The freshwater flounder belongs to the Solidae family. They are native to the Gulf of Mexico.

These fish have a unique appearance and can be a great addition to your aquarium. Their laterally compressed, flattened bodies make them quite a spectacle when kept in an aquarium.

Are you an enthusiastic aquarist, and wish to house this fish species in your aquarium? Then continue reading.

This article will help you get acquainted with the flounder’s housing requirements, breeding, dietary needs, and much more.

Freshwater Flounder Stats

Family: Achiridae
Species: Achirus lineatus
Common Name: Freshwater flounder
Size: Up to 6 inches long.(15cm)
Min Tank Size: 30 gallons.
Habitat: Western Atlantic, Florida, USA and northern Gulf of Mexico to northern Argentina
Diet: Carnivorous, Start on live worms or small fishes. Will not eat flake.
Behavior: Peaceful.
Water: pH 7.5 – 8.2 dH to 20°, temperature range of 72° to 85°F
Note: The specimens occasionally seen for sale are not a true freshwater fish. While they may survive in Freshwater they will not thrive. The addition of marine salt is recommended.
Care: Medium.
Communities: Very calm, never bothers other fish but is known to be picked on by most species.
Suitability: Research first. There are true freshwater flounders from South America (Catathyridium jenynsii) but they are seldom seen.

To begin, the first thing you need to know about any fish species you wish to keep in your aquarium is their basic stats.

The essential statistical information related to this species of fish has been provided in the following table:

Size 6 inches
Tank capacity 10+ gallons
pH 8.0 – 8.2
Water temperature 24°C – 28°C (72°- 86° F)
Hardness of water 12-14 GH
Aquarium strata Bottom dwellers
Level of care Easy to care for

Now that you’re aware of the kind of water quality, temperature, level of care, etc., needed to house this species, biological specifications are next.

The biological specifications of this species have been provided in the following table:

Scientific name Trinectes maculatus
Common name Freshwater sole, freshwater flounder, hogchoker
Origin Gulf of Mexico, Brazil
Lifespan 3-5 years
Genus Trinectes
Species T. maculatus
Family Solidae
Diet Carnivorous diet

General facts about the Trinectes maculatus

One of the most common mistakes people make is that they think they’re buying this particular fish species when they’re not!

People often end up getting Achirus lineatus when they actually intend to buy Trinectes maculatus. So, be sure to ask for the scientific name of the fish species that you purchase.

If you’re interested to house this fish species in your aquarium, you need to know some fundamental factual details about these fish. Now, let’s take a look at some general facts:

  • These fish grow up to about 6 inches in captivity. However, in the wild, the flounder can grow bigger than 6 inches.
  • The unique appeal of this fish lies in its body shape. They have flat, laterally compressed bodies.
  • Their eyes are located on the left side of their body. Gills and mouth are located on the underside of their flattened body.
  • These fish do not have pectoral fins.
  • The body color of the flounders allows them to camouflage themselves easily. They have dark brown or light brown colored bodies.
  • Their underside (called the blindside) is lighter than the left side of their bodies.
  • Their bodies are covered with thin stripes and spots which are either lighter or darker than their body color. Their tails and fins have fringed edges.
  • Unlike their name, these fish need brackish to marine water (when mature) to survive. The pH of the water in the fish tank should be between 8.0 – 8.2.
  • These fish need hard water to survive. The hardness of the water should be 12-14 GH or even higher. Water temperature should be between 24°-28°C (72°- 86°F).
  • These fish are native to the Gulf of Mexico. They were initially found in estuaries between Massachusetts and Venezuela. Now, these fish can be found in freshwater bodies, oceans, and brackish water bodies. They inhabit estuaries and bays.
  • These fish have a life expectancy of 3 to 5 years.
  • The Trinectes maculatus is an egg-laying breeder. They breed during the summer season. There isn’t sufficient information about whether they can breed in captivity.

Freshwater Flounder care

– About the general set-up

The right environmental conditions can allow this fish species to actualize their life expectancy of 3-5 years. Even if you’re a beginner aquarist, these fish can be wonderful for you because they are low maintenance. The only thing you have to ensure is a proper environment so that these fish can thrive.

Tank size is important. The freshwater flounder size is approximately 6 inches in captivity. However, when you buy these fish, they will be between 1-1.5 inches. For juveniles, a 5-gallon tank is a great start. However, as they mature, you will need a tank that is 10 gallons or higher.

Water chemistry is also important. The pH of the water in the fish tank should be between 8.0 – 8.2. Water temperature should be between 24°-28°C (72°- 86°F).

Although these fish are called freshwater flounders, they need brackish water to survive. Adult fish of this species need marine water. The water hardness should be 12 to 14 GH or even higher. Subdued lighting is perfect.

In nature, the flounders are found in estuaries and bays that have muddy, silty or sandy substrates. Therefore, opt for fine-grained marine sand as a substrate in your tank. Other substrate options include marine sugar sand, highest-grade silica sand, and aragonite. A fine-grained substrate will help show off their swimming movements.

They create a ripple effect when they occasionally swim. These flatfish also stick to the sides of the aquarium. Just make sure that you don’t have any sharp particles in your substrate. The flounders stick to the substrate so anything sharp in the substrate could injure them.

You can keep non-toxic driftwood and live plants like Java ferns and Water Sprite as decorations. They will also keep the water clean. Add lava rocks to keep nitrate levels in the aquarium under control. You will also need a strong filtration system to keep the water clean, something like a Bio-Wheel filter.

– Diet

The fish of this species follow a carnivorous diet. Feeding these fish is quite easy. They will live on foods such as blackworms, grindal worms, and adult brine shrimps.

They will also eat frozen food. However, you do have to train them a bit to eat frozen foods. Frozen bloodworms are acceptable to these fish.

You can even feed clean earthworms to the adult fish of this species. Just make sure that you rinse the food before feeding it to the fish. This will help prevent or at least reduce pollution of the tank water.

These fish dwell on the bottom portion of aquariums. So, meaty food options that can sink to the substrate are perfect. You can even train them to eat pellets. You can also chop up clams and squid to feed them.

The flounders have strong sense abilities. They can smell and taste efficiently. So, even if the food they’re given is rinsed, they react quickly.

– Common diseases to tackle

The best way to tackle any disease is to prevent the onset of that disease. As long as you can provide an appropriate environment in the aquarium for these fish, they will thrive. They are generally quite hardy and low maintenance.

Another important part of keeping them healthy is a nutritious diet. You must feed your fish a variety of meaty food options. Rinsing the food before feeding them is also important.

Frequent water changes are imperative. Try to change 25-30% of the water in the tank on a weekly basis. You can even keep lava rocks for regulating nitrate levels in the tank.

Malnutrition is a common issue with these fish. These fish have a habit of nipping the fins of other fish species when kept in a communal tank. If you do see any fin nipping happening, it’s a sign of malnutrition.

– Tank mates

These fish have a peaceful temperament and are quite shy. They mostly remain at the bottom of fish tanks and sometimes stick to the sides of an aquarium. Their body color allows them to camouflage themselves.

In a freshwater flounder aquarium, it’s best if you keep other fish species that need brackish water to survive. Do not keep semi-aggressive fish or large aggressive fish or predatory fish in the same tank as this particular fish species.

Keeping crustaceans or snails in the same fish tank is also not a good idea because these fish will end up eating them. If you keep small fish, there’s a high chance that they won’t survive in the tank with the Trinectes maculatus, but will be eaten.

You may keep live plants. Fish like Puffers are a good match for the Trinectes maculatus. It’s best not to keep too many fish of different species in the same tank.


The freshwater flatfish is a unique addition to an aquarium.

Some of the important factual details about housing, diet, etc., have been reiterated as follows:

  • The flounders need a smooth, silty, or muddy substrate to survive. The substrate should not have any sharp objects or edges on it. This can injure these fish as they stick to the substrate most of the time.
  • You need a strong filtration system like a Bio-Wheel filter to keep the water clean. Try to change 25-30% of the water in the tank on a weekly basis.
  • These fish prefer to eat live food such as brine shrimps, blackworms, and grindal worms. They also eat frozen foods like frozen bloodworms. You can train them to consume pellets as well.
  • Malnutrition is a common problem with these fish. A tell-tale sign of malnutrition is when they start snipping off the fins of their tank mates of other species.
  • These flounders breed in the wild during the summer season. They are egg layers.

If you’d like to add a unique fish species to your aquarium, the Trinectes maculatus is a great option for you. These fish are easy to care for and quite spectacular to look at!

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