Moderate

Freshwater Flounder

By The Aquarium Calculators Editorial Team ·

Achirus achirus

Complete Freshwater Flounder care guide covering carnivore diet requirements, peaceful temperament, minimum 40 Gallons tank setup, and compatible freshwater tankmates. Difficulty: Moderate.

Freshwater Flounder

Quick Answer

Freshwater Flounder (Achirus achirus) is a flatfish adapted to freshwater and brackish environments. It requires a minimum 40 Gallons aquarium with a pH of 7.0 - 8.0 and temperature range of 24-28°C. This carnivore occupies the bottom zone and makes an excellent addition to community setups.

Intro

Freshwater Flounder (Achirus achirus) is a flatfish adapted to freshwater and brackish environments. It lies on its side on the substrate, blending in with the bottom.

Setup

A 40-gallon or larger tank with fine sand substrate (essential for burying). Moderate water flow and good filtration. They need hiding spots (driftwood, caves).

Feeding

Carnivorous; eats live/frozen foods: bloodworms, blackworms, brine shrimp, and small sinking meaty pellets. Feed after lights out.

Compatibility

Peaceful and shy. Keep singly or in small groups. Tankmates must be peaceful and not aggressive feeders: tetras, rasboras, Corydoras. Avoid bottom-feeding competitors.

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Tank Position
Bottom
Water Temp
24-28°C
Adult Size
See profile
Water pH
7.0 - 8.0

Species Characteristics

Adult Size
Lifespan
Growth Rate
moderate
Tank Compatibility
Community compatible
Indoor Aquarium
Yes

Water Parameters

Water Temperature
Humidity
Water pH

Tank Lighting

Tank Lighting
Standard lighting
Light Hours
N/A
Intensity
moderate

Feeding & Diet

Diet Type
Diet: Carnivore
Feeding Schedule
N/A
Live Food Options
N/A

Continue Learning

Recommended Tools

Fish Compatibility Calculator fish compatibility

Health & Disease

Ich (White Spot Disease) common disease • all fish

Related Guides

Understanding pH in Aquariums water parameters • ph

Similar Species

African Leaf Fish Care Guide: Diet & Tank Mates semanticSimilarity Angelfish Care Guide: Tank Size & Diet | The Aquarium Calculators semanticSimilarity Badis Care Guide: Tank Size & Compatibility semanticSimilarity

Frequently Asked Questions

How many Freshwater Flounders should be kept together?
Can be kept singly or in groups of 3 to 5 in a tank of at least 40 gallons (150 liters) with a wide footprint of 48x15 inches (120x38 cm). Freshwater flounders (Achirus spp. and Trinectes spp.) require fine sand substrate (depth 2-3 inches/5-7.5 cm) for burying. Multiple flounders may compete for burying spots but rarely fight if ample space is provided. Provide at least 4 distinct sandy areas. In tanks under 30 gallons, keep only one. Avoid with aggressive bottom feeders (large cichlids, loaches). Note: Many species sold as 'freshwater' are actually brackish and may require marine salt for long-term health.
What are the exact water parameters for Freshwater Flounders?
Target pH 7.0 - 8.0 (brackish species require 8.0-8.4), General Hardness 5 - 15 dGH, Carbonate Hardness 4 - 12 dKH, Total Dissolved Solids 200 - 500 ppm (brackish: 10,000 - 20,000 ppm), and temperature 72°F - 80°F (22°C - 27°C). Identify the exact species: true freshwater flounders tolerate 0 ppt, but many require 1.005-1.015 specific gravity. Fine sand substrate (0.5-1 mm grain) is mandatory to prevent skin abrasions. Maintain nitrates below 15 ppm with weekly 25% water changes. Use a sponge filter with gentle flow; strong currents stress them.
What is the dietary and medication protocol for Freshwater Flounders?
They are ambush carnivores that live on the substrate, requiring 70% protein, 15% fat, 15% plant matter. Feed live or frozen blackworms, bloodworms, live ghost shrimp, chopped earthworms, and sinking carnivore pellets after lights out. They rarely accept dry flakes; use feeding tongs to place food near their mouth. Medication alert: Extremely sensitive to copper (0.05 mg/L lethal) and formalin. Scaleless; use malachite green at quarter dose (0.025 mg/L). Praziquantel is safe. Avoid salt (tolerance <2 ppt for freshwater species). Quarantine with metronidazole at half-dose.
How to breed Freshwater Flounders in captivity?
Breeding is almost never achieved in home aquariums. Requires large shallow tanks (100+ gallons) with brackish water for some species. To attempt, condition a group of 4-5 with live blackworms and ghost shrimp for 6 weeks. Simulate seasonal changes: Lower water level to 6 inches (15 cm), raise temperature to 82°F (28°C) for 2 weeks, then refill with cool (70°F/21°C) water. They are benthic spawners; eggs are deposited on rocks. Eggs hatch in 7-10 days. Fry are free-swimming and require rotifers and infusoria. Not recommended for hobbyists due to specialized larval care.

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