Which of the following is used to control pest fish?

Piscicides

The correct answer is Option (4) - Piscicides

Out of the choices you provided, the answer to control pest fish is: Piscicides

Here's why the other options are not suitable for controlling pest fish:

• Herbicides: These are chemicals that kill plants and are not effective against fish.
• Predacides: These are chemicals that kill predators, which wouldn't be helpful in controlling a specific type of fish (pest fish).
• Ovicides: These kill eggs and would only be effective against fish during their egg-laying stage, not the entire population.

Piscicides are specifically designed to kill fish. They can be used to eradicate unwanted fish populations in ponds, lakes, or other bodies of water. It's important to note that piscicides can also harm other aquatic organisms, so their use should be carefully considered and follow regulations.