Despite the trade name 'Freshwater Flounder', Trinectes maculatus is actually a euryhaline flatfish native to coastal estuaries in North America. While juveniles migrate into fresh water, adults require at least low-end brackish water (SG 1.005+) for long-term health and a normal lifespan. They are highly specialized, nocturnal ambush predators that spend most of their time buried in fine sand. Keeping them on sharp gravel will severely damage their undersides and lead to infection.
Freshwater Flounder At a Glance
Freshwater Flounder Tank Requirements
Will Freshwater Flounder fit in your tank?
Care guides tell you what Freshwater Flounder needs, the next question is whether your tank can safely provide it. Test Freshwater Flounder against your tank size, maintenance needs, and the fish you already keep before you buy.
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Freshwater Flounder Water Parameters
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Freshwater Flounder Temperament & Compatibility
Freshwater Flounder Varieties
Each variety inherits the species defaults above. Only differences are highlighted.
Standard
The standard adult form. Often sold incorrectly by retailers as a purely freshwater fish. They must be transitioned to a brackish environment as they mature to prevent immune system collapse. They are peaceful toward tank mates but will consume tiny shrimp, worms, or fry that sink to the sand at night.
Same care requirements as the base species
Also known as: Adult, Hogchoker Sole
Freshwater Flounder Care Guide Summary
The Freshwater Flounder, scientifically known as Trinectes maculatus, belongs to the Oddballs family group. Adults reach a maximum size of approximately 15 cm and have a depressed body shape with a slow growth rate. Classified as peaceful, this species primarily occupies the bottom zone of the aquarium and produces a medium level of biological waste.
To thrive, the Freshwater Flounder requires a brackish required aquarium with a minimum volume of 110 litres and a tank length of at least 90 cm. Water temperature should be maintained between 20°C and 26°C, with a pH range of 7.5–8.5 and a general hardness of 10–25 dGH. A moderate water flow is preferred.
The Freshwater Flounder is a rewarding species to keep, provided its core environmental needs are met. The Freshwater Flounder is typically available in one standard form.
Freshwater Flounder Habitat Setup
When setting up an aquarium for the Freshwater Flounder, a moderate water flow best suits their natural preferences. Because this species occupies the bottom zone, the aquarium layout should prioritise sufficient floor space with hiding spots among rocks, wood, or dense planting. Useful additions include a sand substrate to accommodate their sifting behaviour. Keepers should note that expect substrate disturbance, so lightweight décor should be secured.
Freshwater Flounder Compatibility Notes
Classified as peaceful, the Freshwater Flounder is adaptable and can be kept singly or in a small group, offering flexibility when planning a community tank. When choosing tankmates, ornamental shrimp are not safe companions and boisterous or fast-moving tankmates may cause this species undue stress. Selecting tankmates that favour different water layers from the bottom zone can help reduce competition and territorial overlap.
Freshwater Flounder Recommended Tank Sizes
Standard aquarium sizes that meet the minimum volume and length requirements for Freshwater Flounder.
30 Gallon Breeder
40 Gallon Breeder
55 Gallon Standard
60 Gallon Breeder
75 Gallon Standard
90 Gallon Standard
Show 10 more tank sizes
Freshwater Flounder Feeding & Diet Considerations
The Freshwater Flounder will hunt and eat ornamental shrimp, making it unsuitable for shrimp-focused setups, will eat fry, so breeding efforts in the same tank are unlikely to succeed, and is primarily active at dusk and dawn, so offering food shortly after lights-off ensures it receives adequate nutrition.
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Frequently Asked Questions About Freshwater Flounder
How big does Freshwater Flounder get?
Freshwater Flounder (Trinectes maculatus) typically reaches a maximum adult size of approximately 15 cm. They have a depressed body shape and a slow growth rate.
What tank size does Freshwater Flounder need?
A minimum aquarium volume of 110 litres and a tank length of at least 90 cm are recommended for Freshwater Flounder. This ensures enough swimming space and helps maintain stable water conditions.
What water parameters does Freshwater Flounder need?
Freshwater Flounder thrives in brackish required conditions with a temperature range of 20–26°C, a pH between 7.5 and 8.5, and a general hardness of 10–25 dGH. A moderate water flow is preferred.
Is Freshwater Flounder peaceful or aggressive?
Freshwater Flounder is classified as peaceful with an aggression score of 2 out of 10. They are generally well-suited to peaceful community tanks.
Can Freshwater Flounder live alone?
Yes, Freshwater Flounder can be kept singly or in a group. They are flexible and adapt well to both setups.
Is Freshwater Flounder safe with shrimp?
No. Freshwater Flounder is known to eat ornamental shrimp and is not recommended for shrimp tanks. Even larger shrimp species like Amano Shrimp may be at risk.
Does Freshwater Flounder have any special tank requirements?
Yes. Freshwater Flounder benefits from sand (sifters) in the aquarium. These features help replicate their natural habitat and promote overall health and well-being.
Top Tank Mates for Freshwater Flounder
These fish are strong compatibility matches for Freshwater Flounder based on water preferences, temperament, adult size, and tank behavior.
Plants That Suit Freshwater Flounder
These plants pair well with Freshwater Flounder based on shared water preferences, layout fit, and how likely they are to hold up in the same aquarium.
Java Fern
Leptochilus pteropus
Java Moss
Taxiphyllum barbieri
Dwarf Sagittaria
Sagittaria subulata
Italian Val
Vallisneria spiralis
Jungle Val
Vallisneria americana
Lemon Bacopa
Bacopa caroliniana
Fish Similar to Freshwater Flounder
Freshwater Sole
Brachirus selheimi
A rare and captivating bottom-dwelling flatfish native to Australia and New Guinea. As an ambush predator, it spends most of its time completely buried in fine sand, waiting to strike at small fish or crustaceans. It absolutely requires a soft sand substrate to thrive and prevent severe abrasions to its delicate underside.
Mbu Puffer
Tetraodon mbu
The largest freshwater pufferfish in the world, originating from the Congo River. Known for their 'puppy-like' intelligence and personality, they recognize owners and interact with them. However, they grow to massive sizes and possess a beak capable of crushing hard-shelled invertebrates. Unlike many puffers, they are true freshwater fish and do not need salt. They require massive filtration and a diet of hard foods (clams, snails) to keep their teeth trimmed.
Arrowhead Puffer
Pao suvattii
A highly predatory freshwater pufferfish native to the Mekong basin. Named for its V-shaped, flattened head, it is a specialized ambush predator that buries itself in sand with only its eyes and upwards-facing mouth exposed. It is notoriously aggressive and will consume or fatally bite any tankmate, regardless of size. Must be kept strictly solitary.
Amazon Puffer
Colomesus asellus
One of the few truly freshwater, community-safe pufferfish. Native to the Amazon basin, these energetic swimmers are known for their bumblebee-like stripes and erratic swimming patterns. Unlike most puffers, they are social and prefer to be kept in groups. CRITICAL WARNING: This species has the fastest-growing teeth of any puffer. They REQUIRE a daily diet of hard-shelled foods (snails, clams, crustaceans) or they will require manual dentistry (trimming) to prevent starvation.
Fahaka Puffer
Tetraodon lineatus
A massive, highly intelligent, and extremely aggressive freshwater pufferfish native to the Nile, Senegal, and Niger rivers. Often referred to as 'water dogs' due to their owner recognition and begging behavior. They are strictly solitary pets that will relentlessly attack and kill any tank mates. They require a diet of hard-shelled invertebrates to keep their ever-growing teeth trimmed.
Freshwater Barracuda
Ctenolucius hujeta
The Freshwater Barracuda, or Hujeta Pike Characin, is an elongated, torpedo-shaped ambush predator. It primarily inhabits the upper water levels. Though peaceful with fish too large to swallow, it is a highly efficient piscivore and will readily consume smaller tank mates like Tetras or Guppies. Known to be skittish and prone to fatal jumping, a tight-fitting lid is strictly required.