Only a few species of elasmobranch (subclass including all sharks and rays) fishes have been observed during courtship and mating. However, stingrays have a system that involves internal fertilization, so it can logically be inferred that mating communication between male and female must happen to an extent that allows the male to insert at least one of his two claspers (male reproductive organs that are modifications of the pelvic fins) into the female’s cloaca to deposit sperm. Elasmobranch fishes have relatively complex endocrine (hormonal) systems; based on knowledge of other vertebrates with similar systems, it is likely that females signal to males through chemical or behavioral cues to indicate when their hormonal state is appropriate for mating.
Rays bear young on a yearly cycle, although pregnancy usually lasts only several months, generally spanning some period in the spring, summer, and fall. River rays (subfamily Potamotrygoninae) begin breeding in September or October. The young are usually born in February, but the duration of pregnancy depends on the specific geographic region and altitude. Gestation may take up to 12 months. Within any given group of rays, individuals appear to go through mating, gestation, and parturition (birth) at the same time as all the other females in the group. Stingrays usually bear between two and six young at a time, after nourishing the embryos with milky fluid (histotroph) secreted by the uterus (see Development for a description of this system, called aplacental uterine viviparity). In some groups the epithelium, or wall, of the uterus has evolved to form trophonemata, elongated villi that extend into the uterine cavity to provide greater surface area for respiratory exchange and histotroph excretion. This advanced system of nourishing young inside the uterus can produce offspring that are relatively large at birth (see Development). According to one investigator, a young ray is rolled up like a cigar during birth, which, along with the lubricating histotroph, facilitates the birth of such proportionally large young. The young ray then unrolls and swims away. Likewise, sting-bearing young are able to pass out of the mother’s body without stinging her because their stings are encased in a pliable sheath that sloughs off after birth.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous
No reported evidence of parental care in Dasyatidae was found. After such extended nurturing inside their mothers’ bodies, young rays come into the sea quite able to feed and fend for themselves (see Development and Reproduction).
Parental Investment: no parental involvement