Koi Anatomy Question

[kayoss]

Hi All

I've been looking at a shiro in a dealer's tank but can't decide if it has a deformity or not - sometimes it looks OK, but other times its head seems to twist to one side.

Do koi have a flexible joint at the end of their spine that allows them to move their heads sideways?

Cheers

Bob

[Gazza]

Hi Bob,

Not as far as i am aware and but if it was i then i would be getting the fish into a bowl where i can have a good look and feel of the fish including turning the fish over as sometimes the deformity can be below the lateral line and is easier to be seen from underneath.

[eds]

Shiros are prone to deformities such as this and have a slight kink or twist just after the head. Often they're really hard to spot and also the pattern can make them look kinked when they aren't and vice versa. Taking a few photos can really help see any issues.

[Manky Sanke]

This question interested me and my intial thoughts were that carp backbones connect directly into the skull so there are no flexible joints that would allow lateral movement meaning that a carp couldn't turn its head left or right unless it curved it's spine.

Or so I thought but, since Duncan is currently busy elsewhere, I asked Paula because she has been dissecting koi for a living for a very long time.

She said the answer to whether there is any lateral flexibility is yes and no. No is the normal answer for the reason above that there are no properly flexible joints between the head and the spine, but yes because in some varieties there is actually a very limited amount of movement although this would be very hard to see.

If the head turns out not to be straight then it won't be because the koi is turning it's head to look to one side, as Ed said, it will be due to a deformity or an illusion due to the pattern.

[kayoss]

Hi Syd

Many thanks for the extra infor mate.

BTW, we've had quite a few new members join us at Kangei since your last visit to us - any chance of an email with the dates you're available to come back please? We meet on the second Wednesday of each month.

Cheers

Bob

[Manky Sanke]

No problem Bob,

I had half a suspicion that the answer to whether a koi could peer round corners might not be as clear cut as it first seemed so it was interesting to find out a bit more but, as usual, my calls to Paula never last less than an hour and yesterday's one was no exception. Since that one was for your benefit, where should I send the invoice for the cost of a 90 minute call?

As for which 2nd Wednesdays I have free - all of them from May until December. Choose one and let me know.

[Duncan]

hi

sorry not been around much working 7 days a week

anyway its impossible for the head to pivot and look around, as the bone directly behind the head to a point around midway between the rear of the head and the leading ray of the dorsal is "solid" bone with no movable joints see photo, there are joints after that to the dorsal

the spine is quite supple but is restricted due to the torsional strength of the dermis, which helps prevent to much curvature of the spine.

Put plainly when the koi swims, a muscle on one side of the koi contracts and pulls the tail around to that side in so doing it stretches the dermis on the opposite side, when the koi needs to either straighten the tail you would think the opposite muscle would contract pulling it back but its the torsion on the dermis that pulls it straight as the muscle relaxes once in the straight ahead possition if they tail needs to go the other way then the other muscle contracts , in other words the muscle contracts to pull the peduncle around once thast muscle relaxes the dermis on the other side which by now is stretch to buggery pulls it back straight again

[kayoss]

Hi Duncan

Many thanks for a terrific explanation - in my sort of language too!

Cheers mate

Bob

[Markey]

The "stretched to buggery" was a little too technical for me, but I get the idea.. LOL