22 U. S. BUREAU OF FISHERIES. 



there is no evidence that it is very abundant or produces serious 

 injury to the host under natural conditions. However, the un- 

 natural conditions under which the fish are necessarily kept at the 

 hatcheries appear to furnish an ideal opportunity for the develop- 

 ment of the parasite, and consequently it has come to be one of the 

 most serious pests with which the fish-culturist has to deal. Over- 

 crowding undoubtedly is one of the conditions that favor its rapid 

 development, and wherever the fish have been given more room 

 there has been a noticeable improvement in their condition. It is 

 believed that improvement in the food would also help in alleviat- 

 ing the injurious effects of Octomitus, and experiments have been 

 planned with this object in view. 



It has been found recently that excessive mortality, which often 

 occurs during distribution, can be greatly reduced by keeping the 

 fish at a much lower temperature than formerly. In fact, fish from 

 the White Sulphur Springs (W. Va.) station, which in previous years 

 had shown the greatest mortality, were carried at a temperature 

 of 40° F. with very little loss. 



A preliminary paper dealing with this parasite was published in 

 the Journal of Parasitology for March, 1923. 



For a number of years the Neosho station has experienced great 

 difficulty with brood fish. The number of eggs produced often was 

 below normal and of such poor quality that a considerable percentage 

 failed to develop. This was most noticeable among the black bass, 

 especially the smallmouth. Many of these fish failed to spawn, and 

 in some of the ponds practically no fry were produced. This station 

 was visited by the pathologist in May, and it was found that the 

 trouble is, in all probability, due to a cestode, Proteocephalus am- 

 hloplitis. The plerocercoid larvse of this tapeworm were found in 

 large numbers in the ovaries of the smallmouth bass, while the ova 

 had failed to develop normally. The larvse occurred throughout 

 the connective tissues of the viscera, but were much more abundant 

 in the ovaries than in the other organs, and in a number of fish 

 examined were so numerous as to effectually prevent the develop- 

 ment of the ova. The same parasite was found in the largemouth 

 bass, rock bass, and blue-gill sunfish, but was not as abundant in 

 these fish as in the smallmouth. Evidently the ponds furnish ex- 

 ceptionally favorable conditions for the development of the parasite, 

 which has seriously curtailed the output of the Neosho station. 



A small percentage of the halibut taken on the Pacific coast are 

 referred to as " wormy," from the fact that the flesh contains many 

 long, white, wormlike structures that render the fish unsalable. 

 These so-called worms are in reality hypertrophied muscle fibers 

 that are infected with an undescribed species of myxosporidian. 

 Tliese parasites live only within the muscle fibers that become greatly 

 enlarged and eventually filled with a glistening whitish mass of 

 spores, which accounts for its wormlike appearance. A description 

 of the parasite and its effect on the fish has been prepared for pub- 

 lication. This condition should not be confused with the so-called 

 mushy halibut, which is apparently due to a small bacterialike or- 

 ganism that develops in the connective tissue surrounding the muscle 

 fibers. The investigations on mushy halibut are being continued and 

 will be reported on later. 



