First just let me say that I'm a Piranha Plant fan, and I've never seen a critique for these creatures so I'm pretty excited to do a critique based on them.
I'm going to state something simple and say that I really like how you drew them in general. They would probably still look great if you didn't color them or what not, and I say this because I always have the hardest time drawing them.
Another thing I admire is the coloring. You didn't overdo the colors at all nor did you "underdo" any of the colors. You seemed to color them just right, and they look simply dazzling.
One more thing I noticed was the background. Like I said before, nothing is overdone, and it looks simple and clean. Simplicity is a great aspect of art and it can be hard to do, but you seem to know it perfectly.
Simple, pretty, and nothing overdone. This picture looks great, and I hope to see more from you.