The little guy is a Gymnochanda filamentosa, AKA Filament Glassfish... I have six of them!
His/her dorsal fin should have some fine fin extensions that are almost as long as the fish's body, about three rays (although if its a female these rays are nowhere near as impressive).
http
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Have you only ever had two?
Does the shop you got them from have more?
What else is sharing the tank with them, besides the Denisonii (Redline Torpedo) Barb and what looks like a form of Rummynose Tetra?
I bought the last eight at my LFS, but sadly two died within 48 hours. The remaining six are doing well, sharing with 10 Golden Kuhlis, Rabbit Snails and six "refugee" Pearl Danios (which i hope to upgrade to my Rio240 again after a juggle of fish between four glass tanks, as Filament Glassfish are extremely intimidated by fast, boisterously feeding fish). Good tankmates are "micro fish" from the Asian region, things like Hengels rasboara; Dwarf Emerald Rasbora; Chilli Rasbora; the African Clown Killifish etc.