FibHLS. 361 



of living exclusively in fresh water, when confined in a lake 

 or river *. 



The circumstance of some fish being capable of living 

 either in fresh or salt water, has suggested the idea of at- 

 tempting to modify the constitution of salt-water fishes, so 

 as to enable them to subsist in fresh water. If the change 

 is attempted to be produced in young fish by degrees, and 

 with caution, the experiment may prove successful, espe- 

 cially with those fish that reside chiefly near the sea-shore. 

 But in the case of fishes which live in deep water, a change 

 not only in the respiratory organs must be produced, but 

 likewise in those of digestion, as they must subsist on a new 

 kind of food. We regard such experiments as curious, but 

 can scarcely bring ourselves to believe that they will be 

 productive of advantage to society. 



We possess but few accurate observations on the distri- 

 bution of fishes, with respect to temperature. Living in an 

 element subject to little variation from the change of the 

 seasons, fishes, like sea-weeds, have an extensive range of 

 latitude as well as longitude through which they roam. But 

 they appear to abound in the greatest variety of species in 

 the equatorial regions, and to diminish in numbers with re- 

 gard to species as we approach the poles. In this country 

 we may observe a certain arrangement of some of the spe- 

 cies with respect to latitude. Thus, the fresh-water fishes 



* The Honourable DAINES BARRING-TON, gives evidence of this in the 

 case of the smelt and the grey mullet. Phil. Trans, p. 312- We are like- 

 wise informed in the Statistical Account of the parish of Lismore (Stat. Ace. 

 vol. i. p. 485.), " That about 50 or 60 years ago, there were some sea- 

 tronts carried to these lakes, the breed of which preserve their distinction 

 perfectly clear to this day. They retain their shining silver-scales, though 

 they have no communication with the sea ; their flesh is as red as any sal- 

 mon, and their taste is totally different from that of the yellow-trout. 



