Journal of National Fisheries University

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Viral edema of carp (VEC) caused by the carp edema virus (CEV) causes economic losses for Japanese koi farms. In this study, we investigated the infectivity and pathogenicity of a domestic CEV isolate (genogroup IIa) in koi carp, common carp and goldfish. The challenge test consisted of 9 groups (n = 15):3 groups each of koi carp, common carp, and goldfish, at 15, 20 and 25℃. These groups were challenged with CEV (3.0×10^3 copies/µL) in duplicate. All koi carp died in the 15 and 20℃ groups, but all survived in the 25℃ group. The surviving koi carp in 25℃ groups showed high PCR positive rates of 66.7 and 73.3%, with VEC histopathological changes observed. For the common carp, 1 and 2 fish died in the 20℃ groups, but no deaths or VEC symptoms were observed in the 15 and 25℃ groups. In all common carp groups, PCR-positive fish were observed along with histopathological changes. For all goldfish groups, no deaths or VEC symptoms were observed. As with the common carp, PCR-positive fish were found in all goldfish groups, yet no VEC histopathological changes were detected. These results demonstrate infectivity of this CEV strain in koi carp, common carp, and goldfish, but low pathogenicity in common carp and goldfish.
Matsumoto Akane Honda Kotaro Takahashi Hiroshi Kondo Masakazu Yasumoto Shinya
PP. 73 - 80
Embryonic development in giant cuttlefish Sepia latimanus was studied using eggs laid from broodstocks reared in captive condition. 26 embryonic stages were examined in this study and the detail process of organ development was clarified under microscope observation. Blastdisc was visible at the animal pole on the yolk at 2.5 hours after fertilizaton (HAF). The first cleavage occurred at 8.6 HAF. Then embryo developed to the morula stage at 22 HAF. Almost surface of the egg was covered with blastoderm at 10 days after fertilization (DAF). Primordia of main organs such as arms, mouth, mantle, funnel, optic vesicle, gills, statocyst, lens and optic ganglion were formed till 14 DAF. At 15 DAF calcification began in the first striation on the shell. Primordium of the shell became visible at 18 DAF. The number of striations on the shell reached to 5, 9 and 14 at 26, 32 and 40 DAF, respectively. Embryo needed 45 days for hatching. Newly hatched larva was 14 mm in mantle length and had 18 striations on the shell. The process of embryonic development in S. latimanus was very similar as S. lycidas, S. esucurenta and Sepiella japonia. S. latimanus is characterized with large newly hatched larva in Japanese sepiids. It was revealed that the large yolk of S. latimanus induces the growth of the body over a long period in the embryonic stage.
Oka Masakazu Tezuka Nobuhiro
PP. 81 - 87