SOLVED. Middle Grade Science Fiction. Clones from the 1990s maybe? [s]

[Joanna G]

Trying to find a book that I think would have been middle grade or YA. I read it in the early 90s I think so from then or the 80s? It was about a boy who cloned himself, but then the clone thought that he was the first one. There may have been further clones by the end as the clones kept cloning themselves?
It turned out that all the clones got a black triangle on them at some point. There was also a goldfish with a black triangle, so they must have cloned that first?

[Paige]

The Duplicate
Julie Decker's review mentions the goldfish

[Joanna G]

Paige wrote: "The Duplicate
Julie Decker's review mentions the goldfish"

Thank you, that looks like the one!

[Paige]

Yay! Glad I could help you find your book.