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AFAIK, there are no dwarf species that will always by nature swim about openly in the aquarium. Most are very reclusive and only come out in reduced or no light. There is the
Dendrochirus brachypterus aka shortfin dwarf noted on <<
wetwebmedia.com>> as being "owner friendly" although rarer to the trade, may be an option. Through personal experience, I have also found the
Dendrochirus zebra to be an open swimmer.
Cheers
Steve