Dolphin

Dolphins are the common aquatic mammals belonging to the family Coryphaenidae. Some species of fishes belonging to the genus Coryphaena. The dolphin C. hippuras are special species for food and games. C. hippuras s also known as Hawaiian as mahimahi and sometimes they are termed dorado in Spanish. The smallest dolphin can grow and reach a length of about 1.5 meters and they can reach the weight of about 30kg. Usually, dolphins have a tapered body, a blunt head, a slender, and a forked tail. Dolphins have a colourful body, which contains bright blue and green colours with irregular, gold-tinted patches on their sides. The dolphin turns vivid and initial bright colour when the fish is caught and brought out of the water. When the dolphin dies, their colour will fade off. Dolphins are usually found in tropical and warm water temperatures. Most of the dolphins are carnivorous and they use to live in groups and take smaller fishes and invertebrates as their feeds. C. equiselis is a variety of dolphin and they are the smaller pompano dolphin.

Dolphins have existed in different sizes. The smallest dolphins are relatively smaller than 1.7 meters long and weigh about 50-kilogram. The Maui’s dolphin can grow up to 9.5 meters and 10 tonnes. Some killer whales belonging to the dolphin family can leap about 30 feet (9.1 m). Many dolphin species exhibit sexual dimorphism. Here, the male dolphins look larger than females. Dolphins have streamlined bodies and two flippers, which are the modified limbs. Usually, dolphins are not flexible like seals, so they can travel only at speeds 29 kilometres per hour for short distances. Further, dolphins will use their conical-shaped teeth to capture fast-moving prey. Common dolphin fish have well-developed hearing, which can adapt to both water and air. Some dolphin fish Mahi can survive as blind with well-developed hearing. Some species from the dolphin family are well adapted for diving to great depths. Every dolphin fish has a layer of fat or blubber under their skin to keep warm in the cold water.

Generally, dolphins can adapt to all temperatures and are widespread over the sea. But most species can prefer the tropical zones of warm water. But some species like right whale dolphins prefer cold climates to survive. Dolphins are carnivorous and they prefer squids and small fishes for their feed. But, few species like killer whales choose large mammals as their prey. Male dolphins will mate with multiple female dolphins, but they prefer matting only once between two to three years. Claves, young dolphins generally born in the spring and summer months. Further, the female dolphins will take responsibility for raising the claves. Some female species will take care of their young ones for a relatively long period of time. Dolphins can produce clicks and whistles and many varieties of vocalizations. Some Japanese people will hunt dolphins and they named that activity dolphin drive hunting, as a result, they are facing threats from bycatch, marine pollution, and habitat loss. The most commonly known popular dolphin species are bottlenose dolphins, while there are around 60 killer whales, which attack human beings. 

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Hybrids in Dolphin

In 1933, three hybrid dolphins are released along the Irish coast. They are hybridized between Risso's and bottlenose dolphins After repeated mating the hybrid calf dolphins are produced. The hybrid calf has bottlenose and rough-toothed characteristics. These common-bottlenose hybrid find their shelter at SeaWorld California. Another dolphin hybrid variety lives around the world and they have been reported as a wild species, which is a bottlenose-Atlantic spotted hybrid. The best known hybrid dolphin is the wolphin, which is a  false killer whale-bottlenose dolphin hybrid, this is one of the fertile hybrids. Currently, two wolphins are living in the Sea Life Park in Hawaii. One was a male born in 1985 and the other was a female bottlenose wolphins. Now they are also kept under wild observation.  

Anatomy of Dolphin 

Dolphins have torpedo-shaped bodies with generally non-flexible necks, limbs modified into flippers, a tail fin, and bulbous heads. Dolphin skulls have long snouts, small eye orbits, and their eyes are located on the sides of their head further, they do not have external ear flaps. Usually, dolphins have conical teeth, which can be used to catch swift prey such as squids, fishes, and some mammals. They breathe through stale air from their blowhole present in the upward blast and it can be noticed in cold air. Then the fresh air enters the lungs. The dolphins have small, unidentifiable spouts. All dolphins have a blubber layer, its thickness will vary depending on climatic conditions, which helps to protect them from predators and buoyancy. It also provides sufficient energy. Dolphins have a two-chambered stomach namely fundic and pyloric chambers, which is similar to terrestrial carnivores. Female dolphins' reproductive organs are located inside the body; they are connected with genital slits on the ventral (belly) side. Male dolphins have two slits one is for the penis and the other for the anus. 

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Characteristics of Dolphin 

Locomotion

Dolphin tuna have two pectoral flippers with a boneless dorsal fin for stability and a tail fin for propulsion. Although dolphins do not have external hind limbs, some species have discrete rudimentary appendages, which may contain feet and digits. The killer whale can travel at the speed of  55.5 km/h (34.5 mph). But other dolphins can travel at  9–28 km/h. Dolphins have fused neck vertebrae, which increases the stability for dolphins to swim at high speed and decreases flexibility. But they cannot turn their heads. But river dolphins have non-fused neck vertebrae, they can turn their heads up to 90°. Dolphin fishes will use tail fin and rear body for locomotion and they will use flippers for steering. Some species can adapt to deep diving and slow their heart rate to conserve oxygen. Hemoglobin and myoglobin store oxygen in body tissues. 

Sensory 

Dolphin ears have unique characteristics to adapt to the marine environment. Dolphins and other marine mammals do not have any difference between the inner and outer ear. Dolphins usually receive their sound through their throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. Dolphins ear is acoustically isolated from their skull with air-filled sinus pockets, which helps them for greater hearing even in underwater. They will send a high-frequency signal through the melon, which is a fatty substance in the skull. This allows them to biosonar for orientation. Hair follicles present in the dolphins are also performing some sensory functions. The eyes of dolphins are small in size, but they have a good degree of eyesight. As the eyes are located on their sides, their vision consists of two fields.  The eyes of dolphins contain a lens and cornea for refraction of light and also contain rods and cone cells to perform vision in both dim and bright light. The olfactory nerves and lobes are absent in dolphins, so they do not have a sense of smell and sense of taste as the taste buds are absent. 

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Behaviours of Dolphin

Dolphins are the most intelligent animals on the earth. They have response mods, sensory apparatuses, and the nature of cognition. Dolphins can live in groups, so they are highly social animals. Depending on their group/pod size, the structures of species greatly vary. Some pods may be created depending on the availability of food. If the pods exceed 1000 dolphins they are known as superpods. Dolphins are communicating through various clicks and whistles. Generally, dolphins use nonverbal communication using touch and posturing. But they can learn a human language in short periods. 

Many dolphins kill porpoises, even without any reason. Researchers found that this may be due to both following the same food habits and similar living conditions. Male dolphins are more aggressive and older a male dolphins have more scars and bites on their bodies. The male bottlenose dolphins are well known to engage in infanticide. Dolphins are known to learn, scheme, teach, cooperate and grieve. The size of the brain is a major indication of the intelligence of the dolphin fish Mahi. Further, they have more self-awareness to protect themselves from defenders. 

Reproduction in Dolphins 

Dolphin’s copulation takes place from belly to belly. They will complete matting within a short span. But they attempt several times. The gestation period for dolphins varies from species to species. The small Tucuxi dolphin takes 11 to 12 months. Likewise, an orca takes around 17 months gestation period. Most dolphins give birth to a single calf at a time. Some dolphins undergo sexual activities even before attaining sexual maturity. The age for attaining sexual maturity varies from species to species and gender. Many species of dolphins also engage in sexual behaviours with other species of dolphins. 

Feeding

Dolphins are carnivores and their feeding methods will vary depending on the species. Fishes and squids are the main food source for dolphins. But some species like false killer whales and orca will take marine mammals as the feed. The feed of dolphins varies depending on their number of teeth. The bottlenose dolphins have conical teeth of about 72 to 116. The orca dolphins have 40-56 teeth. Some other dolphins have 188-268 teeth. Dolphins generally follow the herding feed method. That is the group of dolphins attached to a school of fishes, this is known as a bait ball. Here, the individual dolphin plows the ball and feeds the stunned fishes. Sometimes, dolphins use a corralling method, here the dolphins chase the fishes in shallow water and catch them easily.  Sometimes, bottlenose and orcas dolphins will drive their prey towards the beach to feed it, this is known as beach feeding or strand feeding. 

Sleeping

Usually, dolphins sleep with only one brain hemisphere through slow-wave sleep. So, they will have enough consciousness to maintain their breath and to watch and protect themselves from possible predators. Sleep stages can occur and change simultaneously between both the hemispheres. If both eyes of dolphins are closed, then they are in a fully asleep state and they do not respond to mild external stimulation. Anaesthetized dolphins show a tail kick reflex at their initial stage.