Melanism in the Rock Beauty, <I>Holacanthus Tricolor</I

800 BULLETIN OF MARINE SCIENCE, VOL. 32, NO.3, 1982

BULLETIN OF MARINE SCIENCE, 32(3): 800-802, 1982

MELANISM IN THE ROCK BEAUTY, HOLACANTHUS TRICOLOR, (PISCES: POMACANTHIDAE) IN PUERTO RICO

Patrick L. Colin

Development of excessive melanin in fishes has been documented by numerous authors, but in their bibliographies of fish anomalies Dawson (1964; 1966; 1971) and Dawson and Heal (1976) failed to list records of such development among coral reef fishes. Specimens of the rock beauty, Holacanthus tricolor (Bloch), of the tropical western Atlantic have been collected along the south and west coasts of Puerto Rico exhibiting a wide variety of atypical melanism. The fish normally has only a small blue-edged black spot (slightly larger than the eye) on the posterior portion of the body at sizes near 25-mm standard length (S.L.). This black area expands with growth until at sizes larger than 75-100-mm S.L. to the max- imum size of about 400-mm S.L. it occupies the posterior two thirds of the body (see Bohlke and Chaplin, 1968: pI. 17). Melanistic specimens from Puerto Rico have the black area expanded forward on head and chest. Figure I shows two extreme examples of melanin development collected at the insular shelf edge off La Parguera on the south coast. In several cases the fins were also darkened with localized areas of melanin (such as pec- toral, pelvic and caudal fins in Fig. lB) and the eye often had melanin development. The right and left sides of the same individual often exhibited different degrees of melanin development. Similar melanism has not been observed elsewhere in the western Atlantic in spite of extensive field work over much of the area. Over much of the Caribbean, Bahamas and Florida it is common to see large rock beauties with the front of the head slightly duskier than the rear of the head, but the extreme development documented here has been observed by the author only around Puerto Rico. At the insular shelf edge, 10 km south of La Parguera, it was estimated about 3% of individuals observed had minor development of melanin and less than 1% had extreme occurrence, such as is illustrated in Figure I. A few individuals of one other reef fish, the tomtate (Haemulon aurolineatum), had some abnormal black blotches. These individuals were seen in the same area where melanistic rock beauties occurred, but were not collected. There seems to be nothing unusual about the area, a typical shelf edge reef at 12-20-m depth, where most melanistic rock beauties have been observed. Specimens are deposited in the University of Puerto Rico fish collection (UPR). Melanistic H. tricolor appear to behave normally. In one instance a female about 200-mm S.L. with several black blotches spawned with a normal male, indicating that melanistic fish are probably not reproductively isolated by behav- ioral factors. Except for coloration, the affected fish appeared morphologically normal and it is believed that the observed melanism does not represent a geo- graphic variant of this widely distributed reef fish. Greenfield (1974) briefly described melanism in 5 species of squirrel fishes of the genus Myripristis from the Indo-Pacific in which most melanistic individuals had a random scattering of black scales and areas of black pigment on the body and fins. One collection of 103 individuals of Myripristis pralinus from the Com- NOTES 801

Figure I. Examples of melanism in Ho/acanthus tricolor: A, Specimen 104 mm S.L. (UPR 3452); B, Darkest individual collected, entire head is darkened, 106 mm S.L. (UPR 4354). oro Islands had 23% of individuals with some degree of melanism. This is the only published report of melanism in a reef fish similar to the present observations of which I am aware.

ACKNOWLEDGMENTS

This work was supported by the Division of Ocean Sciences, National Science Foundation grant OCE76-02352. I would like to thank three anonymous reviewers for suggestions improving the manu- script. 802 BULLETIN OF MARINESCIENCE, VOL. 32, NO.3, 1982

LITERATURE CITED

Bohlke, J, E., and C, C. G, Chaplin. 1968, Fishes of the Bahamas and adjacent tropical waters, Livingstone Pub!. Co., Wynnewood, Pa. 771 pp. Dawson, C. E. 1964. A bibliography of anomalies of fishes. Gulf Res. Rpts. I: 308-397. --. 1966. A bibliography of anomalies of fishes, Supplement I. Gulf Res. Rpts. 2: 169-176. ---. 1971. A bibliography of anomalies of fishes, Supplement 2. Gult Res. Rpts. 3: 215-239. ---, and E. Heal. 1976. A bibliography of anomalies of fishes, Supplement 3. Gulf Res. Rpts. 5: 35-41. Greenfield, D. W. 1974. A revision of the squirrelfish genus Myripristis Cuvier (Pisces: Holocentri- dae). Nat. Hist. Mus. Los Angeles County, Sci. Bull. 19: I-54.

DATE ACCEPTED: January 29, ]982.

ADDRESS: Mid-Pacific Research Laboratory, Enewetak Atoll, Marshallistands, % Hawaii Institute of Marine Biology, P.O. Box /346, Kaneohe, Hawaii 96744.