Manuel Arias
Member
The more o2 there is in the water the higher co2 concentration you can keep without fish issues.
There are many more things to consider as well but this statement is true. It doesnt mean there is no limit to how much co2 you can inject obviously.
Out of curiosity, which is the argument for this? I mean, if you can extend your point, as it is interesting, and I might be wrong. F
For many years in fish physiology has been stated that breath in fishes is not linked to the relative concentrations of O2 and CO2, unless CO2 concentrations in water are big enough to block the exchange of CO2 from the blood of the fishes with O2 in the water, or the O2 concentrations are not enough to cover the needs of the fishes. Meanwhile the CO2 levels in water are allowing the excretion of CO2 through the gills , the fishes have adaptations (until some point) to make available the oxygen in the water by increasing the ventilation rate and the cardiovascular activity to compensate the lower rate of exchange of CO2 due to the higher concentrations in the water. The intake of O2 is then driven by the Bohr-Haldane effect as result of the pH changes in blood due to this CO2 transfer. Meanwhile the O2 levels are suitable for the fishes needs (this level is independent of the CO2 levels in water), they have mechanisms to handle the higher levels of CO2 until the point in which the stress caused by the reduction of the gradient of concentrations overwhelms the capacity of the fish to compensate it by other means. As it is this gradient who controls the exchange rate of gases, does not matter if you increase the O2 concentrations in water, as then the fish will not be able to use that available oxygen because cannot remove the CO2 from the hemoglobin in the blood, and then suffocating.
The following figure explain this:
As you can see, it is the relative concentrations of CO2 between body and water what enables the breathing. If the CO2 levels in water are high enough, the gradient indicated in point (4) of the figure is much lower, difficulting the gas transfer. In fact, this gas transfer involving the change of the pH in the blood is what allows to the organism to grasp O2 from the water, via Bohr-Aldane effect, so regardless of the O2 concentration very high in the water, if the CO2 levels in the environment are high the mechanism is not possible.
It has been stated, however, that higher levels of O2 are positive for fishes, meanwhile the CO2 levels are on bay in specific ranges, but the reason for that relies in receptors of the gill´s cells that activate specific patterns of behaviour and physiologic reactions in the fishes. In other words: when the conditions are good the fish relax and suffer less stress. However, as mentioned, this only happen in specific ranges of relative concentrations of CO2 and O2 in water, and there is no general relationship between a better tolerance to CO2 by increasing O2 levels, as the mechanism allowing the breathing is the differences of concentration in CO2 between the blood and the water in a given temperature. In last years some people are publishing about the role of the pH of the environment in the mechanism of gas exchanges between gills and water, but they only point out in the direction that lower pH in the water can reduce the tolerance of fishes to CO2 levels, and not totally related to this discussion.
You can read abut the fishes adaptations and responses to high CO2 concentrations in water in the following paper, which also explains the role of the differences in the partial pressure of CO2 in environment and fishes and its effects:
http://onlinelibrary.wiley.com/doi/10.1029/2004JC002564/pdf
And a good reading about the Bohr-Haldane effect is found here, where you can se that the release of CO2 to the water is what triggers the O2 intake:
http://brauner-home.zoology.ubc.ca/...l-Interaction-between-O2-and-CO2-exchange.pdf
Well, now we smashed it with science. But I think we should move back to the topic of this thread, anyway.