From this pattern:
Keepers by Sara Elizabeth Kellner, but these two are more like carp actually; I even used
this koi fish photo as a model when I was trying to figure out where exactly to position the top fins on their slightly modified bodies. The back part of their bodies is modified, which started as a mistake with one of the fishes, but I liked it so much that deliberately knitted the other fish the same way to give it a more carp-like shape.
I managed to get the shaping of the head of the same fish wrong too (that was some very absent-minded knitting to be sure), but I didn't want to leave it that way, so I struggled to reconstruct the head backwards after I decapitated the poor fish (and removed more than I actually needed to remove because I didn’t quite figure it out!). It took me a lot of trial and error, especially error. I wonder if it would have been less trouble to knit a new front part separately and graft it to the back part with the Kitchener stitch, but the designer-in-training in me couldn’t resist this upside-down knitting experiment.
I also have an unfinished fish that follows the pattern closely, but you'll get to see it when I finish it. :P
I think I've actually seen such fish with orangey-red fins somewhere in real life, and I have a vague memory of my father telling me they were just a more decorative variety of he common carp, and were bred for fishing, but I'm not sure even of that, and keep forgetting to ask him. I don't think they are koi though; koi are just a thing I know from the Internet and they are still so exotic here that they don't seem to have a firmly established name in Bulgarian. Or they may be some different species that is related to the carp. No matter what they were, at least the distant memory inspired me to try this colour combination.
The second fish:
The two fishes together:
They even got their own swimming lanes :)
I sewed through the tail this way to keep the stuffing in its place: