A new species of sillaginid fish, Sillago persicasp. nov., 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 S. sihama complex, show that S. persica closely resembles S. sihama 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 S. persica display a complex structure comprising five broad extensions connected to the swim bladder body, a feature absent in S. sihama 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 S. persica haplotypes and a previously recognized G5 clade haplotype of the S. sihama complex in a strongly supported monophyletic clade sister to S. indica and S. suezensis. Intraspecific genetic divergence within haplotypes of silaginid species and clades of S. sihma ranged from 0.00 to 0.01 (K2P). The S. persica haplotypes matched the G5 clade of S. sihama (0.01, K2P distance) whereas it exhibited 0.18–0.24 K2P divergence from haplotypes of other sillaginid species and clades of the S. sihama complex. A detailed morphological description is provided along with diagnostic illustrations.
