WordNet records no synonym and no antonym for trout. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
flesh of any of several primarily freshwater game and food fishes
any of various game and food fishes of cool fresh waters mostly smaller than typical salmons
Synonyms, antonyms and the broader and narrower relations for trout come from Princeton University’s WordNet. Full sources and licences.