Pacific Science, vol. 53, no. 2: 181-184 © 1999 by University of Hawai'i Press. All rights reserved

Observations of a Probable Hybrid Angelfish of the Genus Holacanthus from the Sea of Cortez, Mexico!

ENRIC SALA,2 OCTAVIO ABURTO-OROPEZA,3 AND JOSE L. ARREOLA-RoBLES3

ABSTRACT: A probable new hybrid angelfish was observed in Cabo San Lucas, Baja California, Mexico. Body coloration was olive brown, with a dark orange area behind the head and a vertical white bar posterior to the pec­ toral fin. The caudal fin was bright orange red, and pelvic fins were pale yellow. Dorsal and anal fin margins were bright blue and pointed. All characters sup­ port the hypothesis that the unidentified pomacanthid is a hybrid of Holacan­ thus passer and H. clarionensis, and we suggest a possible explanation for this interspecific hybridization.

THE STUDY OF HYBRIDIZATION may be use­ wall located in Cabo San Lucas, Baja Cali­ ful in examining patterns of dispersal and fornia, Mexico (22° 52.5' N, 109° 53.6' W). biogeography of fish species. Hybrids can This fish was swimming among king angel­ occur when changes in areas of distribution fish (Holacanthus passer) at a depth of 10 m result in two distinct but related species and was followed and recorded for 8 min coming into contact that, having originated with a Hi8 videocamera. The specimen could in separate areas, did not develop reproduc­ not be identified as any of the four species of tive incompatibility (Margalef 1974). Reports pomacanthids known from the tropical east­ of natural hybridization among marine ern Pacific (H. clarionensis, H. limbaughi, H. fishes, however, are relatively uncommon passer, Pomacanthus zonipectus) (Allen and (Slastenenko 1957, Schwartz 1981). Butter­ Robertson 1994). Although we could not flyfishes (Chaetodontidae) and angelfishes collect the unidentified specimen, we were (Pomacanthidae) contain, in this order, the able to analyze coloration and morphological greatest number of hybrids reported from traits from the video record, characters that marine species (see review by Pyle and Ran­ should be used together as diagnostic char­ dall 1994). Among angelfishes, only 11 hy­ acters in pomacanthids (Pyle and Randall brids and five other possible hybrids have 1994). The fish was swimming off a vertical been reported, none from the eastern Pacific. wall, grazing on turf algae and in the water Here we describe the first probable poma­ column (presumably on zooplankton) at an canthid hybrid from the eastern Pacific and approximate rate of three bites min-I. The suggest a possible explanation for this rare fish spent most of its time swimming back hybridization. and forth, following the wall. On 16 March 1997, an unusual pomacan­ Coloration and markings of the un­ thid was observed by the authors on a vertical identified pomacanthid were intermediate between those of Holacanthus passer and H. ------Glarionensis-t~igun:-l-)~BacKgmund-lxld¥- 1 This research was supported by the Stephen Birch coloration was olive brown, with the head Aquarium at the Scripps Institution of Oceanography (La Jolla) and the Tinker Foundation (New York). darker than the body. There was a dark or- Manuscript accepted 13 March 1998. ange area behind the head, almost forming a 2 Scripps Institution of Oceanography, University of triangle between the nape, the dorsal fin at California at San Diego, La Jolla, California 92093-0201 the level of the posterior edge of the pectoral (fax: 619-534-6500; E-mail: [email protected]). fin, and the midline of the body, whereas in 3Departamento de Biologia Marina, Universidad Au- tonoma de Baja California Sur, La Paz, RC.S. 23080, H. clarionensis there is simply an orange bar Mexico. from the dorsal spine down to the vent. In 181 FIGURE 1. Photpgraphs of A, Holacanthus passer; B, H. clarionensis; C and D, the probable Holacanthus hybrid, taken from a Hi8 videotape. The fish is about 25-30 'em total length. Photos A and B by M. Conlin. Probable Hybrid Angelfish of the Genus Holacanthus-SALA ET AL. 183 addition, a white bar extended vertically, just It has been hypothesized that interspecific posterior to the rear edge of the pectoral fin, hybridization occurs when conspecific mates from the midline of the body to the dorsal are in short supply (Allen 1979). Many hy­ fin; the white bar was shorter and thinner brid specimens result in areas where one spe­ than that of H. passer. The caudal fin was cies of a closely related pair is abundant and bright orange red, without the narrow blue the other species is rare (Randall et al. 1977, margin typical of H. clarionensis. The pecto- Allen 1979, Moyer 1981). Pyle and Randall ral fins were orange. The pelvic fins were pale (1994), however, questioned why an individ­ yellow, almost white. The margins of the ual of a common species would mate with an dorsal and anal fins were bright blue. The fish individual of a rare but closely related spe­ observed was clearly different from the third cies, if conspecific mates are available. In species of Holacanthus in the region, H. lim- Cabo San Lucas, H. passer is a common baughi, because H. limbaughi has a distinct species, but H. clarionensis is seldom seen. white caudal fin and background body col- Although the reproductive unit of H. passer oration is dark blue gray. is the pair (Moyer et al. 1983), sex ratios in The unidentified pomacanthid was ap- the Sea of Cortez are not always 1 :J. A re­ proximately 25-30 cm long (total length). cent study has shown that males may be two Body morphology was very similar to that of or three times more abundant than females in both Holacanthus passer and H. clarionensis, areas subjected to strong currents (e.g., Cabo but the fins showed intermediate traits. Dor- San Lucas), where water column feeding ag­ sal and anal fin margins are rounded in H. gregations occur (unpubl. data). This male­ clarionensis and pointed in H. passer; dorsal skewed sex ratio, observed all year long, may and anal fin margins were clearly pointed in have consequences on reproductive behavior the unidentified pomacanthid, although not of H. passer. Male H. passer usually occupy as much as those of H. passer. and aggressively defend the same area during All observed characters support the hy- reproductive season, and although a male pothesis that the unidentified pomacanthid is may spawn several times in one evening, a hybrid of H. passer and H. clarionensis. We females swim directly back to the reef after a believe it is unlikely that the fish observed is a single spawning (Moyer et al. 1983). Thus, new species ofrare Holacanthus related to the unless males migrate to other areas during two species. Cabo San Lucas is one of the reproductive season, higher numbers of most popular sites in Baja California for males can produce two situations: (1) a single scuba divers (including underwater photog- spawn per male per evening, or (2) some raphers), and as far as we know, there have males spawning several times in one evening been no reports or photographs ofindividuals and other males not spawning at all. In ad­ similar to the one described here. Both parent dition there may also be a number of males species are found in Cabo San Lucas, al- without established spawning territories. though they differ greatly in abundance. Ho- With this excess of males, mating between a lacanthus passer ranges from the central Sea male H. passer and a female H. clarionensis of Cortez to Ecuador and the Galapagos Is- may result. Because only solitary individuals lands (Thomson et al. 1979) and is the most of H. clarionensis have been observed in common pomacanthid in Baja California Cabo San Lucas and male H. clarionensis are J~~_n~llt:z-Q!!Lz_~!Jt.l.1997L~:l:Chingdensi!ieL~~l"e~wt:J!YIJothesL~that~_1!ybrid Q~twee!La up to 20 individuals 100 m-2 (unpubl. data) male H. passer and a female H. clarionensis is and water column aggregations up to 100 in- the most likely scenario. dividuals (Moyer et al. 1983). Holacanthus clarionensis is found at the Revillagigedo Islands and Clipperton Island, but it can also be found in low abundance at the southern ACKNOWLEDGMENTS tip of Baja California (from Cabo San Lucas to Cabo Pulmo) (Thomson et al. 1979, Allen We thank M. Graham for his valuable and Robertson 1994). comments on the manuscript. 184 PACIFIC SCIENCE, Volume 53, April 1999

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