When a fish is used to change your pet into a Torso, it enhances pet's ice, fire, electric and poison armor. It also adds more HP and lightly increases damage as well as the ability to lower enemies armor.
Level 5 Pet
Ice: 15 to 23
Fire: 15 to 23
Electric: 15 to 23
Poison: 15 to 23
HP: 427 to 534
DMG: 32-42 to 37-53