Why do fish change colour when they die?

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Why do fish change colour when they die?

It’s an interesting question that popped into my mind when I saw a picture of some freshly caught wahoo and mahi mahi.

Why do fish change colour at all?

At it turns out lots of fish can change colour.

So, first let’s look at why fish change colour when they are alive. Colour changes fall into two buckets:

1. Slow colour changes occur:
– When fish mature from juveniles to adults
– A result of hormonal breeding triggers (such as in breeding salmon)
– When fish change habitat (think golden billabong barramundi vs silver saltwater barramundi)

2. Fast colour changes happen:
– As a result of stress (like being hooked)
– When they are excited (like when they are hunting)
– For camouflage

So how do they change colour?

There are two kinds of cells that work together to give colour to fishes, chromatophores and iridiophores.

Chromatophores are cells located in the skin of fish that produce various colours such as red, black, blue, white and yellow. There are lots of sub-types of chromatophores but let’s keep it simple for the moment.

Iridiophores are cells responsible for the silvery appearance commonly associated with fish.

These two types of cells will often overlap to create the amazing range of colours we see in many fish. For example the beautiful colours in the mahi mahi I mentioned earlier.

Fish send signals from the nervous system to either concentrate pigments in the centre of the chromatophore cell or distribute them over the whole cell. This moving of pigments within cells acts to either dilute or intensify the appearance of the particular colour.

So what happens when fish die???

When the nervous system stops working fish lose the ability to control their chromatophore cells which mostly return to their dull state.

http://www.fishscience.co.uk/ask-the-expert/tropical/fish-colouration/
https://en.wikipedia.org/wiki/Chromatophore
https://australianmuseum.net.au/can-fishes-change-colour

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