# Anabantoidae, Polpteridae and CO2



## Palm Tree (7 Mar 2013)

Hi, I was thinking, would fish that have lung-like organs have a higher tolerance to CO2 than other 'normal' common fish without the organs?
I read that anabantoids can drown if not given access to air, even if the water is saturated with oxygen. If they are that dependent on atmospheric air then could they deal with a higher level of CO2?
I think a lot of anabantoids generally have come from Hypoxic environments, would these enviroments also have a high concentration of CO2? If so, might they have evolved to have higher CO2 tolerances?

OR

Would they still die due to hypercapina.

It would be great if anyone with some information on the subject could provide their thoughts/ opinions on the subject.
Cheers,
Harvey.


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## ceg4048 (7 Mar 2013)

Hi,
It's a very complicated issue because first of all, it depends on the species. Labyrinth design and efficiency greatly depends on what fish we are talking about. Secondly, the fundamental design of the labyrinth is focused on dealing with hypoxia, not hypercapnia. The role of CO2 excretion is primarily a job of the gills, not the labyrinth, however, during hypercapnia the labyrinth will excrete more CO2 than it normally would do. The cost to the fish is a significant rise in metabolism, because the rate of surface breathing will increase significantly. So although the fish will be less stressed by blood acidosis, it will be greatly stressed by the energy required to expel CO2.

Worth having a read of an oldy-but-goody Blue Gourami research paper (1978) => Bimodal Gas Exchange During Variation in Environmental Oxygen and Carbon Dioxide in The Air Breathing Fish Trichogaster Trichopterus

Cheers,


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## Palm Tree (3 Jun 2013)

I thought I had replied to this thread, but it appears that my reply wasn't posted.
Thanks for the detailed reply.
It would be interesting to try and measure the tolerances of Anabantoids and the like in comparison to similar 'normal' fish, as the levels of tolerance to Carbonic acid should be higher, and I assume that blood acidosis would be the cause of death, not to say that the increased rate of breathing and thus the strain on the metabolism wouldn't also be a major factor in the cause of death.
There is no doubt that some fish such as some _Apistogramma_ may have higher tolerances to CO2 than others, such as _Sewellia_ for example, but how about compared to fish with specialised lungs with large surface areas for gaseous exchange of O2 and CO2 like lungfish, or basic labyrinths like some _Anabantoids._
That would be interesting, mainly the comparison of an _Anabantoid to an_ Apistogramma.


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## plantbrain (3 Jun 2013)

CO2: Larger the fish, the harder it it is, the higher their MET rates, the harder it is, the Warmer the Temp, the harder it is.

You should NEVER have to gas your fish to provide optimal CO2.
I have elephant nose and they very well and grow well, eat from my hand etc.
They are in my 120 Gal which has more light than most any aquarium and plenty of picky wimpy plants.

Folks that gas their fish with CO2 are either having other issues NOT related to CO2, or they are not careful with CO2. Maybe both.
But it's not the usage of CO2, it is the USER.


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## Palm Tree (3 Jun 2013)

Just to let you know as you may have gotten the wrong end of the stick.
I was trying to understand the full role of lung-like organs in fish,  I wasn't suggesting anything to do with aquarium C02 injection. I was just interested in the adaptations of certain fish to live in CO2 rich conditions, as _Apistogramma_ do not to my knowledge have lung-like organs yet they are capable of living in CO2 rich water containing lots of leaf litter sediment.
Like I said I do not believe in pushing fish to there limits in order to achieve a higher concentration of CO2 for plant growth, as that is morally wrong and selfish.


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## dw1305 (3 Jun 2013)

Hi all,


Palm Tree said:


> as Apistogramma do not to my knowledge have lung-like organs yet they are capable of living in CO2 rich water containing lots of leaf litter sediment.


I think _Apistogramma_ are still relatively sensitive to high CO2 levels, but there are a lot of other SA fish from black waters that have adaptations to air breathing (*Arapaimids, Gymnotids, Erythrinids*). The leaf litter is a bit of a red herring, it is persistent due to the toxic compounds contained in many of the leaves, very low nutrients levels and  strongly acidic water, all of which slow microbial action. If you put the same leaves in more nutrient rich, oxygenated alkaline water they will decay much, much quicker. It is the same sort of effect you see when you get peat bogs, the carbon builds up, because the rate of decay is limited by the lack of oxygen and the other essential ions for microbial growth. As soon as you drain the bog and fertilise the peat it oxidises away as CO2. "Holme Fen post" <Natural England - Holme Fen (SSSI and NNR)>.

The reason that relatively fish are adapted to conditions of low oxygen is to do with the genetic cost of any "unsual" adaptation. A good example of this is in the *Loricariid* and *Callichthyidae* catfishes, they form a monophyletic clade (within the Loricarioidea), and some members of each family have a special gas exchange organ in the intestine that allows them to take oxygen from gulped air, meaning that it is almost certainly a conserved feature from their common ancestor.

The fish that can gulp air are all from slow moving swampy waters, where even if low oxygen/high CO2 is a very occasional factor it will still be conserved, because even very short periods of low oxygen will winnow out all those fish who don't carry a combination of genes that allows efficient oxygen uptake from the gulped air.

In the big rivers things are very different, rheophilic Loricariids like _Chaetosoma, Pseudolithoxus _and _Hypancistrus ssp. _will never experience periods of low oxygen, and that means that there will be random genetic drift in the air breathing genes, in exactly the same way that cave fish all eventually become blind and albino. In cave fish there is a cost to producing eyes and pigment once they don't increase survivorship, and in the rheophilic fish natural selection will now work on those genes that give the fish an advantage faster flowing water, and they become stream-lined, have large pectoral fins  etc., and their gill area will reduce to the minimum required, because that fish will be, on  average, slightly fitter than one with luxury extra gill area that it doesn't need. This cost is mentioned in the paper that Clive linked earlier.

The out-come of all of this is that a fish like a _Chaetosoma_ spp. from the cool fast flowing streams of the Andes piedmont, will suffer respiratory distress even in relatively well oxygenated water, where they will gasp air at the surface, although it no longer has the ability to extract oxygen from it.

cheers Darrel


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