Hi there gizmo,  
 
Am sorry to hear about the oscar. 
 
If you require a fish anaesthetic (for handling your fish) in future visit www.aqui-s.com where you will find good info on the subject. AQUI-S NZ Ltd produce the only registered fish anaesthetic in NZ. The anaesthetic is also food grade (registered with zero withholding period) so many fish farms/fish keepers will use it for humane slaughter purposes, as well as general handling procedures like grading, weight checks. 
 
Thanks - Ben