species, the frog-fish or sea-clown (Anlennarius inannoralns = A. hislrio) is a regular dweller 

 among sargassum weed. Although related to the angler-fishes, it is not very like them. Its 

 small squat body, measuring from H to 2 inches in length, can be slightly inflated, and on the 

 snout stand spiny rays erected like horns. The mouth is larger in the vertical plane and the 

 pelvic fins have come to be placed almost beneath the chin. The rough skin is covered with 

 many cutaneous tags and also with parasites. The colours of these small fishes are extremely 

 handsome, there being dark marblings on an orange background and light-blue bands on the 

 fins. The males are distinguished from the females by their more vivid colours. For a long 

 time frog-fishes were thought to build a nest in the sargassum weed, but we now know that 

 the eggs that were attributed to them are those of the flying-fishes that play in these quiet 

 confines. 



Under this " coastal carpet ", that shines golden in the sun, come in succession all the 

 different levels of marine life down to the cold, dark abysses. Here, at a depth of more than 

 3,000 fathoms, blind and degenerate brotulid fishes slide over the ooze. Higher in the water 

 come black, bathypelagic fishes with their luminous organs flashing. Then above these, perhaps 

 at the limit of the isotherms forQoorlQo C, that is towards 500 or 600 fathoms, occurs the myster- 

 ious reproduction of the freshwater eels. Having forgotten their life in the fresh waters of 

 far-ofl' continents they have changed into deep-sea fishes and, after their great journey across 

 the ocean, they finally come together for the long-awaited breeding act. Their transparent 

 eggs are laid to drift in water masses, from which the adults will never return. 



This Sargasso Sea seems to be an immense breeding ground, for below some 270 fathoms, 

 at the lowermost point of the 14oC. isotherm, albacores also come to spawn. The natural 

 historv of these fishes will now be told. 



The epic story of tunny-fishes. 



Whereas the great rovers of the open ocean, the sharks and swordfishes, wander unexpected 

 and alone, the tunny-fishes are masters of the seas of all three oceans; the Atlantic, the Indian 

 and the Pacific. They range over all the tropical and temperate regions of these immense 

 marine expanses. Their schools regularly appear in definite localities, where maritime popu- 

 lations await their arrival as a source of wealth. 



Among fishes they are in a " class " by themselves. In form they are the most highly 

 evolved of the rapid swimmers, being shaped as perfectly as a torpedo. The " midships section " 

 is set forward so as to contend with the resistance of the water and to allow the easy sliding of 

 the backwardly tapering body. Over the rear section, the flow of water is facilitated by series 

 of finlets, and lateral keels strengthen the base of the caudal fin, this being a powerful rudder. 

 Tunny can keep up a speed of 20 knots and cross an ocean in the same time as a large steamer. 



This expenditure of power is made possible by certain anatomical features. The segments 

 of the large lateral muscles fit together in the form of strong, supple cones. A subcutaneous 

 blood system with main branches placed along the muscle surface furnishes a blood reserve to 

 avoid a loss of energy. Unlike other fishes, their temperature does not follow that of the surround- 

 ing medium, but exceeds it by about 8°C. As tunny are essentially stenothermal and live in 

 waters with temperatures never less than 14°, and which may reach 24oC., this means that the 

 muscles are continually kept at temperatures from 22° to 32° C. The character and taste of 

 the flesh recall that of warm-blooded animals, so it is more logical to speak of " tunny-meat ". 



Four species of tunny can be distinguished : 



— bluefin tunny (Thunnus tliynniis (L.); 



— blackfin tunny (Thunnus atlaniicus (Lesson); 



— albacore (germon) (Thunnus alalunga (Gmelin); 



— yellowfin tunny (Thunnus argentiviltatus (C. V.). 



102 



