BONY FISHES AND GANOIDS. 



473 



surface is equally inconspicuous when viewed from beneath against the clear 

 sky above. Their blood has a temperature several degrees above that of the 

 surrounding water, and their flesh receives a larger supply of this fluid than 

 is ordinarily the case, and thus as- 

 sumes a more or less distinctly red 

 colour. So thoroughly are these fishes 

 pelagic in their mode of life, that they 

 even spawn in the open sea. In diet 

 they are carnivorous ; and at the time 

 of year when the various members of 



the herring-tribe seek the shore for the Fig. 9. COMMON MACKEREL. 



purpose of depositing their ova, they 



are pursued by the different kinds of mackerel, which prey either upon the 

 fry or upon the adult. The typical mackerels, or those constituting the 

 genus Scomber, have a continuous first dorsal fin, furnished with weak spines, 

 five or six finlets behind both the dorsal and anal fins, and the scales small 

 and evenly distributed all over the body, the teeth being small, and each 

 side of the caudal fin bearing two short ridges. There are several kinds of 

 mackerel some with and some without an air-bladder and the distribution 

 of the genus includes nearly all seas, although none are found on the 

 Atlantic coast of the temperate portions of South America. Of larger size 

 are the various fishes known under the names of tunny, albicore, and 

 bonito, which collectively constitute the genus Thynnus, and differ from 

 Scomber by the number of finlets reaching to from six to nine, the presence 

 of one ridge on each side of the caudal fin, and the concentration of the 

 scales on the fore-part of the body, where they form a kind of corselet. By 



far the most remarkable and interest- 

 ing members of the family are, how- 

 ever, the sucking-fishes (Echeneis), 

 characterised by the presence of a 

 large, plate-like, adhesive disc, occupy- 

 ing the whole upper surface of the 

 head. This sucker is formed by a 

 structural modification of the first 

 dorsal fin, and in the allied Elacate of 

 the tropical Atlantic, which has no sucker, the fin in question is still repre- 

 sented by a few short isolated spines. Sucking-fishes have minute teeth, 

 both on the jaws and on the palate, and in some cases also on the tongue ; 

 but they all lack an air-bladder. As they generally pass much of their time 

 attached to the under-surface of the body of a shark or a turtle, or the hull 

 of a ship, the back is less exposed to the light than the under-surface, and 

 consequently becomes less darkly coloured than the latter. The smaller 

 sucking-fishes grow to a length of about eight inches, whereas the larger 

 kinds may measure as much as three feet. 



The eighth family of the Cotto-Scombriformes includes the star-gazers 

 (Uranoscopus, Leptoscopus, etc.), the weavers (Trachinus), the Atlantic tile- 

 fish (Lopholatilus), and a host of other types too numerous 

 Family to mention. All these fishes have a more or less elongated 



Trachinidos. and narrow body, which has sometimes a naked skin, but in 

 other cases is clothed with scales. There are one or two 

 dorsal fins, of which the spinous portion is much less developed than the soft 

 part, which is like the anal. Finlets are always wanting ; and the pelvic fins 



Fig. 10. SUCKIKG-FISH. 



