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Discussion Starter · #1 ·
Ask A Marine Biologist - Your Answer!

Hi greg (h2o)

Here is the response to your Question:

What cause''s a largemouth bass to get a red mouth in the spring time. Or anytime. thank you i noticed this in some fish i have caught Thanks for a reply greg

Hi Greg

Unfortunately this is a voluntary service run from Australia so we do not have people with expertise in North American fish.

There are many references to the Largemouth Bass on the web. THe best of these is at

This gives several pages of detailed information on them but does not mention that the mouth turns red in spring.

This behaviour may be linked with spawning which takes place in spring. It can detect red and the male is territorial, defending the nest from other fish. The red colouration may be a warning to other bass to keep them away from the nesting area.

This hypothesis would be better supported if only the male's mouth turned red in spring. I hope this is of some assistance but perhaps you could follow this up with some questions to sites with more information about this bass.

I was unable to find any mention of this colour change in the sites I visited.

MESA web manager

Thanks for asking a Marine Biologist!

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h2o<---says seems like it's a mystery because bass don't speak english, lol I'll try and find a ask a Marine Biologist in Michigan

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maybe the bass was just embarrassed?

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Good one Dan lets have a moment of silence for that Bass of Shame.

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QUOTE(John Maniaci @ Apr 20 2004, 10:37 AM)Stress? Breeding? In sub 50 degree water? Sorry but I dont buy it.

Just my opinion.

Me neither....and I've seen it in both males and females

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Discussion Starter · #7 ·
On 13 Apr 2004 at 20:48, [email protected] wrote:

> Can you please tell me why largemouth bass get a red color on the inside of there mouths in
> the spring time. Thank you in advance.
> greg

I checked with several biologists and all agreed it is due to stress. The colors you are
witnessing are more to do with its state of activity and hormonal levels. If it is in prime
breeding time - it will be good n ready to go blood pumping and full of excitement. It is
likely that it's extra blood pumping you are witnessing making the mouth interior change
color. The fish is over exerted. During breeding - all sorts of things happen to the fish
extra strong colors develope - the tail becomes ragged and bloody, etc. I suspect your
observations are more to do with that.

Now; catch a bass in prime breeding form and in high stress from having just struggled with an angler. Note the colour of the mouth
interior. Check again in half an hour and you will often see that it is paler.

Just as when we exercise, blood rushes throughout our bodies to supply increased levels of oxygen to the muscles and cells which require them -
so too does the same happen in fish. Where we get flushed looking cheeks from the workout - some fish can get the same effect in the mouth.

Glenn May
The Ultimate Bass Fishing Resource Guide
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