How many species of goliath grouper are there? Cryptic genetic divergence in a threatened marine fish and the resurrection of a geopolitical species

Abstract

The goliath grouper Epinephelus itajara (Epinephelidae) is an exceptionally large marine fish that inhabits sub-tropical and tropical waters of the Americas and western Africa. Due to a lack of readily observable morphological variation in specimens across its range, the goliath grouper has been regarded as a single species. We tested the hypothesis that Pacific and West Atlantic populations constitute a single species by analyzing nuclear and mitochondrial DNA sequence data. We found numerous fixed genetic differences for mitochondrial loci between Pacific and West Atlantic goliath grouper (genetic distance D ≈ 3.5% at 16S and D ≈ 6% at cytochrome b; ϕst = 0.98 (p < 0.001) for 16S and ϕst = 0.98 (p < 0.001) for cytochrome b). The nuclear S7 intron showed 3 fixed nucleotide differences between Pacific and West Atlantic populations. Within the West Atlantic, we found few absolute genetic differences (D < 0.01 at 16S and D < 0.02 at cytochrome b), but statis- tically significant population structure based on haplotype frequency data (ϕst = 0.04 (p = 0.05) at 16S; ϕst = 0.14 (p < 0.001) at cytochrome b). These data indicate that (1) goliath grouper in the West Atlantic are subdivided into discrete populations, (2) goliath grouper populations in the Pacific and western Atlantic represent 2 (or more) distinct species, and (3) these distinct populations/species require separate management and conservation strategies. We resurrect the species Epinephelus quinquefasciatus Bocourt 1868 for Pacific goliath grouper.