What Fish Can Live Together? The Complete Compatibility Chart for Beginners

One of the most common mistakes new aquarists make is mixing incompatible fish. The result? Stressed fish, aggression, injuries, and even fatalities. Understanding fish compatibility is essential for building a peaceful, thriving community tank. This comprehensive guide covers everything you need to know about which fish can live together.

Understanding Fish Compatibility

Why Compatibility Matters

Fish have different needs:

• Water parameters: Temperature, pH, hardness vary by species
• Temperament: Some fish are peaceful, others aggressive or territorial
• Size differences: Large fish may eat or bully smaller ones
• Behavior: Schooling vs. solitary, active vs. shy
• Diet: Some are herbivores, others carnivores or omnivores

Incompatible fish lead to:

• Stress and disease susceptibility
• Aggression and fighting
• Hiding and loss of color
• Fin nipping and injuries
• Death from stress or direct attacks

The Four Pillars of Compatibility

1. Temperament Compatibility

Peaceful Fish:

• Generally non-aggressive
• Don't bother tankmates
• Examples: Tetras, rasboras, corydoras, guppies

Semi-Aggressive Fish:

• May defend territory
• Can work in right setup
• Examples: Dwarf cichlids, some barbs, gouramis

Aggressive Fish:

• Territorial and may attack
• Need species-specific tanks
• Examples: Large cichlids, bettas (males), some catfish

Predatory Fish:

• Will eat smaller fish
• Need careful size matching
• Examples: Oscars, pike cichlids, large catfish

2. Size Compatibility

The Rule:

• Don't mix fish where one can fit in another's mouth
• Large fish may see small fish as food
• Even peaceful large fish may accidentally injure small ones

Size Categories:

• Nano fish: <2 inches (tetras, rasboras, small corydoras)
• Small fish: 2-4 inches (guppies, platies, medium tetras)
• Medium fish: 4-6 inches (angelfish, gouramis, larger tetras)
• Large fish: 6+ inches (cichlids, large catfish, some barbs)

Compatibility Guidelines:

• Fish within 2 inches of each other generally safe
• Large fish (6+ inches) need careful consideration
• Very small fish (<1 inch) need protection from larger tankmates

3. Water Parameter Compatibility

Temperature Ranges:

• Cold water: 60-70°F (goldfish, white cloud minnows)
• Tropical: 72-82°F (most community fish)
• Warm tropical: 78-86°F (discus, some cichlids)

pH Requirements:

• Acidic: 6.0-7.0 (South American fish, tetras, angelfish)
• Neutral: 6.5-7.5 (most community fish)
• Alkaline: 7.5-8.5 (African cichlids, livebearers)

Hardness:

• Soft water: Many South American species
• Hard water: African cichlids, livebearers
• Moderate: Most adaptable community fish

Key Principle: Fish from similar regions often have similar requirements.

4. Behavior Compatibility

Schooling Fish:

• Need groups of 6+ to feel secure
• Examples: Tetras, rasboras, danios, barbs
• Don't keep alone or in pairs

Shoaling Fish:

• Prefer groups but can survive alone
• Examples: Some cichlids, larger tetras
• Groups of 3-5 often sufficient

Solitary Fish:

• Prefer to be alone or in pairs
• Examples: Bettas (males), some catfish, large cichlids
• May become aggressive if crowded

Territorial Fish:

• Need defined territories
• Examples: Cichlids, some catfish, some barbs
• Need adequate space and hiding spots

Complete Compatibility Chart

Peaceful Community Fish (Safe Together)

Small Peaceful Fish (<2 inches):

• Neon Tetras
• Cardinal Tetras
• Ember Tetras
• Chili Rasboras
• Pygmy Corydoras
• Otocinclus Catfish
• Endler's Livebearers

Medium Peaceful Fish (2-4 inches):

• Guppies
• Platies
• Mollies
• Swordtails
• Harlequin Rasboras
• Rummy Nose Tetras
• Black Skirt Tetras
• Zebra Danios
• White Cloud Minnows
• Corydoras (various species)
• Kuhli Loaches
• Bristlenose Plecos

Larger Peaceful Fish (4-6 inches):

• Angelfish (with caution - can be semi-aggressive)
• Dwarf Gouramis
• Pearl Gouramis
• Rainbowfish
• Boesemani Rainbowfish
• Congo Tetras
• Larger Corydoras

Semi-Aggressive Fish (Compatible with Caution)

Can Work in Community Tanks:

• Dwarf Cichlids (Apistogramma, Rams)
• German Blue Rams
• Bolivian Rams
• Some Barbs (Cherry Barbs, Checkerboard Barbs)
• Some Gouramis (Blue, Gold, Opaline)
• Siamese Algae Eaters

Requirements:

• Adequate space (larger tanks)
• Plenty of hiding spots
• Compatible tankmates (similar size, peaceful)
• Monitor closely for aggression

Aggressive Fish (Species-Specific Tanks)

Should Not Mix with Peaceful Fish:

• Large Cichlids (Oscars, Jack Dempseys, Convicts)
• African Cichlids (most species)
• Betta Males (with other bettas or similar fish)
• Red-Tailed Sharks
• Tiger Barbs (can work in large groups)
• Some Catfish (Raphael, Pictus)

Best Kept:

• In species-specific tanks
• With other aggressive fish of similar size
• In large tanks with plenty of space

Compatibility by Fish Type

Tetras (Most Species)

Compatible With:

• Other tetras
• Rasboras
• Corydoras
• Small peaceful fish
• Guppies, platies, mollies
• Small gouramis

Not Compatible With:

• Large aggressive fish
• Fin-nipping fish (some barbs)
• Predatory fish
• Very large cichlids

Notes: Keep in groups of 6+ for best behavior and health.

Livebearers (Guppies, Platies, Mollies, Swordtails)

Compatible With:

• Other livebearers
• Tetras
• Rasboras
• Corydoras
• Small peaceful catfish
• Dwarf gouramis

Not Compatible With:

• Aggressive fish
• Fin-nippers (some barbs)
• Large predatory fish
• Very small fish (may eat fry)

Notes: Prefer slightly alkaline water (7.0-8.0 pH). Can be prolific breeders.

Cichlids

Dwarf Cichlids (Rams, Apistogramma):

• Compatible with: Small tetras, corydoras, small peaceful fish
• Need: Soft, acidic water, plenty of hiding spots
• Can be territorial during breeding

South American Cichlids (Angelfish, Discus):

• Compatible with: Larger tetras, peaceful cichlids, some catfish
• Need: Soft water, stable parameters, larger tanks
• Angelfish may eat very small fish

African Cichlids:

• Compatible with: Other African cichlids (same lake)
• Need: Hard, alkaline water, species-specific setups
• Generally not compatible with peaceful community fish

Large Cichlids (Oscars, Jack Dempseys):

• Compatible with: Other large cichlids, large catfish
• Need: Very large tanks, species-specific setups
• Will eat smaller fish

Catfish

Small Catfish (Corydoras, Otocinclus):

• Compatible with: Most peaceful community fish
• Need: Groups of 6+, soft substrate
• Peaceful bottom dwellers

Medium Catfish (Bristlenose Plecos, Clown Plecos):

• Compatible with: Most community fish
• Need: Hiding spots, driftwood (for some species)
• Generally peaceful

Large Catfish (Common Plecos, Large Catfish):

• Compatible with: Large peaceful fish, large cichlids
• Need: Very large tanks
• May become territorial as they grow

Gouramis

Dwarf Gouramis:

• Compatible with: Small peaceful fish, tetras, rasboras
• Can be: Slightly territorial, especially males
• Need: Plenty of plants and hiding spots

Larger Gouramis (Pearl, Blue, Gold):

• Compatible with: Medium peaceful fish
• Can be: Semi-aggressive, especially males
• Need: Adequate space, monitor for aggression

Giant Gouramis:

• Compatible with: Large peaceful fish only
• Need: Very large tanks
• Can be aggressive

Barbs

Peaceful Barbs (Cherry, Checkerboard):

• Compatible with: Most peaceful community fish
• Generally safe in community tanks

Semi-Aggressive Barbs (Tiger, Rosy):

• Can work: In large groups (8+) in large tanks
• May nip: Long-finned fish (angelfish, guppies)
• Need: Adequate space and numbers

Aggressive Barbs:

• Not recommended: For peaceful community tanks
• Best kept: In species-specific setups

Common Compatibility Mistakes

Mistake 1: Mixing Size Extremes

Problem: Small fish with large fish Example: Neon tetras with oscars Solution: Keep fish within 2-3 inches of each other

Mistake 2: Ignoring Temperament

Problem: Mixing aggressive and peaceful fish Example: Betta with guppies Solution: Research temperament before mixing

Mistake 3: Wrong Water Parameters

Problem: Fish from different regions Example: African cichlids with South American tetras Solution: Match water parameters (pH, temperature, hardness)

Mistake 4: Insufficient Numbers

Problem: Keeping schooling fish alone or in pairs Example: Single tetra or pair of rasboras Solution: Keep schooling fish in groups of 6+

Mistake 5: Overcrowding

Problem: Too many fish, not enough space Example: 20 fish in 20-gallon tank Solution: Use stocking calculator to plan appropriately

Mistake 6: Fin-Nippers with Long-Finned Fish

Problem: Barbs with angelfish or guppies Example: Tiger barbs nipping angelfish fins Solution: Avoid mixing fin-nippers with long-finned species

Building a Compatible Community Tank

Step 1: Choose Your Centerpiece Fish

• Select 1-2 larger, peaceful fish as focal points
• Examples: Angelfish, gouramis, rainbowfish
• Ensure compatible with planned tankmates

Step 2: Add Schooling Fish

• Choose 1-2 species of schooling fish
• Keep in groups of 6+ each
• Examples: Tetras, rasboras, danios

Step 3: Add Bottom Dwellers

• Include bottom-feeding fish
• Keep in groups (for schooling species)
• Examples: Corydoras, loaches, small plecos

Step 4: Add Cleanup Crew (Optional)

• Algae eaters and scavengers
• Examples: Otocinclus, nerite snails, amano shrimp
• Ensure compatible with other fish

Step 5: Verify Compatibility

• Check all fish have similar:
  • Temperature requirements
  • pH preferences
  • Size compatibility
  • Temperament match

Tank Size Considerations

10-Gallon Tank (38 Litres)

Best For:

• Small peaceful fish only
• Single species or very compatible small fish
• Examples: 6 neon tetras + 4 pygmy corydoras

Avoid:

• Large fish
• Aggressive fish
• Multiple species of larger fish

20-Gallon Tank (76 Litres)

Best For:

• Small community setups
• 2-3 species of small fish
• Examples: 8 tetras + 6 corydoras + 1 dwarf gourami

Can Support:

• Small peaceful communities
• Some medium-sized peaceful fish

55-Gallon Tank (208 Litres)

Best For:

• Diverse communities
• Multiple species
• Examples: 12 tetras + 8 corydoras + 2 angelfish + 6 rasboras

More Flexibility:

• Can mix more species
• Can include semi-aggressive fish with caution
• Better for territorial fish

75+ Gallon Tank (284+ Litres)

Best For:

• Large communities
• Mixing larger peaceful fish
• Semi-aggressive setups
• Examples: Full discus community or mixed cichlid setups

Special Considerations

Breeding Behavior

• Many fish become territorial when breeding
• May need to separate breeding pairs
• Some species protect fry aggressively
• Plan for breeding behavior in compatibility

Feeding Compatibility

• Ensure all fish can access food
• Bottom feeders need sinking food
• Surface feeders need floating food
• Avoid mixing very different feeding behaviors

Hiding Spots

• Territorial fish need defined territories
• Shy fish need hiding spots
• Aggressive fish need break lines of sight
• Plants, rocks, and decorations create structure

Water Flow Preferences

• Some fish prefer still water (bettas, some gouramis)
• Others need strong flow (hillstream loaches, some barbs)
• Match flow preferences for best compatibility

Using Tools to Plan Compatibility

Stocking Calculator

Use our free aquarium stocking calculator to:

• Plan appropriate bioload for your tank
• See species-specific requirements
• Calculate minimum tank sizes
• Avoid overstocking that causes aggression

Research Before Buying

• Research each species before purchasing
• Check temperature, pH, and size requirements
• Understand temperament and behavior
• Verify compatibility with existing fish

Parameter Tracking

The Fishi mobile app helps you:

• Track water parameters for compatibility
• Log fish additions and behavior
• Monitor for signs of incompatibility
• Set reminders for maintenance

Signs of Incompatibility

Aggressive Behavior

• Chasing and nipping
• Fin damage
• Hiding constantly
• Loss of color
• Refusing to eat

Stress Signs

• Rapid breathing
• Clamped fins
• Hiding in corners
• Loss of appetite
• Increased disease susceptibility

Physical Damage

• Torn fins
• Missing scales
• Wounds or injuries
• Missing fish (may have been eaten)

If You See These Signs:

1. Separate immediately: Move aggressive fish or victims
2. Reassess compatibility: Research what went wrong
3. Provide hiding spots: If keeping together, add more structure
4. Consider rehoming: May need to separate permanently

Conclusion: Compatibility is Key

Building a compatible community tank requires research, planning, and understanding each species' needs. By matching temperament, size, water parameters, and behavior, you can create a peaceful, thriving aquarium where all fish can display natural behaviors and live healthy lives.

Remember: When in doubt, err on the side of caution. It's better to have a simpler, compatible setup than a complex one with constant aggression and stress.

Ready to plan your perfect community tank? Use our free stocking calculator to plan appropriate bioload and see species-specific requirements. For ongoing tank management and parameter tracking, download the Fishi mobile app – loved by over 100,000 fishkeepers worldwide!

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