Yes, Pi did eat the fish.
Based on the provided reference, Pi caught a dorado and, after killing it, he ate it. While initially a vegetarian, the extreme circumstances of being stranded at sea forced him to overcome his principles for survival. The passage explicitly states Pi "manages to land a three-foot-long dorado, which he kills and feeds to Richard Parker," implying that he also consumed some of the fish himself, as he was in dire need of sustenance. Given the scarcity of food and water, it is highly likely that Pi partook in eating the fish to survive.
