A mí me gusta el té.
The difference has to do with emphasis.
In the table below, you can see how gustar can be conjugated for each different subject using this romantic meaning.
Her boyfriend hopes that she like to dance salsa.
Since, fish is a singular subject, therefore, gusta is used with it.
You can complete the translation of a mi me gusta given by the Spanish-English Collins dictionary with other dictionaries: Wikipedia, Lexilogos, Maria Moliner, Espasa Calpe, Grijalbo, Larousse, Wordreference, Oxford, Collins dictionaries.