yes venting is how you determin the sex of a fish, but they do have some other distinctive traits to determin sex of trimacs
Sex differences: Males have extended finnage and display a stronger spot pattern than females. Males are larger and deeper in the body and generally more colorful than females, with a claret-coloured throat. Females also tend to have a black spot on their dorsal fin.<from cichlid madness
Venting is removing the fish from water and with a jewelers lense(think that's what it's called. Seperating into two buckets males/females via looking at the vent hole.
sorry about the profanity guys dint know the policy on this forum,,, but anyways thx for all the input about venting,,, i think gothic_samurai just wanted some attention....