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Blueback Salmon; Sockeye Salmon — Part 3
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The following interesting and pertinent observations on the species of trout are taken, with some modification, from Dr. Gunther:
There is no other group of fishes which offers so many difficulties to the ichthyologist, with regard to the distinction of the species, as well as to certain points in their life history, as this genus. The almost infinite variations of these fishes are dependent on age, sex and sexual development, food, and the properties of the water. The colouration is, first of all, subject to great variation, and consequently this character but rarely assists in distinguishing a species, there being not one which would show in all stages the same kind of colouration. The young in all the species of the genus are barred, and this is so constantly the case that it may be used as a family character. When the young have passed this "parr" stage the colour becomes much diversified. The males, especially during and immediately after the spawning sea son, are more intensely coloured and variegated than the females, immature individuals retaining a brighter silvery colour and being more like the female. Food appears to have less influence on the colour of the outer parts than on that of the flesh; thus the more variegated examples are frequently out of condition, whilst well-fed individuals, with pinkish flesh, are of more uniform though bright colours.
The water has a marked influence on the colours. Trout with intense ocellated spots are generally found in clear, rapid rivers and in alpine pools; in the large lakes, with pebbly bottom, the fish are bright silvery, and the ocellated spots are mixed with or replaced by x-shaped black spots; in dark holes, or lakes with peaty bottom, they often assume an almost uniform blackish colouration.
Brackish or salt water has the effect of giving them a bright silvery coat, with or without few spots, none of them ocellated.
With regard to size, the various species do not present an equal amount of variation. Size appears to depend upon the abundance of food and the extent of the water. Thus the migratory species do not appear to vary considerably in size, because they find the same conditions in all the localities inhabited by them. A widely-spread species, however, like our black-spotted trout, when it inhabits a small mountain pool, with scanty food, never attains a weight of more than a few ounces, while in a large lake or river, where it finds an abundance of food, it reaches a weight of 10 to 15 pounds. Such large trout of the rivers and lakes are frequently described as salmon trout, bull trout, silver trout, steelheads, etc.
The proportions of the various parts of the body to one another vary exceedingly, in the same species, with age, sex, and condition. The fins vary to a certain degree. The variation in the number of rays in any one genus (except Oncorhynchus) is inconsiderable and of no value for specific determination. Although some species appear to be characterized by comparatively low dorsal and anal fins, yet the proportion of the height of these fins to their length is a rather uncertain character. In most of the species the fin-rays are longer during the stages of growth or development. The caudal fin especially undergoes changes with age. The young of all species have this fin more or less deeply incised, so that the young of a species which has this fin emarginate throughout life is distinguished by a deeper incision of the fin from the young of a species which has it truncate in a young state. The individuals of the same species do not all attain maturity at the same age or size. Finally, to complete our enumeration of these variable characters, we must mention that, in old males, during and after the spawning season, the skin on the back becomes thickened and spongy, so that the scales are quite invisible or hidden in the skin.
After this cursory review of variable characters, we pass on to those which we have found to be constant in numbers of individuals, and in which it is difficult to perceive signs of modification due to external circumstances.
Such characters, according to the views of the zoologists of the present day, are sufficient for the definition of species; at all events, in every description they ought to be noticed. The confused and unsatisfactory state of our knowledge of the Salmonidae is chiefly caused by authors having paid attention to the more conspicuous but unreliable characters and who have but rarely noted any of those enumerated here:
1. The form of the preopercle in the adult fish.
2. The width and strength of the maxillary in the adult; in the young and in females the maxillary is proportionately shorter than in the adult male.