Japanese Sea Catfish Uses pH Detecting Whiskers to Hunt

Researchers have found that catfish lurking in Japan's seas hunt by detecting changes in water's acidity levels. A drop in pH levels due to carbon dioxide levels in oceans could impair their hunting abilities.

Japanese sea catfish, Plotosus japonicas, live in dark murky waters. Researchers at Louisiana State University and colleagues have now found that the fish catches prey by detecting slight changes in pH levels of the water.

The research is actually a part of an earlier project started by John Caprio of Biological Sciences at LSU, back in 1984. He and his colleagues in Japan were looking at the taste system in the Japanese sea catfish when they noticed that the fish were using whiskers to detect food.

The team knew that some nerves in the fish were responding to pH changes in water.

"I suspected the response was due to a change in pH caused by some of the tested stimuli," Caprio said. "It was obvious that there were sensory nerve fibers in these fish that were responding to transient lowering of the pH of the seawater; however, what I did not know was what function this response served."

Researchers fitted catfish with electrodes to monitor their hunting activities. They found that the fish were responding to respiration of small sea worms, polychaetes, which are a favorite food of the catfish.

When these tiny worms breathe, they release carbon dioxide and acid. This acid changes the pH of the water. The nerves in catfish pick up these slight variations to catch the worms.

"These fish are like swimming pH meters. They are just as good as a commercial pH meter in the lab," Caprio said in a news release.

Experiments in the lab, too, showed that the catfish would often move towards the side of the tank that had a lower pH than the surrounding water.

According to researchers, the highest sensitivity of the catfish was in natural seawater of pH 8.2. The fish lost its ability to detect prey in water with pH levels less than 8.

The research shows that increase in acidification of the oceans could leave these fish starving.

Ocean acidification is an unfortunate consequence of the industrial revolution. Burning of fossil fuels has resulted in billions of tons of carbon dioxide being released in the environment. Today, the levels of carbon dioxide in water is 390 parts per million and is expected to rise to 900 parts per million by 2100.

"Once the pH of the ocean drops much below 8, shell producing invertebrates can no longer produce their shells," Caprio said. "It is possible that the sensors could adapt to such a change, but we are not certain that this will happen. As of today, what we know is that these sensors work optimally in the vicinity of pH of 8.2, that of normal seawater. If ocean pH drops much below 8, a number of deleterious events are likely to occur."

Previous research has shown that oceanic acidification has impaired sea snails' jumping ability. These snails need to jump to avoid being eaten by other organism. Higher acidity level has also ruined sea urchins' digestion.

The current study will be published in the journal Science.