Fish Are So Sensitive: California Rockfish Developing Anxiety Over Increasing Acidification Of Oceans

By Ajit Jha on December 6, 2013 3:54 PM EST

Canary rockfish
The rockfish, shown here, could be developing serious anxiety over changes in the pH level of its home waters. (Photo: Shutterstock)

A new, multidisciplinary (marine physiology, pharmacology, neuroscience and behavioral psychology) study on the increased impact of carbon dioxide on ocean and marine life has found growing anxiety among fish. 

Scientists have long known that absorption of carbon dioxide into oceans causes surface water to decline in pH and rise in acidity thereby adversely impacting the growth of shells and skeletons of some marine animals. However, the behavioral impacts of ocean acidification were largely unknown to this point. The study for the first time shows that rising acidity levels increases anxiety in juvenile rockfish, a commercial species mostly residing along the California coast. The study by scientists at Scripps Institution of Oceanography at UC San Diego and MacEwan University in Edmonton, Canada was published in the journal Royal Society B: Biological Sciences

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The researchers compared a control group of rockfish kept in normal seawater to another group in waters with elevated acidity levels. They used camera-based tracking software to measure each group's swimming preference — light or dark areas — in the testing tank. This is known to reveal their anxiety; a preference for darkness is indicative of increased anxiety. The researchers found that normal juvenile rockfish moved between light and dark areas of the tank, while fish anxiety drug administered fish preferred darker area. In fact, their anxiety remained unabated even a week after they were placed back in sea water with normal carbon dioxide levels. They regained their normal behavior only after the 12th day in normal seawater.  

The researchers traced the anxiety to "GABAA" (neural gamma-aminobutyric acid type A) receptors, the fish's sensory systems, These receptor are also involved in human anxiety. Changes in the concentrations of ions in the blood as a result of exposure to acidified water reverses the flux of ions through the GABAA receptors leading to a change in neuronal activity reflected in altered behavioral responses. "These results are novel and thought-provoking," said Martín Tresguerres, a Scripps marine biologist and study coauthor.

The ocean acidification, according to this study, might possibly affect fisheries and the normal population dynamics of the fish. This behavior is a matter of concern for juvenile rockfish, according to Tresguerres, because of the variable lighting and shading environments they live in. The observed behavior in the lab, if applicable to the wild under ocean acidification conditions, implies that juvenile rockfish will spend more time in the shaded areas with reduced foraging time and alterations in dispersal behavior, according to Tresguerres. 

While behavioral studies in fish are largely a neglected area of study, it is pretty well known that fish can perform tasks involving learning and memory. Yet, increased anxiety among rockfish could negatively impact the way they function routinely, according to Trevor James Hamilton, a neurobiologist at MacEwan University and coauthor of the study. Although laboratory studies cannot possibly model the acidity levels in oceans to be seen years and decades ahead from now, the tests do reflect the likely adverse impact of ocean acidification on fish behavior, according to Tresguerres. 

Above image courtesy of Shutterstock.

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