Recently, I was given a stunning fish for my pond. He's 8 years old and 6 inches in length (with tail).
He's a vivid, almost shocking yellow in daylight. I put him in an inspection tank when he arrived and under flourescent light, his scales are lemon with a white rim.
His tail fin is joined up until about halfway and all of his fins are slightly rounded. His fins are white with an orange base.
The fins beneath his tail (I think they are called anal fins) are fairly small and are round when flared.

When he swims, he bullies the water out of the way like a bulldog after a bone. When he eats, his mouth distends in a way similar to Koi fish. He can pick up some speed, but is slow to start. Generally, he sticks his muzzle up and wags his way forward until he gains some momentum. He lets the momentum carry him forward until he slows to a near standstill.
It makes him look like he has quite a bolchy attitude and is rather impressed with himself. It's comical and I've fallen in love with him.

I presume it is a male because of the scale-like marking on his top fin (forgive me - I know a lot about fish but I always get the fins' names mixed up! The 'top' fin is the fin behind his head.)

I suspect that he is a Ryukin, but I've never seen or heard of a yellow Ryukin. He has a distinctive bump behind his head. He could be a veiltail or fantail, but I haven't been able to differentiate them.

Is he a yellow Ryukin or another breed?

What you have is  a fantail not a ryukin. The word ryukin means longfin. Your fish has short fins.

my bad- the top picture is actually a really bad shot of one of my small fantails. the bottom one has the head of a golden fantail, Grin, the shortfin Ryukin,and Sklorp, the longfin Ryukin. this is the picture i meant to post- sklorp  with his fins extended.

It said i need more than 3 posts to post links, so... forgive me..

finally i can post my pictures.  I love the yellow colored ones.


(Link is not visible to guests. Please register to view.)


(Link is not visible to guests. Please register to view.)

where did you purchase said fish? i have been looking for lemon yellow ryukin for years now, and noone has ever bred them.

Thanks for the responses to my question

Youkou has changed dramatically in the year since I adopted him. He is now close to 8 inches in length and has changed color from a lemon yellow to a rich orange and red combination. I've read that goldfish change color when their environment, especially light and diet, change.
The photo of Youkou in my previous post was taken a few days after I received him, this time last year. He'd been living in a green water tank without artificial light or filtration. His diet consisted of algae and aquatic plants. I believe it was the semi-dark environment and vegetarian diet that caused his color to be the lemon yellow. After I received him, I put him in my pond, and Youkou, or 'Goldzilla' as he has now been nicknamed, had access to insect larvae, earthworms, tadpoles and mosquito fish, as well as algae, aquatic plants and a variety of goldfish pellets. The new, varied diet and sunlit environment transformed his previous yellow color to a rich, deep orange.

This is him now:

(Link is not visible to guests. Please register to view.)

(Link is not visible to guests. Please register to view.)

I've shown him to a number of goldfish breeders and all agree that he is a round-tailed variety of Ryukin, but was probably sold as a feeder fish because of his joined tail and round snout. So he's no prize-winner, but he still elicits a positive response from all who see him, due to his size, age and friendly nature.

I discovered that this year marks Youkou's tenth birthday, as he was apparently a year old when his previous owner got him. To celebrate, I've moved him into an 80 gallon tank in my living room, where he lives with two 2-year-old comets, a 1-year-old fantail, a 3-year-old black moor and a four-month-old Tamaryu (Single caudal fin, single anal fin offspring of two Ryukins. I'm a sucker for adopting other people's unwanted goldfish...) Youkou is the tank master, leading the other fish around the tank and head butting any fish that takes a snap at the little Tamaryu. He comes to greet me whenever I approach the tank. The honeymoon might be over, but I'm still in love... 
I'm expecting him to show his true colors now, as he has plenty of light and a varied diet. I believe that in another year or two, he will become a true red.

So he's not a yellow Ryukin, but a red Ryukin who was once yellow due to a restricted environment.

It's exciting to discover that a yellow Ryukin is possible under certain circumstances, but I fear that my experience might lead to other fish keepers experimenting with their fish, so I'd like to point out a few things;
Youkou's previous home was a natural, if not very attractive environment. The tank was heavily planted and had green, nutrient-rich water. Youkou could eat as much algae and plant matter as he wanted - he was not restricted to a daily feeding schedule. The tank was topped up regularly with river water, and the previous owner did not put any form of chemicals into the tank, not even in the form of tap water.
If you wish to try for a yellow Ryukin by creating a natural light environment and vegetarian diet for the fish, I would suggest that you research Walstad tanks, as well as the nitrogen cycle, before attempting such a feat. Simply turning off the lights and filter  will most likely cause a bacteria bloom in the tank, which may harm the fish, so planning and preparation is essential.

Cheers,
Fleabie

That is a wonderful story! You are like, a fish-saver or something. ITs good that your ryukin got his colour back!   But I thought ryukins didnt have a dorsal fin...? Or am I thinking of something else?

Thats the one! yea I saw the gallery pics of ranchu and lionchu... no dorsal fin but the ryukins did hahaha. I'm not particularily fond of the ryukin, their deep bodies are a little much for me. I'll stay with little eggshaped fishies.

well, to each his own I guess!

His body shape is kinda' cute too, looks a lot like a lemon (: So it'd probably make a really cute and entertaining childrens' book actually The lemon ryukin that turned orange~

Ohh.. I could so write a story about it hahaha... I want to soo bad... maybe after my st*pid exams are done..

^^ I'm actualy proficient at writing.. I could so pull it off... Have you guys read any of my poems (ones not relating to goldfish?) They actually arent bad, but I'm always looking for poeple willing to give it a try.

On my mputer right now.. I want to put them on a site but my technological expertise has backfired on me and I cant put them up. So i'd be happy to PM them to anyone wanting to read them (I have two short stories in there two, so.. yea..)

I am interested too