My day

Today was very fine, i was in university studying the eating habits of fishes.

Today was very good. I studied the eating habits of fish at college.

English rule:

The word 'study' is changed to the word 'studied' as past tense(something that already happened).

Drop the letter 'y' and change it to the letter 'i' then add the suffix -ed which becomes studied.

My day

Today was just fine. I spent the day was at my university studying the eating habits of fish.