Because they are such close cousins, its pretty much a krappshoot, especially until they mature. But some have distinguishing features
hartwegi should have an overbite
bifas have a longitudinal stripe, and a blotch above the lateral line

synspillum/melanurum no stripe, a series of blotches

breidhori

argentea

often confused with argentea is regani, but quite different

bocourti and Chuco intermedia

hartwegi should have an overbite
bifas have a longitudinal stripe, and a blotch above the lateral line

synspillum/melanurum no stripe, a series of blotches

breidhori

argentea

often confused with argentea is regani, but quite different

bocourti and Chuco intermedia
