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Fast Facts About Pond Fish

By: Dr Gareth Evans - Updated: 2 Jul 2020 | comments*Discuss
Fish Brain Bodies Lateral Line

For many pond owners, the chance to have a few fish swimming their way through the water-lily stems is a big part of the reason they built their water feature in the first place. Anyone who keeps fish in their pond will soon find themselves knowing a good deal about how to look after these quietly fascinating creatures, even if they didn’t before, but there’s a lot more to our fishy friends than just feeding them and keeping an eye out for disease.

With that in mind, here’s a few fast – and generally little-known – facts about the remarkable group of animals that lurk at the bottom of our ponds.

Sense and Sensibility

  • The average fish’s brain is fifteen times smaller than that of a similar sized bird or mammal.
  • Fish that are active during the day see colour at least as well as humans do.
  • The lateral line is sensitive to currents and vibrations in the water.
  • Laboratory tests using underwater mazes have shown that fish have good spatial awareness and are good at making decisions using visual clues.

Fish Bodies

  • A fish can control its own buoyancy by adjusting the amount of gas in its swim bladder.
  • The number of vertebrae in a fish’s backbone depends on the species, but generally it’s between 40 to 80, although any eels visiting your pond may have 200 or more!
  • Most common pond fish have between 40 and 50 scales in their lateral line.
  • The scales of a fish have growth rings, just like a tree, and can be used to work out its age.

Long Life

  • Coldwater fish can live for a surprisingly long time; rudd may live to be 12, while carp often make the ripe old age of 50.
  • The record for the longest lived goldfish is held by Tish, who died in 1999 – having lived for 43 years after first being won as a prize at a funfair in Yorkshire.
  • The longest goldfish in actual length measured 47.4cm (18.7 inches), snout to tail-end and is owned by Joris Gijsbers of The Netherlands.

About Koi

  • The Koi is a domestic version of the Common Carp (Cyprinus carpio)
  • Although they are often associated with Japan, Koi originated in China over 1,600 years ago.
  • The Japanese word Koi means ‘carp’, but it also sounds like the word for affection, which explains why the fish became popular symbols of love and friendship in Japan.

External Threats

  • A single heron can eat over 300g of fish a day – and double that if it’s raising young!
  • It has been estimated that poor husbandry accounts for over 90 per cent of fish health problems.
  • In the US, racoons are said to kill more pond fish than cats; in some areas of Britain, foxes are starting to give our moggies a run for their money!
There are around 30,000 species of bony fish in the world – about as many as every other kind of vertebrate combined – and they’ve been around for over 200 million years. Even though only a minute fraction of their number are commonly kept in garden ponds, those that are can lay claim to an impressive pedigree, and give us an insight into some of the incredible biological adaptations that have made them so very successful. However colourful and relaxing they may appear as they gently make their way through their underwater world on a sunny summer’s day, there’s a lot more to our pond fish than meets the eye!

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a week ago i used anti blanketweed and all that has happened is it turned my water blue ! Will this fade?
jovial - 2-Jul-20 @ 11:52 AM
Hi I inherited a pond that is overcrowded with way too many goldfish. Apart from three water lilies, nothing else really grows in it and the water is quite murky. The pond does not have that many overhanging trees or shrubs close to it, only two small maples and it does get quite a lot of sun for most of the day. The previous owner used to feed the fish and told me they had over a hundred goldfish living in this pond at one time. The pond is 8000mmx3000mmx600mm (depth). I will have the pond cleaned out next week and so will change the water in it almost completely apart from the water from the uppermost layer that will be saved to keep the fish while cleaning is done and to be reintroduced to the pond to speed up the rebuild of bacteria. I plan to add a dechlorination solution to the pond and some benefitial bacteria too before I put the fish back in it. I also plan to give away as many goldfish as I can on the day. My plan is to keep only ten of them in the pond. My question is:I was told by the pond maintenance person I called to do the job that I should stop feeding the fish after maintenance is over. That way the fish will have to fend for themselves and eat their own spawn and the numbers shouldn't go back to what they are now BUT will they survive without any food? Or should we only feed them from time to time? The maintenance person is also talking about introducing new planting to the pond but the previous owner told me that the goldfish ate all the plants they tried to add to the pond apart from the lilies. What would you advise? Many thanks.
terrasal - 18-Apr-17 @ 8:42 PM
shirleybear - Your Question:
Why do fish jump up in the pond ? also twisting around , which I think it is a sign of happiness am I right ?

Our Response:
Sometimes they jump and twist because they're looking for insects at the top of the water. Some people say they jump to clean their gills but we don't really know.
PondExpert - 16-Sep-16 @ 12:38 PM
Why do fish jump up in the pond ? also twisting around , which i think it is a sign of happiness am i right ?
shirleybear - 15-Sep-16 @ 12:52 PM
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