Answer: a lot of
Step-by-step explanation:
The given blank is to be filled with one of the given quantifiers.
The quantifier "a lot of" is used mainly for uncountable goods or a plural number of countable goods. It is also preferred in cases of representing a huge amount of something.
However, "much" is not preferred for such a huge amount compared to the former quantifier.
In this case, fish is a countable plural entity and therefore, we prefer to use "a lot of."