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What are the benefits of having fish in our pond? Are there drawbacks for wildlife?

Our large pond, which has been part of the farm landscape for at least 450 years, is teeming with fish. They’re a mixture of carp - ghost, mirror, Koi are the ones that I know, as well as gold fish, which are also a type of carp. They range from tiddlers spawned this year, to enormous beasts which could be a decade or more old.

The gold fish were there when we arrived in 2017 and later we were given 8 larger carp. This was early in our time at Langdon, when we were much greener - we knew nothing of carp and ponds, no idea of how quickly they would breed, how much we’d enjoy them, nor what impacts - for good and for bad - they would have on the pond ecosystem.

We have learned a lot about the pros and cons of having fish in a pond, and so here’s a round up of what we’ve learned so far.

The Pros

Wonderful to watch and interact with

The first thing we realised was that watching them is an absolute pleasure. Minutes seem to evaporate as you sit mesmerised by their going and coming, their leisurely gliding and then sudden darting. It’s arguably the most relaxing thing to do in the garden - an opportunity for mindful slowing down which is big plus in our fast, always distracted, lives.

They’re fun too. In the summer you can sit and dangle your feet in the water - they’ll come over and kiss your feet, no doubt mistaking them for something tastier!

Fish feet kisses (Sound on!)

Attract exciting fish-eating birds

If we had a smaller pond and there weren’t so many of them, we might not be fans of birds coming to feed on the fish, but in our case we love the diversity of birds that the fish attract. Magnificent herons are our most regular visitors, but we’re also sometimes honoured with visits by cormorants, egrets and even king fishers! We wish they'd all visit more often - and have a bit more luck with their fishing to keep the carp numbers down.

A heron swooping down to the pond

Reduce pond weed

The carp population’s rampant appetite has drawbacks, as I’ll discuss later, but it also has one excellent benefit. Many ponds, especially ones exposed to as much sunlight as ours is, have trouble with pond weed such as a algae, blanket weed and duck weed. These weeds deoxygenate the water which is damaging to the other pond wildlife.

A few years ago, when there were a lot less fish, the pond was covered in duck weed and had other large weeds growing up from the bottom. As they’ve grown in number, the carp have dealt with both types of weed without us needing to consider more expensive, time-consuming or chemical-based solutions.

You can read more about this here and watch a video here.

The Cons

Voracious appetite reduces other wildlife

We learned fairly early on that fish will eat amphibian young - tadpoles or larvae - and so if you want frogs or newts to come to your pond, avoid putting fish in it. It was too late for us by then, so we resolved to set up another, fish-free, pond somewhere else in the garden.

Last year however, as we watched the numbers of carp go from the tens to the hundreds, we did some more research into carp in particular, and learned they can be more detrimental to wider pond biodiversity than other fish. This is because they breed fast and eat voraciously, wiping out invertebrates such as damselfly and dragonfly larvae. (Read more on fish and wildlife ponds here)

We have only seen a couple of frogs since we’ve been here, and none last year, so presumably the carp are not giving them a chance to breed successfully. We do have dragonflies and damselflies though. I can’t say if there are less than before. Hopefully, for them, the balance has not tipped too far in favour of the fish.

Should we feed the fish?

Until recently, we only fed the fish occasionally, just for our own entertainment to be honest. It was clear that they had enough food in the pond, and I didn’t want to ‘encourage’ these rampant breeders by making them too fat and happy! However, we have recently been advised that feeding them a moderate amount (this is carp pellets from the pet shop) will supplement their diet, hopefully curbing their appetite enough to give other wildlife more of a chance. Daily feeding will also keep them healthier and disease-free - perhaps a better approach overall to having a healthy pond?

John feeding the fish

Is it safe to swim in?

Over the last few years we have enjoyed swimming in the pond. It’s plenty deep and big enough, and on a hot day there’s nothing better than slipping into the cool water. The fish quickly make a dash for it when you get in, so they’re not a bother at all. It has always ‘felt’ clean, but as the carp numbers increase, I begin to be not so sure. This year I plan to send off lab tests on the water to make sure there’s nothing nasty in there.

Swimmers loving the water - summer 2021

How can we control the numbers of carp in the pond?

It seems that the carp numbers are only going in one direction - up! And while they have their benefits, we don’t want them to dominate the pond to the detriment of other wildlife and our own enjoyment of it for swimming.

Last year we recruited George Leeks from Stillwater Management to advise us on how to deal with the carp. His advice was that it is nigh-on impossible to completely eliminate carp from the pond now that they are in. We would have to drain the entire pond and then wait many months for it to refill - not a road we are willing to go down. Even if we did this, some of the carp would likely bury down into the mud bottom out of sight, only to re-emerge later.

His recommendation was that we resign ourselves to a periodic removal of as many fish as possible, every 6 years as so, as their population reaches a critical size. When their numbers are low, we might have more problems with pond weed and have to tackle this without their help, but at the same time the invertebrates and amphibians that they prey on will fight back. As the numbers increase again, the pros and cons will reverse. I hope that we will be able to find a balance that works well for us all.

We will have George back to do a fish removal in another year or two. And the story of the pond will continue…

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