Manta Ray Reproduction
General information about the reproductive habits of manta rays
The reproduction of these fish maintains some similarities with sharks, since they are close relatives. Manta rays are large fish and just like other species they develop within eggs, however, the mother does not release them; it gives birth to live offspring. How can this happen?
We know that animals experiencing birth through which the offspring are born developed are called mammals, and those that lay eggs are oviparous. But there is another name applied to any species that grows in an egg inside the mother’s body and hatches right there, being born alive. In this sense, the manta rays are ovoviviparous animals.
Furthermore, fertilization is internal and involves sexual union of two individuals. This means that the male has to enter one of their copulatory organs called claspers in the female cloaca to transfer its sperm and allow fertilization.
The age at which sexual maturity is reached is not known completely for sure, but it is believed that females take longer to reach sexual maturity than males. In Manta alfredi species, females are mature from 8-10 years of age and males at 6 years of age, approximately, when the width of the disc is about 2.5-3 meters in diameter. Manta birostris females reach maturity also between 8-10 years or to a later age, while members of the opposite sex mature when their disc’s width is 4-4.5 meters. Despite these data, the age when maturity is reached varies from region to region.
Fertility is very low in comparison with other fish because females usually have 1 or 2 offspring maximum at a time. Manta rays deliver once about every 2-5 years and can have offspring for about 30 years. Of course, half of births occur during the first 24 or 25 years.
Courtship and mating
The mating seasons are different. Apparently, in Japan, the giant manta ray mates during the summer and in the Maldives greater reproductive activity was observed during October, November, March and April.
Of course, mating takes place in warm waters and often around the cleaning stations. When males are in heat, they tend to “casually” wander in the stations in search of a receptive female; the latter is likely to release sex hormones in the water to communicate its willingness to mating.
The courtship process may take several days and perhaps even weeks. What happens during this time is very interesting: usually several males congregate around a receptive female and compete to mate with her. This creates what is known as “train mating” characterized by about 25-30 males, arranged one behind the other, following the female’s movements while she leads them all.
At the end of this test, the female chooses a male and it bites its partner’s left pectoral fin to hold her. Then it positions itself so that bellies of both are bonded, and inserts one of its claspers in the female cloaca. The coupling lasts several seconds and usually the female stands still. After mating the male goes away and never returns to take part in parental care.
After fertilization the offspring develop in eggs inside the womb. Inside the egg, embryos are fed by the yolk.
The female hoses the eggs for approximately 1 year (12 to 13 months) until hatching occurs. Then, the young are born alive and independent from the first moment they leave the mother’s body. Delivery usually occurs at night and in shallow water.
“Small” manta rays can measure more than 1 meter in diameter, and since they have few natural predators, they don’t need parental care as such. During the first year of life, babies tend to double in size.
It is believed that these animals have a long life expectancy and longevity is estimated to be at least 40 years.