It seems certain to me that injuries, retardations of the growth by overstocking, 

 certain hereditary' characters, carp lice, too muddy pond bottoms, seldom draining and 

 neglect of ponds as well as strong feeding favor the occurrence of pocks. Occasional 

 observations also lead to the conclusion that a lack of animal nutrition also favors 

 pocl: formation. rVrthemore, I do not want to deny that a lack of ILme can favor pock 

 formation. The addition of fish meal to the food provides aid in both cases and actual- 

 ly works advantageously. 



The fishes in general do not perish from an attack of pocks, but according to Staff 

 and Sawicki, the growth is retarded up to 50 percent. Transferring into other ponds or 

 into running water, even transferring into reservoirs will -often in a few weeks cause 

 the disappearance of the epidermal proliferation, which make the fishes unsalable, as I 

 have frequently determined in experiments. Pond sanitation prevents renewed occurrence. 



D. Fungus Parasitic Diseases . 



1. Filamentous fungus faold) parasitic diseases . 



Saprolegnia attack . The wallknown, cotton-like water mold or fish mold (Saprolegnia. 

 and Achlj-a) is not an actual disease producer, but rather a "parasite on weakness". It 

 always settles only on sick, injured and stored fishes which, of course, are soon des- 

 troyed by it. It naturally is more injurious to the gills than to the skin. The Sapro- 

 legina also occur on the eyes, in the mouth and on the fins. They also attack perished 

 fish eggs (Fig. 30), and in extensive mold attacks they even transfer quickly to living 

 eggs. The more tender the tissues of the host, the more profound is the attack and 

 penetration. All injuries of the fishes especially in fishing out and in transferring 

 are to be avoided, diseases are to be avoided ^at the right time, perished eggs should 

 be removed every two or three days from the brood apparatuses (see Chapter V,3,5). 



Gill rot . There are two known forms of gill rot caused by Branchiomyces sanguinis 

 Plehn on the one hand, and Branchiomyces demigrans Tlfundsch on the other hand. The 

 former occurs in carps and tenches (carp gill rot), the latter in tenches and pikes 

 (pike gill rot). In the tench, therefore, two distinctly different kinds of gill rot 

 occur. In both forms and with all species of fishes, the gill filaments become colored 

 partly white, partly blackish-red (especially the upper ones. Fig. 65), because the gill- 

 filament veins are penetrated and obstructed by fungus filaments which have a width of 

 about 9 to 15 moi (microns). The external picture is quite changeable, Branchicmyces 

 sanguinis occurs only in the vessels and in the tissue of the gills; the otherwise very 

 similar Branchicmyces demigrans forms strongly refractive branched tube-bundles on thie 

 outside of the gills, With a strong obstruction of the veins, rapid destruction (Fig, 65) 

 and a saprolegnia attack of the gills, takes place, similar to sickening by acid water. 

 The molds thereupon form spherical spores of about 5 to 7 mi (microns) which fill the 

 tubules everywhere. The hemoglobin content of the carp blood can be about 20 to 30 per- 

 cent over the normal value of 55 to 60 percent, and the blood can have an Increased 

 coagulability. 



Gill-rot is a summer disease, which in by far the most cases, occurs shortly after 

 very hot days during the period frc«n May to August, when the water is about 23°C. There 

 are exceptions of course. Scheuring and Gaschott observed a case at 14° to 16''C. in May, 

 TTundsch observed a mortality with pikes at 21*0. Another tench mortality frcm Branch- 

 iomyces dem1 grans started as early as the 6th of May, the losses during the first days 

 are mostly ver;' great, in the course of about eight days they again subside. The disease 

 therefore runs a very rapid course. Small and large fishes are attacked. Perished carps 

 at times remain in a natural position at the pond shore. The total losses mostly amount 

 to 10 to 50 percent according to Schaeperclaus, 



Particularlj;^ endangered are the "too good" ponds, whose water shows an increased 

 content of organic substances or is even turbid. Gill rot occurs preponderantly when 

 mowed over-water plants, or cultivated ground fertilization plants in the pond or grasses 

 rot in the water. The oxygen content at this time is as high as usual, the occurrence 

 of the molds' in the oxygen rich blood of the gill lamellae veins obviously indicates a 



200 



