which were similar to those in the CBC trial. This study indicated that the injection of cortisol depressed the non-specific immune functions of the grass carp and increased its susceptibility to disease.

S U M M A R YA copper/zinc superoxide dismutase (Cu/ZnSOD) gene and a manganese superoxide dismutase (MnSOD) gene of the human parasite Clonorchis sinensis have been cloned and their gene products functionally characterized. Genes Cu/ZnSOD and MnSOD encode proteins of 16 kDa and 25 . 4 kDa, respectively. The deduced amino acid sequences of the two genes contained highly conserved residues required for activity and secondary structure formation of Cu/ZnSOD and MnSOD, respectively, and show up to 73 . 7% and 75 . 4% identities with their counterparts in other animals. The genomic DNA sequence analysis of Cu/ZnSOD gene revealed this as an intronless gene. Inhibitor studies with purified recombinant Cu/ ZnSOD and MnSOD, both of which were functionally expressed in Escherichia coli, confirmed that they are copper/zinc and manganese-containing SOD, respectively. Immunoblots showed that both C. sinensis Cu/ZnSOD and MnSOD should be antigenic for humans, and both, especially the C. sinensis MnSOD, exhibit extensive cross-reactions with sera of patients infected by other trematodes or cestodes. RT-PCR and SOD activity staining of parasite lysates indicate that there are no significant differences in mRNA level or SOD activity for both species of SOD, indicating cytosolic Cu/ZnSOD and MnSOD might play a comparatively important role in the C. sinensis antioxidant system.

SummaryA wrap method adaptation combined with AutoCAD2005 and Scion Image for Windows were used to determine the surface area of a fish. Compared with the corresponding r 2 and F of many models, the most accurate formula: S = 752.15W 0.675 (r 2 = 0.999, F = 18362.94, P < 0.0001) for estimating the surface area of common carp was obtained. Similarly, the fin formula: S = 1834.12W 0.708 (r 2 = 0.992, F = 2690.47, P < 0.0001) was also obtained for the same purpose. It was proven that these two formulae gave good estimates of surface and fin areas of four strains of common carp: Yellow-river carp, fancy carp, mirror carp and Xingguo red carp.

Redescription of Myxobolus pyramidis Chen, 1958, from gill lamellae of allogynogenetic gibel carp, Carassius auratus gibelio (Bloch), is presented in this paper to complete Chen's description. The diagnostic characters of the myxosporidia are: ovoid round, greyishwhite polysporous plasmodia, averaging (159±21)×(72± 6.5) μm in size; spore pyriform in front view with smooth surface and symmetrical valves, convex-shaped in sutural view with straight and thick sutural line, averaging (10.5±1.1)×(10.3±0.9)×(6.1±0.2) μm in size; two equal pyriform polar capsules averaging (5.5±0.7)× (3.5±0.2) μm in size with distinct intercapsular process and polar filament wounded in five to six coils. The histological effects of the pathogen were observed by light microscopy, and the parasite-host relationship was discussed.

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Neutralizing complement C9 in grass carp Ctenopharyngodon idella sera with rabbit anti-C9 sera against fish complement C9, demonstrated that bactericidal activity against Aeromonas hydrophila of the C9-deficient fish sera was greatly impaired. These results indicated that the fish complement C9 plays a key role in pathogen killing through the lytic pathway.