AsianScientist (Jun 13, 2014) – Animals incorporate a number of unique methods for detecting prey, but for the Japanese sea catfish, Plotosus japonicus, it is especially tricky given the dark murky waters where it resides. Scientists have now found that these fish are equipped with sensors that can locate prey by detecting slight changes in the water’s pH level.
The paper, published in the journal Science, is the first report of any fish using pH to find live prey.
“What makes this so interesting is that the discovery was unexpected, quite serendipitous,” said Professor John Caprio, who conducted the research with colleagues from Kagoshima University in Japan.
The fish were outfitted with electrodes that allowed the recording of the fishes’ responses to water of varying pH. It was during this time that they determined that the function of the sensitivity of the fishes’ barbells to minor changes in water pH was due to the respiration of small sea worms, polychaetes, a primary prey of the sea catfish.
The sea worms live in tubes or burrows in the mud. As the worms breathe, they release tiny amounts of carbon dioxide and acid, producing a slight decrease in the pH of the seawater that the nocturnal sea catfish detects.
“These fish are like swimming pH meters. They are just as good as a commercial pH meter in the lab,” Caprio said.
For the behavioral experiments, the researchers placed the fish in aquariums filled with seawater, along with the sea worms, which were placed into glass tubes within the coral substrate of the aquarium. Using infrared photography, they showed that the nocturnally active fish spent significantly more time in the vicinity of the worms than in other locations in the aquarium.
The researchers also confirmed that the catfish were attracted to a location in the aquarium where seawater of a slightly lower pH was being emitted from a small tube even when no worms were present. In addition, the fish became extremely active, searching for food and even biting repeatedly at the end of the tube.
The catfishes’ sensitivity was highest in natural seawater of pH 8.2, but decreased dramatically at pH less than 8. These findings imply that the food-locating abilities of Japanese sea catfish could be compromised by ocean acidification, the ongoing decrease in the pH of the Earth’s oceans due to uptake of carbon dioxide from the atmosphere caused in great part by man-made activities.
Studies show that prior to the industrial revolution, carbon dioxide levels were approximately 280 parts per million. Today, it is 390 parts per million, and scientists predict that the levels could increase to 900 parts per million by the year 2100. According to the National Oceanic and Atmospheric Administration, the oceans absorb about a quarter of the carbon dioxide released in the atmosphere each year, resulting in increasing acidified seawater.
“Once the pH of the ocean drops much below 8, shell producing invertebrates can no longer produce their shells,” Caprio said. “Our work could possibly be an indicator of the possible effects of ocean acidification on marine vertebrates. If ocean acidification continues at its same rate, we do not know if marine life will be able adapt to such a rapid alteration in pH.”
The article can be found at: Capiro et al. (2014) Marine teleost locates live prey through pH sensing.
Source: Louisiana State University; Photo: Tyrone Adams/Flickr/CC.
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