|dc.description.abstract||Black hamlet (Hypoplectrus nigricans)
was observed to vary in coloration and morphology in Puerto Rico, Mexico and Belize. H. nigricans from Puerto Rico exhibited a larger, grayish body (pectoral fins transparent), with long and pointed pelvic fins, and lunate caudal fin, while individuals from Mexico and Belize exhibited a smaller, darker body (including pectoral fins), with shorter and no pointed pelvic fins, and a truncated caudal fin. Occurrence of coloration and morphology variations of H. nigricans had not been previously
noted, and this is the first record of such in the western Atlantic. Color variants are known for at least four species of poplectrus; however, these variants
appear to be sympatric in the same geographic region.
In contrast, H. nigricans variants may be allopatric. Smaller, darker variants were not found in Puerto Rico, while larger, grayish variants were not found in Mexico or Belize. Reasons for the occurrence of geographically segregated H. nigricans variants are not fully understood, but a hypothesis that may explain it, still needing further testing, is ongoing