Most fishes don’t have the natural ability or have developed lungs for that matter, to survive on land. On the other hand, if they stay out for too long, they’ll dry up, suffocate and die since the maximum for hardy pet fishes can only survive out of water for up to 10 minutes.
How do fish breathe underwater?
The fish does not have lungs like us, but it has gills that allow it to breathe underwater. Because there is oxygen dissolved in the water…
The water enters through the fish’s mouth, then it passes through the gills and comes out at the level of the gills. At the passage, the gills, traversed by the blood, capture the oxygen of water. The blood then supplies all the organs of the fish’s body with oxygen.
Thus, the fish can breathe underwater. They do not need to come to the surface regularly to live, as do marine mammals, dolphins, and whales, which have lungs.
How long can a fish survive out of water?
The rescue of the beluga whale caught in the Nepisiguit River, New Brunswick, has raised the question: how can a marine species survive outside its environment? For this occasion, Whales Online spoke with Dr. Émilie L. Couture. A member of the Department of Veterinary Medicine at the Université de Montréal, she assisted the young beluga during its relocation in the St. Lawrence.
First of all, it is important to know that the beluga is a mammal. What is the difference between a fish and a marine mammal? While a fish absorbs oxygen dissolved in the water by creating a current that circulates through its gills, the beluga, like other mammals, breathes oxygen from the air and must surface to catch its breath. Therefore, there is no risk of suffocation when it is kept out of the water. Although it does not need to be submerged to breathe, specific adaptations to the marine environment still give it several disadvantages to terrestrial life.
The first challenge to overcome is the difference in density between water and air. The weight of a cetacean is usually supported by water. Out of the water, the large layer of fat is no longer supported and can damage organs and muscles. To relieve the pressure on its body, the beluga can be transported on a stretcher. For travel by plane or truck, the adult beluga will be placed in a box filled with water. If it is smaller, however, it can be placed on a memory foam mattress, as was the case for the Bathurst beluga. This pressure management is essential for the comfort of the animal, but also to ensure that it does not have any difficulty breathing. When a whale runs aground, the cause of its death is often related to this pressure. The crushed muscles release a protein, myoglobin, which reaches the kidneys and becomes very toxic.
The second key factor to control is temperature. The beluga whale is a mammal native to the Arctic and therefore swims in very cold waters. Although it lives in a freezing environment, it is an endothermic species: it is warm-blooded and must produce its own heat. As a consequence, it has a thick layer of fat that allows it to maintain its internal temperature at around 35-36 degrees in water that is often around 4 degrees. Exposed to higher air temperatures, this excess heat will tend to accumulate. The weather and the time of day are therefore factors to be taken into account, although “the urgency of the situation often leaves little room for this kind of control”, reminds us Dr. Émilie L. Couture. In addition, the composition of his skin, which contains neither keratin (proteins that protect against UV rays, among other things) nor sweat glands (glands that secrete sweat), makes him even more susceptible to increases in internal temperature. To counter these problems, beluga whales in the open air must be constantly sprayed with water and covered with damp sheets. Heat loss occurs mainly in the blood vessels circulating under the skin of the flippers and they are therefore priority areas to hydrate.
The fact that a beluga can survive a terrestrial episode does not mean that it is adapted to it, this is why the emersion time will always be reduced to a minimum.