Koi growth regulated by Somatostatin

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Koi growth regulated by Somatostatin

September 22, 2016 - 17:15

The growth of all fish is not regulated by growth inhibitory hormones, but Koi and goldfish growth is.  Read a short answer of why Koi and goldfish do not outgrow their ponds by clicking on the title or picture...

I received a fairly lengthy question yesterday from the UK. To summarise the question, it was about whether goldfish only grow to the size of the tank.
Growth in fish, like other organisms, are influenced by many factors including nutrition and hormonal influences. The one thing though, the people mean when they talk about talk about goldfish growing to the size of its tank is to do with their regulation of growth hormones. Goldfish are one that produce growth inhibitory hormones (e.g. somatostatin) and in nature, it’s their way of reducing intraspecific competition by suppressing growth of other goldfish. This is a particularly useful survival mechanism especially if you’re a “big fish in a small pond”! In a tank situation, and if partial water changes are not performed regularly, this hormone can build up and suppress the goldfish itself! And in this way, it is also a survival mechanism whereby it will not outgrow its pond!
Other fish do not produce such potent hormones and this is why they can outgrow the aquarium they live in. These fish tend to be “big fish in a big pond”. Their survival strategy is to get as big as they can to avoid being eaten by someone else. The barramundi and Murray cod are great examples of such fish.
Fish wastes are generally not ideal for fish to live in. They would have anti-nutritional effects and nitrates are known to suppress the immune system. If conditions are not optimal, fish will not thrive and will not grow.

Br. Dr. Richmond Loh, The Fish Vet, Perth, Western Australia

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