PlanetCatfish.com

after all that has been said here,
http://www.planetcatfish.com/forum/view ... =7&t=30836
I must ask the above question.

It would be difficult to be 100% sure from that photo alone.

What angles/body parts would help?
there is one more shot here, third from the bottom
http://www.planetcatfish.com/forum/view ... =2&t=30939

Well your quesstion made me open up this case once more.

It seems like one of the "easiest" visual keys would be two pairs of mental barbels. Lima has them equal and/or forward of the "pointy tip" at the gular and elongatus has them equal or posterior tho that same point. At least according to the paper in one of the other Sorubim threads here.
This has gotten me to realize that my juvenile Sorubims probably are elongatus.
My attempts to count finrays on my cats also indicate elongatus.
I still have to investigate my older Sorubim a bit more closely.
Seems like elongatus doesn't reach the same sizes as lima. I find that very positive indeed.

From your picture it's of course impossible to tell for sure but since the barbels seems to be closer to the eyes rather than the lower (mandible) jaw tip I'd guess you have elongatus as well.

There are more differences between them but those are partly impossible or very hard to see on a living fish in a tank.

I also guess there are several photos in the Cat-elog that have to be checked out further.

Photo below is of one of my young ones.

I'd also add that elongatus seems to have a genrerally more slender body than lima but this is more of a subtile feeling rather than something to rely on.

Nice info, Back! Thanx. Now I need to look under my Mr Bean somehow, maybe during his next bout of swimming exercises tonight.

BTW I had to look it up: Gular skin (throat skin), in ornithology, is an area of featherless skin on birds that joins the lower mandible of the beak (or bill) to the bird's neck. ...

Have not found for fish but I see very pointy, sharp feature on your guy right between the front pair of barbels and assume it is what you mean.

What about the ray counts? Can you give us a run down?

I don't know any other word than gular. But you're right in your guessing. Its the "area" in between left and right lower jaw bones. The detail to check out is if the barbels are mainly fore or aft of the tip of the V.
At least that's how I've understood it. I might be wrong also.

Counting fin-rays doesn't seem to give a 100% correct species determination but might give a hint. According to the paper I refered to most limas have 9 pectoral finrays and elongatus 8.
However it obviously differs a bit with a few individuals having one more ore one less.

Then there are of course a few more Sorubim species but they seems to be rarer in the trade and they also appears show a few other characteristics - even though not always obvious.

ok, my pic is not nearly as wonderful as Back's but the positioning of the barbels appears similar to that of Back's fish. Hence, likely elongatus !?

whatever Sorubim it is,I'd be careful with companions; it's already very thin and young Sorubim can starve to death when kept with too many other fish that compete for the food.

Thanx for concern, Alex! He always holds out for meaty meals - pieces of raw fish, shrimp - refusing to take pellets or flakes (about 3-6 different kinds offered) or even bloodworms (!). He's been like that since fall 2009 when I got him. His two new companions (limas?) as of 1 week ago are a bit smaller but not nearly as picky - they gorged themselves yesterday. He ate yesterday pretty good too. He does get thin sometimes but I am not too worried.