# Help - fish being gassed



## Reuben (11 Feb 2014)

Hi

I purchased 9 Harlequin rasbora at the weekend and although I have not adjusted my Co2, they appear to be having problems with it.

The cardinal and black phantom tetra and ottos - which have been in the tank for a year - are all fine and in very good health.

The rasboras looked pretty weedy in the shop, but I figured they were either young or in need of feeding up.

Basically 3 hrs after Co2 comes on three of them show major distress drifting and spinning out of control or gasping at the surface. Obviously I stop the Co2 straight away, and 30mins later they are all fine. All my other fish are behaving normally during this.

So are the rasboras able to acclimatise to Co2 injection? Is there a physical adaptation a bit like humans adaptation to altitude? Or it there some underlying issue that I'm not aware of.

Bit frustrating as when I turn the Co2 off I then have to turn the lights out a bit after for obvious reasons.

This is bolstering the feeling I have that the low tech approach (by which I mean no Co2 addition but still large water changes) is generally conducive to a better living environment for the fish - assuming plant health is good -(a'la bucket!).

Hope someone can help with this, I'm not keen on reducing my Co2 (then lighting) as I've finally cracked the application of Co2 to grow plants well, and not all the fish - within the rasbora group are affected.

Thanks


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## tim (11 Feb 2014)

May take them some to time to adjust, I've found a little stronger surface agitation can help.


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## Reuben (11 Feb 2014)

Thanks tim, so presumably there's some physical adaptation going on then?


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## GHNelson (11 Feb 2014)

You got to remember these fish have come from well aerated shop tanks.
So will need  time to adjust...so as Tlm suggests up the surface agitation.
You can still run the Co2 if there is good gas exchange.
Tom Barr explains this somewhere in one of his posts.
hoggie


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## tim (11 Feb 2014)

Not sure what happens tbh, just based on my experiences over the last 12 months or so, I recently added some beckfordi pencils to my 3ft tank they all settled nicely apart from 1 which stayed at the top until I raised an outlet slightly, I do think certain fish tolerate co2 levels better than others.


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## parotet (11 Feb 2014)

Can you please tell us a bit more about Barr's thread about this?  I want to try to look for it and read it...


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## NatureBoy (11 Feb 2014)

Usually fish acclimatise pretty quick so long as they are given a no CO2 start point...when fish are consistently struggling when other fish are fine can indicate that the fish are affected by parasites in their gills, the fact that you say the fish are a bit weedy could again indicate they have an internal parasite...watch them closely, and observe if any other symptoms present themselves.


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## Reuben (11 Feb 2014)

Thanks all, 

In terms of surface movement I'll try and up it, though not much scope for this without breaking the surface up (bubbles).

So in terms of acclimatising them do I, monitor them when Co2 goes on and once they show signs of affect switch off Co2 then lights -  Basically shorten the 'day' so they have less exposure, then gradually lengthen the day.

Or is there some other method, I don't know about?


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## ceg4048 (11 Feb 2014)

Reuben said:


> So are the rasboras able to acclimatise to Co2 injection? Is there a physical adaptation a bit like humans adaptation to altitude? Or it there some underlying issue that I'm not aware of.


Yes, there is a physiological adaptation that fish make and although it's a simple idea, it's not easy for the fish to execute.
When you add CO2 to a tank the injected gas increases the partial pressure of CO2 in the water.
Normally, in an unpressurized water (i.e non-injected tank or natural body of water) the concentration of CO2 in the fishes body is higher than the concentration of CO2 in the water. The gas will therefore flow across the gills from the higher bloodstream pressure to the lower pressure in the water. If the water is CO2 injected then the CO2 partial pressure in the water is high enough that it pushes back against the bloodstream CO2 pressure. This "adverse pressure gradient" block the efficient evacuation of CO2 from the bloodstream.

Just like in your dropchecker, the CO2 that remains in the bloodstream causes a fall in the bloodstream pH. This condition is called blood acidosis. Low blood pH can have a lethal effect on systems such as nervous system, kidney and so forth. The most important effect is that of the circulatory system. Red blood cells carry a protein called Hemoglobin.

The hemoglobin has a dual function:
1. It attracts and holds CO2 molecules in order to transport them away from the tissues that produce CO2 via normal respiration.
2. It attracts and holds Oxygen molecules from the gills and transports them to the tissues.

When the hemoglobin is in the capillaries and in the vicinity of the CO2 producing cells there is the dropchecker effect and the pH is acidic.
Under acidic conditions, hemoglobin has a strong attraction for CO2 and a weak attraction for Oxygen.
So hemoglobin releases it's payload of Oxygen where it's needed and exchanges the Oxygen for a new payload of CO2.

When the hemoglobin reaches the gills, the pH is normally higher (more alkaline) and under alkaline conditions hemoglobin has a strong attraction to Oxygen and a weak attraction for CO2. So this protein drops it payload of CO2 in exchange for a new payload of Oxygen. The high partial pressure of CO2 at the gills normally allows the CO2 to cross over the gill membrane into the water.

This is the normal mechanism, however, as you can surmise, when the external CO2 pressure is high, the CO2 does not escape, and this causes the pH near the gills and everywhere else in the bloodstream to become more acidic. The hemoglobin then has a greater tendency to hold on the the CO2 and less tendency to attract Oxygen, which is the exact opposite of how the system should function. The result is hypoxia.

The mechanism the fish uses to combat this condition it to produce and excrete more bicarbonates (HCO3-) into the bloodstream. As you're aware, bicarbonate is an alkaline buffer and it therefore neutralizes the carbonic acid produced by the dissolution of the CO2 in the blood.

It takes about 24-48 hours to produce a sufficient quantity of bicarbonate, depending on the amount of CO2 you are injecting, to neutralize the Carbonic acid. Neutralization of the blood acid returns the normal functioning of the hemoglobin almost to 100% of what it was.

The fish that are already in the tank have long ago adjusted to CO2 concentration and already have extra bicarbonate flowing in the bloodstream whereas the new fish, having come from a non injected tank have not made the adjustment and require a lot more time.

Reducing the injection rate, temporary aeration, water changes and so forth help the fish to transition.

What I do (controversial, as usual) is when I get new fish, I just keep them in the bag without opening it overnight and turn the lights off to reduce stress. In the bag the fish release CO2 and the concentration builds at a slow rate. It gives their bodies time to increase the bloodstream bicarbonate level so that upon release the next morning they have a better chance of adapting to the CO2 level in the tank.

Check this post which shows some videos of blood movement in humans. It's the same concept for fish. The interface between body and environment is the only difference (air sac vs gill membrane).
not enough oxygen... | UK Aquatic Plant Society

Cheers,


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## Reuben (11 Feb 2014)

Thanks, for a superb explanation!  Certainly helps decide how to sort the problem when you're given such a comprehensive and logical answer!
Cheers!


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## GHNelson (12 Feb 2014)

ceg4048 said:


> Reducing the injection rate, temporary aeration, water changes and so forth help the fish to transition.[/quote


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## Reuben (12 Feb 2014)

Thanks all,

I kept the Co2 the same, increased the surface disruption (so a few bubbles formed) and cut the lighting level in half.

Fish have been absolutely fine.

Another learning experience via UKAPS!


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## MikeC1408 (17 Mar 2014)

Funny you should mention harlequin Rasboras. I just installed CO2 at the weekend and introduced 6 of these fish. They spent mist if the first hour it so chasing the small bubbles round the tank eating them.


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