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Corydoras in a Bag

Question: When I buy Corydoras Catfish they are always packed in a separate bag, why?

Answer: In nature many animals, including fish, have some unusual methods of self-defence. Some, such as the Skunk, produce bad smells, others produce bad tastes to discourage predators from biting them, while a small group actually take it to the extreme, they produce poison to kill any predator who eats them. Its not clear how this helps the victim who has already been eaten, but it is quite a nice line in "Revenge".

Anyhow, to answer your question, Corydoras are one of several species of fish which have special cells in their dermis capable of producing toxins. As I noted before, the purpose of this evolution is not fully understood, but it is known that high levels of stress, such as being netted into a bag for transportation, can trigger these cells into action and release poison into the water.

Although not totally immune, Corydoras are very tolerant of these toxins, certainly more so than any other unfortunate fish who may be in the same bag. It is for this reason that Corydoras are always packed separately.

Just while we are discussing Corydoras it is worth noting that this is not their only line of defence. As members of the wider Catfish family Corydoras are also equipped with three venomous spines, the leading ray of the Dorsal and each of the Pectoral fins. All Catfish have these spines which can be extended to prevent predators from swallowing them. In some species the venom is so mild as go un-noticed should a human be pricked. However this is not the case with Corydoras. Many fish keepers well remember their first encounter with a Corydoras spine, it is not dangerous to humans, but it does sting something terrible..


Maroon Clownfish in an Anemone