must agree . channa deserve there own species tank . gachua however is one of the very few you may get away with mixing . the problem is though in a mixed setup the gachua would hide most of the time (there quite shy species anyway) and you probably would not see much of it , gachua are really not keen on fish as food so tank mates would be things like larger rainbow fish ect . second problem is size allough some gachua would be happy in a 33g my indian calcutta gachuas are now around 10inch and still growing and would be cramped in a 33g without tankmates . and lastly some gachua are sub-tropical and would not fair well in tropical tank and there aint that many sub-tropical fish in lfs to house your gachua with.
to be honest i would, depending on tank diamensions ,probably go for channa orientals as theese grow slower and stay a lot smaller than gachua and you could keep a nice breeding pair in your tank or possably a pair of channa sp assam
