166 FISH GALLERY. 



Most are pelagic, a few occur in the depths of the sea ; many, such 

 as the Mackerel and Tunny, are valued as food. 

 Mackerel. In the Mackerel, Scomber scombrus, 704, the fins are small, 

 and the tail is deeply forked. The colours are beautiful and the 

 general design is a dark green-blue on the back, with about 30 

 irregular black bands across the back and down the sides, and with 

 a delightful play of pink and pale green on the belly according to 

 the position in which the fish is held. This sheen is observable 

 in the dried skin and is due to an interference of light-waves 

 caused by minute particles of guanin or some other substance of a 

 uric acid nature in the skin. 



The Mackerel ranges from the south of Norway to the Canary 

 Isles, and throughout the Mediterranean, also along the Atlantic 

 coasts of the United States of America. Like the Anchovy it 

 invades the North Sea during the summer months and retires 

 before the winter. The shoals of Mackerel follow the Clupeoid 

 fishes in their migrations ; on the British coasts they usually leave 

 the open sea and approach the land in their pursuit of the young 

 Pilchards and Sprats. The Mackerel is generally taken near the 

 surface in drift nets and occasionally near the bottom in trawls j 

 the most productive British fisheries are off the south-west coasts 

 of England and Ireland. 



The Spanish Mackerel, Scomber colias, 706, is essentially a 

 fish of the Mediterranean and adjacent Atlantic, but occasional 

 stragglers are caught as far north as the Channel Isles and the 

 English coast. It is sometimes called the Spotted Mackerel because 

 of the distinctive blotches or spots ; it has an air-bladder, which 

 is wanting in the common Mackerel. 



In the genus Thunnus the anal and the second dorsal fins have 

 each from 7 to 10 Unlets, and the front, undivided portions are 

 deep and short-based ; the stalk of the tail has a distinct lateral 

 keel supported by a bony ridge of the vertebral centra ; the 

 pelvic fins are small, the pectorals are more or less elongate ; the 

 scales of the pectoral region are crowded and form what is called 

 Tunny, the ' corselet/ The Tunny [Thunnus thynnus, fig. 4, p. 14) is one 

 of the largest Tel eostean fishes, and grows to 10 feet and a weight 

 of 1,000 lbs. It is abundant in the Mediterranean and ranges to 



