Icefish breeding colony discovered in the Weddell Sea

Environment | Tundras and Poles

By Julia Riopelle, Co-Editor in Chief

Published March 7th, 2022

A vast breeding colony of Jonah’s icefish, Neopagetopsis ionah, has been discovered in the southern Weddell Sea, Antarctica. The surprising discovery now prompts more questions about the behaviour of these unique icefish, the associations between Antarctic benthic communities and calls for support to establish a marine protected area.

Neopagetopsis ionah, also known as Jonah’s icefish, is an Antarctic fish that dwells on the continental shelf and slope of the Southern Ocean. This unique fish is the only known vertebrate to lack both red blood cells and haemoglobin—the iron-rich proteins that carry oxygen to the body’s cells—as they mature into adults.

A vast icefish breeding colony discovered in the Antarctic. | Purser et al. (2022) / Current Biology

Now the icefish have struck another sense of wonder, when a team led by Autun Purser, a deep-sea biologist working for the Alfred Wegener Helmholtz Centre for Marine and Polar Research, studied the Antarctic deep seafloor at Filchner Trough using the Ocean Floor Observation and Bathymetry System (OFOBS)—a towed camera system that is able to collect images and videos of the deep seafloor. The collected images revealed a scene that perhaps looked otherworldly.

A vast breeding colony of notothenioid icefish had been discovered. The researchers identified 16,160 fish nests within a 45,600 kilometre-squared area, with most nests containing one adult guarding approximately 1,735 eggs.

When extrapolating this number past their sample sight to an area of 240 kilometres-squared, the team believes that this vast breeding colony contains an estimated 60 million active nests and as much as 60,000 tonnes of fish biomass.

‘The collected images revealed a scene that perhaps looked otherworldly.’

‘To our knowledge, the area surveyed harbours the most spatially expansive continuous fish breeding colony discovered to date globally at any depth, as well as an exceptionally high Antarctic seafloor biomass,’ write Purser and his team.

The nests consist of coarser black rock fragments framing the outer edges, whilst being filled with a more diverse range of rocks, likely carried by the ice shafts, in the centre. Having eggs laid on rock fragments is a common strategy of Channichthyidae fish, the family of fish to which the icefish belong, as it allows them to to maintain aerations and cleanliness, as well as prevent eggs from being taken away by the current.

The team also recorded that the eggs in this colony, located at a depth range of 430 to 535 metres, have a 25% higher abundance than those on the southern extreme of the Filchner Trough—indicating more favourable conditions. This could possibly be due to the temperature conditions of the southern Weddell Shelf, recorded at -1°C to 0°C, as due to the many troughs present, modified warm deep water is able to flow upwards onto the Shelf.

Map of Antarctica viewed from above the South Pole. Location marker indicates the eastern flank of the Filchner Trough, where the icefish breeding colony was discovered. | NASA

The extent of the N. ionah fish biomass, as well as breeding colony size, may provide strong reasoning and increased support for the establishment of a marine protected area (MPA). Currently, there is only a proposal for the creation of an MPA in the Weddell Sea, which was developed by Germany and submitted by the European Union to the Commission for the Conservation of Antarctic Marine Living Resources four years ago.

With threats of climate change and marine fisheries, the Southern Ocean is an important site to preserve, due to its countless species—from benthic invertebrates to larger leopard seals, orcas and humpback whales—and strong upwelling currents that allow for nutrient cycling. The Weddell Sea itself experiences the pressures of krill fishing and thus the establishment of an MPA would increase the resilience of marine ecosystems to biotic and abiotic threats.

Whilst the epifauna (organisms living on the sea or riverbed), associated with the breeding community had low diversity and abundance, the team observed that the presence of the colony supported a growing invertebrate community in the area. Images showed that the dead N. ionahs carcasses provide food for scavenging octopi, brittle stars, star fish, pycnogonids (sea spiders) and other opportunistic fish species.

‘The area surveyed harbours the most spatially expansive continuous fish breeding colony discovered to date globally.’—Purser et al.

Another case for support of an MPA, is that the team also believes that the work N. ionah puts into building the nests—which involves the digging up and loosening of the seafloor sediment—could contribute to the local benthic microbial loop.

Productive microbial loops are strong indicators of healthy marine ecosystems. The term describes a trophic pathway that moves aquatic biomass, in the form of dissolved organic carbon, throughout different levels of the ocean. Essentially, it is a form of nutrient cycling, as the icefish are releasing dissolved organic carbon from the Weddell Sea sediment.

New questions arise from this one-of-a-kind discovery; how and how often do icefish build nests? Are the nests reused in successive breeding seasons? How do these icefish conduct their mating and spawning behaviour? And, do Weddell seals hunt for icefish within or near this vast breeding colony?

Perhaps the answers to these questions will provide more incentive to establish marine protected areas, in order to safeguard the mysterious and wonderful biodiversity hidden in the depths of our oceans.

Featured Image: Jay Ruzesky

German Federal Ministry of Food and Agriculture (BMEL) (2018) ‘Marine Protected Area in the Weddell-Sea, Antarctica.’ United Nations. Available at: [Accessed March 6th, 2022]

Jabr F. (2012) ‘How the Antarctic Icefish Lost Its Red Blood Cells But Survived Anyway.’ Scientific American. Available at: [Accessed March 6th, 2022]

Purser A., Hehemann L., Boehringer L. et al. (2022) A vast icefish breeding colony discovered in the Antarctic. Current Biology. Volume 32, issue 4, pages 842-850.

Shifting fish distributions in warming sub-Arctic oceans and the implication on fisheries

Environment | Tundras and Poles

The female scientists leading citizens to protect the world's coldest region

Sustainable Leaders | Global