414 A HISTORY OF FISHES 



to fish ciilturists. Tumours and growths of various kinds have 

 been described in some of our food-fishes, but by comparison 

 with other animals, marine fishes seem to suffer from very few 

 specific diseases: it is among the fresh-water forms, and more 

 particularly among those living under artificial conditions, that 

 predisposition to serious maladies is most marked. These 

 maladies may be due to bacterial infection, to animal or 

 vegetable parasites, to bad feeding, to pollution of the water, 

 and to physical causes of all kinds. 



Among the more serious epidemic diseases is that known as 

 Furunculosis or "Ulcer Disease," and the damage caused by 

 this malady to the stocks of Salmon and Sea Trout has reached 

 alarming dimensions in recent years. It is due to a specific 

 germ. Bacillus sahnonicida, which invades the blood-stream and 

 is thus distributed through every organ of the body. It is 

 highly infectious, being spread by the contact of infected with 

 healthy fish, or by the discharge of the germs from the body of 

 a diseased fish into the water: there is also reason to believe 

 that perfectly healthy fish may act as carriers without them- 

 selves developing the disease. So far, it has been possible to do 

 very little in the matter of treatment, but the prompt notification 

 of outbreaks, and the quick removal and burial of dead fish 

 from infected waters, may do much towards preventing the 

 spread of the disease. The "Salmon Disease," so-called because 

 it is most prevalent in Salmon and Sea Trout, is likewise caused 

 by a bacillus [B. salmonis pestis), and this invades the tissues of 

 the fish, gaining entrance through an abrasion or ulceration 

 of the skin, multiples rapidly, and forms areas of mortified flesh 

 which form ideal soil for the growth of a deadly fungus (see 

 below). In "Tail-rot" and "Fin-rot," particularly rife among 

 Goldfish and other cultivated species, bacilli of one kind or 

 another are again the causative factors. The tail or fins become 

 gradually frayed and stringy, finally disintegrating and dropping 

 off. Ichthyophthiriasis or "White-spot Disease" is another 

 very common fish malady, the \ictim being covered with white 

 specks, each of which represents a minute pit eaten through 

 the scale pigment by a protozoan parasite. Such an attack is 

 not necessarily fatal in itself, but the resulting sores are nearly 

 always attacked by fungus spores which eventually kill the 

 fish. The parasitic protozoa, known as Myxosporidia often 

 cause epidemic diseases of a serious nature, the epidermis of the 

 gills, the fins, and certain internal organs, developing creamy 

 white, wart-like growths or tumours in which bacilli develop 



