Rewrite of my initial write-up.
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Here is a small write-up I made on lima shovelnose (LSN) or Sorubim lima/elongatus.
Most important: lima maxes out at 2 feet, elongatus at 1 foot. All Sorubim for sale are labeled common or lima shovelnose, never elongatus.
I used to think the vast majority of LSN sold in the US were the smaller-growing elongatus because I had almost never seen a LSN over 1’ in person. Mine never grew beyond 11", which made me assume they were elongatus, but now I know I had not kept them long enough. I had seen only several photos of US-kept 18”-24” LSN (e.g.,
https://www.monsterfishkeepers.com/forums/threads/huge-lima-shovelnose-catfish.123938/). Our European peers say they see 2' LSN more often than we do in the US, but now I think this is because they are in general better, more mature keepers and keep their fish more successfully and longer.
Out of my latest batch of 18 LSN bought at 3” in 2015, today, 5 years later, half grew to 18”-20” while half is still at 12”-14”. This leads me to assume the larger are S. lima & the smaller S. elongatus & to withdraw my initial supposition that mostly elongatus is offered in the US.
It is hard to tell lima vs elongatus for laymen; here is my attempt at ID back in 2010:
http://www.planetcatfish.com/forum/viewtopic.php?f=13&t=30938 Next thread describes our LSN experience with photos & videos & a relevant excerpt from the most recent genus revision, which states the ID key is the position of the chin barbels vs gular apex:
https://www.monsterfishkeepers.com/forums/threads/lima-versus-elongatus-id-thread.524497/
The Planet Catfish entry for elongatus
http://www.planetcatfish.com/common/species.php?species_id=697 offers kind of a soft ID: "Very generally, Sorubim with spots are usually S. elongatus. They are more of a black water species and, as with most such species, tend towards more variable, spotted patterning."
The info on SeriouslyFish
http://www.seriouslyfish.com/species/sorubim-lima/ is well written & arranged. The notes say: "(S. lima is) Distinguished from S. elongatus by having modally 9 pectoral rays; 21 anal-fin rays; 16 gill rakers..." The page does not state the counts for elongatus anywhere. Neither have I found a species page for S. elongatus. Unless I am missing something, I find this odd & not as helpful as it could have been otherwise. All other pointers refer to things that are subjective. Nevertheless, I enjoyed reading the page & learned a lot.
These ambush predators head stand with minimal motion ~vertically among vegetation & debris mimicking a twig or plant & wait for a prey. Young fish like the kin’s company & often would head stand together, tightly aligned, like mine did half the time when they were 6"-10”. Adults largely lose the gregarious trait.
LSN need not live feeder fish. They are smaller predators that snatch smaller fish, crustaceans, & insects in the wild, anything that fits in their collapsible mouth, which is relatively & surprisingly big for their slender body structure. I always feed mine pellet & frozen - small whole fish, cut fish, raw, crust-on shrimp, etc. all presoaked in VitaChem. They can do very well on pellet. My last batch started on cut fish but with time took to pellets (offered to tank mates) all by themselves & have been taking 50% or more pellets while thriving and & growing well. If I recall correctly Necrocanis of MFK reported his specimen doing exceptionally well on pellets too. When very small, mine like freeze-dried & fresh bloodworms, plankton (mini-shrimp-like creatures), etc. LSN growth is not fast, perhaps 6"-7" in one year starting from ~3".
