Bacciger harengulae의 生活史에 關한 硏究

Studies on the Life History of Bacciger harengulae

The cercaria of Bacciger herengulae which is parasitized on the gonad of solen strictus was investigated in order to reveal its entire life history. The area covered for the study was in the vicinity sea of Naechodo, the estuary of the Kum river in the western coast of Korea during the period of 1980-1983. Morphology and development as well as infection rates of sporocystand cercaria within solen strictus were examined. For accomplishing the objectives of this study, an artificial infection experiment and some investigations on the second intermediate host, the final host and the growing stages were also studied in both laboratory and natural habitat of Solen strictus. According to the study, it was revealed that the first intermediate hosts were Meretrix lusoria, Solen strictus, Tapes japonica and Laternula limicola, the second intermediate host was Palaemon(Exopalaemon) carinicauda and the final hosts were Konosirus punctatus and Harengula zunasi. A mature sporocyst which was found in the gonad of Solen strictus was 4.0X0.2-0.21mm insize, and the cercaia with 27 pairs of setae, each seta consisting of 6 tufts, was 270X147μm in body size and 550X52μm in tail size. Oral sucker(52X42μm), pharynx, vental sucker and two testese were obviously seen within the carcaria. The excretory vesicies of cercaria were in V-shape and the flame cell were formula was expressed as 2[(3+3)+(3+3)]=24. The infection of cercaria in the first intermediate host, solen strictus, was found throughout the year regardless of the water temperature, and its mean infection rate was 9.67% during the study period. The infection rate fluctuated with temperature, the highest being 28.0% at 28.0℃ water temperature in July and the lowest 2.4% at 19.5℃ in October, and it increased in proportion to the shell length on the host. But cercaria was not detected at below 4.0cm in size of the host. Mature cercariae were found 6 months from May to October when water temperature was above 19.5℃. On the other hand, when water temperature was below 19.5℃, only immature cercariae and sporocysts were found. The cercariae were active for 35 hours and survived for 71 hours at 20℃, and 29 and 34 hours at 25℃ respectively, whereas the cercariae were inactive at less than 20℃ in water temperature. Cercaria, from Solen strictus, approached shrimp of 1-3 cm in body length as its second host. Then, it began to intrude in to the muscle of shrimp after 2-3 hours. The infected cercaria formed cyst after 7-8 hours, and became mature metacercaria, 420X310μm in size, 15 days after infection. The infection rate of metaceria to shrimp in the laboratory was highest, at 25℃ being 61%, and at 20℃ 17%. The infection rate of metacearia in shrimp was highest in the first abdominal segment, followed by cephalothorax, the second, and fifth abdominal segments, and in that order. Also, the infection rate of metacercaria in wild shrimp was high 9.6-11.1% at 26.5℃ in June, and low 1.56-2.5% at 28-29.5℃ from July to August. The infected shrimp with metacercaria was experimentally fed to Konosirus punctatus in the laboratory in order to know its final host. The metacercaria developed into the adult worm, 440-520X310-360μm in size. The infection rate of adult worm to Konosirus punctatus and Harengula zunasi ranged 87.3 to 100%, the mean being 95.2%, regardless of body length of their hosts. The infection rate was 100% in June and July, but it decreased in September and October. The size and body structure of the trematode observed during the present study were well agreed with those ievestigated by Yamaguti(1938) thus, it may be concluded that the adult worm it identified as Bacciger haregulae.