The submarine fish, also known as the dark green triggerfish (scientific name: Tetraodon nigroviridis), because of its appearance resembles a mini-submarine, so it is named. The submarine fish lives in tropical freshwater and steamy waters, and its adult body length can reach 17 centimeters. When frightened or encountered by natural enemies, it will quickly inhale water or air to make itself expand and grow larger, and the spines on its skin will also stand up, like a ball of spines in the water, so that natural enemies who want to devour it will have no way to swallow it, so as to achieve the effect of self-defense. Its beautiful spotted pattern and naive appearance also make it a common ornamental fish. The submarine fish is a carnivorous fish with sharp teeth that can easily break the hard shells of crustaceans and shellfish and prey on the flesh inside. It also preys on other small fish, sea worms and other creatures.