SALMONID^ OF BRITAIlSr. 



Family— SALMONIDiE, MiiUer. 



Pseudobranchiae present. The margin of the upper jaw formed mesially by 

 the premaxillaries, and laterally by the maxillaries. Barbels absent. Two 

 dorsal fins, the anterior containing rays : the posterior, which is the smaller, 

 being adipose. Pyloric appendages, as a rule, present and usually numerous. 

 Body scaled, head scaleless. Air bladder large, simple, and with a pneumatic 

 duct. The ova pass into the cavity of the abdomen before being extruded. 



Tlii.s family is characterized, among bony or tdeostean fishes, by tho large size 

 of its blood discs. 



Geological appearance. — No fcssils representing fresli-water forms Lave as yet 

 been discovered; but the marine smelt, Osmerus, is found in the greensand of Iben- 

 busen and the schists of Glaris and Licata. A species of Mallotits is also present 

 in the clay nodnles in Greenland, whose age has not been determined. Some 

 sujiposed marine forms have likewise been recorded from the chalk at Lewes, 

 co-existing with fossils of the genus Beryx, and they have been located in the 

 genera Osmeroides, Acrognatlius, and Aulolepis. 



Geographical distrihution. — The Salmonida3 consist of marine and fresh-water 

 fishes, the latter being normally restricted to the Arctic and temperate portions 

 iif the Northern hemisphei'e with the exception of the genus Hetropinna, found in 

 New Zealand rivers. Absent from India and Africa, they have during the present 

 century been artificially distributed to many portions of the globe where they arc 

 not known to have existed previously. In the Northern hemisphere the fresh- 

 water forms are present between the latitudes 45° and 75°, and one species has 

 been captured so far north as 80°. In fact they are residents of cold and tem- 

 perate waters and do not noimally extend to where the water is very warm. 



The species of some of the genera, as Argentina, which arc included in this 

 family, do not enter fi-csh waters : others again as the smelt, Osmerus, ascend so 

 far as the tide reaches but rarely beyond, while the salmon is an auadromous form 

 which passes up rivers even to their higher portions and here it forms its nest, 

 deposits its eggs, and its young are hatched and reared. Trout, char, and graj'ling 

 may pass their entire existence in fresh waters, but all these forms have been 

 captiarcd in salt water.* Consequently it becomes evident that some species of 

 the same genus may be living in the sea while others are exclusively resident in 

 fresh waters, demonstrating how anadromous 6sh may change into resident fresh- 

 water ones. Also in certain species, ns the common trout, some examples may be 

 found residing a great part of the year in fresh or in brackish watci-s, others in 

 fresh. We are thus able to follow an unbroken chain connecting sea forms of the 

 salmon family with others that appear to normally pass their entire existence in 

 fresh water, but which latter have in every genus furnished examples that have 

 been captured in the ocean. 



This gives rise to the inquiry wLether the Salmonidse are descended from a 

 marine or fresh-water ancestry ? a question of importance to the fish culturist 

 should he be debating upon the possibility or rather probability of successfully 

 rearing and subseciuently breeding salmon in fresh waters without deterioration, 

 ]>rovided they ai'c unable to migrate to the sea. 



That strictly fresh-writer fishes are intolerant of saline water is well known, 

 thus carj)S are deleteriously aifected, usually dying on the addition of salt water, 



* Specimens of several deep sea genera belonging to this family have been secured by our 

 exploring exjieditious. 



