Who are “we” to say?
Firstly, that depends who “we”” are.
If “we” are vegans, it is because catfish are not vegetables.
If “we” are Jews, it is because Siluroides do not have scales, but either naked skin or bony plates. Therefore they are not kosher. Not kosher is not kosher, don’t ask me to justify it biologically. If you want to be frum, eat kosher, that’s all.
If “we” are anyone else, then the question turns on what do we mean by “catfish”.
The huge biodiversity of catfishes
There are over 3000 species of catfish in the world and they demonstrate vast diversity. From the candirù of South America which swims up people’s urethra if they urinate in the water, all the way up to giant Pangasias or Siluris species among the largest freshwater fishes of the world. Plus various marine species also.
Just to be clear about how astonishing that fact is, it means that 1 in 20 of the vertebrate species in the world is a species of catfish, in Siluriformes. There’s no other order of vertebrates like that. And the cladists have been trying to break it down until they were looking like clado-masochists, and the geneticists have been getting frenetic and still the Siluriformes is reckoned to be all the product of a single putative common ancestor.
Some species of catfish deliver toxins, some electric shocks, some like Corydoras or Otocinclus are too tiny to be of use as food, but are very popular in aquaria. Some species makes sounds, some get out of the water and walk about, some are transparent and you can see right through them.
There is one catfish fossil despite all of this, its name is Corydoras revelatus and the author has held it in the palm of his hand in the non-public area of the British Museum of Natural History thanks to the kindness of the late Dr Gordon Howes, ichthyologist.
Catfishes which are regularly eaten
The catfishes most commonly farmed as food are European catfish, Silurus glanis. As long as you have got one from sustainable sources they make good eating. I recommend “som fri”” in Russia or the Ukraine. Clearly they are a sports fish too, and in these cases we put them back, we don’t take them and eat them.
In the US it is channel cats, the Ictalurus and Ameiurus species which the song “Walking in Memphis”” references in the words “they got catfish on the table””. These are also fine eating as long as they are fished from sustainable and legitimate sources.
In the Amazon region they eat large Loricariids like Plecos. If you should be there as a tourist and are not a Vegan or kosher Jew, you might want to try one.
A lot of tropical rivers though are home to parasites that can transfer to people. And here I come onto the kind of catfish which has become more popular in supermarkets in recent years, namely Panga.
These can be farmed in particularly polluted parts of the Mekong river. I suggest you don’t make these a part of your menu, although trying them once might be ok.