03-11-2011, 08:05 PM
CO2 Dangers in Vivaria
Thomas Falk Swedish Dendrobates Society
This article first appeared in Tilgiftaren' the newsletter of the Swedish Dendrobates Society. We wish to thank Lars Österdahl for translating it from Swedish.
Preparing for a short field trip I wanted to make sure that my four newly metamorphosed E. tricolor would have constant access to food during my absence. It seemed a good idea to move them to an old 30 litre aquarium that contained a layer of old oak and beech leaves in varying degrees of decomposition that was being used as culture of soil invertebrates like springtails and small woodlice. The resident fauna was supplemented with a fair number of vitamin dusted small fruit flies.
Aquarium type
Returning from the trip I found a froglet sitting on the glass wall, and as there seemed to be a lot of fruit flies left, I did not rush to return the frogs to their normal terrarium. To my dismay, when I decided to do so a few days later, I found the second froglet on the soil surface in a cramped position with its hind legs stretched and the front part of the body raised on the front legs. A little deeper in the leaf layer a dead froglet was found in about the same position, hind legs stretched and head bent upwards. The fourth frog was nowhere to be found and it had probably entered the food chain of the soil fauna.
The two still living young were quickly moved to a 'hospital tank' with wet moss. The larger of the two, the one I had found sitting on the glass, quickly recovered and ate flies the same day. The smaller regained some mobility in its hind legs in the next 24 hours, but it had recurrences of jerks of the hind legs, and I never saw it eat. It died after another two days. The surviving frog was kept under observation foursome weeks until it was returned to the original terrarium, where it developed normally.
Terrarium type
Had the frogs been struck by some kind of infection, or could it be that the frogs had become victims of some poisoning? I realized that I had not modified the aquarium in the same way as my frog terraria. This one had no vent openings close to the bottom. I began to suspect that the frogs had become victims of carbon dioxide poisoning.
Carbon dioxide a threat
Carbon dioxide (CO2) is an odourless gas that normally makes up 0.04% vol. of the atmosphere. In mammals expired air normally contains 4% CO2 as a result of metabolism. An increased level of CO2 in the air makes it more difficult for the body to get rid of this waste product, and the body reacts with increased breathing activity. If the carbon dioxide cannot be removed from the blood a lower pH results, which seriously affects the salt balance, a state called "acidosis". Breathing in a CO2 level of about 5% leads to unconsciousness in a human and higher levels can be lethal.
The sensitivity to levels of the gas varies between organisms. Animals living in the soil or among fermenting material have the highest tolerances. One soil living species of springtail can survive in up to 35% whereas another, living in the vegetation does not tolerate more than 2%. It results from the decomposition of leaf litter, from fermentation, and from respiration.
Carbon dioxide is over 60% heavier than air. In a vivarium with insignificant air movement CO2 will accumulate in the lower parts and a gradient results with the higher concentration at the bottom. If the terrarium has no opening at a low level a death trap may result. Other possible waste gases in a terrarium, like methane or ammonia are much lighter than air, and thus easier to vent away.
Drainage of heavy gas
CO2 ExperimentIn order to test the CO2 hypothesis I got three one-week-old E. tricolor froglets from a friend. They were placed in a small bottle with an inlet hole under the bottom material (Leca; peat moss; leaves). A fine meshed screen covered the upper opening. The frogs soon found their favourite places where they sat after feasting on the fruitflies that had also been introduced.
When I saw that everything looked normal I let CO2 enter the bottle through the inlet. After a few minutes the frogs began showing signs of restlessness, jumping around in an aimless manner. After another minute the first signs of cramps began to show, and two of the small frogs fell on their backs. Soon all three lay motionless with their hind legs outstretched and no visible breathing movements under their chins. To prevent certain death I ended the CO2 influx and ventilated the bottle. No visible improvement occurred until after about 5 minutes oxygen enriched air was blown into the bottle. Since no breathing was present, any gaseous exchange had to take place entirely through the skin.
The first signs of life were seen after about 15 minutes and after another 5 minutes all three frogs were sitting upright, breathing normally. A few hours after the experiment they were all feeding, and with no lasting symptoms.
Experiment with low Oxygen
Since the production of CO2 is often connected with the consumption of oxygen it is possible that the result of this experiment was due to low oxygen rather than high carbon dioxide. For this reason a second experiment was performed with the same set up and the same frogs. This time argon gas was used instead of carbon dioxide. Argon is an inert, non-poisonous and odourless, non-combustible gas. As the oxygen inside the bottle disappeared, the frogs moved around in a much calmer way than in the CO2 experiment. After a few minutes they opened their mouths in a strange way, as though yawning. No cramps were observed, but they sat shrunken. After another minute the breathing movements ceased and they no longer reacted to touch. The experiment was terminated, and oxygen-saturated air was blown into the chamber. After five minutes all three frogs had recovered.
Interpretation
In order to reduce the stress and avoid unnecessary harm to the frogs, the two experiments were performed more rapidly than would be the case under natural conditions. The experiments show that an increased level of CO2 causes unrest and cramps, whereas the low oxygen situation is characterized by a languid attitude without unrest or cramps. Therefore it must be assumed that the death of the three original tricolor was not a result of a too low oxygen level.
Air movement when lid is opened
Simple calculation shows that in a closed compartment the CO2 level can reach lethal levels long before the oxygen level gets too low. Therefore oxygen depletion is no real risk in a transportation box or a terrarium.
The experiments have strengthened my assumption that the frogs died from CO2 that had accumulated near the bottom of the tank, with a number of other factors playing a part:
1. The lid lay on glass flanges that were meant to keep springtails etc. in. The only ventilation was a small gauze type net in the cover, which made air movement difficult.
2. The lighting was a 5W compact fluorescent lamp placed above the cover glass. This gave minimal convection inside the tank.
3. Only a small plant was present in the tank and in the lowlight it had little chance of absorbing a significant amount of carbon dioxide.
4. The leaf litter was "ripe" and the population of soil invertebrates considerable.
5. Small pieces of banana were fermenting, thus producing CO2 (and alcohol).
6. The tank was left almost a week without the usual daily opening of the cover. This provided ample time for the heavy carbon dioxide to accumulate at the bottom.
How common are CO2 problems?
The loss of my E. tricolor froglets is probably not a unique event in the hobby. One hears reports of 'unexplained' deaths in cases where old aquaria, plastic containers etc have been used for temporary holding frogs, for instance in quarantine practice or directly after metamorphosis which means when the frogs are extra sensitive to stress. As long as the cover is lifted every day for the input of fruitflies, the build-up of stagnant CO2 rich air at the bottom is made impossible. When the terrarium is left unattended for a few days, perhaps with extra fly bottle inside to provide food in the unattended period, the combined effect of the extra fermentation and the poor ventilation can be fatal. Deaths among a group of froglets or a quarantine tank tend to be blamed on infections or parasites, but the real culprit may well be an unsuitable tank.
Thomas Falk Swedish Dendrobates Society
This article first appeared in Tilgiftaren' the newsletter of the Swedish Dendrobates Society. We wish to thank Lars Österdahl for translating it from Swedish.
Preparing for a short field trip I wanted to make sure that my four newly metamorphosed E. tricolor would have constant access to food during my absence. It seemed a good idea to move them to an old 30 litre aquarium that contained a layer of old oak and beech leaves in varying degrees of decomposition that was being used as culture of soil invertebrates like springtails and small woodlice. The resident fauna was supplemented with a fair number of vitamin dusted small fruit flies.
Aquarium type
Returning from the trip I found a froglet sitting on the glass wall, and as there seemed to be a lot of fruit flies left, I did not rush to return the frogs to their normal terrarium. To my dismay, when I decided to do so a few days later, I found the second froglet on the soil surface in a cramped position with its hind legs stretched and the front part of the body raised on the front legs. A little deeper in the leaf layer a dead froglet was found in about the same position, hind legs stretched and head bent upwards. The fourth frog was nowhere to be found and it had probably entered the food chain of the soil fauna.
The two still living young were quickly moved to a 'hospital tank' with wet moss. The larger of the two, the one I had found sitting on the glass, quickly recovered and ate flies the same day. The smaller regained some mobility in its hind legs in the next 24 hours, but it had recurrences of jerks of the hind legs, and I never saw it eat. It died after another two days. The surviving frog was kept under observation foursome weeks until it was returned to the original terrarium, where it developed normally.
Terrarium type
Had the frogs been struck by some kind of infection, or could it be that the frogs had become victims of some poisoning? I realized that I had not modified the aquarium in the same way as my frog terraria. This one had no vent openings close to the bottom. I began to suspect that the frogs had become victims of carbon dioxide poisoning.
Carbon dioxide a threat
Carbon dioxide (CO2) is an odourless gas that normally makes up 0.04% vol. of the atmosphere. In mammals expired air normally contains 4% CO2 as a result of metabolism. An increased level of CO2 in the air makes it more difficult for the body to get rid of this waste product, and the body reacts with increased breathing activity. If the carbon dioxide cannot be removed from the blood a lower pH results, which seriously affects the salt balance, a state called "acidosis". Breathing in a CO2 level of about 5% leads to unconsciousness in a human and higher levels can be lethal.
The sensitivity to levels of the gas varies between organisms. Animals living in the soil or among fermenting material have the highest tolerances. One soil living species of springtail can survive in up to 35% whereas another, living in the vegetation does not tolerate more than 2%. It results from the decomposition of leaf litter, from fermentation, and from respiration.
Carbon dioxide is over 60% heavier than air. In a vivarium with insignificant air movement CO2 will accumulate in the lower parts and a gradient results with the higher concentration at the bottom. If the terrarium has no opening at a low level a death trap may result. Other possible waste gases in a terrarium, like methane or ammonia are much lighter than air, and thus easier to vent away.
Drainage of heavy gas
CO2 ExperimentIn order to test the CO2 hypothesis I got three one-week-old E. tricolor froglets from a friend. They were placed in a small bottle with an inlet hole under the bottom material (Leca; peat moss; leaves). A fine meshed screen covered the upper opening. The frogs soon found their favourite places where they sat after feasting on the fruitflies that had also been introduced.
When I saw that everything looked normal I let CO2 enter the bottle through the inlet. After a few minutes the frogs began showing signs of restlessness, jumping around in an aimless manner. After another minute the first signs of cramps began to show, and two of the small frogs fell on their backs. Soon all three lay motionless with their hind legs outstretched and no visible breathing movements under their chins. To prevent certain death I ended the CO2 influx and ventilated the bottle. No visible improvement occurred until after about 5 minutes oxygen enriched air was blown into the bottle. Since no breathing was present, any gaseous exchange had to take place entirely through the skin.
The first signs of life were seen after about 15 minutes and after another 5 minutes all three frogs were sitting upright, breathing normally. A few hours after the experiment they were all feeding, and with no lasting symptoms.
Experiment with low Oxygen
Since the production of CO2 is often connected with the consumption of oxygen it is possible that the result of this experiment was due to low oxygen rather than high carbon dioxide. For this reason a second experiment was performed with the same set up and the same frogs. This time argon gas was used instead of carbon dioxide. Argon is an inert, non-poisonous and odourless, non-combustible gas. As the oxygen inside the bottle disappeared, the frogs moved around in a much calmer way than in the CO2 experiment. After a few minutes they opened their mouths in a strange way, as though yawning. No cramps were observed, but they sat shrunken. After another minute the breathing movements ceased and they no longer reacted to touch. The experiment was terminated, and oxygen-saturated air was blown into the chamber. After five minutes all three frogs had recovered.
Interpretation
In order to reduce the stress and avoid unnecessary harm to the frogs, the two experiments were performed more rapidly than would be the case under natural conditions. The experiments show that an increased level of CO2 causes unrest and cramps, whereas the low oxygen situation is characterized by a languid attitude without unrest or cramps. Therefore it must be assumed that the death of the three original tricolor was not a result of a too low oxygen level.
Air movement when lid is opened
Simple calculation shows that in a closed compartment the CO2 level can reach lethal levels long before the oxygen level gets too low. Therefore oxygen depletion is no real risk in a transportation box or a terrarium.
The experiments have strengthened my assumption that the frogs died from CO2 that had accumulated near the bottom of the tank, with a number of other factors playing a part:
1. The lid lay on glass flanges that were meant to keep springtails etc. in. The only ventilation was a small gauze type net in the cover, which made air movement difficult.
2. The lighting was a 5W compact fluorescent lamp placed above the cover glass. This gave minimal convection inside the tank.
3. Only a small plant was present in the tank and in the lowlight it had little chance of absorbing a significant amount of carbon dioxide.
4. The leaf litter was "ripe" and the population of soil invertebrates considerable.
5. Small pieces of banana were fermenting, thus producing CO2 (and alcohol).
6. The tank was left almost a week without the usual daily opening of the cover. This provided ample time for the heavy carbon dioxide to accumulate at the bottom.
How common are CO2 problems?
The loss of my E. tricolor froglets is probably not a unique event in the hobby. One hears reports of 'unexplained' deaths in cases where old aquaria, plastic containers etc have been used for temporary holding frogs, for instance in quarantine practice or directly after metamorphosis which means when the frogs are extra sensitive to stress. As long as the cover is lifted every day for the input of fruitflies, the build-up of stagnant CO2 rich air at the bottom is made impossible. When the terrarium is left unattended for a few days, perhaps with extra fly bottle inside to provide food in the unattended period, the combined effect of the extra fermentation and the poor ventilation can be fatal. Deaths among a group of froglets or a quarantine tank tend to be blamed on infections or parasites, but the real culprit may well be an unsuitable tank.
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