Darth pike is quite right about 'Heros', but my understanding is that Heros is still pending for a more definitive classification to establish a new genus. This will hopefully include a few species such as beani and salvini. However, exCichlasoma is still quite exceptable for now.
I would like to give an opinion on your Rio Carolino fish. In my opinion that fish dosen't resemble sp. coatzacoalcos Rio Carolino, infact it dosen't resemble any population of sp. coatzacoalcos, therefore i would question the infomation of your lfs. Someone has something mixed up somewhere.
As far a the systematics of sp. coatzacoalcos, it is still classesd as undescribed. Its kind of frustrating as this fish has been in the hobby for almost 28 years. These were once thought to be a variation of zonatus, but many experts believe that there are enough traits to seperate and classify them as 2 seperate species.
This what i know and certainly not conclusive, but many experts appear to avoid the questions regarding seperation. If we look at distribution. Sp coatzacoalcos are found in the upper parts of the coatzacoalcos basin in the province of Oaxaca, Atlantic side. This includes populations from Rio Jaltepec, Rio Junapan, Rio grande, Rio ajal, Rio Almoloya. True zonatus populations are reported to be on the Pacific side,
Rio Zanatipec, Rio Niltepec and Rio Tehuantepec. I have talked to many hobbyist who have collected wild zonatus populations and they say it's all in the tail. The germans knicknamed them "Rotschwanztheraps" (Red tailed theraps).
If we compare the type locality zonatus (Niltepec, southern Oaxaca) then to me there are some key differences. The type locality zonatus has almost completely red caudal and a lot of red on the end base of the dorsal fin. I've also noted that the pectoral fins have a red hue. These traits are more apparent in younger fish as older fish loose these colours and will display a red band on the caudal fin. This extensive red colouring is displayed on Mo's earlier photos of he's zonatus and also to some extent on the fish described on the thread. Sp. coatzacoalcos display more yellow colouration on the caudal fin. The black lateral stripe is consistant on both species, but zonatus appear to display black markings on the upper body, while sp. coatzacoalcos display black on the lower part. Sp. coatzacoalcos sometimes display a red band across the upper part of the mouth, but this is not always a trait as the Rio Grande population lack this and are almost completely blue. This is why the species interest me, there is so much variation between populations. Sp. coatzacoalcos display a bright yellow colouration when spawning, especially with pairs observed in the wild. This i believe dosen't happen with zonatus.
If anyone has a copy of Aqualog book 3, there's a good idea of what the type locality zonatus looks like. These are my own personal observations and are certainly not conclusive, but until the systematics of the fish have been officially worked on and presented, we will still be debating if the fish are the same species. I hope the fish will be officially described in the near future.
Sorry for the long explanation, as i noticed on this forum a lot of people get the names and identification wrong. I see many people who claim to keep zonatus are infact sp. coatzacoalcos. I would even question Don Conkels zonatus, especially the Rio Nachintal population thats mainly offered, i have no idea what the Rio Jaltepec population look like. so i hope this may have answered a few questions.
Regards,
Lee Nuttall.