Variability in the number of rays and specification of the dorsal fin formula of the black scorpionfish Scorpaena porcus Linnaeus, 1758 (Pisces: Scorpaenidae) from the Black Sea

Out of the morphological criteria for the fish species, the meristic (countable) characters are of the key role, in particular the number of rays in the fins. It is one of the stable signs of fish morphotype not subjected to size and age variability. At the same time, it is a clear taxonomic criterion. The aim of the work was to study the variability in the number of rays in the dorsal fin and to specify its formula for the black scorpionfish inhabiting the Black Sea off the coasts of the North Caucasus and Crimea. In total, 232 individuals of the black scorpionfish were investigated; those were sampled from six areas of the Black Sea off the coasts of the North Caucasus (Bolshoi Utrish, Magri, Loo, and Adler) and Crimea (Sevastopol and Feodosiya). The number of rays in the dorsal fin of each fish was counted, with dividing them into hard (unbranched) and soft (branched) ones. As established, the total number of rays in the dorsal fin of the black scorpionfish inhabiting the coasts of the North Caucasus and Crimea averaged (22.1 ± 0.02); the number of hard rays, (12.0 ± 0.01); and the number of soft rays, (10.1 ± 0.03). All three indicators are characterized by low variability (coefficient of variation is lower than 10 %). Fish caught off the coasts of the North Caucasus and Crimea differ statistically significantly from each other in the number of soft rays in the dorsal fin [(10.1 ± 0.03) and (10.0 ± 0.04), respectively] and in the total number of rays in the dorsal fin [(22.1 ± 0.03) and (22.0 ± 0.04), respectively]. The analysis of the results obtained reveals six possible variants of the dorsal fin formula for the black scorpionfish. Those are: D XI 10; D XI 11; D XII 9; D XII 10; D XII 11; and D XIII 10. The most common variant is D XII 10 averaging 83.2 % (75.0–88.9 % depending on the area). The updated dorsal fin formula for the black scorpionfish inhabiting the coasts of the North Caucasus and Crimea has the following form: D (XI) XII (XIII) (9) 10 (11). The formula can be used when compiling the species guides of the Black Sea fish. The results obtained were compared with those of other researchers. The causes for the disagreement between the results were analyzed.