The scientific name of sea pig is finless porpoise, which belongs to the national second-class aquatic wild protected animal. Sea pigs usually live in the coastal waters near the freshwater junction of Yu Xian. Their life habits and physical characteristics have important scientific research value in the fields of bionics, military science and medicine, and they are called "Bohai River God" by fishermen in Bohai Bay.

The porcupine looks like a dolphin and is small, with a body length of about 150 cm and a weight of 100-200 kg. The whole body is leaden or grayish white. The head is blunt and round, and the forehead bulges slightly forward; Kiss is shorter and wider. There is no ridged fin, and the posterior part of the back has obvious raised fins on the caudal fin, which is about 3-4 cm high. The flippers are wide and sharp at the end, which is about one-sixth of the body length. The caudal fin is also large, and the horizontal width of the two caudal leaves is about a quarter of the body length.

The upper and lower jaws are almost the same length, the teeth are short, and the left and right sides are flat and shovel-shaped. The eyes are small and inconspicuous. The first five cervical vertebrae are healed, and the ribs are usually 14 pairs. The middle part of the body is the thickest, and the cross section is approximately circular. There is no dorsal fin on the back, and the flippers are large, triangular, with sharp ends and five fingers. The caudal fin is large and divided into two leaves, which are horizontal.