DEPARTMENT OF MARINE BIOLOGY. 209 



The Significance of the Colors of Tropical Reef Fishes, by W. H. Longley. 



The months of June and July 1916 were spent at Tortugas in continued 

 investigation of the colors and color-changes of reef fishes. 



Three things were attempted: first, to obtain from nature submarine 

 photographs of some of the fishes whose changes in color and shade depend 

 upon the character of their environment; second, to ascertain the food and 

 time of feeding of as many species as it might be convenient to examine; 

 third, to determine to what extent green color is correlated with the habit 

 of living upon reef flats covered with turtle grass {Thalassia testudinum). 

 Incidental observations were also made which supplement those of other 

 seasons. For example, an additional labrid (Xyricthys sp.) has proven to 

 have the same interesting habit of burying itself in the sand at night that 

 has been described for Iridio and Thalassoma; and, besides 8 already reported, 

 adaptive color-changes have been noted in the following species: Epine- 

 phelus striatus, Neomcenis griseus, Scorpcena plumieri, Siphostoma mackayi, 

 and Sparisoma hoplomystax. 



As the photography was attempted under novel conditions, and the 

 possibility of obtaining positive results could be determined only by experi- 

 ment, much of the effort expended bore no immediate fruit. Some prints 

 were secured, however, which show that many of the most striking facts 

 regarding change in the pattern and shade of fishes in their normal habitat 

 may eventually be presented pictorially. 



The camera used was a Folmer and Schwing No. Graphic, which takes a 

 picture 2f by 1| inches in size. It was inclosed in a water-tight brass box 

 having plate-glass windows in the front and rear, and above. Necessary 

 adjustments of film, shutter, etc., were effected by screws guarded by flax 

 and grease packing. In every essential respect this apparatus was satis- 

 factory, for objects could be readily located in the finder, and a dozen expo- 

 sures could be made without sending it to the surface to be opened and 

 reloaded. It may be added, for the benefit of any who might think of 

 attempting similar studies, that one should avoid having the photographic 

 apparatus much heavier than the water it displaces. Additional weight inter- 

 feres with ease and rapidity of movement and multiplies the labor of hold- 

 ing the camera in one position until the fish to be photographed appears to 

 advantage. 



No good pictures were taken at depths exceeding 12 feet, but with a wide- 

 open stop an exposure of one-tenth of a second sufficed at that level between 

 10 and 2 o'clock on cloudless days. When this was learned from preliminary 

 experiments, effort was concentrated successfully upon photographing three 

 species — Ahudefduf saxatilis, Epinephelus striatus, and Lachnolaimus maximus. 

 The first is small, bright in color, and very active, but abundant in certain 

 places. The others are large, decidedly sluggish, and occur singly, except as 

 two or three of the last may occasionally be seen together. 



By repeated random shots at schools of Ahudefduf pictures have been 

 obtained, which show that when the fish is viewed from the side and a lower 

 level, at a distance of 12 to 15 feet its blue-gray markings are completely 

 resolved into the blue-gray of the water about it. Its contour is effaced, and it 

 is visible merely as a series of more or less disconnected parallel bars of brown 

 and yellow. With the others the necessary procedure is different. The 

 same individual may be found day after day in one place. Hence, by exercis- 

 ing patience a series of pictures portraying all the phases which either species 

 displays may be secured by leading a single fish from one characteristic envi- 

 ronment to another and photographing it in each. Through offering them 



