Little is known about the mating systems of ocean fish, although they are thought to have paired courtship (Muus,1964; Hutchins, 2004). Some individuals are thought to spawn in the Sargasso Sea. (Hutchins, 2004; Muus, 1964)
Little is known about the breeding behaviors of ocean sunfish. Off the coast of Japan, spawning is thought to occur between August and October (Nakatsubo et al., 2007). Female ocean sunfish can produce over 300 million eggs each breeding season, making them the most fecund extant vertebrate (Bass et al., 2005). Their eggs are very small, with an average diameter of 0.13 cm (Pope et al., 2010). (Bass et al., 2005; Nakatsubo et al., 2007; Pope et al., 2010)
Little is known regarding parental investment of offspring in ocean sunfish.