Long-spine porcupinefish (Diodon holocanthus). X-ray of a section through an inflated long-spine porcupinefish, showing the spines (thin, white) that surround its body. To ward off predators porcupinefish inflate their body by pumping water into their stomach. The body becomes a round rigid ball bristling with spines. When the fish is relaxed the spines lie flat against the body. This specimen measures 9 centimetres in length.