Corydoras poison themselves?

[Jordan_Deus]

I was watching a lecture by a corydoras breeder (linked below), in the lecture he mentions that corydoras produce some sort of toxin from a gland near their fins when scared. This leads them to dying. In his lecture he recommends putting them in a bucket and scaring the daylights out of them before bagging them in fresh water, this will keep them alive until you can get them settled in their new home. I want to know if this is actually a risk when buying corys form a LFS and if so do the LFS know to do this?

Thanks,
Jordan

Link:

He explains about the toxin at 10:52.

 

[Byron]

I don't want to listen to the hour-long speech, but I can answer your question on the toxin.

Some aquarists have had Corydoras fish die in the bag on the way home from the store. The fish can secrete a white milky substance, probably from the base of the pectoral spine. It occurs when the fish is severely stressed. Chasing it around a tank with a net can cause severe stress. This is an extremely potent toxin, capable of killing the fish in the bag within seconds.

I know some cory experts recommend scaring the fish nearly to death in the store tank or a bucket, but I view this as extreme, risky, and certainly severely stressful. I have never had this occur, and I have bought dozens of cories over the years. But I will not stand in front of the store tank and insist the employee catch this or that fish; if I want five cories, the first five in the net does it. If one looks odd in the bag, I may exchange it. But I am not going to subject the fish to such treatment, as this can cause permanent internal damage that the fish will not recover from; I don't know how much scaring the fish need to excrete the toxin, I've never observed it, but it must be severe. And this level of stress can weaken the immune system, and other things in the fish.

When buying a group of cories, it is a good idea to separate them out in individual bags. For one thing, it means not all of them will die if one does secrete this toxin. But they also have sharp pectoral spines that can be locked into place, and will easily tear through a plastic bag...or your finger. Loaches also have this spine. Never handle cories or loaches.

Edit. I thought I had some data about this, but I cannot track it down now. Ian Fuller, an English aquarist with a vast knowledge of the Corydoradinae actually documented this toxin release in 2002, accidentally; he was filming some C. sterbai in a show tank and caught the release. The photo was subsequently published I think in the magazine Amazonas. In nature, this is a defense mechanism; any predator about to swallow a cory gets a mouth full of poison and releases the cory pronto. The cory itself is not harmed, but in the confines of an aquarium or a bag, things change.

 

[Jordan_Deus]

I don't want to listen to the hour-long speech, but I can answer your question on the toxin.

Some aquarists have had Corydoras fish die in the bag on the way home from the store. The fish can secrete a white milky substance, probably from the base of the pectoral spine. It occurs when the fish is severely stressed. Chasing it around a tank with a net can cause severe stress. This is an extremely potent toxin, capable of killing the fish in the bag within seconds.

I know some cory experts recommend scaring the fish nearly to death in the store tank or a bucket, but I view this as extreme, risky, and certainly severely stressful. I have never had this occur, and I have bought dozens of cories over the years. But I will not stand in front of the store tank and insist the employee catch this or that fish; if I want five cories, the first five in the net does it. If one looks odd in the bag, I may exchange it. But I am not going to subject the fish to such treatment, as this can cause permanent internal damage that the fish will not recover from; I don't know how much scaring the fish need to excrete the toxin, I've never observed it, but it must be severe. And this level of stress can weaken the immune system, and other things in the fish.

When buying a group of cories, it is a good idea to separate them out in individual bags. For one thing, it means not all of them will die if one does secrete this toxin. But they also have sharp pectoral spines that can be locked into place, and will easily tear through a plastic bag...or your finger. Loaches also have this spine. Never handle cories or loaches.

Edit. I thought I had some data about this, but I cannot track it down now. Ian Fuller, an English aquarist with a vast knowledge of the Corydoradinae actually documented this toxin release in 2002, accidentally; he was filming some C. sterbai in a show tank and caught the release. The photo was subsequently published I think in the magazine Amazonas. In nature, this is a defense mechanism; any predator about to swallow a cory gets a mouth full of poison and releases the cory pronto. The cory itself is not harmed, but in the confines of an aquarium or a bag, things change.

Very informative! When you say bag Cory's separately do I request from the LFS each fish be put in a separate bag? Something tells me not all LFS will be to pleased with that.

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[Byron]

Very informative! When you say bag Cory's separately do I request from the LFS each fish be put in a separate bag? Something tells me not all LFS will be to pleased with that.

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To be honest, I have never gone this far. One local importer does bag cories with only two or three to each bag, for this reason. I personally feel that if I am prepared to take the first five cories the person nets, one bag is probably safe.

Another thing is to avoid stress on the trip home. I put the bags in my fish cooler which not only maintains the same temp, but is completely dark. People that keep lifting the bag of fish to look at them are adding more stress to an already highly stressed fish.