ハマチの外部寄生吸虫Benedenia seriolaeの生態に関する研究 : Ⅰ. 夏季における成長，産卵などについて

Studies on the biology of Benedenia seriolae, an ectoparasitic trematode on the yellowtail : I. on the growth and spawning of the fluke in summer

Kasahara Shogoro

広島大学水畜産学部紀要

Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University

　ハマチの外部寄生吸虫Benedenia seriolae の生態について，その多数の寄生がみられた小割養殖場のハマチを用いて研究を行ない，これまでに次のような結果を得た.
1) 夏季(水温22°-26℃)においては虫体長は直線的に増加し，寄生初期0.5mm のものが寄生後20 日間で約5.8mm (成熟)に成長した.
2) 休形は成長lこ従って変化し，体幅の体長に対する割合は寄生初期は約40%で細長いが，体長4.8mmに達したものでは約60%となり成虫体形を示した.
3) 産卵は体長5.4mm 以上に達したものに多くみられ，その平均産卵数は5.8mm 前後のものでは170 ， 6.7 mm前後では245 であった.
4) 生育適温の高温限界は約29℃ であると認められた.

The author has been carrying out some biological studies on Benedenia seriolae with the aim of finding effective method for controlling the fluke. Observation has been made on this ectoparasite infecting the yellowtail in the fish-culture farms in Shizuoka Prefecture. Following results have sofar been obtained with special emphasis on the growth and spawning of the fluke during the summer.

1) At water temperatures of 22-26°C, the fluke attaching to the skin of host fish appears to grow in body length almost linearly in relation to time, since it was observed that the young fluke which measured about 0.5mm shortly after attachment attained the body length of about 2.8, 4.7 and 5.8 mm respectively in 10, 15 and 20 days.

2) The shape of the fluke gradually changes with growth; for instance, the ratio of body breadth to body length was 0.4 in the young with body length of 0.5 mm, while it was 0.6 in the individuals measuring 4.8mm in body length and resembling the adult in body shape.

3) The spawning of the fluke was observed in the mature individuals 5.1-7.1 mm in body length which were separated from host fish and kept alive in glass vessels for a few days. Average number of the eggs laid by each individual was 170 in the group of smaller flukes (about 5.8 mm) and 245 in the group of larger flukes (about 6.7 mm). It was also inferred that the fluke continues to grow in body size
after attainment of maturity and spawns several times.

4) The fluke infecting the skin of host fish is apparently inaffected by water temperatures upto 28°C, but the majority leaves the host to die when exposed to temperatures of 29-30°C for 24 to 41 hours. Therefore, it may be that detachment of the fluke is caused at water temperatures of about 29°C and above.

Fishing industry. Fisheries [ 660 ]

jpn

広島大学水畜産学部

[ISSN] 0440-8756

[NCID] AN00213563