When we headed out for our Christmas travels I stuffed a bag full of co-ordinating, guy-coloured, stash yarns and a 5.5 needle. With lots of knitting time while doing our elder care, I managed to finish the scarf in record time.
Pattern: My own. Cast on 150 ?? 200?? - my memory fails me - let's say a bunch of stitches. Work in garter stitch - that is 2 rows - of each colour, working through the colours and and repeating them randomly.
The only thing about knitting a lengthwise, garter-stitch scarf to meet Fred's specification of 'no fringe' is that there were lots of ends to weave in. Since I did 2 rows of knitting before changing colour, all those tails were at the same end of the scarf. That did make for a slightly wonky, thicker-at-one-end scarf, but I'm guessing the fish won't mind.