106 SALMONID^ OF BRITAIN. 



are destitiTte of lakes, as tliey would certainly require considerable range and 

 abundance of food. For in sucli cases lakes would be to the land-locked salmon 

 as the sea is to the anadromous form, and the derision with which the statements 

 of Norwegian ichthyologists that these fishes were the descendants of Salmo 

 salar was received in this country must now be admitted to have been an error. 



What are the limits of reproduction among the salmon ? is a question which 

 has often been jDropounded, but to which various replies have been given. 

 Among fishes generally it exists to a very different degree, thus our catadromous 

 eels would seem to pass many seasons in a sterile condition, only reproducing 

 their species when they descend to salt water. In the salmon, although it is 

 evident that the male is capable of producing milt before it is twenty-four 

 months of age, such is very deficient in marital powers, while in the female 

 eggs seem rarely to be developed prior to its being thirty-six months old. 

 The trout and the char will furnish eggs and milt when nearly two years of 

 age, but even among these fishes the female is rarely so far advanced as the male. 

 Among salmon permanent or temporary sterility may occur. Thus in those 

 cases in which it is permanent* such may be owing in some individuals to their 

 not being sexually developed, as observed by Siebold, or to a mechanical difii- 

 culty in the ova being extruded : or if extruded the eggs themselves may be 

 sterile, due to the spermatozoa being of too great a size to enter the micropyle 

 of the ovum, or sterility may be consequent upon some physiological cause, 

 possibly as close interbreeding, deficiency of food, or unsuitable residence,t 

 affecting the reproductive system to such an extent as to preclude the 

 formation or at least the fertility of the eggs. And, lastly, hybridity 

 may be a cause, and which will be considered when the various hybrids 

 are described. Cases of temporary sterility are seen, as in clean-run salmon 

 ascending our rivers every month in the yeat', while it is manifestly impossible 

 that such as do so, as I have described, in November (see p. 69) could breed 

 that season, and they evidently vrere not kelts that had bred. But in such fish 

 a very slight development of milt or roe may be detected by means of the 

 microscope.]: These seasonally sterile fish would seem to corroborate the view 

 advanced by Mr. Atkins that salmon breed on alternate years (see p. 79). 



Hybridism in a natural state is supposed to be rare as regards the salmon, but 

 that such may take place has been proved by Rasch, Sir James Maitland, and 

 others who have fertilized their ova with the milt of the trout and of the char, and 

 vice verm, and obtained fertile progeny, as will be treated of further on. ^ These 

 fish do not lose their anadromous instincts when the period of migration arrives, so 

 could not be utilized as a land-locked race§, on the supposition that they would be 

 sterile and so lose the desire to migrate seawards. 



Respecting stocking rivers with " alevins," or young salmon in which the 

 yolk-sac is very nearly or just absorbed, various opinions are held. Some 



* Widegreu considered that the form of the caudal fin and the colours of the fish are 

 connected with the development of the sexual organs : as wiU be referred to when treating of 

 trout. , , . 



t Some fish, although apparently in good health, will not breed when kept ni an aquarumi. 



% Mr. Ffennell gave evidence before a Parliamentary Committee that clean salmon with only a 

 thread of milt or roe in them are found in rivers during December, January, and February, and 

 he considered that these fish do not spawn until the November or December following, remaining 

 ten or twelve months. in the fresh water, their ova developing until they are ready to spawn, 

 and that, although discoloured, due to their residence, they are very good eating. _ Brown 

 (Stormo7i{fieI<h E.rjKriments), pp. 94, 95, caught one of these fish in a Sutherlandshire river and 

 gave the same report. He also remarked that the foregoing fish are strong, able to overcome falls 

 and penetrate to the extreme feeders of the rivers, whereas those fish which do not leave the sea 

 until heavy with spawn could not overcome falls or ascend any considerable distance. 



§ Professor Baird (United States Fisheries Bcport, 1875-7G, p. 13) observed, " Another subject 

 of consideration by the convention was the hybridizing of fisli, with a view of repiovmg the 

 instinct of migration, and by the atrophy of the sexual apparatus, allowing a more rapid accession 

 of flesh and fat, as is the case of hybrids and castrated domestic animals." Professor Brown 

 Goode remarked, 1884, respecting hj-brid salmonidaj being likely to remain in the head ^yaters of 

 the streams : " Such is the theory of certain English experts, but it occurs to me that their theory 

 is without very good foundation." 



