Studies on a New Trypanorhynchan Larva, Callotetrarhynchus sp., Parasitic on Cultured Yellowtail-II
On the Source and Route of Infection
1969 Volume 35 Issue 4 Pages 351-357
Details
1969 Volume 35 Issue 4 Pages 351-357
Anchovies, Engraulis japonica (HOUTTUYN), in the Bungo Channel and the Sea of Suo and Iyo havour frequently a white worm of 14-48×1.6-4.0mm in size in their body cavities (Fig. 1). This anchovy worm resembles closely a nematode-shaped paratite which is occasionally found in the body cavities of yellowtails in farms in the Bungo Channel area and is suspected to be a immediately previous stage of the plerocercus of a new species of the genus Callotetrarhynchus1). Anchovy is a main feed for the yellowtail culture. These facts suggest that the yellowtail bladder worm may come from the anchovy.
In order to study this problem three infection experiments were carried out in different seasons in somewhat different ways and yielded the following results.
(1) The majority of the anchovy worms which were engulfed with feed by yellowtails or forced alone into the stomachs attacked fishes. The infectious rate was 53.8 to 71.5%.
(2) The anchovy worms which had received into the stomach penetrated the stomach wall within a short period of time (Fig. 2 and 3) and moved to various parts of the body cavity. Inactive worms were thrown into the intestine and excreted sooner and later.
(3) The worm settled at any parts of the body cavity were encysted with a tissue membrane from host and developed gradually into plerocercus.
(4) The scolex of the plerocercus was exactly the same as that of Callotetrarhynchus sp. reported in the previous paper1) both in the arrangement and shape of the hooks on the tentacles and in the size and proportions of the bothridium, sheath and musclar bulb.
(5) The activity and develepment of the anchovy worm in the body cavity of yellowtail were thought to be definitely affected by water temperature. The penetration of the worm through the stomach wall required over 4 hours in winter but less than 1 hour in summer, and the formation of the scolex was noticed 25 to 30 days after infection in summer, while not until 50th day in winter.
