CERTAIN INFLUENCES ON THE MIGRATION OF FISHES. 97 



circumstances. If an apparently ripe fish, from which it is found impossible to obtain 

 ova, be taken from ice-cold water and placed in a tank, the inflowing stream of which is 

 gradually raised from 32° to 50° Fahrenheit, it will be found under such conditions to 

 yield its eggs freely. 



Some time ago, when trying to obtain ripe salmon in the river Nith, I found it quite 

 impossible, though a large number of the fish were taken. I found, however, that fish 

 were spawning freely in the river (Jluden, which is a fork of the Nith. I had ther- 

 mometers placed in the two streams, and the result bore out the opinion I had previously 

 formed, namely, that the water of the Cluden was warmer than that of the Nith. 



On a stream of my own I have noticed repeatedly that during a mild spawning 

 season trout avoid one of the tributaries. The reason is that the temperature of this 

 tributary is so much lower than that of the main stream. It is very little affected by 

 the weather, being mostly spring water. But let the weather be reversed and hard 

 frost set in, the fish then take this tributary freely because the water is several degrees 

 warmer. I have remarked other instances in which the same thing occurs. 



It has been said that the temperature of the sea being colder than that of the 

 rivers the fish leave it, seeking a higher temperature. 1 have not noticed this so much 

 myself, but I have seen it mentioned as the experience of some writers, and have also 

 seen it recorded in the Government fishery reports and elsewhere. But this I have 

 noticed, that the temperature of the sea, in some places at least, during the late spring 

 months is often a great deal higher than that of the rivers, very often varying 10° F. 

 or more. It has often puzzled naturalists why salmon run up the rivers in spring and 

 summer, and many reasons have been put forth, such as change of food, to get rid of 

 parasites, to escape from seals, etc. But none of the reasons brought forward will 

 bear much scrutiny. 



The following, however, has occurred to me: Knowing how important it is on a 

 trout farm so to feed and care for the fish in the spring as to build up the ova, .which are 

 then developing in the ovaries, and knowing that the proper or improper treatment of 

 the fish at this time means a lot of good or bad ova the following season ; knowing also 

 what a great effect temperature has on the spawning offish, one would infer that the 

 high temperature of the sea water has such an effect on the reproductive organs that 

 it may compel the fish to leave the warmer waters of the sea and take refuge in the 

 rivers. These early fish, too, are the best fish, and Aery naturally so, clean-run fish 

 as we call them. 



When the water of the sea is of a low temperature, as in early spring, we do not 

 get in our Solway rivers such a large run of fish as we get later on. In the month of 

 March, for instance, when the east winds are blowing, the fish do not run nearly so 

 well as in April, and they do not run so well in April as in May. From 1880 to 1884 I 

 took up my residence at a place on the coast called Douglas Hall, where a considerable 

 salmon fishery existed, there being four stake nets fishing over a dozen pockets or 

 pounds. So regular was this spring run that, although the fishing legally commenced 

 in February, the nets were not put on before the end of March, and some of them in 

 April, because it was not remunerative to put them on earlier on account of the scar- 

 city of salmon. But later on, as the sea became warmer, a good many fish were found 

 running. If the weather remained cold and the temperature of the sea remained at 

 alow point the fish did not run; but as soon as the state of things was reversed, no 

 matter what the day of the month, in came the fish. 



F. C. B. 1893—7 



