From King Dictionary of Contemporary English
Related topics: Fish
tiddlertid‧dler /ˈtɪdlə $ -ər/ noun [countable] British English informalHBF a very small fish
Examples from the Corpus
tiddlerHis tongue regularly darted out of his mouth and flicked this way and that along his lips like a tiddler under water.The tiddlers of the aerospace world are also expanding.If they were tiddlers he always threw them back.