O.niger
O.sifontesi
O.kneri
What are main differences between these species? There is hardly any photos from the others than well known O.niger.
O. sifontesi

O. sifontesi

O.niger

In that case, and based on the images above, it would appear that we have both O. niger and O. sifontesi here at Bolton (I had though we had O. niger and O. holdeni).Silurus wrote:holdeni is tentatively considered a synonym of niger.