Fishes. 1409 



however, several circumstances connected with them, which may in 

 some measure influence them, the facts can be vouched for, though 

 their influence may be denied. 



It is a well-known fact among all who have investigated the habits 

 of fish, that cold retards the development of the ova ; that they ad- 

 vance to maturity according to the temperature of the season. If the 

 season, therefore, be a cold one, the spawning of the mackerel is re- 

 tarded, and so much is this sometimes the case, that the young are 

 overtaken by winter while they are yet very small. During winter it 

 %rows but little compared with its rapidity during the summer 

 months ; and therefore in the following spring, it does not perform the 

 reproductive functions till late, and if there are several cold seasons 

 in succession, not till very late, hence we find that in some seasons 

 the mackerel are in roe during the winter. Cold, though it can retard, 

 cannot suspend this function, and the young are sometimes not alive 

 till spring, when the fishermen tell me, they may be seen in thousands 

 at the surface of the water basking in the sun. Thus then the 

 mackerel may, and does breed at two distinct seasons of the year, oc- 

 casionally. This has given rise to the opinion that some fish breed 

 twice in the year. This I believe, however, is never the case ; though 

 distinct fish do at opposite periods : if the spawning be retarded for 

 several seasons, the young of that period will accumulate, till their 

 migrations will seem to constitute the migrations of the whole, and 

 what began from seasonal peculiarities will be continued permanently 

 as long as that generation lasts. I cannot find from any one of the 

 fishermen that, what they call " the same fish," ever vary the periods 

 of their movements except for a few weeks. They all maintain the 

 spring and autumnal spawning fish are not the same; their meaning 

 being that those fish which spawn at opposite times are not identical. 

 In proof of this, they affect to point out differences in their appear- 

 ances and markings. No two mackerel are alike, but the fishermen 

 detect a difference which none but a practised eye can detect. On 

 this point I was for a long time sceptical, but am now brought over 

 to their way of thinking, and can detect the differences as readily as 

 themselves. It is, however, not so easy in the mackerel as in the pil- 

 chard, which are liable to the same revolutions in their movements. 

 In the pilchard these markings are so distinct and so many, that 

 I have sometimes thought them sufficient to constitute specific diffe- 

 rences. The periods of revolution or transition, are, like all similar 

 times, characterized by irregularity and confusion, and are described 

 as such by our fishermen. But if we examine them with a knowledge 

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