DEVELOPMENT AND GROWTH OF SALMON-FRY. 557 



as the streams and ponds in which they have existed from their birth abound 

 with every species of insect food peculiar to the river, and, at the same time, the 

 fishes themselves (which are certainly the best test), are in the highest possible 

 health and condition, and correspond in every respect with those in the river. I 

 have already stated that the young of the salmon remain in the river for the first 

 two years after then* birth, being then known under the various local denomina- 

 tions of parrs, pinks, fingerhngs, &c. &c. However, in order to prevent any mis- 

 conception of the terms employed in the com'se of these details, I shall adhere to 

 the name parr, as being the designation by which tliis fish is most generally 

 known in Scotland. 



The early or late hatching of the salmon-spawn in the river is no doubt in a 

 great measure regulated by the temperature which may prevail after its deposi- 

 tion. In severe winters, when the temperature of the river for many weeks barely 

 exceeds the fi-eezing point, the ova remain in the gravel at the bottom of the 

 stream during that period with the living principle comparatively suspended, 

 until the more genial temperature of the spring brings that principle into more 

 active operation. In the course of experiments made in the beginning of 1838, 

 I had an opportunity of observing the different effects of temperature in faciUta- 

 ting or retarding the development of the salmon-spawn. In ova placed in a 

 stream of spring water, the average temperature of which was 40°, the embryo 

 fish was visible to the naked eye by the end of the 60th day, and was hatched on 

 the 108th day after impregnation. That which the same parent deposited the 

 same day in the river, the average temperature of which during the eight follow- 

 ing weeks did not exceed 33°, was not visible to the naked eye until the 90th 

 day, and was not hatched until the 10th Maj% that is 131 days after impregna- 

 tion. The temperature of the river, however, during the last forty days of that 

 period, had considerably increased, and on the day on which the fishes were 

 hatched, it had attained an elevation of 60°. Were it, then, the fact that the 

 young salmon migrate to the sea the same season they are hatched, the effects of 

 a mild or a rigid winter would alone regulate the period of their departure from 

 the river. This, however, is not the fact, as the main body of the salmon-fry re- 

 gularly quit our rivers about the first or second week in May, whatever may have 

 been the temperature of the previous winter, and in this particular instance 

 they were actually descending the river in shoals on the very day (10th May) on 

 which that season's produce were only emerging fi-om the ova. 



Owing to the great family likeness which is known to exist amongst the 

 young of the several species of the genus Salmo in then* early stages, an idea has 

 been entertained that unscientific observers are in the practice of confounding the 

 progeny of the whole of the migratory species indiscriminately under the too ge- 

 neral name of Parr. To obviate this inconvenience, and to mark the distinction 



