Abstract
In order to examine the resistance of the eel to Saprolegnia parasitica, experiments were made, with the following results, on the possibility of the fungus infecting healthy uninjured fish, on the part played by injury in susceptibility to infection and on the ability of the fungus to invade the living tissues. The fish used in the experiments were elvers and yellow eels ranging from 8 to 43cm in body length.
1) Neither elvers nor yellow eels became affected with Saprolegnia when they were in a sound condition.
2) Injury greatly lowered the resistance of elvers to Saprolegnia. Primary lesions of the skin caused by slight abrasion became the loci of zoöspore infection, from which the hyphae likely penetrated into the surrounding normal tissues of the victim.
3) Yellow eels have a high resistance to the fungus. Infection of them failed to occur even when they were injured by cutting deep on various parts of the body, by scraping a sizable portion of the skin, or by excising the skin from a small area of the body surface.
4) The mycerial growth frequently developed on coagula or slimy masses which appeared ordinarily on the surface of wound and were regarded as consisting of wound exudate and cellular debris. The growth, however, never penetrated from them into the tissues of the injured area.
5) Zoöspore infection took place easily on large necrotic areas produced on the body surface, the hyphae growing vigorously there. The mycelium, however, did not invade the surrounding living tissues, so far as the vitality of the fish was maintained.
