First morphometry, reproduction, and genetic data for Blennius ocellaris (Linnaeus, 1758) from the Black Sea

Two specimens of the butterfly blenny, Blennius ocellaris, were caught off the coast of Ordu (Black Sea, Turkey) in April 2021 by trammel net. The aim of this paper is to further document occurrence and distribution of the butterfly blenny for the Black Sea and for Turkish marine ichthyofauna and to provide first morphometric, reproduction, and genetic data on this species to the Black Sea fauna species. Some morphometric and meristic characters were measured and presented as the percentage of total length (TL%). All morphometric measurements except eye diameter, pre-anal length, and maximum body depth were higher in the male individual. It was observed that the head makes up almost 1/4 of the body. It was determined that the ripe eggs were in their final stage of development (Stage IV). Gonad’s weight of a female individual was 2.85 g and the number of eggs was determined as 2993. The mean egg diameter was measured as 1070.7 ±15.63 μm (from 1050.2 to 1123.1 μm). The mitochondrial DNA gene regions of 16S rRNA and COI of the specimens were sequenced and analyzed. The generated partial sequences of COI and 16S rRNA were 621 bp and 551 bp, respectively. The maximum likelihood tree generated with the COI gene sequences retrieved from the GenBank database demonstrated geographic region-based distinction and sequences of the Black Sea specimens nested with the reference specimen sequences from the Western Mediterranean Sea and the Sea of Marmara.