Diamond Moonfish

About

The diamond moonfish (Monodactylus argenteus) is one of those species that looks almost two-dimensional in the water. A highly compressed, silvery disc with yellow-tinged fins and two bold vertical black bars through the head. It ranges widely across the Indo-West Pacific, from the Red Sea and the east African coast all the way out to Samoa, where it inhabits mangrove estuaries, tidal creeks, and the brackish margins where rivers meet the sea. Juveniles sometimes push into fully fresh water, but adults are committed to brackish and marine conditions, so this is not a fish you can keep long-term in a freshwater community tank. In the wild these fish cruise in large, loosely organized schools, and that behavior carries over into the aquarium. Keeping a group of five or more helps them settle and reduces the territorial friction that can surface when individuals are kept in smaller numbers. They are active, open-water swimmers and they get big, approaching ten inches at maturity, so a spacious tank is a genuine requirement rather than a suggestion. Diet is not complicated; they accept most meaty and prepared foods readily. An intermediate-level species, mainly because of the brackish chemistry needs and their eventual size rather than any particular fussiness.