Kelvin K P Lim and Jeffrey K Y Low
Sex reversals are known in many fishes which live in social groups. The social structure of anemonefishes (Amphiprion spp.) in an anemone consists of two large breeding fishes and several small individuals. The largest and most dominant member is female, but when she is absent, the largest male will change his sex to female, and the next largest fish becomes a functional male. On the other hand, many wrasses and groupers begin their adulthood as females, but are able to change to males later in life.
Most fishes practise external fertilisation, where the eggs and sperm meet outside the bodies of the spawning fish. A common fish in our canals, the molly (Poecilia sphenops) practises internal fertilisation. The anal fin of the male fish is modified into a flexible projection (gonopodium). Through this he introduces sperm into the female's genital pore during spawning. The eggs hatch within the female and she actually gives birth to live young.
The priapus fishes (Neostethus spp.) have their sexual organs located under their throats. The male has a copulatory organ called the priapium with one or two long projections known as the ctenactinia. The ctenactinium is believed to be used for holding on to the female in the act of spawning.
While some fishes leave their eggs to their own destinies, others practise parental care. Those that do, like the anemonefishes and damselfishes, often aggressively guard their spawn. The male seahorse (Hippocampus spp.) has a pouch under his belly in front of his tail where the female deposits her eggs. There the eggs are kept safe until the babies hatch, and the father then expels them to fend for themselves. Then there are fishes like the tilapia (Oreochromis mossambicus) and the cardinalfishes (family Apogonidae) that brood their eggs in one of the parent's mouths.
Coastal Marine Habitats
Fishes and Man
About the guidebook
From A Guide to Common Marine Fishes of Singapore by Kelvin K P Lim and Jeffrey K Y Low
Published by the Singapore Science Centre and sponsored by BP
©Raffles Museum of Biodiversity Research and Singapore Science Centre