From that wiki page: > A small fish, especially the three-spined stickleback My wife, a neuroscientist researching three-spined stickleback, has never come ac

From that wiki page: > A small fish, especially the three-spined stickleback My wife, a neuroscientist researching three-spined stickleback, has never come across the term 'tiddler'. Midwestern US. So, yes, I would say it is solitarily British slang.