214 Dr. Mac Culloch on the changing 



The Gadus Barbatus, or whiting, and the Tricirratus, or rockling, 

 occur in abundance in those Highland sea-lochs where the water is 

 at times perfectly fresh, from the magnitude of the rivers in rainy sea- 

 sons ; not quitting their haunts even when it is deeply tinged by the 

 colour derived from peat. From their permanence in those situa- 

 ations, and from being taken of all sizes, they probably spawn 

 there; and, if so, they offer, like the common river flounder and the 

 pike, perfect examples of the permanent convertibility of the habits 

 of these species. 



The Cottus Quadricornis, a native of the Baltic, also ascends 

 rivers, as does the GasterosteusPungitius, or stickleback, in our own 

 country. The Pleuronectes Platessa, or plaice, as has already been 

 observed, is naturalized to fresh water in East Friesland : and the 

 P. Flessus, or common flounder, is well known to be permanent 

 in the Thames and other rivers, far within the fresh water, although 

 equally a salt-water fish. The P. Roseus has also been taken in the 

 Thames. I am further informed that a sole was kept in a fresh- 

 water pond in a garden, by a person whose name I need not quote, 

 for a great many years ; and if the plaice and flounder can be so 

 naturalized, it is not unlikely that this wouldprove true of the 

 whole genus. 



Although the mackerel is rare in Scotland, it is sometimes taken 

 in the lochs of the western highlands, where the water, from the 

 entrance of rivers, is nearly or absolutely fresh ; a proof at least, 

 as in many other fishes, that whatever aversion they may have to 

 residing permanently in fresh water, whether from the want of food 

 or for other reasons unknown to us, they experience no difficulty 

 in respiring in it. 



The Mugil Cephalus, or mullet, which is a sea-fish, not only 

 ascends rivers, but has been introduced and detained in ponds ; 

 offering another example, like the plaice, of the possibility of per- 

 manently naturalizing a sea-fish to fresh water. This fish does not 

 necessarily spawn in rivers ; since, in England, it performs this 

 operation on the sandy and muddy shores of the sea. Yet, in 

 Asia minor, it appears that it always spawns in the rivers, ascending 

 the Sturmus, the Meander, and others for this purpose, and pro- 



