82 DEPARTMENT OF THE NAVAL SERVICE 



6 GEORGE V, A. 1916 

 NATURE OF THE DISEASE, 



Fishermen were agreed as regards the symptoms and general appearance of the 

 dead and dying fish. Many saw sores, abrasions, and discoloured spots, especially on 

 the caudal third of the body. A fisherman who owns a salmon stand on North Beach, 

 Richibucto harbour, "dipped" a quantity and sent them to his family, but numbers 

 were found unfit for the table. The disease was most evident in the flesh of the 

 caudal peduncle. 



The schools were described as crowding into very shallow water, and their move- 

 ments were feeble, irregular, and similar to what might be expected of exhausted and 

 dying fish. 



CONDITIONS. 



The spring had been late. Cold weather had continued far into June and even the 

 average July weather was cooler than usual. The spring run of coast herring was the 

 poorest for years — the fishery a failure at many points along the coast. Predaceous 

 fishes were no more numerous than in other years, though cod were found closer in- 

 shore than usual, and generally refused bait, but were caught freely in salmon nets, 

 an unusual occurrence. In July, jelly-fish were exceedingly abundant, surpassing any- 

 thing known for years, but it does not seem they were much in evidence during the 

 herring epidemic. The lobster catch, above the average up to the time the herring 

 appeared, suddenly fell off, and even the ubiquitous, greedy crab failed to enter the 

 traps. Food was probably in abundance, the herring dying in the off shore waters as 

 well. No schools of squid were seen. 



MATERIAL. 



As already remarked, I was able to secure two dead fish only and the caudal part 

 of a third; which, on examination, proved exceeding interesting; and, taken in con^ 

 nection with some of the facts referred to above, leaves little room for doubt that 

 they were victims of the general infection. The specimens were 17-5 and 18 cm., 

 respectively, in length, and the tail fragment probably belonged to one of the same 

 size and age. One had a sore on the side of the caudal peduncle near that fin, which 

 communicated with a canal-like cavity, extending forward under the lateral line 

 nearly the whole length, but here and there broken into two parallel cavities. No 

 opening occurred on the opposite side, nor was there any on the second fish; but a 

 series of dark patches were seen on all, and dissection revealed the open passages 

 everywhere under the lateral line. The fragment had an opening and a cavity extend- 

 ing forward. The three fish had died of a disease similar to that affecting the fish 

 referred to by the salmon fishermen. 



The location and appearance of these cavities are shown in figs. 3 and 4. Com- 

 paring them with 5, they are seen to occupy the region of the " red meat " or the 

 highly vascular and nerve tissue beneath the lateral line, which is especially rich in 

 lymph and blood. The walls of these cavities and the adjacent muscular and vascular 

 tissue were largely a mass of minute microscopic organisms of extraordinary protean 

 forms (see figs. C to 18, inclusive) and members of that group of parasitic protozoa 

 known as the Myxosporidia. They are credited with being the cause of widespread 

 epidemics among fish and other animals. They infest the tissues of the body of 

 their hosts, multiply rapidly and in many cases become lethal, death being due appar- 

 ently to the gradual exhaustion of the system and certain toxic effects. The para- 

 • site was not by any means confined to the tissues mentioned, but occurred in the 

 liver, the kidneys, intestinal tract, and abundantly in the blood found coagulated in 

 the sinuses and auricle. 



The method of infection is not fully known, but is believed to be by the mouth 

 and intestinal tract. The minute spores may be swallowed directly by the fish, taken 



