136 SALT-WATER FISHES 



mucous covering which extends over its body diminishes 

 friction with the water, and inside as well as out everything is 

 so disposed as to give the perfection of equilibrium and facilitate 

 rapidity of movement through the water. Our common 

 mackerel fills almost as efficiently the ideal of a swift fish, 

 and it would be difficult to name another capable of such 

 activity in either rough or smooth water, in the state of freedom 

 or hooked in the mouth and thereby handicapped. 



Carangidae 



The Horse-Mackerels 



The Horse-mackerel (Caranx trachurus), or Scad, though 

 sufficiently distinct from the true mackerels to preclude all 

 risk of confusion, nevertheless recalls the mackerel in outline, 

 and is always captured in its company, unless it is in a shoal of 

 its own kind. The fish is recognisable by the row of sharp 

 scales along the lateral line, as well as by its duller blue-grey 

 colouring, and the presence of only eight (instead of eleven 

 or more) spines in the front dorsal fin. In size it resembles 

 the mackerel, a large example of either measuring about 

 20 in., and individuals exceeding that length being the 

 exceptions. In weight, too, 3 lb. is the approximate limit. 

 Its habitat is also, like that of the mackerels and their allies, 

 southern, nor does it, from all accounts, find its way as far 

 north as the other fish. The two swim in company on the 

 south coast ; but the scad is more commonly taken on the 

 ground-lines, when the mackerel shoals have " broken up " 

 and gone to the bottom, than on the surface-lines in early 

 summer. Similarly, the scad occurs in the trawl more often 

 than in the drift-nets. These results, therefore, seem to point 

 to its keeping closer to the bottom than the mackerel. It 

 is even more uncertain in its migrations, though, by reason 

 no doubt of its commercial unimportance, these have been 

 but little studied. In 1897, as a case in point, thousands 



