Fish have prepared for Cape drought for millions of years
The Cape galaxias fish has a mysterious habit of repopulating dry river beds, seemingly out of thin air
Stockpiling water is popular in parched Cape Town – but not only among humans.
Scientists believe a little-known fish in Cape rivers may have been doing this since the dawn of time to survive drought conditions.The Cape galaxias, a “relic fish” whose ancestors populated the super-continent of Gondwanaland that split apart millions of years ago, has a mysterious habit of repopulating dry river beds, seemingly out of thin air.
Turns out the wily fish may survive dry spells by insulating itself in underground water bubbles – a technique observed in some other fish and aquatic invertebrate species, according to a team of freshwater scientists studying Cape rivers.
“We are actually starting to think that it (the Cape galaxias) goes down into the sediment and builds a cocoon around itself to secure some water on its gills and the sensitive mucous membranes that line its body,” said Jeremy Shelten, a researcher at Cape Town’s Freshwater Research Centre (FRC). “As long as it has that (water) it can survive for a few months.”“It is a trait that would make a big difference in terms of climate warming. If we can understand how a species is equipped to deal with the disappearance of surface water then it is a pretty big deal,” he said.Shelten and his colleagues are currently sploshing up and down several of the peninsula’s rivers to reveal this fish’s ecological secrets in the context of climate change, which is expected to raise water temperatures by around 2°C over the next 50 years, according to FRC director Dr Helen Dallas. They have recently observed several local rivers dwindle and disappear, including the so-called “perennial rivers” supposed to flow throughout the year.
“What we are seeing on the maps are that some rivers labelled perennial are not flowing anymore. There is a shift from perennial to seasonal,” Shelten said.This shift was likely to impact on fish behaviour, he added.
In one recent case the entire fish population of a large section of river was stranded in one little pool about one metre long – which subsequently dried up altogether. “I managed to save about 20 of them,” said freshwater researcher Toni Olsen, currently busy with a study of thermal dynamics for her Masters thesis at the University of Cape Town.By monitoring fish response to fluctuating water temperature, these researchers hope to establish which species are likely to be more resilient to climate warming, Olsen said. To date the Cape galaxias appears to be a tough customer. “It’s about how hot they can handle basically,” Olsen said.
Fish typically start losing their balance when “thermally stressed” – one of several behavioural signs periodically observed in experiments designed to examine thermal tolerance.
Shelten said there were several species of Galaxias scattered throughout the Southern Hemisphere, each with its own unique characteristics. “These fish are really ancient. They are Gondwanan relics which means they are so old they were around when Africa was connected to America, and the hypothesis is that as Gondwanaland broke up it took these fish with them and then they speciated (evolved into separate species) – and that’s why we now have different species around the world.”