SPAWNING AND BIPARENTAL EGG-CARE IN A TEMPERATE FILEFISH, PARAMONACANTHUS-JAPONICUS (MONACANTHIDAE)

Reproductive habits of a temperate filefish, Paramonacanthus japonicus , were studied on a rocky reef at Tsuyazaki, Fukuoka, Japan, from 1989 through 1990. Males had territories of 30-70 m2 and defended them fro m conspecific males and potential egg predators such as another filefi sh, Stephanolepis cirrhifer. Egg masses were found on the sandy bottom in male territories. Individual discrimination of males and females o ccurring in three male territories revealed that males and females sta yed in stable pairs during one month of observation in 1989. In these stable pairs, males fed only within their territories, but females occ asionally foraged outside. The occurrence of egg masses within male te rritories and biparental egg care showed that fish were reproducing as monogamous pairs. Contrary to this, males tagged in 1990 changed thei r territories after the disappearance of females, and males and female s mated polygamously. Spawning was observed only four times during the study period, between 1633 and 1754h. Prior to spawning, the female p repared a spawning bed on the sandy bottom. The male nuzzled the femal e and the pair spawned, touching their gonopores on the spawning bed. Spawning was very quick and took only 1-3 seconds. The adhesive eggs w ere spherical with a diameter of 0.56 mm. They were mixed with sand pa rticles and formed a doughnut-shaped mass of about 4 cm in diameter. O ne egg mass contained 3300-3800 embryos of similar developmental stage , which hatched 2-3 days later. P. japonicus appears to be monogamous but may also practice polygamy when pair-bonds are unstable.