BREEDING AND HOW AFFECTED BY TEMPERATURE. 27 



1885. At the same time milt was obtained from some of these hybrids and used 

 to impregnate 4500 eggs of Lochleven trout ; these hatched on February 2nd, 

 but the mortality was large, being upwards of half the eggs, while there were 

 many deformities and some dropsies among the offspring. Males are evidently 

 more matured for breeding-purposes than are females of the same age. I would 

 here advert to a remark I published in 1883,* that in the fresh waters of India 

 due to indiscriminate net-fishing the young (of many forms of fish) have to be 

 raised from ova of such as are merely one or two seasons old, while the younger 

 the parent the smaller the eggs, and this is probably one mode in which races of 

 fish deteriorate. 



Although it is known that among mammals, breeding from two nearly related 

 parents — as brother and sister — frequently gives rise to deteriorating offspring, it 

 has notbeen shown that this consanguinity deleteriously effects to so great an extent, 

 or even at all, the lower classes of vertebrates. Reasoning from analogy we must 

 suppose that the infusion of fresh blood improves piscine races, and instances have 

 been adduced when from local circumstances fish have deteriorated and an 

 improvement has occurred on the cessation of the deleterious conditions, some- 

 times aided by eggs from a fresh stock having been introduced. It would appear 

 that from young parents or deteriorated breeds small offspring are raised, but 

 unless other circumstances combine, fine fish kept in suitable water have been 

 raised from eggs of normally small breeds, but doubtless large eggs are most likely 

 to produce larger and more rapidly growing offspring. Possibly if eggs are 

 insufficiently aerated while incubating the resulting young are stunted, while 

 similar results ensue on crowding alevins. 



The period at which breeding takes place can be aSected by many circum- 

 stances, the chief of which may be briefly enumerated as follows : — the age of 

 the parent : the race or variety as to whether it is strong or weak, healthy or 

 unhealthy : obstructions, whether natural or artificial, but which occasion difficulty 

 in obtaining access to the breeding grounds : their habitat, as residents of the 

 colder north or more sunny localities : the range of waters through which they can 

 rove : climatic and seasonal variations whether such are normal or abnornal : the 

 character of the water : the geological formation of the country : its elevation : the 

 abundance or the reverse of food : whether the fish are kept in confinement or in 

 a wild state, and if disturbed or not. 



This brings one to consider whether seasons or changes of temperature 

 exercise any marked influence on the time of the year when these fishes spawn ? 

 If they do we ought to be able to observe such among the trout and Anadromous 

 Salmonoids despatched in the form of ova to Tasmania from, this country. 

 Turning to Mr. Allport's account {Froc. Zool. Soc. 1870, p. 25), we find a most 

 marked instance of such a result.f We know the cold season in that portion of the 

 globe corresponds with our summer, and the first brook trout which were spawned 



* Indian Fish and Fishing. Great International Fisheries Exhibition, 1883 series, p. 27. 



t Sir Humphry Davy, writing from Southern Austria, on May 28th, 1827, remarked that "the 

 char I got this morning with mature eggs was just about to spawn, yet in England they spawn in 

 the winter. If summer is the spawning time of the char and trout of the lakes of Southern 

 Austria, it is connected with or owing to the waters at that time being of the temperature best 

 fitted for the purpose, most of these lakes being fed by mountain streams, frozen in the winter, 

 and full in summer from the melting of the snow." Herr Geistbeok (Nature, 1886, p. 375) 

 remarked of the German Alpine lakes, that " small depths and large affluent streams are causes 

 of a higher temperature in summer and a lower in winter. Cooling in autumn goes on more 

 rapidly than heating in spring, for in the autumn the upper layers of water get heavier consequent 

 upon cooling and then sink, being replaced by others, tEl the entire mass reaches the temperature 

 of the greatest density, but in spring the circulation fails. Large affluents, too, by promoting 

 mixture cause rapid heating. Down to 6 or 8 metres' depth in midsummer the fall of temperature 

 is very slight ; thence to 18 metres a rapid fall, which continues to about 50 metres : below 50 

 metres the temperature is about constant." In Sweden, Artedi observed that the salmon spawned 

 in the middle of the summer. Livingston- Stone (Bulletin United States Fishery Commission, 

 1882, ii, p. 12) observed of S, qidnnat, that, raised in the United States it did not spawn in the 

 Californian time, but in the S. salar time, November or very near so. We also know that, as a 

 rule, in very hard winters when the spawning grounds are frozen spawning is usually deferred, 

 and when very cold weather has unexpectedly set in, salmon have been observed to stop their 

 ascent of rivers and return to the sea. 



