Internal fertilization permits the development of several interesting and diverse modes of reproduction. Developing embryos are dependent solely on the yolk reserves within their eggs. This type of oviparity is different from that of bony fishes. The shell also permits attachment to the substrate and embryonic respiration. The eggs must survive unguarded for weeks or months until they hatch.
Parental care is unknown in elasmobranchs.
The hatchlings are small compared to the non-ovoviviparous sharks since they are limited by the amount of yolk reserves in the egg. For instance a newborn whale shark may emerge from the egg at 14 inches. The adult is the largest fish in the ocean, reaching at least 40 feet. A more advanced reproductive strategy is the maintenance of relatively large embryos in the uterus until development is complete. This is the most common reproductive strategy in sharks, affording shelter from predation and environmental hazards, and producing large embryos.