98 Part second. 



A fish only found in the Aquarium at certain seasons is the Bellows- 

 flsh, also called the Trumpeter or Sea-snii:)e, Centriseus (Fig-. 54). 



The peculiar order of Plectognathi are characterised by the posses- 

 sion of an immobile upper jaAV and a spiny or armoured skin. They 

 are almost all tropical kinds; many , such as the Urchin-fish or Sea- 

 hedgehog-, the Globe-fish, and the Trunk-fish, are usually well represented 

 by dried specimens in Natural History Museums. The Bay of Naples 

 contains two examples of this curious order of fishes: the Sun-fish, 

 Orthagoriseus, and the File-fish, Balistes (Fig-. 77). The former has 

 up to the, present been one of the greatest rarities of the Aquarium, 

 and has rarely lived longer than a week, so that we can give no 

 interesting details of its habits. Balistes, however, is always present (in 

 tank 18) from spring till winter, and is very remarkable; its short body 

 being out of all proportion in height, and its mouth provided only with 

 very few teeth. It is a lively fish, loving companionship, and endowed 

 with great curiosity. It is, however, only in summer that it shews its 

 real nature, and specimens in the Aquarium always die at the commence- 

 ment of winter. It lives on mollusks and crabs , which it grinds 

 up with its sharp teeth, making- so much noise in so doing, that it can 

 be heard through the glass of the tank. It used formerly to share a 

 tank with the Turtle, but never let the latter get a meal, and it had 

 to be separated from the Lobsters, as it used to attack their eyes. 



We may now turn to the true pelagic «errant» forms, the Mackerels. 

 Just as the Petrel and the Frigate-bird spend their life hovering over 

 the endless expanse of the ocean, so the Mackerels rove about below 

 the surface of the sea, approaching the coasts only periodically, when, 

 however, they are caught in enormous numbers. 



Repeated trials to keep these shy but active fishes in the Aquarium 

 have been unsuccessful. Nor can we expect the Tunny, or its ally, the 

 Swordfish, two roving forms, to live in the cramped surroundings of 

 our tanks. They all career about madly for a few hours and then die. 

 Only one small genus of Mackerel, Liehia (Fig, 42), becomes accustomed 

 to its captivity and lasts out like Balistes during- the summer months; 

 its skin shines like silver. To the same order as the Mackerels belongs 

 the. « Cuckoo », Cappos (Fig. 53). Unlike its relations it lives at a 

 depth of 30 to 40 fathoms, but it also thrives well in the shallow water 

 of our Aquarium. 



