120 SALMON AND TROUT. 



and February following, a few fish continue to run which 

 have been usually considered as 'barren' without capability 

 of spawning ; but this notion was proved by the late Mr. 

 W. F. Ffennell to be erroneous. Upon dissection he found 

 that the females had ova in them perfectly developed, although 

 not larger than mustard seed, whilst in the males a thin thread 

 of milt was always discernible. 



These fish, of which many ascend the Tay in November 

 and the three following months, remain nearly a year in the 

 fresh waters before spawning, and although their colours gra- 

 dually become darker in consequence, they are to all intents 

 and purposes ' clean fish,' and are exceedingly good eating. 



The term ' clean fish ' is used as the antithesis of ' foul fish ' 

 a term applied to all salmon which have either not recovered 

 from the effects of spawning, or in which the roe or milt has 

 arrived at a great degree of maturity. 



The so-called barren salmon appearing at a time when most 

 fish are spawning, or are just recovering from the process, illus- 

 trates what I believe to be the most important fact connected 

 with the history of salmon, viz. that the principle of a divided 

 migration, already referred to, is not confined to the parr on 

 going to the sea, or to the smolts on their return from it, some 

 as grilse, and some as spring salmon, but that it also extends to 

 the old and adult fish after spawning one portion of these 

 latter coming back into the rivers during the following summer, 

 and the rest not until the spring succeeding it ; in other words 

 (and this is the gist of the whole), that at least a proportion of 

 salmon spawn only every alternate year. The design of this law 

 or instinct which, when once apprehended, will be found to 

 explain many of the perplexities in the history of the salmon is 

 intelligible enough. It is evidently to insure a supply of clean 

 fish throughout as large a portion of the year as possible, and 

 to enable each river to support the greatest stock a result 

 which could only be obtained by such a provision as the above. 

 It is also doubtless intended to insure an equal distribution of 

 fish throughout the whole length of the river. These salmon, 



