A duel of fins and wings
Johannesburg - It is fins versus wings in a duel fought in the air where the fish wins.
This week, academics from North West University revealed to the world the first-ever footage of a predatory fish plucking a bird from the sky.
And it wasn’t a once-off – the scientists had watched tigerfish catch at least 300 swallows over 15 days.
The discovery, made at a small dam in the Mapungubwe National Park in Limpopo, surprised the researchers, but the real wow came when they worked out how the fish did it.
Professor Nico Smit, co-author of the study, said the fish’s brain had to figure out the angles of attack, making corrections to image distortions caused by refraction – all in a split second.
The feeding, Smit and the researchers found, begins in the late morning when the barn swallows come in low over Schroda Dam, skimming the water.
From data gleaned from five radio-tagged tigerfish, the researchers have been able to work out how these fish stalk and catch their prey.
“They swim below the birds, following the same line,” Smit said. “They match the bird’s speed, then they move faster than the bird just before they strike.”
The tigerfish launches from the water ahead of the bird.
Swallow and fish meet in mid-air, and 16 big, razor-sharp teeth do the rest.
Sometimes the strike is enough to stun the bird and cause it to drop into the water.
The fish will then circle the bird, taking bites out of it.
The study also found that the fish either attacked from just below the surface or from deeper water.
“The strikes from deeper water were more successful, and they surprised us more as they really have to compensate for refraction,” Smit said.
But not every attempt is successful.
“We originally thought that this was unique to the Schroda population, but there have been reports from other areas of sightings of tigerfish doing this,” Smit explained.
It was a sighting by Smit’s co- researcher Francois Jacobs that alerted them to the phenomenon. Jacobs had gone to Schroda Dam to radio-tag fish, when he saw the unusual feeding behaviour.
“We said ‘no way’,” Smit said. “Francois said he would show us, and when we went back, we saw it.”
But birds do get their own back.
Heading into the middle of the dam to catch swallows makes the tigerfish vulnerable to one of their biggest predators – fish eagles.
Now having recorded bird-eating behaviour in the Schroda population, the professor and his team will be heading to other sites around the country to see if they can spot the same phenomenon.
Fishermen are already e-mailing Smit regarding their bird-eating fish tales.
Once they would have been considered fishy, but now science is taking notice. - The Star