First in situ observations of the free-floating gelatinous matrix of blackbelly rosefish Helicolenus dactylopterus (Delaroche, 1809)

Reproductive mode in blackbelly rosefish, Helicolenus dactylopterus, has been debated since around 1900, and to our knowledge, there is no previous report on free-floating egg masses of H. dactylopterus. Some authors claim a viviparous strategy, others oviparous, or that the species displays a zygoparous or embryoparous form of oviparity. The most recent publications (ovarian studies) consider H. dactylopterus as zygoparous due to release of developing zygotes in the early phases of development. We report on the first free-floating, gelatinous egg mass matrices of H. dactylopterus, observed in situ. The first egg matrix was observed from Haganes, Bergen, Norway on 10 April 2020, at 20 cm depth. Live eggs were mostly of the same size (similar to 1 mm), and at late blastula stage. Ethanol-preserved eggs were obtained for DNA barcoding, employing sequences from the cytochrome c oxidase subunit I gene (COI). COI showed 100% similarity with sequences of adult H. dactylopterus. The second egg matrix was observed from Drengevika, Sveio on 12 April 2021, while diving at 15 m depth. Helicolenus dactylopterus is previously known for internal fertilization, and the in situ observations of these free-floating matrices, including embryos at late blastula stage, confirms theories of a zygoparous strategy.