Oh noes! high CO2 levels ‘can make fish swim towards predators’

From the UNIVERSITY OF EXETER and the department of fish and chips comes this “study” which appears to be nothing more than an opinion piece.


Climate change impairs survival instincts of fish and can make them swim towards predators
Fish farms may hold key to studying the impact of rising CO2 on marine life, and if fish could adapt to climate change

Climate change is disrupting the sensory systems of fish and can even make them swim towards predators, instead of away from them, a paper by marine biologists at the University of Exeter says.

Research into the impact of rising CO2 has shown it can disrupt the senses of fish including their smell, hearing and vision.

High CO2 levels can impair the way they behave, including making them swim towards predator smells instead of away and even ignoring the sounds that normally deter them from risky habitats.

According to a paper published today in the journal Global Change Biology by Dr Robert Ellis and Dr Rod Wilson, climate-change marine biologists at Exeter University, these abnormal behaviours have been linked to the effect of CO2 on how the brain processes signals from sensory organs.

CO2 levels are predicted to be 2.5 times higher in the oceans by the end of this century.

The report’s authors Dr Robert Ellis and Dr Rod Wilson believe that fish farms, may be the key to establishing the long-term impact of CO2 on marine life.

In their paper, Lessons from two high CO2 worlds: future oceans and intensive aquaculture, Dr. Ellis and Dr. Wilson, alongside a colleague from Chile (Dr. Urbina), show that farmed fish often live in CO2 conditions 10 times higher than their wild cousins.

The scientists believe that further study of farmed fish – which already provides as much seafood for human consumption as that caught in the wild – may be crucial for understanding how aquatic species will evolve to climate change.

The captive fish farm populations living in high CO2 levels already amount to “a giant long-term laboratory experiment”.

“Aquaculture may provide an ‘accidental’ long-term experiment that can help climate-change predictions,” said Dr. Ellis. “There is the enticing possibility that fish and shellfish previously grown in high CO2 aquaculture conditions over multiple generations can offer valuable insights regarding the potential for aquatic animals in the wild to adapt to the predicted further increases in CO2.”

The aquaculture industry may also benefit from what the climate change scientists study too. The abnormal behaviour seen in wild fish may not matter in farmed fish, as they are provided with abundant food and shelter and they have no predators to avoid. But while extremely high CO2 can reduce digestion efficiency in cod, recent research suggests that relatively small increases in CO2 may actually act as a growth stimulant in some fish.

Dr. Rod Wilson said: “Our research will allow fish farmers to optimise conditions, and specifically CO2 levels, to improve growth and health of their fish, profitability and the long-term sustainability of the industry. This is really important given that aquaculture is the only way we will increase seafood production to feed the growing human population, particularly given wild fish stocks are overexploited”.


This paper doesn’t appear to be anything more than a collection of opinion, in my opinion. It is open source, so you can judge for yourself here:


Lessons from two high CO2 worlds – future oceans and intensive aquaculture

Robert P. Ellis, Mauricio A. Urbina, Rod W. Wilson

Exponentially rising CO2 (currently ~400 μatm) is driving climate change and causing acidification of both marine and freshwater environments. Physiologists have long known that CO2 directly affects acid–base and ion regulation, respiratory function and aerobic performance in aquatic animals. More recently, many studies have demonstrated that elevated CO2 projected for end of this century (e.g. 800–1000 μatm) can also impact physiology, and have substantial effects on behaviours linked to sensory stimuli (smell, hearing and vision) both having negative implications for fitness and survival. In contrast, the aquaculture industry was farming aquatic animals at CO2levels that far exceed end-of-century climate change projections (sometimes >10 000 μatm) long before the term ‘ocean acidification’ was coined, with limited detrimental effects reported. It is therefore vital to understand the reasons behind this apparent discrepancy. Potential explanations include 1) the use of ‘control’ CO2 levels in aquaculture studies that go beyond 2100 projections in an ocean acidification context; 2) the relatively benign environment in aquaculture (abundant food, disease protection, absence of predators) compared to the wild; 3) aquaculture species having been chosen due to their natural tolerance to the intensive conditions, including CO2 levels; or 4) the breeding of species within intensive aquaculture having further selected traits that confer tolerance to elevated CO2. We highlight this issue and outline the insights that climate change and aquaculture science can offer for both marine and freshwater settings. Integrating these two fields will stimulate discussion on the direction of future cross-disciplinary research. In doing so, this article aimed to optimize future research efforts and elucidate effective mitigation strategies for managing the negative impacts of elevated CO2 on future aquatic ecosystems and the sustainability of fish and shellfish aquaculture.


59 thoughts on “Oh noes! high CO2 levels ‘can make fish swim towards predators’

  1. You think this is idiotic, just wait and see what happens if (probably when, unfortunately) the Hildabeast wins next month.

  2. Well, I’ll admit its a stupid paper, but its no “climate change will lengthen bee tongues”…

    • As with a glass of cold beer that loses CO2 as it warms and becomes “flat”, won’t the ocean lose, not gain, carbon dioxide if it warms? Of course, it’s a big “if” that it’s going to warm at all.

    • There is 45 times more Carbon in the oceans that in the atmosphere.

      The ocean Carbon is rising by about 0.005% per year and in 100 years at current and projected rates, it will increase by about 1.0%.

      So, yeah, these guys have no ability to do (non-global-warming-type) math. 250% is a very long way off of 1.0%.

      And the fish will probably not notice 1.0% given they have evolved when the atmosphere component was 10 times higher.

    • As someone who likes to fish, that surely makes me a predator. Does this new “science” mean that, from now on, all I need to do is show up and wait? And think of the savings by avoiding having to buy bait!

  3. “Many papers… show CO2 impact on fish behavior.” NOT TRUE. There are several papers showing minor physiological changes in fish at higher CO2, but generally not on survival or reproduction, all listed in the following reference. There is exactly and only one paper (according to its own abstract about being first) showing the behavior claimed by this Exeter paper. It is Heuer et. al., Scientific Reports 6: 33216 published on line 9/13/2016. Happen to have read about it last month via the usual science alarm sites. Easy to google.
    Mainly from Cook U in Australia with support from U Miami’s Rosentiel School, from the ARC Center of “Great Barrier Reef is dying infamy”. (Recall Jim Steele’s recent takedown of ARC GBR nonsense.) They caught spiny damselfish out on the GBR. Half control, half gassed for 4 days at 1900uATM (which works out in seawater to about 1800ppm!!!). Then dissect some to show GABA brain receptor chemical imbalance in the gassed fish but not the controls. Why GABA? Because it is sensitive to HCO3 ion gradient (and not just in fish) — so they have the answer before the experiment. Then put remaining fish sequentially in a two seawater flume experimental box where one flume had a chemical alarm clue. Paper has a picture of the flume setup with one dyed. The gassed damsel fish spent more time on average in the alarm flume than the controls. Total number of fish: 20. Total time in flume box: 2 minutes, three minute ‘rest’, then 2 more minutes with flume sides switched. And thus was new warmunist fish alarm created, which Exeter further spun in the echo chamber with amazing reaction times.
    BTW, in humans the GABA receptor is the target for benzodiazepines (Valium, Xanax). So fish get tranquilized by CO2 at 3x the level the IPCC AR5 expects in 2100. Who knew?
    More classically typical ‘climate science’.

    • It has been a couple of years since I looked at the pH literature, but Ristvan is probably correct. Except for chemical papers the only antique paper (last century) cited, probably not much examined was by Jim Cameron. I would suggest that the authors look at his other papers, some with others, on species he researched, including blue and fiddler crabs and gar, all which live in some really cruddy water, pH wise that is. He and I studied at the same laboratory back before carbon dioxide was known to be toxic at environmental levels.

      One of the most common marine cultured fish is the striped mullet, which not only lives in such cruddy places, but even eats the stuff. Our laboratory studied so much on mullet physiology I cannot begin to even think of how it might be important to this subject. Well, maybe that predators have similar responses to prey.

      Have rarely looked at papers in that journal, but my impression has been that it does not deserve to be considered as science.

    • “3x the level expected in 2100″… if there is any effect at all on the brain in the experiment couldn’t it just be CO2 intoxication? You can also intoxicate, cause damage, and even kill a human being by making them ingest more water than they would under any sane circumstance.

  4. If you’re a budding young researcher and you need a grant, you ain’t gonna get one unless your project is titled something like “How global warming affects [fill in the blank]”.

    That’s no doubt where studies like this one come from.

  5. Purely speculation, or as pointed out, opinion. That said, Henry’s Law would dictate that as carbon dioxide in the atmosphere increases so, with no other physical changes, will the amount of carbon dioxide absorbed into the oceans. Of course, if the global temperature increases according to the AGW hypothesis then the oceans should also warm and therefore absorb less carbon dioxide. But…it all depends on what happens to the carbon dioxide absorbed into the oceans. A significant amount will be consumed by photosynthesis, no doubt some will be converted to carbonates, the rest will likely be chemically buffered and the reversible conditions to which Henry’s Law applies will not be applicable. Therefore a figure of 250% increase is likely merely guesswork.

  6. Actually, it is the fact that they are farmed fish. Domesticated animals typically have a brain 25% smaller than their wild counterparts.

  7. So, how did anything survive the Cretaceous when world temperatures were 10°C higher than they are today?

  8. Hmmm….so fishermen should just use live bait and let it find the fish?
    Keep using the fish that are caught as bait and eventually they will catch the biggest fish in the lake?
    This smells a bit fishy to me.

  9. Fish that have a higher tendency to swim towards a predator will (ipso facto) be less likely to pass on their genes to the next generation. Their fishy friends with higher CO2 tolerance will be successful breeders. Nature adapts. Who wasted their (or more likely “our”) money paying for this dim-witted research?

  10. RIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIGHT!!!!!!!!!!!!!!!!! Dr Robert Ellis and Dr Rod Wilson have jumped the shark. Fonzie says “Great Move?”

    • Following this study to its logical conclusion, I think it means that Killer Whales and Great White Sharks will jump on to the decks of fishing boats as they pass by.

    • They didn’t even say what predators the fish swim towards. Are they assuming that the all-powerful trace gas will cause Salmon to swim towards Grizzly Bears?

  11. I haven’t gone back and looked but this one seems to be similar to others I’ve read or heard summaries. You have to wonder how repetitions with really no new information get published.

    Taking a fish and dump it into water with much greater CO2, lower pH and then see what happens soon after the shock is valid science? Ignore Henry’s law and ignore the long periods of adjustment that would happen getting to their doomsday is valid? This climate change fish science sounds a lot like the joke about a guy who hires the accountant who answers a question with “tell me what result you want.”

  12. farmed fish – which already provides as much seafood for human consumption as that caught in the wild“. There’s something not quite right with that statement. Technically, it may well be correct, but just think about it. Farmed fish have to eat in order to grow. Typically, they eat more than 2 units of food to put on 1 unit of weight. Typically, they are fed seafood. So the oceans are being stripped of seafood in order to provide a much smaller amount of farmed fish. It’s not a good equation. [Note. Farmed beef has a similar equation, but cows eat grass, which humans can’t eat. I suspect that humans could very easily and profitably eat the seafood that farmed fish are fed.]

  13. As the great Shemp Howard says,..” OOh! OOh!” Raising his hand. “I get it.”

    The grant predators swim towards the CO2,.. no matter what form it takes. ;-)

  14. Considering the traumatic levels of academic stupidation they were no doubt exposed to, I would postulate their piscean specimens were driven to suicide.

  15. Not knowing that CO2 partitions 50 to 1 into water, these clowns think that a little rise in atmospheric CO2 will significantly increase the oceans’ CO2. If the atmospheric CO2 went up 10%, ocean CO2 would go up by 2% of that 10%, which is 0.2%, which is way smaller than the normal variation of CO2 in the oceans. THey forget that CO2 will rise at night when everything in a coral reef is respiring and decrease during the day when the photosynthetic portion of the reef is actively consuming CO2. If we doubled CO2, which is not going to happen, it would mean only a 2% increase in the oceans. Tempest in a teapot or an alarmist mind, same thing.

  16. The fish will be fine. I’m hugely more worried about the impact on CO2 on climate scientist behavior. It appears to interfere with the cognitive processes and send them into all kinds of strange convulsions. Perhaps I should seek a research grant to create a computer model of the process? If we fail to act soon, I fear the species is headed for extinction. Oh wait… :-)

  17. First sentence of abstract – “Exponentially rising CO2 (currently ~400 μatm) is driving climate change and causing acidification of both marine and freshwater environments. “.

    It should ring alarm bells when there are three significant errors in the first sentence.

    1. CO2 levels are not rising ‘exponentially’, they are rising approximately linearly. The rise earlier was at an increasing rate with time, but this is now barely the case.

    2. CO2 levels are not driving climate change – the climate has been changing in various manners irrespective of the CO2 content of the atmosphere.

    3. Changes in CO2 levels are not causing acidification of marine and fresh water environments. The normal level of seawater pH is from 8.0 to 8.4, that of freshwater varies according to the rocks over which the water has run, plus the various additives from cars, farming, chemical industries, soap, detergents, human wastes, etc. Various correspondents here have shown that the change in marine pH from increased atmospheric CO2 is minimal, and still keeps sea water well over on the basic side. No acidification there.

    OK perhaps I have misinterpreted things – if so, please correct me.

  18. Fish evolved in the Cambrian when atmospheric CO2 was at 10,000-20,000 ppm.

    So now we are to believe that fish are turning suicidal with CO2 increasing from 350 to 400ppm?

    Maybe instead organisms are delerious with delight that with CO2 returning toward safe levels, the threat to the biosphere of CO2 starvation is receding.

    The remaining threat to them is now from the life-hating necrophiles who regard life-giving CO2 as the enemy.

  19. Easy way to end the speculation and see what’s really what. Just drop some major fish predators in the fish farm waters and see if the fish swim towards the predators. Shouldn’t take long if there’s enough CO2 present. Not all climate change research has to be done by thought experiment.

  20. Where do these idiots get ocean CO2 will “increase 2.5 times by 2100??

    Oceans currently contain roughly 38,500 billion tons of carbon dissolved as carbonic acid, of which human CO2 emissions since 1750 have only added around 700 billion of this total, after burning 30% of known fossil fuel reserves…

    How can burning ALL remaining fossil fuels add 60,000 gigatons of carbon to the oceans?

    What an absurd paper.

  21. This is another reference to Bad OA studies that were outed by Chris Cornwall, which I wrote about here and here.

    The real message of the new study, which should be shouted around, is:

    “In contrast [to repeated scare stories of the dangers of minor increases in atmo CO2], the aquaculture industry was farming aquatic animals at CO2 levels that far exceed end-of-century climate change projections (sometimes >10 000 μatm) long before the term ‘ocean acidification’ was coined, with limited detrimental effects reported. It is therefore vital to understand the reasons behind this apparent discrepancy. “

  22. This assertion is just as accurate as their claim that CO2 causes catastrophic global warming.


  23. In case anyone wants to do a real literature search on the subject here is a start.
    Moss, S. A, and W. N. McFarland. 1970. The influence of oxygen and carbon dioxide on fish schooling behavior. Mar. Biol. 5:100-107.
    Baker, C. L. 1941. The effects on fish of gulping atmospheric air from waters of various carbon dioxide tensions. J. Tenn. Acad. Sci.16(1):39-50.

    And what will do when they discover a real toxic compound out there.
    Eddy, F. B. 2005. Ammonia in estuaries and effects on fish. J. Fish. Biol. 67:1495-1513.Stopping urination sounds reasonable. Actually I read something where they want to keep cattle away from streams.

    • New Zealand has legislation and rules to keep livestock out of streams and waterways and farmers now are being required to fence waterways in a endeavour to preserve the quality of water. A recent outbreak of campylobacter which saw most of the residents of a small town on the East coast of the North Island affected has been blamed on fæcal contamination by dairy cows but the source of contamination has not been identified.

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