34 



T. XISHTKAWA. 



causing the red coloration of the sea on the shore of Bombay. According 

 to Dr. WhiteJegge the cause of discolored water of Australia in 1891 was 

 Glenodinium rubrum. In 1893, Dr. Mead discovered a species of 

 Gymnodenium in the "red-water" of Narragansett Bay, Mass , U. S. A. 



Usually the appearance of discolored water is accompanied by a great 

 mortality among fishes, mollusks and shrimps. According to the 

 observation of a pearl-oyster culturist, in the later part of August, 1899, 

 large streaks and patches of yellowish-red water floated about with the tide 

 in the Bay of Toba. Fishes, which were kept in baskets floating on the 

 surface of the sea, were damaged by them. Fishermen easily caught 

 the littoral fishes by spearing, for the fishes had became very sluggish 

 in the discolored water. Even Haliotis or Ear-shell seemed to suffer. 



Bat whether the presence of minute organisms, the Peridiniales,^? - 

 se is the immediate cause of this mortality or not is uncertain. I put 

 some pearl-oysters, Meieagrina martensii, in the most highly colored 

 water kept in a porcelain jar. After 24 hours, I found that they 

 suffered no injury, although the water was still swarmed with 

 Gonyaulax. A simillar effect was obtained by Dr. Mead with 

 Gymnodenium. I observed that the stomach of the pearl-oysters 

 was filled with Gonyaulax and many empty shells were found in 

 the intestine, which shows that Gonyaulax forms suitable food for the 

 pearl-oysters, although these usually feed upon the Bacillariaceae. Thus 

 the presence of Peridiniales, it appears to me, can not be the immediate 

 cause of the destruction of fishes. The water which is fitted for the 

 sropagation of Peridiniales and unsuitable for the existence of the usual 

 plankton, is probably also unsuitable for the fish life, or the dead bodies 

 of an enormous numbers of peridiniales sinking to the bottom decompos- 

 ing and putrifying there may eventually become injurious to other 

 organisms. This point however needs further examination. 

 Imperial Fisherus Bureau, 

 Tokyo. 



