Do Koi Eat Tadpoles? (And How to Prevent it – Some Are Toxic!)

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Will Koi Eat Tadpoles & Frogspawn? (And How to Prevent It)

Koi with their mouths open
Tadpoles fit perfectly in the large gaping mouths of koi, though they generally aren’t predatory fish. Photo from pxfuel

If you’ve ever fed koi, you’ll know that they are avid eaters. Once they know that food is coming, their large, gaping mouths can seemingly gasp in excitement at the water’s surface. These omnivorous fish can be fed with a wide variety of treats, from proteinaceous worms to plant-based wafers. As they may attempt to eat pretty much anything that they can fit into their mouths, you may find yourself wondering if they’ll consume the tiny critters that lurk in your pond.

The good news is pond koi generally aren’t predatory fish. Whether or not you wish to have tadpoles swimming about in your pond, it would be unwise to rely on koi to decimate their populations. That being said, koi can definitely consume a tadpole or two. Mostly harmless, tadpoles fit perfectly in koi’s mouths. This is not necessarily a bad thing, but read on if you’re concerned about the potential dangers of tadpole consumption and ways to prevent this from occurring.

Likelihood of Koi Eating Tadpoles

Western toad tadpoles
Toad tadpoles (pictured) can harbor a toxin to keep your fish away. Koi will most likely spit them out due to their unpleasant taste. Santa Monica Mountains National Recreation Area / No copyright

When fed regularly, koi will rarely feel the need to eat tadpoles. They may be more likely to eat frogspawn (eggs), which are stationary and harmless. If your koi have missed a meal, they may search for natural sources of nutrition. This naturally-sourced meal can sometimes include tadpoles, but will also be supplemented with edible aquatic plants (if present in your pond).

The type of tadpole can influence the likelihood of consumption. Frog tadpoles are normally safe for koi, but toad tadpoles may harbor a toxin to keep your fish away. Koi that are adventurous enough to eat toad tadpoles may find themselves disgusted by the taste and may spit them out. From then on, they’ll likely be smart enough to avoid eating tadpoles.

For the most part, you can expect koi and tadpoles to coexist peacefully, especially if you have an ecologically balanced pond.

Can Koi Control Tadpole Populations?

A toad's egg string
You should keep an eye out for amphibian spawn, like these toad eggs, and remove them before they hatch. Jens Cederskjold / CC BY-SA 2.0

Shortly after a favorable amphibian mating period, you may find yourself with an obscene number of tadpoles in your pond. Though they may put more pressure on your pond filter, these tadpoles will eventually mature into frogs and make their way out of your pond. If you’re impatient for them to leave or you find that they alter the balance in your pond, you can try to get your fish to help you.

A large koi population can help reduce tadpole numbers, but you may have to decrease feeding sessions to get them to do so. There’s no guarantee that your koi will make a real dent in tadpole numbers, however. It also wouldn’t be ideal to keep starving them until they do.

You will likely have to complement your koi’s efforts by manually fishing out tadpoles. You can also keep an eye out for amphibian spawn (but you must make sure you don’t confuse them with fish spawn), and remove the eggs before they hatch.

Benefits and Drawbacks of Tadpoles

A large group of tadpoles underwater
If there are too many tadpoles in your pond it can be disadvantageous & stress the pond environment. Hefin Owen / CC BY-SA 2.0

Frogs and tadpoles will naturally occur in all outdoor fish ponds. Depending on the type of water feature you wish to cultivate, tadpoles can be beneficial or disadvantageous in your pond. When populations are controlled by a well-balanced system (i.e. overcrowding is prevented by both limiting resources and a healthy food chain), the benefits tend to outweigh any drawbacks.

Drawbacks occur when hundreds of frog eggs hatch at the same time. The introduction of these new inhabitants can stress the pond environment. Some drawbacks are listed below:

  • Reduced dissolved oxygen levels due to oxygen uptake and waste production by tadpoles
  • Transfer of diseases from infected frogs/tadpoles to fish
  • Toxins potentially carried or emitted by toad tadpoles to ponds
  • Visiting prey (snakes, birds, carnivorous mammals) lured to your pond by the abundance of tadpoles
  • Adult frogs or toads eventually wreaking havoc in your garden once they have left the pond

If tadpoles are present in small numbers, they bring many benefits to outdoor ponds. Apart from being rich sources of protein for you fish, they can provide many ecological services, such as:

  • Control of algal populations and biofilm accumulation as they are herbivorous grazers in the first few weeks of life
  • Control of insect larval populations, including mosquito larvae, and other benthic pond organisms as older tadpoles become carnivores
  • Increased biodiversity and occupancy of bottom niches in the food chain hierarchy (this may improve the ecological stability of your pond, increasing its potential to sustain itself as a natural system)
  • Eventual increase of amphibian populations in your garden, enhancing pest control of mosquitoes, slugs, snails, flies, and other destructive organisms

How to Prevent Koi From Eating Tadpoles

Tadpoles swimming past rocks
Rocks & stones can increase the number of hiding places for tadpoles, making it harder for koi to eat them. Sebastian Werner / CC BY 2.0

If you’d like to secure small populations of tadpoles or discourage your fish from consuming them (for safety/sanitary reasons), you can increase the structural diversity of your pond. More floating, marginal, and pond bottom plants will effectively shelter tadpoles and ensure that they are regularly provided with food.

Rocks, stones, and wooden features would also increase the number of hiding places. Apart from adding structures, make sure your koi are regularly provided with protein-rich fish feeds. If these suit their nutritional demands, they are unlikely to search for food elsewhere.

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