toxic Cory's...

[Magnum Man]

it was news to me, when they shipped some Cory's with a granule of carbon, that they can emit a toxin... has anyone ever rated them by the strength of their toxin???
unless they are all the same, there are probably informal lists of Cory species that died in shipping... so maybe some of the newer species are more toxic, as they figure out ways to ship them??? I'm sitting here watching my gang, and wondering how "tough" they are??? are they the "Jets or the Sharks"

 

[GaryE]

The toxin is a warning chemical. A lot of fish release chemicals when they are stressed, to warn their species of perceived dangers. That's another good reason for water changes, by the way.
In one evolutionary branch of the Cory group, the warning chemical is toxic in small bodies of water. It has to be concentrated to be dangerous, and what better place than a shipping bag? The fish is stressed, there is almost no water, and they can poison themselves. Shippers will scare the fish before packing, to get the toxins out, then pack them in clean water with something to absorb any leftovers. Good shippers in South America who handle expensive Corys single pack them - I have a bunch of jars some of my 'Corys' arrived in here. With newly found species, they don't want to take the risk of identifying whether their fright chemicals are toxic or not.

These aren't attack toxins. They're part of the poorly understood chemical communication systems our fish have. They just happen to be toxic in situations their evolution never faced. No creature has adapted to being shipped in a tiny bag from Brazil, Peru or Colombia to the rest of the world.

 

[Magnum Man]

so likely still unstudied, as to weather one species is more toxic than the next, or release's more, than another... I'm not worried about them, more just curious

 

[GaryE]

I found a paper once where it was studied, but it was early stage stuff. No one funds that kind of learning, although I'm sure a search for pdfs on Cory toxicity would cough up some new info. Right now, people tend to assume there is some toxicity with all of them, on a better safe than sorry basis. From what I've read, that isn't true, but they all do have fright chemicals. They just aren't all toxic.

 

[CassCats]

Dr. Eric Thomas (online name is usually Beckateen) studies this toxin, but it's ongoing as far as I am aware.

 

[gwand]

Here is some information. I can’t download the entire article

The Reversal of Self-Poisoning in Bronze and Albino corydoras: A Recent Study Sarah Hamade​

New Visions in Biological Science Vol. 7, 3 December 2021 , Page 31-36
https://doi.org/10.9734/bpi/nvbs/v7/15107DPublished: 2021-12-03

Abstract​

The Albino corydoras is a variation of the Bronze Corydoras that advanced through the aquarium trade. They tend to display a pale pink body with red eyes. The fact that these Albino corydoras are specifically bred for the commercial ornamental fish trade renders them blind as they are commonly injected with a bright red dye. Corydoras is a genus of freshwater catfish that belongs to the family Callichthyidae and the subfamily of Corydoradinae. Corydoras are small fish, estimating between 21-100mm and averaging at 57mm. The unique ability to use their body armor scales and sharp, commonly venomous spines allows them to protect themselves from predators. Alongside this, the Corydoras can self-poison when threatened, a common feature of many species of Corys, which enables them to deliver poisonous mucus from their gills causing surrounding fish to expeditiously die. The process of self-poisoning causes tremendous stress on the Corydoras, often resulting in death. This study focuses on the process of self-poisoning and insight into its reversal in Bronze Corydoras and Albino corydoras. The purpose of this study is to inform marine biologists and educate aquarium hobbyists on possible reversing mechanisms that could save the lives of many Corydoras.