rescued plec, please ID

[MatsP]

Right, here's the reply from Jon Armbruster:

That is probably P. disjunctivus, but it ranks as one of those I can't really tell very well - P. pardalis and P. disjunctivus are a nightmare.

From this, I assume Jon Armbruster is therefore saying that a vermiculated belly is NOT necessarily diagnostic of disjunctivus? If it was, we could still do with Eric's photos as we don't have any photos of live disjunctivus, but Jon's answer suggests that he can't be certain as to the ID.

I will ask for a clarification.

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Mats

[MatsP]

Ok, so that didn't clear things up very much.

It isn't quite that simple. The belly in P. disjunctivus only has vermiculations, P. pardalis has either just spots or short vermiculations with some free spots. Not very useful I know. What also works is that P. pardalis has the vermiculations on the back of the head whereas P. disjunctivus has spots. It appears as if there may have been some introgression in the pet trade which further compounds matters - along with no detailed study of color variation across the range.

So, put simply: It's a mess, and you can't say for sure what is what. Except it appears that P. multiradiatus doesn't look at all like either of P. pardalis or P. disjunctivus!

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Mats

[Suckermouth]

I was expecting that sort of response from Jon...

Mats,

I just got the same reply from Jon myself. Looks like we both went right to the source. And he's right that pic of his specimen isn't the best for a live ID. I also got a copy of his 2004 article from him with the key to Loricariidae. I'll be changing my "my cats page later". Looks like I'm still on the hunt for Mutliradiatus. I may just have to take a field trip to Florida or Texas myself and see what I can catch. But I did just grab 12 more of these today from a LFS, so hopefully i'll end up with a male.

Take care everyone

If Jon Armbruster can't identify them well, you can bet that the people who are using his key to identify invasive fish aren't going to be doing much better.

[MatsP]

If Jon Armbruster can't identify them well, you can bet that the people who are using his key to identify invasive fish aren't going to be doing much better.

And that is if they are using a key at all, rather than some book that they found in the local library or some such. If you are not aware that there is a dozen (give or take) species of Pterygoplichthys, and about 700 different other plecos, it is fairly easy to jump to the conclusion that the first pleco you find in a book is the one you are looking at - after all, they are quite different from all the other fishes that we find in generic aquatic species books. I have an old aquarium book. It's a Swedish translation of "Freshwater tropical fishes", John Gilbert (editor), et. al. from 1970. It has exactly four species of of Loricariidae: Farlowella acus, Otocinclus flexilis, Plecostomus punctatus and Xenocara dolichopterus (that's the names GIVEN in the book, I'm not saying they are completely correct - the X. dolichopterus definitely look like the true

Ancistrus dolichopterus

, but the remainder could be any of the common fishes sold under these names).

Now, in a more modern book, there may be another few species, and one of them may be a Pterygoplichthys. And if it's not too far off, it will probably be taken as "that's the one".

I'm not saying the people who are doing this sort of research are incompetent as such, but we here at Planet Catfish tend to be VERY specialized in catfish, and have several books about this subject alone. We will take a tiny difference between two fishes and try to figure out if that makes it a different species or not.

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Mats

[Suckermouth]

Ah, that's true. There's a paper about invasive Pterygoplichthys in the Philippines that was talking about how the fish that were reported were identified Hypostomus plecostomus, but they didn't find any Hypostomus and found only Pterygoplichthys.

[Carp37]

Thanks for the clarification Mats- by introgression I assume Jon means hybridisation?

If Jon Armbruster can't identify them well, you can bet that the people who are using his key to identify invasive fish aren't going to be doing much better.

That's almost a certainty, but as that key is pretty much the definitive Pterygoplichthys identifier Jon should really revisit that split on the key and put a few caveats on the split between pardalis and disjunctivus. I'm not trying to knock Jon, as I know how difficult it is to put together a coherent and usable identification key for people with only a passing knowledge of the organisms concerned- I remember the Linnaean Society's key on nudibranchs (sea slugs) had its first dichotomy as "carnivorous or vegetarian"(!)- how do you test that- see if your specimen eats a piece of seaweed?

[MatsP]

Thanks for the clarification Mats- by introgression I assume Jon means hybridisation?

That's how I understood it, yes.

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Mats

[Suckermouth]

Yes, introgression is caused by hybridization. You can technically have hybridization without introgression, such as with sterile hybrid young; introgression means that the hybridization allows mixing of the gene pools, which means hybrids are fertile.

[Shane]

Yes, introgression is caused by hybridization.

If there is one group of loricariids where hybridization has taken place and actually led to loricariid hybrids turning up in the hobby frequently and in large numbers... it makes sense it would be these. I highly doubt that SE Asian or Florida fish farmers took care to distinguish carefully amongst a group of very similar looking species when they started their programs (or added additional breeding stock at a later date). This is especially true as in all cases I know of they are pond bred. Once dumped in a murky breeding pond there are not a lot of chances to spot subtle differences and separate the breeding stock.
Short of proper testing we can not say this is the case for sure, but I do not think anyone would rule it out as a distinct possibility.
-Shane

[Carp37]

this makes sense if they're allopatric (have non-overlapping distributions)- the Cat-eLog has specific localities for disjunctivus, but pardalis is just "widespread in the Amazon river system", so I'm not sure if they ever occur together naturally. We did have a Pterygo in this forum about a year ago, supposedly farm-raised in Australlia, that was different enough from all the species we've got pictures of to suggest it was either a new species, or a farm-raised hybrid (I've searched for the thread but can't find it ).