The key is two words "fish" and "fishing". One is the noun fish, and the other is the method of fishing.

It means it's best to teach a mermaid how to fish.

It can be extended to help others, not just a specific thing, but also a teaching method, that is, to send Buddha to the West and help others to the end.

Another explanation is that it is better to teach people to fish than to teach them to fish. If you give someone fish, you can only save him for a while, but giving him fishing can solve his lifelong needs.

It is better to teach a person how to get than to give, because he has been taught all his life.