Caprio et al. 2014 demonstrated the existence of a pH-sensing ability in P. japonicus. In a background ocean water substrate with a pH of 8.2, this species of catfish could detect its prey’s respiration under the sand which decreased the local pH by 0.1 pH decline. This pH decline is due to the carbon dioxide from the seaworms (Polychaeta) dissolving in the salt water, hydrogen ions are released, and carbonic acid is formed dropping the local pH of the worm's environment. If P. japonicus lived in a more acidic environment, such as 7.8 pH, would it detect a linear decline of 0.1 pH decline or a logarithmic decline? In other words, do these catfish sense a linear drop in pH, I.e., or a drop in the logarithmic ratio between background pH and local pH drop? P. japonicus would detect a logarithmic decline in a more acidic environment. A greater drop in pH (&lt;pH 8.0) was also shown to exhibit activation of the pH-sensing organ of P. japonicus (Caprio et al. 2014). As more carbonic acid is required to drop the pH at a logarithmic rate, this supports the claim that catfish do detect a ratio drop of pH rather than the linear drop. To test our hypothesis, we must first determine the logarithmic ratio between background ocean pH and potential localized variations, such as those caused by P. japonicus’s prey. Our experiment begins with Ocean water collected from Nahant Beach in Nahant MA. This Ocean water is treated as a buffer solution using sodium carbonate or sodium hydroxide to reach a background pH of 10.0. We then decreased the pH of the ocean water in whole number increments, tracking the amount of titrating solution in mL. The titrate solution has a fixed number of moles of H+ ions and H2CO3. Hence, we can establish the logarithmic ratio needed to decrease the ocean water between whole numbers. From this buffering equation, we can extrapolate the ratio of pH drop to P. japonicus needed to detect its prey in more acidic environments. Ocean Acidification is thought to be a significant worry for these catfish, as their prey detection organ will not be able to sense the decline in pH at lower levels. The significance of our experiment is the method adaptability of the lone pH sensing organ on the catfish barbels regardless of the pH levels dependent on Ocean Acidification.

Something smells pHishy: A method for testing adaptability of pH sensing organ in P. japonicus

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