Watch my red shark fin swordtail fish giving birth to 137 babies and still going on. It's her second litter in 6 months. The signs of pregnant fish giving birth are her gravid spot getting darker, her belly in box shaped, she often rub her belly against the aquarium decors, and mostly rest at the bottom of tank. She is lyretail wagtail swordtail fish. The lifespan of swordtail fish is 3 to 5 years and they can grow up to 17 cm. Swordtail are cousins of platy fish , Xiphophorus family. Swordtail is freshwater fish and are livebearers like guppy fish, molly fish and platy fish. They give birth to young ones same as how molly fish giving birth and guppies giving birth. And in their lifetime swordtail fish can give birth to 2000 to 2500 babies.