Ovaries of an Angler

What am I looking at?

This is a cross section through the ovary of an anglerfish. The ovary membrane is green (1), immature eggs contained within the ovarian follicles are red (2), and mature eggs are gold (3).

Biology in the background

The anglerfish is a deep-sea fish that can live up to 1,000 feet below the surface (about 305 meters). Very little light reaches organisms that live at such a depth. Anglerfish have taken advantage of this by developing a bioluminescent bulb on a stalk above their mouth. When it’s lit, this bulb attracts other small fish and invertebrates straight toward the fish’s mouth, where the prey can be easily snapped up.

When female anglerfish are ready to reproduce, they release their eggs into the water in a large, gelatinous mass that can reach up to three feet long (about a meter) for some species. Then male anglerfish release their sperm into the surrounding water to fertilize the eggs. Interestingly, in some anglerfish species, the male is much smaller and permanently fuses with a female’s body and they share the same circulatory system.

The ovaries of this anglerfish are about 1 millimeter across, or roughly 13 times larger than the width of a human hair.

Technique

This image was created using a type of light microscopy called widefield illumination.