| Main Ref. | |
| Appearance refers to | |
| Bones in OsteoBase |
| Specialized organs | |
| Different appearance | |
| Different colors | |
| Remarks |
| Striking features | striking barbel(s) |
| Body shape lateral | elongated |
| Cross section | oval |
| Dorsal head profile | more or less straight |
| Type of eyes | more or less normal |
| Type of mouth/snout | more or less normal |
| Position of mouth | sub-terminal/inferior |
| Type of scales | |
| Diagnosis |
Rhamdia itacaiunas is diagnosed from all congeners by the pectoral fin spine with serrations on both sides; caudal fin upper lobe pointed and longer than lower lobe; mouth deeply cleft to near the vertical at the anterior margin of the eye; eyes in advanced position, distinctly closer to the snout than to the operculum hind margin; adipose fin 23.3-28.4% of SL or 96.2-127% of HL; maxillary barbel 41.2-53.8% of SL or 190-231% of HL; broad tooth plates. |
| Ease of Identification | likely to be confused with closely related species. |
| Lateral Lines | Interrupted: No |
| Scales on lateral line | |
| Pored lateral line scales | |
| Scales in lateral series | |
| Scale rows above lateral line | |
| Scale rows below lateral line | |
| Scales around caudal peduncle | |
| Barbels | |
| Gill clefts (sharks/rays only) | |
| Gill rakers | |
| on lower limb | |
| on upper limb | |
| total | 5 - 7 |
| Vertebrae | |
| preanal | |
| total |
| Attributes | first rays forming locking device |
| Fins number | 1 |
| Finlets No. | Dorsal |
| Ventral | |
| Spines total | 1 - 1 |
| Soft-rays total | 6 - 6 |
| Adipose fin | present |
| Attributes | forked; with dorsal filament |
| Fins number | 1 |
| Spines total | |
| Soft-rays total |
| Pectoral | Attributes 1st ray hardened with locking structure |
| Spines 1 | |
| Soft-rays 8 - 9 | |
| Pelvics | Attributes more or less normal |
| Position abdominal behind origin of D1 | |
| Spines 0 | |
| Soft-rays 6 - 6 |