Abstract
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 sporocyst and 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 $4.0-4.3{\times}0.2-0.21\;mm$ insize, and the cercaia with 27 pairs of setae, each seta consisting of 6 tufts, was $270{\times}147{\mu}m$ in body size and $550{\times}52{\mu}m$ in tail size. Oral sucker($52{\times}42{\mu}m$), pharynx, vental sucker and two testese were obviously seen within the cercaria. The excretory vesicles 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 regardlless 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 $28.0\%\;at\;28.0^{\circ}C$ water temperature in July and the lowest $2.4\%\;at\;19.5^{\circ}C$ in October, and it increased in proportion to the shell length on the host. But cercaria was not detected at below 4.0 cm in size of the host. Mature cercariae were found 6 months from May to October when water temperature was above $19.5^{\circ}C$. On the other hand, when water temperature was below $19.5^{\circ}C$, only immature cercariae and sporocysts were found. The cercariae were active for 35 hours and survived for 71 hours at $20^{\circ}C$, and 29 and 34 hours at $25^{\circ}C$ respectively, whereas the cercariae were inactive at less than $20^{\circ}C$ 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. $420{\times}310{\mu}m$ in size, 15 days afer infection. The infection rate of metaceria to shrimp in the laboratory was highest, at $25^{\circ}C$ being $61\%$ and at $20^{\circ}C\;17%$. 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 $26.5^{\circ}C$ in June, and low $1.56-2.5\%$ at $28-29.5^{\circ}C$ 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, $440-520{\times}310-360{\mu}m$ in size, within the intestine of Konosirus punctatus 20 days after infection. The adult worm was oval shape and $20-24{\times}11-20{\mu}m$ 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 the 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 harengulae.
서해안 금강하구의 내초도에서 1980년 7월부터 1983년 10월까지 맛조개(Solen strictus)의 생식소에 기생한 Bacciger 속 cercaria의 생활사를 구명하고자 sporocyst 및 cercaria의 형태와 발육과정, 기생률을 조사하였다. 또한 제이중간숙주 및 종숙주를 실험실에서 인공감염실험과 함께 내초도자연환경구에서 조사하여 metacercaria와 성충의 발육과정을 조사 연구한 결과 지금까지 밝혀진바 없는 Bacciger harengulae의 생활사가 구명되었다. Bacciger harengulae는 맛조개, 대합, 바지락, 띠조개가 제일중간숙주이고, 밀새우를 제이중간숙주로 하며, 종숙주는 전어, 밴댕이로 밝혀졌다. 맛조개의 생식소에 기생된 성숙한 sporocyst의 크기는 $4.0{\sim}4.3{\times}0.20{\sim}0.21$ mm이고, cercaria는 체부 $270{\times}147{\mu}m$, 미부 $270{\times}147{\mu}m$의 크기로서 꼬리 양측에 27쌍의 강모속과 1개의 강미속은 6본의 가닥으로 되어있다. cercaria의 체내에는 구흡반($52{\times}42{\mu}m$), 인두($32{\times}25{\mu}m$), 복흡반($52{\times}50{\mu}m$)과 2 개의 정소와 V자형의 배설낭이 뚜렷이 나타나며, 화염세포식은 2[(3+3)+(3+3)]=24이다. 3년에 걸쳐 맛조개에 기생하고 있는 cercaria의 평균 기생률은 $9.67\%$ 였는데, 이것은 수온의 변화와는 관계없이 연중기생된다. 기생률이 가장 높은 시기는 수온 $28.8^{\circ}C$인 7월($28.0\%$)이고, 가장 낮은 시기는 수온 $19.5^{\circ}C$인 10월($2.4\%$)이었다. 맛조개의 cercaria 기생률은 각장이 클수록 높았으며, 4.0cm 이하에서는 cercaria가 검출되지 않았다. cercaria가 성숙되는 시기는 년중 수온이 $19.5^{\circ}C$이상 상승하는 $5{\sim}10$월까지며, 수온 $19.5^{\circ}C$이하가 되면 미숙한 cercaria만이 검출된다. Cercaria는 수온 $20^{\circ}C$에서 35시간, $25^{\circ}C$에서는 29시간까지 활력이 있었으며, 생존시간은 각각 71시간, 34시간이었으나 $20^{\circ}C$이하에서는 운동력이 활발하지 못하였다. 맛조개에서 유출된 cercaria를 밀새우에 감염시킨 결과 2{\sim}3시간후에 근육에 기생하였고, 기생한 cercaria는 $7{\sim}8$시간후에 cyst를 형성하였으며, 15일이 경과되어 $420{\times}310{\mu}m$의 성숙한 metacercaria로 발육되었다. 실험실에서 수온 $20^{\circ}C$일때 밀새우의 metacercaria 감염률은 $17.0\%$ 이었고, $25^{\circ}C$때는 $61.0\%$의 높은 감염률을 나타냈으며, 감염된 부위는 제일복절, 두흉부, 제이, 삼, 오복절의 순으로 감염되었다. 내초도의 자연 서식장산 밀새우의 metacercaria 감염률은 수온 $26.5^{\circ}C$인 6월에 $9.6{\sim}11.11\%$, 수온 $28{\sim}29.5^{\circ}C$인 7,8월에는 $1.56{\sim}2.50\%$의 감염률을 나타냈다. metacercaria가 감염된 밀새우를 사육중인 전어에 먹인 결과, 20일후 전어의 장에서 $440{\sim}520{\times}310{\sim}360{\mu}m$의 성충으로 발육되었고, 성숙한 충난은 $20{\sim}24{\times}11{\sim}20{\mu}m$ 크기의 타원형이었다. 실험실에서 검출한 것과 동일한 성충이 내초도의 자연산 전어, 밴댕이에서도 체장과 관계없이 $87.3{\sim}100\%$(평균 $95.2\%$) 검출되었으며, 6, 7월에는 $100\%$ 검출되나, 8, 10월에는 $87.3{\sim}88.9\%$로 그 검출률이 낮아졌다. 전어에서 발육된 성충의 크기와 내부형태를 Yamaguti(1938)가 밴댕이에서 검출한 것과 비교한바, 동일하므로 이 흡충을 Bacciger harengulae로 동정하였다.