That would be there fins, as this would help them move quickly away.
Most fish are defenseless so there response to an attach is not fight but flight.
There are of course those fish the have built in defenses: Piranha - Sharp Teeth & Jaws and Pufferfish - Long External Spines & Poisons.
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Armadillos will use their claws to defend themselves.
A fish's mouth is typically located on the front part of its body. This positioning allows the fish to easily catch prey and feed on the organisms in its environment.
its body
lungs
The cod is a fish species and not a body part. It is a type of marine fish that is commonly used in cooking and is known for its mild flavor.
front
scales
A fish breaths through it's gills.
each part is used to protect a fish from danger in its own specific way
their gills
mouth or gills