i 9 4i CATALOGUE OF FISHES OF TORTUGAS j^ 



Acanthurus caeruleus Bloch and Schneider. Blue tang 



Although Dr. Longley referred to the blue tang many times in his field notes, 

 no discussion of it was found among his manuscripts. To the synonymy in 

 Jordan, Evermann, and Clark's Cheeky list (1930, p. 362) should be added Teuthis 

 helioides Barbour (Bull. Mus. Comp. Z06L, vol. 46, 1905, p. 127, pi. 3) in accord- 

 ance with Dr. Longley 's list in Carnegie Institution of Washington Year Boof{ 

 No. 31 (1932, p. 300). 



This species evidently is common, as it was often observed. Generally it was 

 seen in company with hepatits. Its habits are slightly different, however, as it is 

 less of a bottom fish, and was often seen swimming high. It was commonly ob- 

 served on alga-covered bottom near shore, as well as some distance offshore 

 among coral heads and gorgonians, in water 10 to 12 feet deep. Once it was listed 

 from white sandy bottom. 



Its food, like that of hepatus and bahianus, consists wholly of vegetable matter, 

 but mixed with less sand and debris. Its digestive organs are typical of a vege- 

 table feeder, its stomach being large and rather thick-walled, and the intestine 

 very long. A specimen 122 mm. long had an intestine 475 mm. long. 



In color it is variable. Some large ones seen in about 9 or 10 feet of water, 

 swimming 4 or 5 feet above bottom, were very deep blue. Some individuals over 

 pale sandy bottom were described as "very light." A small individual, about 60 

 mm. long, was seen in two color phases. In one phase it was "yellow with three 

 narrow dark stripes on the body, angulated with apex forward; these about 

 width of pupil." In the other phase the body was "olivaceous, and apparently 

 what had previously been the dark stripes were now light: essentially a reversal 

 of the former pattern." A large one with white bands also was observed. 



The following notes appear in Dr. Longley's field data: "The young are clear 

 yellow, and this may appear as an alternative phase to the typical blue in speci- 

 mens up to 100 or 125 mm. in length. Have not seen it in larger ones. In the 

 yellow phase the iris and the margin of dorsal are blue, and the caudal yellow 

 with a blue margin. In the full blue phase the margin of the caudal is often more 

 blue than the remainder of the fin. The blue of the adult is sometimes so dark 

 as to be almost black, but the caudal lancelets are white in all phases." Another 

 observation reads: "I noticed the yellow replaced by blue in a specimen 62 mm. 

 long." 



The collection contains 7 specimens, 60 to 150 mm. long. They are now uni- 

 form light brown to dark brown, with dorsal, caudal, and anal margined with 

 black. One small specimen retains dark stripes on the dorsal and anal fins that 

 run parallel with the contour of the body at the base of these fins. 



A short, deep fish, with a steep anterior profile; caudal fin deeply lunate, with 

 acute lobes, the upper one slightly the longer. The following proportions are 

 based on 2 specimens, 86 and 150 mm. long, and the enumerations on 5 speci- 

 mens: Head 3.1 to 3.25; depth 1.4 to 1.5. Eye in head 2.6 to 3.3; snout 1.3 to 1.4; 

 interorbital 2.9 to 3.1; caudal peduncle 2.8 to 3.0; pectoral 1.0. D. IX,27; A. 111,25 

 or 26; P. 16 or 17. 



Atlantic coast of tropical America northward to Florida, sometimes straying to 

 Cape Cod. S. F. H. 



