ANADROMY: GENERAL CONSIDERATIONS. 39 



While recognizing various known and unknown supercessory, subcessory, and ac- 

 cessory factors as involved in the evolutional development and present manifestation 

 of the anadromous 'habit,' Gurley (p. 414) emphasizes that of temperature as of prime 

 significance, stating that the facts '. . . demonstrate the presence of a temperature 

 responsive nerve mechanism . . .' and indicate the necessity of recognizing that, '. . . 

 besides the convenient, naked eye anatomical characters utilized for classification, a 

 number of physiological characters exist which are perhaps less immediately evident, 

 but which are none the less real and important.' 



In fish culture and artificial distribution, if not elsewhere, these physiological characters 

 are the essentials to be regarded. The fact that this or that ichthyologist pronounces 

 the rainbow trout, and steelhead trout, or the Atlantic salmon and 'landlocked salmon' 

 identical or distinct, affects the culture and distribution of the forms favorably or un- 

 favorably only to the extent that the pronouncement conforms to the physiological 

 characters and their significance. 



Gurley very forcibly argues that the environmental factor, or the immediate stimulus 

 to which the spawning migration is a physiological response, is a definite temperature 

 trend. This fact 'plays a dominant role in the fish's life.' The tendency of Salmonidae 

 to seek cooler water for procreation is, he states (p. 415) ' . . . their fundamental dy- 

 namic character, the character which is back of their migrations and habitats, which 

 latter have, in turn, developed their generic and specific differences.' 



Day (1887, p. 27-28) adduces a few instances of change of spawning time by acclima- 

 tized fish in conformity to differences of temperature. In consideration of whether 

 seasons or changes of temperature exercise any marked influence on the time of the year 

 when fishes spawn, he says: 



'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 [Great Britain]. 

 Turning to Mr. Allport's account (Proc. Zool. Soc, 1870, p. 25) we find a most marked 

 instance of such a result. We know the cold season in that portion of the globe corre- 

 sponds with our summer, and the first brook trout which were spawned in Tasmania 

 occurred on July 3rd, 1866; by the 7th of August fourteen females had been stripped, 

 and shortly afterwards five pair of trout were observed constructing redds in the River 

 Plenty. During June, July and August, 1867, the trout were again stripped of their 

 ova artificially. In this country [Great Britain] trout spawn at different periods in 

 different rivers, from about September to February. The very first Tasmanian bred 

 trout hatched from EngUsh trout eggs have not selected for spawning the months 

 adopted by their ancestors in this hemisphere, but have chosen others which are better 

 suited for their purpose, clearly demonstrating the possibUity of trout being capable 

 under changed conditions of varjdng the period of the breeding season.' 



From the foregoing it is evident that salmonids do not spawn by the calendar, and are 

 not only 'capable' of varying the breeding season under changed conditions, but are 

 also compelled to do so or fail in reproduction. In the early days of fish culture, data 

 were not available to indicate this essential fact, and for years thousands of doUars 



