Rhomboid Mojarra
The rhomboid mojarra is a small, deep-bodied silver fish that moves through Brazil's estuaries, mangroves, and sandy bays from the northeast coast down to the southeast.
It's a staple of artisanal fisheries and a reliable target for shore anglers working tidal flats and mangrove edges. Not a large fish, but abundant and willing — and in many coastal communities, more important to the dinner table than to the sport fishery.
Scientific Name: Diapterus rhombeus
Also known as carapeba, carapeva, carapicu
- Deep, strongly compressed body with a distinctly rhomboid (diamond-like) outline — taller relative to length than most estuarine fish you'll encounter alongside it.
- Overall bright silver with yellowish tints on the pelvic and anal fins; the spiny dorsal fin has a dusky edge — useful for separating it from similar mojarras.
- Mouth is highly protrusible and points downward when extended, adapted for picking food off soft bottoms; jaws look toothless but carry fine brush-like teeth.
- Typical catch runs well under 30 cm; the species can reach 40 cm, but fish that size are uncommon in most Brazilian estuaries.
What to know
Habitat Distribution
- Native to Brazil's Atlantic coast; documented from the northeast (including Todos os Santos Bay in Bahia and the Mamanguape estuary in Paraíba) south through Rio de Janeiro (Baía de Sepetiba, Baía de Guaratuba in Paraná).
- Primarily an estuarine and inshore species — sandy bays, tidal mudflats, mangrove lagoons, and brackish channels are its core habitat.
- Juveniles commonly use hypersaline lagoons and shallow brackish water as nursery areas; adults can push into nearly fresh water during certain tidal and seasonal conditions.
- Depth range runs from the shallows down to about 70 m, but anglers encounter it almost exclusively in inshore, shallow-water environments.
Key Locations
- Todos os Santos Bay, Bahia — documented spawning aggregations at the mangrove fringe; a well-studied population.
- Baía de Sepetiba, Rio de Janeiro — subject of multiple population studies; a productive estuarine system for this species.
- Baía de Guaratuba, Paraná — documented in biological studies; typical mangrove-estuarine habitat on the southern coast.
- Estuário do Rio Mamanguape, Paraíba — noted as part of local artisanal fisheries in the northeast.
Specific Spots
- Mangrove root tangles at the water's edge — the fish use this structure as refuge, especially during and after spawning aggregations, and feed along the fringe on the falling tide.
- Tidal mudflats and sandy-bottom shallows where the bottom-oriented mouth can work efficiently; look for feeding fish on the flood tide as water pushes onto flats.
- Current breaks at estuary channel edges, where tidal flow concentrates small invertebrates and the fish stack up to intercept them.
- Mangrove lagoon interiors during calm, warm conditions — schools hold in the shallower back sections and move toward the mouth on the ebb.
Rhomboid Mojarra FAQ
Answers from onWater's species guide.
What are the best lures and bait for Rhomboid Mojarra?
Fresh or frozen shrimp, whole small shrimp or pieces, is the go-to natural bait across Brazil's estuarine fishery for this species; fish it on a light bottom rig just off the mud.
When is the best time to fish for Rhomboid Mojarra?
Available year-round in estuarine systems along Brazil's coast, but spawning aggregations concentrate fish at mangrove fringes during the cooler mid-year months (documented in August in Todos os Santos Bay).
How do you catch Rhomboid Mojarra?
Most anglers in Brazil target rhomboid mojarra from shore or small boats along mangrove edges and tidal flats, fishing natural baits on light bottom rigs. Working the flood tide as water pushes onto shallow flats and into mangrove channels is the most productive approach.
What do Rhomboid Mojarra eat?
Feeds primarily on small bottom-dwelling invertebrates, worms, small crustaceans, and organic detritus, rooted out of soft mud and sand with that downward-pointing protrusible mouth. Small soft-plastic grubs or natural baits like shrimp and bloodworms fished on or near the bottom match this feeding style directly.
Where do Rhomboid Mojarra live?
Native to Brazil's Atlantic coast; documented from the northeast (including Todos os Santos Bay in Bahia and the Mamanguape estuary in Paraíba) south through Rio de Janeiro (Baía de Sepetiba, Baía de Guaratuba in Paraná).
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