THE SALMON FAMILY 53 



To return to the alevins in the gravel, at first the 

 mortality amongst them is not great, but as soon as 

 they begin to move about and get under the larger 

 stones, their enemies play havoc amongst them. 

 Sticklebacks and other small fish hunting in the 

 gravel take then* share, murderous-looking larvae and 

 caddis worms crawling into the darkest recesses 

 still further diminish their numbers ; and their 

 constant enemy, the eel, is always on the look out 

 for them. 



At five weeks old the alevins have acquired a more 

 fish-like appearance, the fins are quite distinct and the 

 adipose fin prominent, but notice that the tail fin is 

 very unlike that of the adult trout. Though the alevins 

 still derive some nourishment from the yolk sac for 

 another week or two, they now begin to swim, and start 

 feeding on minute infusoria. Next, the little fish tackle 

 the young of tiny crustaceans, such as the cyclops and 

 daphnia, or water-flea. At seven or eight weeks old the 

 fins are separate and the yolk sacs have disappeared, and 

 the alevins are now dignified by the name of " fry." 

 Cyclops, daphnia, water-spiders, small beetles, larvae of 

 water-flies, and young snails are now added to their 

 dietary, and occasionally they are able to nip off the 

 heads of their old enemies, the caddis worms, before 

 these insects are able to withdraw into their protecting 

 cases. If fortunate, the alevins come across a water- 

 cress bed, where freshwater shrimps abound. The 

 young of these crustaceans afford the best of food for 



