Abstract
The purposes of this study were to evaluate the present species classification, to develop genetic methods for diagnosing morphologically indistinguishable juveniles, and to investigate the potential for introgressive hybridization for species of the percoid fish genus Centropomus (Pisces: Centropomidae). We analyzed specimens representing all nominal species using allozyme electrophoretic data and sequence data from a 618-base-pair portion of the mitochondrial DNA (mtDNA) 16S ribosomal RNA (rRNA) gene. Outgroup taxa from the confamilial genus Lates were also included. Results of the allozyme analysis, based on 27 presumed protein-coding gene loci, were in good agreement with the most recent taxonomic revision of the genus. All morphological species were identifiable by diagnostic allozyme loci except the largescale fat snook C. mexicanus (also known as the constantino snook), which was distinguishable from its sympatric sibling species, the fat snook C. parallelus by a significant allele frequency difference at G3PDH* and Mexican snook C. poeyi which was distinguishable from its transisthmian sister species, white snook C. viridis by a significant allele frequency difference at GPI-1*. Results of the 16S rRNA analysis were also highly congruent with the morphologically based taxonomic revision. All morphological species were unambiguously characterized using 16S rRNA sequence, including those species not identifiable by allozymes. The number of autapomorphic base substitutions for each species ranged from 2 to 12. The minimum number of base substitutions that separated any pair of taxa was 11; no substitutions were observed within taxa. Composite restriction patterns generated by five restriction endonucleases distinguish the 12 nominal species. For species identification, keys based on allozymes and on restriction enzyme analysis of the 16S rRNA gene were formulated for the genus. No conclusive evidence for recent or ongoing hybridization between species was observed.
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