308 FRESH-RUN RHINE SALMON IN NOVEMBER. 



all its bearings, I now venture to propose a solution to 

 the question. 



These clean-run fish are a Secondarij Migration of 

 salmon — a spring migration, in contradistinction to 

 an autumn migi-ation. I have shown above that the 

 amount of fat upon the j)yloric appendages will be a safe 

 guide to ascertain the real history, travels, and position 

 of a given fish. I therefore apply it as a key to help to 

 unlock the mystery of the spring fish. 



These clean-run fish, therefore, in my opinion, are 

 those who have laid up a sufiicient amount of fat during 

 the time they have remained in the sea (dating from the 

 kelt stage) to last them during their stay in fresh water; 

 and I fancy (although I have no direct grounds as yet 

 to prove it) that they are the early kelts of the j)revious 

 year, who having reached the sea, say in January, 1868, 

 now reappear as clean-run fish in February, 1869, or, 

 may be, even as very large fresh-run fish in 1870 ; much, 

 however, depends upon the quantity and quafity of food 

 they find in the estuary ; there are, I understand, 

 enormous numbers of smelts in the estuaries of the 

 Dutch rivers, and the food aftorded by these, combined 

 with other causes, goes a long way to make the Ehine 

 fish to lay up its stock of fat quickly, and therefore 

 renders it ready to proceed all the earlier on its upward 

 pilgrimage. I believe large numbers of smelts are also 

 found in the estuary of the Tay. The early fish, there- 

 fore, having laid up a sufficient quantity of fat for their 

 inland sojourn, do not wait till the descent of the autumn 

 floods ; but they avail themselves of the spring floods, 

 being tempted by the state of the temperature and the 

 great body of descending water, which informs them 

 their road is clear, and also by the non-necessity of their 

 remaining longer in the sea. This theory, I think, may 



