Tropical or Coldwater Fish? Firstly consider the size of the aquarium that you want to keep and the space that it is going to fit into. In the long term Goldfish and Fantails are going to grow larger than most tropical community fish, and will therefore need a larger aquarium. It is also worth considering who the fish and aquarium are for. Children may like to see the larger bright colours of the coldwater goldfish. However with Tropical Fish you can have a wider selection o