乐生活How do researchers discover that whale sharks are oviparous — 300 embryos pregnant in 1995; fetuses are still alive
Before 1995, researchers generally believed that whale sharks lay eggs – females ovulate and eggs hatch small sharks in vitro. This is based on the reproductive pattern of other whisker sharks.
However, on July 15, 1995, fishermen in Taiwan captured a pregnant whale shark, 10.6 meters in length, and found more than 300 embryos in it. The largest embryos are already viable. On the contrary, there are more than a thousand unfertilized eggs in the ovary.
Embryos that have developed in the body are divided into two categories:
1. In the eggshell, still with yolk sac;
2. There is no yolk sac and it is in the stage of free movement. This is a typical sign of oviposition.
Fifteen of these embryos are fully developed and still alive. They are between 58 and 64 centimeters long. Researchers take them out and raise them. Until November 1995, four months later, two of the whale sharks survived and ate plankton normally (Fig. 1).
These embryos have different stages of development, indicating that they have different fertilization times. Female whale sharks have the ability to store sperm (as do many other species of sharks) and can preserve male sperm for a long time and fertilize in stages.
So far, researchers have reached a consensus that whale sharks are oviparous. Note: Whale sharks are IUCN-rated endangered species and CITES Appendix 2 species.
Reference:
Joung, S. J et al. (1996). The whale shark, Rhincodon typus, is a live bearer: 300 embryos found inone’megamamma’supreme. Environmental Biology of Fishes 46: 219-223.
Figure 1: Babies of whale sharks still alive after removal
Figure 2: Removal of a dead fetus (pictures from the above paper)
