PROGRESS IN BIOLOGICAL INQUIRIES 33 



PATHOLOGY 



As noted in the last report, the bureau, at the request of the East- 

 ern Trout Growers Association, undertook an investigation of 

 the so-called "soft-egg'' disease, which during the last few years 

 has caused serious losses among brook-trout eggs at a number 

 of commercial hatcheries in New England. Owing to the short time 

 during which the disease is prevalent, it was impossible to complete 

 the investigation during the season of 1924. However, it was found 

 that the trouble is due to an external parasite, possibly an ameba, 

 which forms small holes in the egg membrane. A continuation of 

 the investigation was planned for the spawning season of 1925, and 

 for that purpose M. C. James visited some of the hatcheries, but no 

 trace of the disease could be found. With one exception, all the 

 hatcheries reported an entire absence of the disease throughout the 

 season. In the case of the single exception noted, a slight outbreak 

 occurred in one trough late in the season but was quickly brought 

 under control. 



The absence of the disease during the spawning season of 1925 

 from hatcheries in which formerly it was prevalent can only be 

 ascribed to the use of thoroughly sanitary measures, which were 

 adopted on the bureau's recommendation when the disease was 

 found to be due to an external parasite rather than to some obscure 

 cause such as improper food. 



At the request of the Connecticut State Board of Fisheries and 

 Game, Dr. H. S. Davis made an investigation of an outbreak of a 

 little-known fin disease at the State hatchery at Burlington, Conn. 

 This disease apparently has been prevalent for several years at the 

 Windsor Locks hatchery, where it has caused serious mortality, and 

 evidently was introduced into the Burlington hatchery with fish 

 transferred from Windsor Locks. The disease causes the fins to 

 become badly frayed, the dorsal and caudal fins being affected most 

 seriously. 



Owing to the pressure of other work, it was impossible to devote 

 sufficient time to the disease to arrive at any definite conclusion as 

 to its cause. However, the experience of the hatchery staff indicates 

 that the disease can be controlled by the use of a dilute solution of 

 potassium permanganate followed by strong salt baths at frequent 

 intervals. 



POLLUTION 



At the request of the Louisiana State Conservation Commission, 

 Dr. H. S. Davis made an investigation of pollution in the Dorcheat 

 Bayou from the surrounding oil fields, of which there are several. 

 Numerous complaints had been received -Jjy the commission that 

 pollution from the oil wells had resulted in serious mortality of 

 fish in the bayou. It was found that under ordinary conditions 

 pollution from the oil fields was sufficiently dilute so as not to 

 affect the fish in the bayou seriously, although practically all life was 

 destroyed in small tributary streams that drained the oil fields. 

 However, during periods of exceptionally low water, which occasion- 

 ally occur, many fish are killed below the point where the pollution 

 enters the bayou. 



