of the Fishery Board for Scotland. 



43 



Provisional Conclusion. 



In reviewing the above work, the micro-organisms found present were : — 

 I. Vibrio-like bodies in all the superficial lesions, but which were not 

 found in any of the cultures, nor in sections. 



II. Micro-cocci ; chiefly staphlococcus pyogenes aureus in all the super- 



ficial lesions examined, and in the blood in most cases in pure 

 culture. 



III. The Bacillus Coli Communis in the superficial lesions and also in 



cultures from these. 

 Consequently, since these micro-organisms are so closely identified with 

 sewage, it is difficult to avoid the conclusion that the fish had died from 

 some form of septicemic poisoning, and possibly caused by infection from 

 these sewage-borne micro-organisms. 



How Infection may Take Place. 



Johnston, Fisheries Laboratory, Liverpool, informs me that a few years 

 ago he observed at Port Erin a similar epidemic, and that the signs and 

 progress of th'e disease was very similar to that which I have described in 

 this paper. A large number of the plaice impounded in the spawning pond 

 died rapidly from some apparently infectious disease. He came to the 

 conclusion that the- disease was due to a fungus, and that it was probably 

 conveyed to the fish by means of insects, of which large numbers floated 

 about on the surface of the pond. 



Johnston also informs me that he has frequently observed how readily 

 superficial ulceration follows in fish which have received the slightest 

 external injury, even from trivial surface lesions produced when caught in 

 the trawls. 



Then, as marine fish approach inshore they must become more liable, 

 through various causes, to receive small superficial abrasions, which may be 

 just sufficient to allow micro-organisms to find a lodgment ; and that this 

 will more readily occur in the neighbourhood of sewer outlets into the sea 

 has frequently been observed by M'Intosh and others, who have noted the 

 remarkable influence which such outlets have in attracting fish to such areas. 



Thus, while infection by contact in the open sea is possible, there is 

 greater opportunity for such to take place inshore, especially in the vicinity 

 of sewage outlets, and much more so when the fish are confined in tanks. 



On the other hand, although it appears that fish may be very susceptible 

 to external microbal attacks through superficial lesions, it appears that they 

 can swallow great numbers of bacteria with apparent impunity. 



Many fish feed directly on sewage when available, and especially many of 

 the Crustacea, the smaller and often microscopic forms of which, such as the 

 Copepoda, may be said to act as the scavengers of the sea shore. They feed 

 almost entirely on sewage, and are present in vast numbers, and in their turn 

 they become one of the chief sources of the food supply for the larger fish. 



Further, we know that fresh-water fish must swallow large numbers of 

 bacteria in so many sewage-polluted streams. 



Again, in an article on the " Decomposition of Fish and its Detection," 

 which appeared in the Twenty-sixth Annual Report of the Fishery Board for 

 Scotland, I pointed out that marine fish which were caught near the shore 

 or the mouths of inland rivers, or near the discharge of sewage effluents, 

 contained large numbers of bacteria of the sewage type, and which were 

 readily isolated from the intestinal contents, whereas in proportion to the 

 distance out at sea at which the fish are caught the bacteria decreased ; and 

 in fish caught far out at sea, or in a sewage-free locality, very few such 

 micro-organisms could be detected. These results were generally in accor- 

 dance with those of Houston, and in close agreement with those .of Eyre, 

 D 



