Travel the main rivers of the Amazon and you can see two very different dolphins in the same stretch of water: the large, pink-tinged boto and the small, grey tucuxi. They look superficially similar to a passing eye, but they belong to separate branches of the dolphin family tree and behave quite differently. Here is how to tell them apart. For the full boto profile, see our pink river dolphin species guide.
The quick answer
The pink river dolphin (Inia geoffrensis) is a true river dolphin — bigger, pinker, with a long beak, a bendable neck and a low ridge instead of a fin. The tucuxi (Sotalia fluviatilis) is a small grey dolphin descended from ocean-going stock, with a classic triangular dorsal fin and a stiffer neck. If it is large and pink with no real fin, it is a boto; if it is small, grey and fin-backed, it is a tucuxi.
Family: distant cousins, not siblings
The boto belongs to the family Iniidae, the true river dolphins. The tucuxi sits in Delphinidae, the same family as familiar ocean dolphins, and only colonised fresh water more recently. They share a river but not a recent ancestor.
Size and colour
The boto reaches up to about 2.5 m and is the largest of all river dolphins; adults often turn pink. The tucuxi grows to roughly 1.5 m and stays grey above with a paler underside — it never turns pink.
Body shape: fin vs ridge
The clearest field mark is the back. The tucuxi has a distinct triangular dorsal fin, like a scaled-down ocean dolphin. The boto has only a long, low ridge and no true fin, paired with a longer, more slender beak and a bulging melon forehead.
How they move
The boto's unfused neck vertebrae let it turn its head nearly 90 degrees and thread through flooded forest after prey. The tucuxi has a stiffer, fused neck and tends to stick to open channels and lakes, often surfacing in a brisker, more conventional dolphin roll.
Conservation: both in trouble
Both species are now Endangered on the IUCN Red List — the boto assessed in 2018, the tucuxi in 2020 — and a long-term Brazilian study found both declining steeply in the same waters, with boto numbers halving roughly every decade. They face overlapping threats from gillnets and habitat pressure, which is why river-focused protection helps both at once.
| Feature | Pink River Dolphin (boto) | Tucuxi |
|---|---|---|
| Family | Iniidae (true river dolphin) | Delphinidae (oceanic lineage) |
| Adult length | Up to ~2.5 m | Up to ~1.5 m |
| Colour | Grey turning pink with age | Grey, paler below; never pink |
| Back | Low ridge, no true fin | Triangular dorsal fin |
| Neck | Flexible, unfused vertebrae | Stiffer, fused neck |
| IUCN status | Endangered (2018) | Endangered (2020) |
Because both dolphins share the same threatened rivers, protecting their habitat protects them together. WARN supports local partners in Brazil and Colombia doing exactly that; you can learn about that habitat work if you would like to help.
Read the full Amazon river dolphin wildlife guide for the facts, IUCN status and conservation context — or donate to WARN to help fund the local partners protecting this species.
