30 



aquatic ILitt 



host is found, the young parasite attaches 

 himself thereto, boring into the epidermis. 

 An otherwise diseased fish is particularly 

 in danger, as it is usually covered with a 

 layer of slime which is favorable to the 

 purposes of the pest. It bores into the 

 membrane and, rotating within the cyst, 

 proceeds to feed upon the vital fluids of 

 the unfortunate host. 



A knowledge of the life-history of the 

 parasite is necessary that it may intelli- 

 gently be combatted. As we have said 

 before, the pest begins its life as a free- 

 swimming, microscopic creature. Hav- 

 ing fastened to the host, it feeds for a 

 period varying from a few days to a 

 week or two, depending on the tempera- 

 ture of the water. The warmer the water 

 the more rapid is the development. Then 

 the parasite leaves the host, dropping to 

 the bottom of the aquarium in a jelly- 

 like cyst. 



At this stage of its progress, authori- 

 ties differ. Some writers, such as Hofer, 

 in his "Fischkrankeitcn," state with as- 

 surance that the only method of propa- 

 gation is by division. The parasite, they 

 say, divides into two, these two into four, 

 the four into eight, and the eight into 

 sixteen, up to certain limits, which some 

 observers have placed as high as several 

 hundred. Others who have made a 

 minute study, such as Harvey A. Van 

 Cott, declare with equal conviction that 

 it multiplies in two ways: by division as 

 we have already described, and also by 

 the formation of spores, even while still 

 on the body of the host. Hofer denies 

 this. He says: "The previously dissem- 

 inated view that the multiplication of the 

 Ichthyopthirius parasite takes place 

 within the pustule and that the escaping 

 young immediately seek a host in their 

 vicinity has been shown to be false by 

 recent investigation, a circumstance that 

 is important in the treatment of the dis- 

 ease." 



Whether the pest multiplies only when 

 quiescent on the bottom of the tank, or 

 whether it also forms spores while on 

 the body of the fish, remains a disputed 

 feature. We believe that we are safe 

 in saying that it multiplies in both ways ; 

 on the bottom of the tank by division, 

 and also by the formation of spores. 

 Further, it seems that some investigators 

 have found these to take place both on 

 the fish and also in the water. When 

 spores are formed, the crescent-shaped 

 nucleus seems to widen out within the 

 cell, and then break up into many minute 

 granules. Then the cell wall breaks, and 

 these "granules" swim out, each one a 

 voracious pest. 



If the German theory is true, that the 

 adult parasite drops from the fish to the 

 bottom of the tank, lies there in a qui- 

 escent state for some hours, and then 

 multiplies, the remedy would be simple. 

 It would be necessary only to change the 

 water three times a day, say at 6 A. M., 

 2 P. M. and io P. M. • In so doing the 

 pests that fall to the bottom will be 

 washed away gradually, until within a 

 week or two none are left. We have 

 known this treatment to be attempted in 

 several instances with good results. One 

 man reported two years ago that he had 

 saved a tank of Haplochilus cHaperi in 

 this manner. In the same way another 

 saved a number of Xiphophorus hetleri 

 and Lebistcs rcticulatits. But we know 

 of other repeated attempts where this 

 treatment either failed, or in case the 

 parasites seemed to be washed away, the 

 fishes later refused to eat and apparently 

 died of starvation. 



( )ne aquarist states that the surest way 

 is to place the fish in swiftly flowing 

 water, of the proper temperature, of 

 course. He argues that whatever may 

 be the correct method of propagation, the 

 (Concluded on page 32) 



