I purchased two male guppies and two females several months ago.I had to work away from home for six months and the tank was maintained by my partner.In the intervening period needless to say the guppies reproduced.I have now returned to a tank with about thirty guppies both male and female and more arriving every day.I am concerned about the overcrowding.What can I do ? If I have to put several of the fish down to reduce the numbers, what is the most humane way to do this ? My local dealer is not interested in taking any of the fish.