Julii cory vs three-line cory
The tank is labelled 'julii cory'. Almost every time, it is not one. Does it matter, and how would you tell?
Short answer
Look at the pattern rather than the label. Corydoras julii carries discrete round spots that stay separate; C. trilineatus has spots that join into a reticulated net, and a dark lateral line. The husbandry is close enough that a keeper is unlikely to come to harm — what is lost is the ability to know what you own, which matters if you ever want to breed it or replace a lost fish.
Side by side
| Dimension | Julii corydoras | Three-line corydoras | Favours |
|---|---|---|---|
| Head and body pattern | Discrete round spots, separate from each other | Spots joined into a reticulated network | — |
| Lateral line | Weak or absent | A distinct dark stripe along the flank | — |
| Adult size | 4–5.5 cm | 5–6 cm | — |
| How often it is actually in the shop | Uncommon | The great majority of fish sold as 'julii' | Three-line corydoras |
| Native range | North-eastern Brazil | Western Amazon | Neither |
| Temperature | 23–26 °C | 22–26 °C | — |
| Minimum group | 6 | 6 | — |
Which to choose
Julii corydoras
Choose the julii deliberately only if you have checked the pattern yourself and want that species specifically. Buying it by label is close to a coin toss.
Three-line corydoras
Choose the three-line if you want the fish that is in front of you, which it almost certainly is. It is a good corydoras in its own right and nothing about it is a substitute.
One caveat
Neither identification survives a mixed shop tank. Corydoras hybridise readily in captivity, and stock of uncertain parentage is common enough that pattern is evidence rather than proof.