We collected our fantail goldfish yesterday from my parents... they've been fish sitting over Christmas.

We noticed that his tail had gone red! Like visible veins.

He's acting odd. Either very still, & flying around crazily fast.

This isn't a joke, but when I usually come into the living room, it sees me like 5m away, & gets excited about getting fed.

Nothing today. Just not interested in the food.

I put my hand near it, & it swam quickly up, then returned back into the same corner, & it's moving.

But when it did swim, there were what I can only describe as silky bits in the water, like fragments of cotton wool.

Any fish experts know what's going on, & what we need to do?