you can kill the monster fish be luring it with you to the bottom near the mines and then the fish will follow you and get itself killed by a mine.Make sure that before attempting this you go to the cheats option in the main menu and type chain so that you will become invisible and even a mine cannot kill you.
Cheat for anyone who need it
MEAT
Extra meat in water
BITE
Eat victims in one bite
BLOOD
+ 200 000 litres of blood
FISH
Be the monster fish
CHAIN
Invincible
BOOST
Boost anywhere anytime
Hi DhruvTK Thank you for your suggestion. It will be forwarded to the game developers.