OBSERVATIONS ON SAPROLEGNIA INFESTING FISHES. 169 



It is by the germination of these zoospores that the fungus chiefly propagates 

 itself. They are asexual and short-lived, but are continually produced in enormous 

 numbers, and are easily carried to their hosts by means of their cilia. The double 

 swarming also favors distribution, and thus tends to render infection more probable. 

 The fungus gains entrance to its host by its germ-tubes, which pierce the tissue. 



Besides the zoosporangia with their zoospores, the Saprolegniacew have another 

 reproductive stage, consisting of autheridia and oogonia, the mature spore form of 

 these being the oospore. In the fungus studied these were never found. They are 

 quite apt, however, to be produced less abundantly than the zoosporangia and zoos- 

 pores, even rarely, according to some authors,* and at special seasons only. While 

 the generic distinctions of this group of fungi are based mostly on the characters of 

 zoosporangia and zoospores, the classification of the species depends almost entirely on 

 the character of the autheridia, oogonia, and oospores. It was impossible, therefore, 

 to determine exactly the species to which this fungus belongs. 



Enough was seen, however, to show that it belonged to what was indiscrimi- 

 nately called Saprolegnia ferax before De Bary's system of classification was proposed. 

 By this author, however, 8. ferax is divided into several distinct species, and with one 

 of these, 8. mixta (as described by Fischer in Rabenhorst's Kryptogamen-Flora), the 

 fungus in question seemed most nearly to agree. During November it was said that a 

 decided change in the appearance of the fungus on affected fish took place. Perhaps 

 if material could have been then obtained, the mature form might have been found. 



In the cultures made a parasite frequently appeared upon the fungus itself. This 

 was what Cornu first called Olpidiopsis saprolegnia'. It belongs to the same great 

 group (Phycomycetes) as does the Saprolegnia. It consisted of oval sporangia devel- 

 oped in the spherically-enlarged ends of the Saprolegnia filaments. The zoosporan- 

 giuin formed a short tube, which pierced the wall of the host filament, and it was 

 through this that the numerous small zoospores escaped. This parasite so enlarged 

 the ends of the filaments it occupied as to make them visible to the naked eye. 



The development of the fungus was of such a character as to render it a serious 

 pest in the aquarium, and various efforts were made by those in charge to lessen its 

 ravages. The tanks were drawn down once or twice a week, but this did not diminish 

 the disease to any great extent. The standard remedy — salt — placed in the bottom of 

 the tanks seemed to lessen the disease, and baths of salt water improved the appear- 

 ance of the fish, destroying the fungus to some extent. Experiments were tried to 

 determine the effect of salt water of different degrees of density on cultures of the 

 fungus. The ordinary sea water of the aquarium was strong enough to cause a shrink- 

 ing and collapsing of the protoplasmic lining of the fungous filaments soon after these 

 were placed in it. Cultures on flies also failed to develop when placed in this water 

 even when considerably diluted ; but in one part of sea water to five parts of fresh 

 a vigorous growth of the inoculated fungus was once obtained. 



No special care had been taken to isolate healthy fish as they were brought in 

 and it was suggested that this measure was wor^h a trial, notwithstanding the fact 

 that an occasional culture had been obtained from the filtered water just before its 

 entrance into the tanks. A tank was consequently selected, emptied, and thoroughly 

 scrubbed throughout, and washed all over with a four per cent solution of carbolic 

 acid. It was then rinsed with fresh aquarium water and emptied, after which it 



•Walpole and Huxley, in Twenty-first Report Inspectors of Fisheries, England and Wales. 



