Guppi fish is one of the most popular freshwater tropical fishes. The picture above is my main guppi aquarium. The largest guppi is a female guppi. A female guppi can grow to 6cm, larger than a 3cm male guppi. The orange male guppi is a rare mutation. His tail shape doesn't look like a normal guppi. The same is true with the yellow guppi. He is a spike tail guppi; also a type of rare guppi. The guppi on top is a young guppi. I don't know what he will grow to be. Guppi fish like plants in their tank, which I have a lot of. Why guppi fishes give birth to young guppis, they will eat the young. Which is why you need plants for the guppi to hide in.