Fish more tolerant than expected to low oxygen events

October 22, 2019

Fish may be more tolerant than previously thought to periods of low oxygen in the oceans, new research shows.

The surprising discovery, from research by the University of Exeter and the Centre for Environment, Fisheries and Aquaculture Science (Cefas), was made when investigating the importance of carbon dioxide (CO2) during "hypoxic" (low oxygen) events.

The study shows that natural increases of carbon dioxide during low oxygen events make sea bass 20% more tolerant to hypoxia.

Researchers believe this occurs because the blood chemistry of sea bass changes in response to higher CO2 levels.

In turn this makes it easier for haemoglobin in their red blood cells to transport oxygen during a hypoxic event.

"The standard methods used to measure the response of fish to hypoxia do not usually take into account the associated rise in CO2 levels that always simultaneously occur in nature," said lead author Daniel Montgomery, a marine biologist at the University of Exeter.

"During hypoxic events, respiration by bacteria in the water causes CO2 levels to increase as oxygen drops.

"Our results indicate that this CO2 may play a key role in the ability of fish to tolerate hypoxic events, by enabling their blood to continue absorbing oxygen at lower environmental oxygen levels."

Improving our ability to predict the consequences of hypoxia for fish species is critical.

We know already that climate change is increasing the occurrence and severity of hypoxic events in oceans across the globe.

This means that hypoxia tolerance may become increasingly important for the success of many fish species.

"Although our results indicate that fish may be more resilient to hypoxia than previously thought it is key to remember that fish are also having to cope with multiple stressors in their environment," Montgomery said.

"Climate change is causing warming of the world's oceans as well as increased hypoxic events and fish in warmer waters are more vulnerable to low oxygen conditions."

The researchers studied responses to hypoxia in European sea bass (Dicentrarchus labrax), an ecologically and economically important species in Europe.

They now aim to investigate how common this response is in other fish species and how climate change will impact hypoxia tolerance of these fish.

Dr Silvana Birchenough, co-supervisor of this work based at Cefas, said: "This research is vital to understand how fish species will be able to adapt and react as climate change alters environmental conditions in the oceans.

"This work will enable us to improve empirical data to test and evaluate our current models of how fish populations will be affected in the future, providing the potential for making better predictions and thus protecting and conserving our fish stocks under a changing climate."

Daniel's PhD supervisor at the University of Exeter, Professor Rod Wilson, said "At one level Dan's work provides an elegant example of how environmental CO2 influences blood chemistry which then exquisitely enhances the ability of haemoglobin in fish red blood cells to manage oxygen delivery to their tissues.

"At the other end of the scale, it suggests a profound influence of these molecular processes on the fitness of individual animals, and ultimately the likely fate of fish populations in our rapidly changing oceans."
The paper, published in the journal Scientific Reports, is entitled: "Rising CO2 enhances hypoxia tolerance in a marine fish" and is freely available online at

University of Exeter

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to