Category: Reproduction

In one of the most astonishing feats of the animal kingdom, a single female ocean sunfish can produce up to 300 million eggs in one spawning season. This extraordinary reproductive output makes it the record holder for the highest egg count of any fish and, indeed, any vertebrate on Earth. The vast number of eggs highlights a crucial survival strategy in the marine world, where very few offspring will ever reach maturity.

Placental mammals are born with a finite number of ova at birth, and their eggs are a key example of one in which egg yolk is absent. This is a sharp contrast to the eggs of birds, reptiles, and fish, which are all defined by their rich, yolky interiors. The absence of yolk in these tiny eggs is an evolutionary adaptation.