If you re looking to be geographically correct, Rhamdia catfish come from Mexico, and may be found in the same waters as Herichthys carpintus.
The ones I've seen diving in the cenotes of the Yucatan are usually @ 8"-10", very similar in looks to bullheads of the northern part of N America, and would not get too large for your tank, and eat your cichlids, like some of the other suggestions above.
https://www.youtube.com/watch?v=91QTH8OsKoE
The ones I've seen diving in the cenotes of the Yucatan are usually @ 8"-10", very similar in looks to bullheads of the northern part of N America, and would not get too large for your tank, and eat your cichlids, like some of the other suggestions above.
https://www.youtube.com/watch?v=91QTH8OsKoE