Many people think of the mammal when they hear the word “dolphin”, and about 20 to 30 years ago, restaurants began calling them by their Hawaiian name, Mahi Mahi, so diners wouldn’t be confused.

Two species of dolphin roam the oceans: the common dolphin, Coryphaena hippurus, and a smaller species, pompano dolphin, Coryphaena equisetis, which often mix together.

Both species are voracious feeders and grow very rapidly. Pompano dolphin are smaller and may reach their full size in a year. Common dolphin grow much larger, and most reach double-digit weights in a year or less. Their lifespan is typically only two to four years, so they must grow quickly to reach the 50-pound sizes which are caught with surprising frequency.

In one study at the Monterey (Calif.) Aquarium, a male in their large tank reached 37 pounds in its first year.

A 11/2-pound dolphin was caught and placed in a SeaWorld exhibit of schooling fish. This dolphin had an unlimited food supply, and it grew so fast it was visibly noticeable. It lived only 18 months, but reached 68 pounds. This weight increase equaled 3.69 pounds a month. 

The most-impressive story comes from the University of Miami’s aquaculture program. On Dec. 19, 2014, they introduced a small bull dolphin, not weighed but estimated at 5-6 pounds, into a tank at their Virginia Key Experimental Hatchery. This fish was in optimum conditions with no predators and an unlimited food supply. On Sept. 24, 2015, after 9 months in the tank, it weighed 56.4 pounds, a growth rate of 5.5 pounds a month

Growth rates will not be as dramatic in the wild, as food is not as readily available, and it would require more energy to feed. Still, these experiments show the potential growth rates for dolphin and makes it easier to understand how some reach 60 pounds plus in only for years in the wild.