What are the little brown fish in my pond?
What the heck are those little brown fish in my pond -- are they baby Koi? This is a common question for people after we build someone a pond. Most of the time, they don't even notice them until their Koi or goldfish start becoming friendly. Once the hand-feedings start, they suddenly realize that there are a bunch of little brown fish in the pond. No, they are not the result of your Koi or goldfish fish breeding. They are Gambusia Affinis, commonly known as Mosquito Minnows, and they are part of the reason that a well-built pond is the cure for a mosquito problem.
What Do Mosquito Minnows Do?
They are vector control. Mosquito minnows' main purpose in life is to seek out and eat mosquito larvae in a body of water (as small as a mud puddle!). This is their all-time favorite food. That's not to say that they're not opportunists, as well. They will happily munch on Koi food, too, when given the opportunity, which is when people usually start noticing that they're there. All of a sudden, there are a bunch of little brown minnows darting around amongst the colorful pond fish. Water naturally attracts mosquitoes, so a pond full of hungry fish (and Mosquito Minnows) will keep those blood suckers under control.
Do I Have to Feed Mosquito Minnows?
Nope. They feed themselves: first and foremost, on mosquito larvae. If none of that is available, they'll eat whatever they can get, including roe (fish eggs). Yep, they are also population control for your Koi and goldfish. In fact, fish eggs are their second-favorite food source. As long as you have these in your pond, you will not have baby Koi or goldfish and your planned population will be maintained.
Mosquito Minnows are a Self-Controling Population
If no mosquito larvae is present, and there are no fish eggs to eat, then they turn cannibalistic. So, when times are good (lots of food), they multiply like crazy (they have live babies every 4-6 weeks). When food is scarce, they eat each other, thus being a self-controlling fish population. It may seem harsh, but that's part of life in and around water: the cycle of life.
OTHER POSTS YOU MIGHT ENJOY:
WHAT SHOULD I DO ABOUT BEES IN MY POND?
7 TIPS TO KEEP POND WATER CLEAN
KEEPING KOI & POND FISH: 3 BASIC RULES