抄録
As is well known, the eggs of Ayu, after being spawned, attach to gravel of stream beds by their adhesive membranes, thus tolerating current action. But little work has been done concerning their adhesive power.
In the present study, the authors attempted to estimate the adhesive power of Ayu eggs by means of two different methods. The first method consisted of determining the critical level of current velocity above which eggs could no longer maintain their position, by exposing sample of eggs attached to the inner wall of small glass tubes to water flows of varying velocites. The second method consisted of picking up sample of eggs adhere to gravel by forceps one by one and measuring the weight of the gravel which could be just raised by being supported by the adhesive membrane.
These two methods gave similar results which were summarized as follows. The adhesive power of Ayu eggs ordinarily lay between 200 and 500 dynes, although they were varied according to spawners and spawning conditions, but not the stage of development of eggs themselves, ranging from 180 to 1345 dynes.
According to the present authors' observations (unpublished), on the other hand, the current velocity in the bottom layer of the spawning bed of Ayu is generally below 40cm. per second. The hydraulic pressure which would be given to the egg by this current velocity is estimated to be less than 500 dynes. Hence, the adhesive power may be said to be well adapted to the surrondings.
