THE PERCH 43 



they arise from emotional excitement, as is the case with the 

 rock goby (Gobius niger\ a marine fish, which turns from 

 ashen grey to a dark, angry smoke-colour when in pursuit of 

 prey. In the perch, as in the common trout and many other 

 fish, the skin responds sympathetically and automatically, but 

 by a mechanism not hitherto satisfactorily explained, to the 

 various colour rays reflected from surrounding objects. 



The degree in which fish of the Perch Family possess this 

 sensibility to colour environment, however temporary, happens 

 to have impressed itself upon my attention more forcibly in the 

 case of another member of the family, namely, the American 

 black bass (Micropterus salmoides], than in that of the common 

 perch. The black bass bears a strong general resemblance to 

 the British perch. Some years ago, having reared a number 

 of these bass from the yearling stage in a disused mill-pond, 

 and desiring to turn them into a large lake for naturalisation, 

 I had the said pond drawn with a net. The first draught brought 

 out half a dozen bass nine or ten inches long. The general tint 

 of these fish on back and sides was a rich dark olive-green. 

 Placed in a wash-tub, whereof bottom and sides had been 

 bleached to a whitish hue, they appeared very dark indeed. 

 A cloth was laid over the tub to prevent the bass leaping out, 

 and the net was made ready for a second draught. In fifteen 

 or twenty minutes, when some more fish were brought to the 

 tub, the first lot had completely changed their tint, being 

 closely assimilated to their new background. 



While treating of the perch, I have dwelt in some detail 

 upon this phenomenon of colour change, not because it is 

 the only fish of that family, but because it is the 

 only British fish in which the obvious intention of such 

 change, namely, concealment, is defeated by the permanence 

 of conspicuous markings. In other respects, similar aids to 

 invisibility are present in the perch as have been observed in 

 other vertebrates, both terrestrial and aquatic. For instance, 

 the belly of this fish is pure white, as is the case with so many 



