“The fish is like a swimming pH meter.” Acid for breath
Seawater normally varies between 8.1 and 8.2, but Caprio found that a drop of just 0.1 – a slight increase in acidity – was enough to get the fish hunting. This is measured on the pH scale: 0 is completely acidic, 7 is neutral and 14 is completely alkaline. Instead, they found that the fish respond most strongly to slight variations in the acidity of seawater. So his team applied one after another to the fish’s whiskers to find out which ones triggered the hunting behaviour. The fish largely ignore empty tunnels, so how do they know which ones are occupied?Ĭaprio had assumed that the catfish could smell chemicals from the worms, such as amino acids. When they do, they rapidly suck out the worms. Thanks to infrared footage of them hunting in laboratory aquariums, in pitch darkness, they knew that the fish rapidly home in on the U-shaped tunnels that polychaete worms dig in the sand. John Caprio of Louisiana State University in Baton Rouge and his colleagues have been studying the catfish for several years. It feeds on worms living in sandy tunnels dug into the seabed. Try not to breatheįirst described in 2008, the Japanese sea catfish only lives around the southern tip of Japan and the volcanic Ryukyu Islands that arc south-west towards Taiwan. The catfish is the first fish we know of that homes in on prey by detecting changes in water acidity. Just like Leary’s counterculture rebels, acid is key to its success – but not the mind-altering kind. That’s how it hunts worms, hiding in the seabed, at the dead of night. For the Japanese sea catfish, a better motto would be “tune in, swim down, suck worms”.
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