IMPLANTATION OF THE GLOCHIDIUM ON THE FISH 5 



Hookless glochidia are essentially gill-parasites. They 

 cling to the tips and along the sides of the filaments in large 

 numbers. They may attach to the fins, but their grasp in such 

 situations is insecure, and they are usually brushed off before 

 the completion of the metamorphosis.* 



The most successful infections were made on large-mouth 

 black bass, Micropterus salmoides, on Fundulus diaphanus, and 

 on the green and red-spotted sun-fishes, Apomotis cyanellus and 

 Lepomis humilis, respectively. The crappie, Pomoxis annularis, 

 was also used but it is difficult to keep these fishes alive in the 

 laboratory until the completion of the parasitic period. 



The ripe glochidia were carefully removed from the gills 

 of the mussels and placed with the fishes to be infected in small 

 aquaria or other vessels. A comparatively small number of 

 glochidia were used in order to guard against the danger of 

 over-infection which may readily occur if the glochidia present 

 are too numerous, or the fish are exposed to the infection for 

 too long a time. As Harms (9) says, the fish are seldom injured 

 by infection of the fins, no matter how heavy it may be, but 

 they are often killed by over-infection of the gills. However, 

 if the glochidia are crowded together on the fins too closely, 

 successful implantation is prevented and after a short time 

 they drop off. An exposure of from five to thirty minutes was 

 usually found necessary to insure an adequate infection. The 

 glochidia were kept stirred up so as to distribute them as evenly 

 as possible through the water. The gills of the fishes were ex- 

 amined with a hand-lens at frequent intervals during the ex- 

 posure, and when the requisite number of glochidia had become 

 attached, the fishes were quickly removed to a tank, into 

 which running water was introduced. 



According to Schierholz, the infection of the gills and fins 

 takes place to about the same degree, but this is not true of my 

 experience, since I have often observed that glochidia of both 

 the hooked and hookless types will attach to the gills in large 

 numbers, while at the same time the fins show only a very 

 slight infection. If the glochidia develop normally, they remain 



