1474. 



ZOOLOGICAL SOCIETY BULLETIN 



living much upon seaweed. The Bermuda chub 

 runs in schools of hundreds, and specimens are 

 sometimes taken weighing over fifteen pounds. 



The name rudder-fish has been given it on 

 account of its habit of following vessels at sea. 



The photograph presented in this Bulletin 

 is especially interesting, as it shows two of the 

 color phases it can assume. The camera hap- 

 pened to record one of them in the spotted 

 phase, to which it can change instantly. 



On one occasion, when the flow of water had 

 been stopped on account of repairs to a circu- 

 lating joump, and the air-pump started instead, 

 all of the seven Bermuda chubs in the tank at 

 once assumed the spotted phase, which was re- 

 tained an hour or two until the flow of water 

 could be resumed. The white spots were un- 

 usually sharp and distinct over the entire body, 

 except on the head, but all the fins remained 

 verj^ dark. A pure white band developed across 

 the top of the head, with longitudinal white 

 bands along the jaws. All the fishes were swim- 

 ming very actively, and were much excited over 

 the fountain of white air bubbles escaping from 

 the air tube at the bottom of the tank. 



We have found by experiment that many 

 species of tropical fishes can be made to change 

 their colors or markings at any time by shut- 

 ting off the water supply and starting the air 

 pump. The writer described many of the in- 

 stantaneous color changes of fishes in the Aqua- 

 rium in the Report of the Zoological Society for 

 1908, but the color changes of the Bermuda chub 

 were not observed at that time. It is not often 

 that these chameleon tricks of the fishes can be 

 caught by the camera. 



THE BLACK TRIGGERFISH 



(Melichthi/s radula, var. piceus) 



By L. L. Mowbray 



WHILE collecting specimens for the New 

 York Aquarium at Turk Island, B. W. 

 I., in June, 1916, I found the black 

 triggerfish (Melichthys radula, var. piceus^, in 

 large numbers, living on what is known to local 

 fishermen as the ledge. A ledge is the edge of 

 a shallow reef, and this ledge is sunk in six or 

 seven fathoms of water, while just beyond it 

 the water is from twenty to one hundred fath- 

 oms deep. 



The black triggerfish is so ravenous that it 

 will take bait of an}'^ kind, which, of course, 

 makes it easy to catch. When I asked one fish- 

 erman if the triggerfish would bite in all sea- 

 sons, he replied in the affirmative, and added. 



"I believe they would eat a man if they got the 

 chance." After observing some captured speci- 

 mens I could not help agreeing with him. When 

 caught and placed in a collecting tank, the first 

 would attack the later arrivals, and always 

 about the eyes. In this way 75 per cent of the 

 catch were blinded. 



The fish when swimming appears to be jet 

 black with a white line at the base of the dorsal 

 and anal fins, and another, finer white line on 

 the caudal fin. Removed from the water, how- 

 ever, and its coloration more closely observed, 

 it proves to be a beautiful blue-black, with a 

 greenish ventral aspect. The breast and cheeks 

 are yellow ochre, blue and yellow lines radiate 

 from the eyes, and the delicate lines on the cau- 

 dal fin and at the base of the dorsal and anal 

 fins, are pale blue. Each scale is edged with 

 pale blue, forming a lozenge-shaped pattern, 

 the acute apex of which is vertical. In my 

 opinion it is the most beautiful of the Atlantic 

 triggerfishes. 



Prof. Poey described this fish from the West 

 Indies, as not very common, under the name of 

 M. piceus. He regarded it as identical with 

 the East Indian form, Balistes buniva, ringens, 

 or nic/er, which he thought had been wronglj^ 

 identified. 



Dr. Gilbert described the black triggerfish 

 as M. bispinosus, overlooking the third dorsal 

 spine, which is, in fact, so short as to be hardly 

 more than a stump and most difficult to detect 

 in some specimens. Dr. Gilbert's specimens 

 were from Clarion and Socorro Islands. The 

 fish has also been taken at the Galapagos Is- 

 lands, Honolulu, and Johnston Island in the 

 Pacific, and identified as M. radula, althougli 

 the type appears to have come from the Island 

 of Ascension, which is the type locality of Bal- 

 istes vetula and many other species found in 

 the West Indies. 



INIr. R. C. jNIurphy, of the Brooklyn Museum, 

 has recorded Balistes vetula from South Trini- 

 dad, a small island in lat. 20° 30" south, long. ^ 

 29° west. 



St. Helena, Ascension, and South Trinidad 

 lie in the track of fishes crossing the South At- 

 lantic from the East Indies via the Cape of 

 Good Hope. The currents and southeast trade 

 winds, as well as the temperature, are favor- 

 able to fishes making this journey, the temper- 

 ature — the most important factor — being 70° F. 

 or higher, north of lat. 25° south. These is- 

 lands are therefore all likely places for the 

 fishes to be found, especially when it is remem- 

 bered that the South Equatorial current flows 

 to the westward without interruption until it 



