A Riddle

[Duncan]

your getting there Lee

remember what i said in the relaxed position the gill are always shut , as in if you open them they shut on their own !

i'll put you all out of your misery tonight when i have access to my photo's im at work right now

dunc

[StuW]

does it control the buccal valve and thus help in the process of drawing in fresh water and opening the gill plates at the same time acting something like a cam shaft?

[Duncan]

ooooh stu you are so close im trying to get a conclusion up but im snowed under

[tomy2ponds]

I cant think of a better way to describe this so bear with me is it like a fulcrum when one end is open the other is shut sort of like a beam engine working on a central pivot,I bet I am miles off track now

[Duncan]

hi guys i have the photo's i need now as of last night

Lee, your half there its not as clear cut and both actions are not equal

[Gazza]

Hi Dunc,

I take it its got to work like some kind of non return valve set up so one open and one closed and visa versa

[Duncan]

Here we go at last, this is a hard process to describe so please bear with me if I’m not articulate enough to describe it adequately.

Basically this bone “basihyal” is attached by muscle /tissue to the under side of the lower part of the mouth ( buccal valve), its also attached via muscle to the inner side of the outer skin of lower jaw so its sandwiched in-between the inner and outer lower jaw surfaces.

This is what it looks like when dissected with sinew attached but this was attached to the upper and lower parts of the lower jaw by muscle





And once you get past the sinew this is what you left with quite an elegant looking device




As the buccal cavity rises the tip of the bone rises with it (now I’m not sure if the bone does the pushing or is simply pulled along for the ride by the buccal plate, but there is substantial red muscle attached to the bone on both sides). This rising action causes the basihyal to pivot on a fulcrum point towards the back applying backward pressure gradually applying pressure rearward on each of two bones in turn behind it, which terminate ventrally dead centre between the two gill covers and the gill covers begin to open from this lower central point as a result.







Not: If you look at your koi breathing the gills don’t actually open equally from top to bottom. There is actually no opening from the top or middle all the opening happens from the bottom only and the hinge if you like and want to put it as simply as possible is right at the top of the operculum. In other words the widest opening is right at the bottom of the gill cover and from its widest point when fully open as you move up the gap gets less and less till it vanishes to nothing at the very top (tapered). see diagram




This is because the lower part of the gill cover is therefore opening mechanism is made up of several bones long bones each side forming a “V” shape and as the “basihyal’s” rearward action starts to apply pressure in the centre of this “V” one bone slides and applies pressure to the next and so on and so on till the gill plate is fully open and this “V” shape is at it shallowest but widest position .





as the gill closes the mouth lengthens and gill narrows






As the pressure is applied all these bones slide against one another kind of like but in a different way to how an aperture works on a camera lens or threw sub stage on a microscope but the action is more linear this action begins with the “basihyal” bone moving up and in so doing applying rearward pressure. See picture for all the bones involved in the gill cover movement

As the buccal cavity starts to lower so does the “basihyal” and the pressure comes off those rearward bones the operculum begins to shut, this as I say like a Caterpillar motion in other words as one motion starts the other does not start straight away but gradually comes into play and in fact can over lap at certain points as it goes the other way the same is true see below how the girth of the gill covers becomes narrow and the length increases

So we have covered the mechanical action of the gill and the part this bone plays in that the “basihyal” bone by its action pushes possible directly and indirectly up to 11 bones if my maths are right all to open the gill in the correct order to enable breathing

So want we have is in a basic sense mouth open gill shut mouth closed gill open but as we will see this is an over simplification









It’s also worth noting that the lower mandible is not attached to the upper in anyway and in fact is an extension of one of the gill bones.






So now we get to the results of these actions the actual breathing and oxygenation process

Just like us if the fish merely opens its mouth nothing much happens the air inside or in this case the water holding oxygen remains stationary that’s not desirable, so what happens?

There are three components at work here that make breathing possible for carp maybe four but you will see what I mean later. For us to breathe the organ where the oxygen is needed to enable this is a long way away from the mouth the source of O2, this is of course our lungs, which are a muscle as well that expand and contract drawing air and pumping air. This is our pump This presents a whole lot of other difficulties to the human that the fish does not have to deal with ( I.E the mixing of fresh and stale air ).

The koi’s lungs if you want to put it that way are right by the source of O2 but it’s still not as easy as you would think. remember in 1 litre of air there are 200 cc of oxygen in 1 litre of water there is only between 4 and 10 cc of oxygen so the carp as to be very good at extraction this

A lot of the functions I’m about to relay to you happen at the same time as one another sometimes over lapping it took me quite some time to gather this information and understand the mechanics of it what appears to be a very simply process is in fact very complex in its choreography very complex.

There are three/four pieces of anatomy at work here to list them starting with the mouth. The gill plate (operculum) there is a wide membrane on the trailing edge of the operculum and this plays a major part on breathing, in fact there would be not much point in the gill opening and closing without it . There is the buccal valve and cavity. The buccal cavity is the portion of the mouth where your tongue normally lies. in the carp it’s a pillow like pad that rises and falls when needed. All these components create negative and positive pressure and this enables water to flow across the gill membrane. Further to this to be super-efficient the gill filaments are only ONE cell think in other words between the blood and the pond water is just a one cell division, this enables the transfer of oxygen under partial pressure to be super-efficient and O2 transfer capable where otherwise it would not be possible.

Right as a starting point, let’s assume the mouth is closed the mouth cavity is at its smallest volume/capacity in effect its empty

To start out the fish begins opening its mouth, as we have discovered this does not achieve any of the much needed drawing in of fresh water so what happens is the buccal valve/pad in the cavity starts to drop/fall. This action of the buccal valve puts a draw or negative pressure on the cavity and the mouth and begins sucking in fresh water. At the same time the gill plate the main big operculum starts to expand outward to accommodate maximum inflow this put further negative pressure on the oral cavity. Because of this high negative pressure the membrane around the edge of the big gill plate gets sucked down and forms a tight seal on the koi’s body at the gill edge this put further pressure on the mouth cavity. Because now the only relief for all this negative pressure is the mouth entrance the mouth fills to capacity with fresh oxygenated water at which point the mouth closes.

So what happens next?

With the mouth shut the buccal cavity begins to rise this starts to displace the water, this in effect puts positive pressure on the oral cavity this positive pressure lifts the membrane off its seat on the edge of the gill plate and water starts to move across the gill filaments. Next the buccal valve starts to move back down into its fully retracted position this action starts the gill plates to contract inward and apply the last piece of positive pressure on the water and the gill membrane flaps outward as the water drafts past it and finally the oral cavity is empty once more, but before this is achieved the mouth has already begun to open.

This is a suck-squeeze-blow action but the suck and blow overlap at the extreme ends of their respective cycles

I heard the term “caterpillar drive” don’t know where but this describes this this process perfectly it performs exactly how a caterpillar moves or one of this metal spring toys the slinky. And remember all these actions overlap one another to the naked eye you won’t be able to differentiate between process cuz some act simultaneous

I managed to find these diagrams which may help in your understanding











in Chris’s koi this bone had torn away from the inside of the mouth and the tissue on the bottom was pulling it down ward and it was sticking /pushing the skin out ward there was no way it was ever going to reattach to the inside of the mouth so it was redundant

[boogatee]

interesting .... does this explain why her gill plate movements are more pronounced?

[Duncan]

yes there will be nothing hold them in check also she wont breath as well
as she did before but i dont think unless we get down to 4ppm O2 saturation this will cause her any distress but below that where normal capr can just about cope i dont think she will do so well

but on the plus side she dont have that bone shoving her throat OOP

dunc

[Gazza]

Great stuff Dunc

A little more complex than I thought but very well described on how the fish actualy functions in all the ways just to breath,mother nature is a clever thing

[tomy2ponds]

I always find it amazing how clever nature is sometimes complex and other times very simple but nearly always perfect.

[Duncan]

Lee

for us breathing is relatively easy, for koi quite frankly its a bit of a bugger, but nature found an elegant and artistic way around it that leaves me speachless!

[tomy2ponds]

Your not wrong there Duncan