The question of whether a shark can sneeze requires understanding the fundamental differences between terrestrial and aquatic biology. While animals must clear irritants from their nasal passages, the anatomical mechanisms for achieving this vary widely. To understand the shark’s situation, it is necessary to first define the physiological requirements of a true sneeze, which is an involuntary reflex response to irritation.
What Does It Mean To Sneeze?
A sneeze, technically known as sternutation, is a protective reflex that results in the convulsive expulsion of air from the lungs. This forceful action removes foreign particles or irritants stimulating the mucous membranes lining the nasal cavity. For this expulsion to occur, the organism must possess lungs capable of drawing in a large volume of air, followed by a rapid contraction of the respiratory and abdominal muscles. The nasal cavity must also connect to the respiratory tract, allowing the high-pressure burst of air to travel from the lungs and out through the nose and mouth. Without this integrated system, a true sneeze is physiologically impossible.
How Sharks Process Water and Odors
Sharks belong to a group of fish called elasmobranchs, and their anatomy differs from air-breathing vertebrates. The nostrils, or nares, located on the underside of the snout, are exclusively dedicated to the sense of smell (olfaction). Unlike in mammals, the shark’s nasal passages are completely separate from the respiratory system; they do not connect to the mouth or the gills. Water flows into an incurrent aperture and passes over the olfactory sac, which is lined with sensitive sensory cells called olfactory lamellae. These cells detect minute chemical traces in the water, giving the shark its strong sense of smell. Sharks rely on gills for oxygen extraction and lack the lungs required to generate the forceful puff of air necessary for a sneeze.
The Shark’s Clearing Mechanism
Since a shark cannot sneeze, it utilizes the constant flow of water and other behaviors to keep its olfactory passages clean. The simplest clearing mechanism is the natural current of water that flows through the nares as the shark swims forward. This process, often enhanced by the shark’s natural swimming motion, continuously flushes the olfactory sacs, effectively removing any particles or debris that may have entered. Some species of shark that are more sedentary or bottom-dwelling may also employ subtle muscular contractions around the nasal cavity to pump water through, providing a more active flushing method. Observed behaviors that resemble a sneeze in videos, such as rapid head shaking or forceful expulsions from the mouth, are more likely to be the shark clearing its throat or performing gastric eversion. Gastric eversion is a process where the shark literally pushes its stomach out of its mouth to cleanse it of indigestible items. While they cannot perform the air-driven reflex known as a sneeze, sharks possess effective mechanisms to ensure their specialized olfactory passages remain functional.