Growth is a natural process in any living organism, including animals. It refers to the irreversible increase of an organism's size over time. For animals, growth is determined by a complex variety of factors, although these can be reduced to three main categories: environment, nutrients, and gene pool.
Just like size, life span, and habitat, the growth rate of animals is another factor that can be used to distinguish them. This brings us to our list of the fastest-growing animals in the world.
1. Sunfish (Mola mola)
Sunfish are unique and massive fish known for their distinctive flattened bodies, large size, and remarkable appearance. Their scientific name comes from the Latin "mola," meaning "millstone."
As one of the world's heaviest bony fishes, sunfish weigh up to 2,204 pounds (1,000 kilograms) upon reaching adulthood. The highest recorded weight of this species was 5,070 pounds (2,300 kilograms), almost double the weight of a midsize car.
Aside from their heavy bodies, sunfish are also known for their very fast growth rate, up to 1.81 pounds (0.82 kilograms) per day. In an engaging memoir, author David Powell describes his encounter with a captive sunfish that gained 882 pounds (400 kilograms) in just 15 months.
2. African Turquoise Killifish (Nothobranchius furzeri)
The African Turquoise Killifish made headlines in 2018 when it was recognized as the fastest maturing vertebrate in the world. Native to the African continent, this organism is a species of Killifish, which is only known to exist in Mozambique and Zimbabwe.
Experts found that although the average lifespan of this aquatic creature is only between four to nine months, it takes only 14 days to reach sexual maturity. This means that African Turquoise Killifish need only two weeks from hatching to be able to reproduce.
3. Blue Whale (Balaenoptera musculus)
This gigantic marine mammal holds the record of being the largest animal to have ever existed. The maximum length of a blue whale is 98.10 feet (29.9 meters), and the maximum weight is 173 tonnes. Researchers found that its growth rate reaches 200 pounds (90 kilograms) daily.
Despite its huge size, the blue whale is not a predator. This giant creature maintains a diet largely consisting of tiny plants called krill. Mostly, they are entirely harmless to humans, allowing researchers and divers to come extremely close to them in the water.
4. Red kangaroo (Macropus rufus)
This marsupial is the largest of all kangaroos and the largest terrestrial mammal native to Australia. It has extremely long and powerful hind legs and feet.
The red kangaroo starts about the size of a bean, weighing 0.03 ounces (one gram). However, it can grow to 180 pounds (82 kilograms), an increase of about 96,000 times its birth weight.
Male red kangaroos can grow up to a head-and-body length of 4 feet 3 inches to 5 feet 3 inches (1.3 to 1.6 meters). Its tail adds 3 feet 11 inches (1.2 meters) to the total length. Females are considerably smaller, with a head-and-body length of only 33 to 41 inches (85 to 105 centimeters) and a tail length of 26 to 33 inches (65 to 85 centimeters).
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