REARING THE YOUNG FRY. 185 



one at the upper end will have a fin or two half gone. 

 This disorder is not always fatal, by any means, for 

 some will recover ; but if either of the pectoral fins. are 

 nearly destroyed, or if fungus has set in, the trout 

 will probably die. 



One cause of this disease is the biting of other fish. 

 Young trout, like cub bears, are irritable in their na- 

 ture, and do not like to have others come too near 

 them, but will snap and bite their companions when 

 they show a disposition to crowd. The result is that 

 their fins frequently get mutilated, and present the 

 appearance just described. They show this irritable- 

 ness especially when they are left unfed for a while 

 and get very hungry, the hunger, perhaps, having a 

 double agency in making them bite at each other. 

 This unnecessary cause of the evil should at least 

 be avoided. When you discover any young trout 

 with injured fins, take them out and put them by 

 themselves, where they have plenty of room, plenty 

 of water, and plenty of food. Some will die, per- 

 haps half. With the others the fins will grow out 

 again, and the trout in a few months be as well as 

 ever. 



13. Black ophthalmia. This is a strange disease. 

 You sometimes observe a fish becoming very black 

 and inclined to separate from the rest. He is some- 

 what emaciated, refuses food, and is less easily fright- 

 ened than the others. If you examine his eyes, you 

 will see that the tissue of the pupil is more or less 

 destroyed and his eyesight much injured, which is the 

 cause of his not being frightened at your approach. 



