STUDY OF FISHES 



149 



o 



In the second or third spring after their birth they put on 

 their silvery " sea-jacket," are about seven inches long, and 

 descend to the sea as " smelts." In the 

 sea they feed voraciously, e.g., on young 

 herrings and haddocks, and on the eggs of 

 crustaceans, and grow large. 



In fifteen to eighteen months or more 

 they return to the rivers as " grilse," per- 

 haps two to five pounds in weight, and they 

 are able to spawn. Thus the story begins 

 again. After spawning, the salmon are out 

 of condition and have to return to the sea 

 to regain their full vigour. It may be safely 

 said that most, if not all, of the mature 

 salmon's energy is accumulated during the 

 time it spends in the sea. Although they 

 develop slowly, they grow quickly, arid 

 they may live to a good age, attaining a 

 weight of fifty to seventy pounds in very 

 fortunate cases. 



Attention may be directed to the colour- 

 changes in the course of the life-history and 

 in the course of the year, to the gymnastic 

 feats of leaping, to the combats of the 

 males, to the numerous risks that beset the 

 salmon at different times, to the fact that 

 they sometimes return to the same river, 

 and so on. The life-history of the salmon 

 should be contrasted with that of the 

 flounder, the eel, the lamprey, and 

 others. 



Life-History of Eel. In many parts of 

 Britain the annual " eel-fare " is a familiar 

 sight in spring. Myriads of young eels or 



elvers, 3 to 5 inches long, no thicker than knitting-needles, come 

 swarming up the rivers from the sea. They are already at least 

 a year old. They were hatched in deep water on the continental 

 shelf to the west of Britain ; they have had a fasting period of 



FIG. 53. The early develop- 

 ment of the salmon. The 

 figures are nearly twice 

 the natural size. I, The 

 fertilised egg ; 2, the egg 

 just before hatching ; 

 3, the newly hatched 

 salmon with its yolk- 

 sac ; 4 and 5, the larval 

 salmon nourishing from 

 its yolk-sac (y.s.\ which 

 gradually decreases as 

 the body of the fish in- 

 creases ; 6, the young 

 salmon about six weeks 

 old, when the yolk has 

 been completely ab- 

 sorbed. 



