If the federal government says that fish is healthy for you the demand for fish will

The demand will Increase.

Explanation:

If the federal government says that fish is healthy for you, then the demand for fish will increase.

This is because the citizens generally believe what government says is good for them. People know that government is more concerned about their better future, about better medical conditions, about better food options, about better health conditions, etc. So when government says that fish is healthy for you, people will definitely go for buying the fish and thus the demand for the fish will increase. In this scenario, people will be willing to pay for the fish, increasing the demand for it.