Is CO2 causing your fish to act strange?

A new study published in the journal Scientific Reports, links neurological impairment in some fish to increased carbon dioxide levels. Researchers at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science and the ARC Centre of Excellence for Coral Reef Studies at James Cook University studied Spiny Damselfish (Acanthochromis polyacanthus) in this first-of-its-kind study.

The fish were collected over a three-week period from the reefs around Lizard Island, Australia and separated into two groups—those exposed to ordinary CO₂ “control” conditions and those exposed to elevated CO₂ levels. What they found was that increases in CO₂ alters brain chemistry in certain fish and causes a disruption in behavior.

Following four days of CO₂ exposure, the damselfish were subjected to a behavioral test, and brain and blood chemistry were measured to confirm findings. To study their behavior, the fish were placed in a two-choice flume system and where given the choice between control seawater or water containing a chemical alarm cue.

In the wild, under normal ocean condition, the damselfish will typically avoid the particular cue since it represents the smell associated with an injured fish of its own species.

The researchers found that the damselfish exposed to elevated carbon dioxide levels were spending significantly more time near the chemical alarm cue than the control fish, a behavior that would be considered abnormal. The measurements of brain and blood chemistry provided further evidence that elevated CO₂ caused the altered behavior of the fish.

“For the first time, physiological measurements showing altered chemistry in brain and blood have been directly linked to altered behavior in a coral reef fish,” said UM Rosenstiel School Maytag Professor of Ichthyology and lead of the RECOVER Project Martin Grosell, the senior author of the study. “Our findings support the idea that fish effectively prevent acidification of internal body fluids and tissues, but that these adjustments lead to downstream effects including impairment of neurological function.”

The study, titled “Altered brain ion gradients following compensation for elevated CO₂ are linked to behavioural alternations in a coral reef fish,” was published in the Sept. 13 online issue of the journal Scientific Reports. The study’s co-authors include: Rachael Heuer; Martin Grosell; Megan J. Welch and Jodie L. Rummer and Philip L. Munday from the ARC Centre of Excellence for Coral Reef Studies at James Cook University.

The National Science Foundation, a University of Miami Koczy Fellowship, and the ARC Centre of Excellence provided funding support for the study. Heuer was also funded by an NSF Graduate Research Fellowship to conduct the research. [RSMAS]