Fishes are aquatic vertebrates that are characterized by paired fins, scales and gills. ifns are used for movement, scales for protection and gills for exchanging gases. Fish are very varied
and adaptations to aquatic life include various modes of feeding, specialized structures for gas exchange, paired fins for locomotion, and even more!
Reproduction in fishes
The eggs of fishes are fertilized either externally or internally, depending on the species. In many fish species, the female lays the eggs and the embryos in the eggs develop and hatch outside her body. Fishes whose eggs hatch outside the mother’s body are oviparous. As the embryos of oviparous fishes develop, they obtain food from the yolk in the egg. In contrast, in ovoviviparous species the eggs stay in the mother’s body after internal fertilization. Each embryo develops inside its egg, using the yolk for nourishment. The young are then “born alive”, the way the young most mammals are. A few fish species, including several sharks, are viviparous. In this kind of animals, the embryos stay in the mother’s body as they do in ovoviviparous species. However, these embryos obtain the substances they need directly from the mother’s body, not from material stored within an egg. The young of viviparous species are also born alive.
Respiration in fishes
Most fishes exchange gases using gills located on either side of the pharynx. The gills are made up of feathery, threadlike structures called filaments. Each filament contains a network of fine capillaries that provides a large surface area for the exchange of oxygen and carbon dioxide. Fishes that exchange gases using gills do so by pulling oxygen-poor water out through openings in the sides of the pharynx.
Some fishes, such as lampreys and sharks, have several gill opening. Most fishes, however, have a single gill opening on each side of the body through which water is pumped out. This opening is hidden beneath a protective bony cover called the operculum.
A number of fishes have an adaptation that allows them to survive in oxygen-poor water or in areas where bodies of water often dry up. These fishes have specialized organs that serve as lungs. A tube brings oxygen from the air to this organ through the fish’s mouth. Some lungfishes are so dependent on getting oxygen from the air that they will suffocate if prevented from reaching the surface of the water.
