A Demonstration of Nesting in Two Antarctic Icefish (Genus Chionodraco) Using a Fin Dimorphism Analysis and Ex Situ Videos

Abstract

Visual observations and videos of Chionodraco hamatus icefish at the “Acquario di Genova” and histological analyses of congeneric species C. hamatus and C. rastrospinosus adults sampled in the field provided new anatomical and behavioral information on the reproductive biology of these white blooded species that are endemic to the High-Antarctic region. During the reproductive season, mature males of both species, which are different from females and immature males, display fleshy, club-like knob modifications of their anal fin that consisted of a much thicker epithelium. Histology indicated that the knobs were without any specialized glandular or sensorial organization, thus suggesting a mechanical and/or ornamental role of the modified anal fin. In addition, the occurrence of necrotic regions at the base of the thickened epithelium and the detachment of the knobs in post-spawning C. hamatus males indicated the temporary nature of the knobs. The role of these structures was confirmed as mechanical and was clarified using visual observations and videos of the behavior of two C. hamatus during a reproductive event that occurred in an exhibit tank at the “Acquario di Genova”. The reproductive process included pre-spawning activity, preparation of the nest, egg guarding and successfully ended with egg hatching. When the spawning event approached, the male prepared the nest. The nest was constructed on an accurately selected bottom surface, which was flattened and maintained free from sand or debris by a combination of radial body movements and continuous anal fin sweeping, thus demonstrating the important mechanical/abrasive function of the anal fin knobs. The present data are the first records of active nesting in icefish and clarify the meaning of dimorphic temporary structures, whose function would have been difficult to obtain in the field.

Intergeneric hybrids inform reproductive isolating barriers in the Antarctic icefish radiation

“…Furthermore, hybrid hatching peaked at 132 dpf (~4.5 months), which was well before hatching of N . coriiceps embryos (6 months post fertilization) cultured in similar conditions 43 but almost identical to the 138 days reported for the hooknose icefish Chionodraco hamatus 45 , suggesting that the hybrid embryos developed at a normal rate. While these results demonstrate the absence of early and drastic genetic incompatibilities, we cannot rule out the possibility that hybrid larvae, juveniles, or adults would be significantly less fit than parental species in terms of survival, growth rate, or mating success 46 .…”

“…Our knowledge of the daily timing of icefish reproduction is limited to the C . hamatus , which in captivity appears to reproduce at night 45 . Whether C .…”

Embryogenesis and early skeletogenesis in the antarctic bullhead notothen, Notothenia coriiceps

“…In contrast, eggs and zygotes of the Blackfin icefish Chaenocephalus aceratus , the Naked dragonfish G. acuticeps , the Patagonian rockcod Patagonotothen ramsayi , and several other species are negatively buoyant and are laid in circular mounds, in shallow depressions, or on rocks on the ocean floor (Detrich et al, ; Evans et al, ; Kock et al, ; Jones and Near, ; Arkhipkin et al, ). Several species of Antarctic Notothenioids brood their offspring, while the Chionodraco hamatus male builds the nest using seasonally modified, club‐like anal fins and the female subsequently guards eggs in the nest (Ferrando et al, ) [see (Ferrando et al, ) for review].…”

“…For comparison, the sub‐Antarctic Patagonian rockcod Patagonotothen ramsayi , when cultured at its habitat temperature of 5 °–6 °C, hatches in just 24 days (Arkhipkin et al, ). The first recorded natural mating of Antarctic fish in the Northern Hemisphere involved a pair of Chionodraco hamatus (hooknose icefish, see Desvignes et al, for etymology) that had been cultured for three years at ‐1 °C in an Italian aquarium; mating occurred in February and hatching in late June, about 19 weeks after fertilization (Ferrando et al, ). In the Ross Sea, Pleuragramma antarcticum appears to hatch in November, about 4 months after fertilization (Vacchi et al, ).…”

Life history strategies of the Scotia Sea icefish, Chaenocephalus aceratus, along the Southern Scotia Ridge

“…Slow somatic growth and late sexual maturity (around 5-8 years in several species) are other common features of icefish life history. Parental care has been documented in six species of channichthyids (Detrich et al 2005;Kock 2005;Kock et al 2006Kock et al , 2008Ferrando et al 2014;Knust and Schröder 2014), and nest guarding is suspected in other icefish (e.g. Chionodraco spp.…”