This species is distinguished from all its congeners by the following: differs from P. stellatus by the absence of stripes on the dorsal and anal fin rays (vs. presence); differs from P. flesus with more than 99.999% certainty using genotypes of at least three of the outlier loci which were genotyped in this study (Loci 886, 3599, and 1822), with dorsal-fin rays 46-59 (vs. 51-66) and anal-fin rays 35-41 (vs. 35-45). Reproductive traits (viz. egg morphology and buoyancy, as well as sperm physiology) are distinct diagnostic characters with eggs of P. solemdali become neutrally buoyant at salinities between 16 and 21.5 psu and are 0.99 ± 0.05 mm in diameter, whereas the eggs of P. flesus in the Baltic Sea are larger, 1.3-1.5 mm, and reach neutral buoyancy between 11 and 18 psu). Spermatozoa of P. solemdalis activate at minimum salinities between 2 and 4 psu (vs. required salinity above 10 psu for P. flesus) (Ref. 119386).