what causes an orca's dorsal fin to collapse
Captive killer whales Scientists from the National Marine Fisheries Service (NMFS) have reported that "the collapsed dorsal fins commonly seen in captive killer whales do not result from a pathogenic condition, but are instead thought to most likely originate from an irreversible structural change in the fin's collagen over time. Possible explanations for this include: (1) alterations in water balance caused by the stresses of captivity dietary changes, (2) lowered blood pressure due to reduced activity patterns, or (3) overheating of the collagen brought on by greater exposure of the fin to the ambient air."[65] According to SeaWorld's website, another reason for the fin to bend may be the greater amount of time that captive whales spend at the surface, where the fin is not supported by water pressure.[66] The Whale and Dolphin Conservation Society says that dorsal fin collapse is largely explained by captive killer whales swimming in small circles due to the inadequate space in which they have to swim.[67] SeaWorld, however, claims that "Neither the shape nor the droop of a whale's dorsal fin are indicators of a killer whale's health or well-being."[66]
Aquatic locomotion Many fish swim through water by creating undulations with their bodies or oscillating their fins. The undulations create components of forward thrust complemented by a rearward force, side forces which are wasted portions of energy, and a normal force that is between the forward thrust and side force. Different fish swim by undulating different parts of their bodies. Eel-shaped fish undulate their entire body in rhythmic sequences. Streamlined fish, such as salmon, undulate the caudal portions of their bodies. Some fish, such as sharks, use stiff, strong fins to create dynamic lift and propel themselves. It is common for fish to use more than one form of propulsion, although they will display one dominant mode of swimming [16] Gait changes have even been observed in juvenile reef fish of various sizes. Depending on their needs, fish can rapidly alternate between synchronized fin beats and alternating fin beats [17]