very difficult to sex, what size is the tank, sounds like you have a chienese algae eater which do get aggressive esp with others of same species as they mature to around 8+inches,,,best kept in sub tropical conditions around 20c...... need a nice large tank,,,what size tank do you have?and what fishes?this thread will be moved as it is in wrong section
Yeah Personally I would aviod them all togeather, But if you have a large enough tank to assure you get a variety of males and females, it's best to get 6 or so if you're really into them.