Sillago persica sp. nov., a new sillaginid (Perciformes, Sillaginidae) from the Persian Gulf

A new species of sillaginid fish, <i>Sillago persica</i> <b>sp. nov</b>., is described from 30 specimens collected along the southern coast of the Persian Gulf (Busher), Iran. Morphological comparisons with 15 congeneric species, including members of the <i>S. sihama</i> complex, show that <i>S. persica</i> closely resembles <i>S. sihama</i> in meristic counts and coloration but is clearly distinguished by a unique swim bladder morphology. The posterior sub-extensions of the anterolateral swim bladder extensions in <i>S. persica</i> display a complex structure comprising five broad extensions connected to the swim bladder body, a feature absent in <i>S. sihama</i> and other sillaginids. Additional diagnostic characters include distinct meristic, morphometric, and coloration traits. Molecular analyses of mitochondrial cytochrome c oxidase subunit I (COI) sequences corroborate this species' distinctiveness, with phylogenetic reconstruction placing <i>S. persica</i> haplotypes and a previously recognized G5 clade haplotype of the <i>S. sihama</i> complex in a strongly supported monophyletic clade sister to <i>S. indica</i> and <i>S. suezensis.</i> Intraspecific genetic divergence within haplotypes of silaginid species and clades of <i>S. sihma</i> ranged from 0.00 to 0.01 (K2P). The <i>S. persica</i> haplotypes matched the G5 clade of <i>S. sihama</i> (0.01, K2P distance) whereas it exhibited 0.18-0.24 K2P divergence from haplotypes of other sillaginid species and clades of the <i>S. sihama</i> complex. A detailed morphological description is provided along with diagnostic illustrations.