the elusive for my aquarium

[Renegade Aquatics]

It may not be easy to tell black from brown.

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If I am not mistaken, apart from size the only other difference is that A. nebulosus has serrations on the pectoral spines and A. melas does not

 

[thebiggerthebetter]

Yes, the large teeth on the back of pectoral spine is all I know too.