Sexual Dimorphism and Pair Spawning into a Sponge by the Filefish, Brachaluteres ulvarum, with a Description of the Eggs and Larvae

Abstract

Sexual dimorphism, reproductive behaviour and early development of a small filefish, Brachaluteres ulvarum, were studied in the field and an aquarium. Males were larger than females (twice body weight) and showed a remarkable colour change during male-male competition during the reproductive season. A single male often followed a gravid female, although a pair-bond was not fixed. Only the larger male with more intense nuptial colouration continued to court until spawning. When the gravid female assumed a spawning position on the osculum of the calcareous sponge, Grantessa mitsukurii, the male also pushed his abdomen onto the osculum. Spawning by the female took 20-30 sec, whereas the male quickly departed. Parental care was not observed after mating. The eggs were demersal and adhesive, being the largest recorded (0.82mm in diameter) among monacanthids. Hatching occurred 6-8 days after spawning (19-22°C), newly-hatched larvae measuring 1.93-2.35mm in total length. Sexual dimorphism and pair spawning into the sponge are discussed in comparison with other monacanthids.