Semi-Aggressive Fish Care Guide

Bold and Boisterous

As the name suggests, these fish are generally peaceful and calm, but can be territorial or boisterous. These fish tend to have a lot of personality and have interesting interactions between fish. Semi-aggressive fish include a wide variety of species that can coexist with others - with the right planning and monitoring. They’re known for their bold personalities and fascinating behaviors, making these fish a lot of fun to watch and keep as pets!

Behavior: Semi-aggressive fish are more likely to claim territory, exhibit pushy behavior, or nip at slower tank mates. While some do well in groups, others do best as single specimen within your larger community of fish.

When keeping fish as pets, there are no guarantees that the fish will get along. You should always monitor your fish for signs of stress or aggression and be prepared to relocate the fish from the aquarium.

It can also be helpful to rearrange or add decor to create additional territories and hiding places. Live plants help maintain water quality and provide hiding places for fish. Often, the more plants and décor, the more you see your fish! A tank with lots of variety in plants and décor is more interesting and less stressful for your fish, a bit like offering new toys or beds to your dog or cat!

Semi-Agressive Fish Types

Angelfish

SIZE: Up to 6" tall

LIFESPAN: 8-12 years, potentially longer in ideal conditions

EXAMPLES: Glo Angelfish (Pterophyllum scalare), Black Angelfish(Pterophyllum scalare), Veil Angelfish (Pterophyllum scalare)

TANK SIZE: 50+ gallon

WATER TEMP: 76-86° F (24-30° C)

HABITAT: Natural gravel and a few ornaments/rocks. Lots of live plants are preferred.

BEHAVIOR: Semi-Aggressive.

SCHOOLING: They will do well individually or in groups of 2 to 4. Monitor groups for aggression.

COMMUNITY: Angelfish do well with most community fish and many semi-aggressive fish. They prefer a tall, heavily planted tank.

NATURAL DIET: Insects and crustaceans.

FOOD: High quality tropical fish flakes and frozen fish food occasionally

Barbs

SIZE: Up to 3"

LIFESPAN: 4-7 years, potentially longer in ideal conditions

EXAMPLES: Tiger Barbs (Puntigrus tetrazona), Cherry Barbs (Puntius titteya), Gold Barb (Barbodes semifasciolatus)

TANK SIZE: 10+ gallon

WATER TEMP: 68-79° F (20-26° C)

HABITAT: Natural gravel and a few ornaments/rocks. Lots of live plants are preferred.

BEHAVIOR: Semi-Aggressive

SCHOOLING: Yes, they typically prefer groups of 5 or more. Monitor for signs of aggression.

COMMUNITY: Barbs can often coexist peacefully with many community fish but can be boisterous and may fin nip if stressed or lacking enrichment.

NATURAL DIET: Small insects and crustaceans.

FOOD: High quality tropical fish flakes and frozen fish food occasionally

Dwarf Cichlids

SIZE: Up to 3”

LIFESPAN: 2-3 years, potentially longer in ideal conditions

EXAMPLES: Balloon Belly Ram (Mikrogeophagus ramirezi)

TANK SIZE: 10+ gallon

WATER TEMP: 81-86° F (27-30° C)

HABITAT: Natural gravel and a few ornaments/rocks. Lots of live plants are preferred.

BEHAVIOR: Semi-Aggressive.

SCHOOLING: They will do well in groups of 2 to 4. Monitor groups for aggression.

COMMUNITY: Dwarf cichlids do well with most community fish. Many semi-aggressive fish are more boisterous or territorial than Balloon Belly Rams so use caution with semi-aggressive fish.

NATURAL DIET: Insects and small crustaceans.

FOOD: High quality tropical fish flakes and frozen fish food occasionally

Gourami

SIZE: Up to 6"

LIFESPAN: 3-5 years, potentially longer in ideal conditions

EXAMPLES: Honey Gourami, Dwarf Gourami, Blue Gourami

TANK: 10+ gallon for Dwarf and Honey Gourami, 29+ for Blue Gourami

WATER TEMP: 75-80° F (24-26° C)

HABITAT: Natural gravel or sand, a few large ornaments/rocks, and live plants.

BEHAVIOR: Semi-Aggressive

SCHOOLING: No. They may get along, but males can occasionally be aggressive towards others of the same species.

COMMUNITY: This group looks stunning in a heavily planted tank and can cohabitate with peaceful fish and often with semi-aggressive fish.

NATURAL DIET: Small insects and crustaceans.

FOOD: High quality tropical fish flakes and frozen fish food occasionally.

Freshwater Sharks

SIZE: Up to 6" for Red-Tailed and Rainbow, 14” for Bala Sharks

LIFESPAN: 4-10 years, potentially longer in ideal conditions

EXAMPLES: Glo Rainbow Sharks (Epalzeorhynchos frenatum), Rainbow Sharks (Epalzeorhynchos frenatum), Bala Sharks (Balantiocheilos melanopterus), Red-Tailed Sharks (Epalzeorhynchos bicolor)

TANK SIZE: 50+ gallon

WATER TEMP: 68-80° F (20-26° C)

HABITAT: Natural gravel and a few ornaments/rocks.

BEHAVIOR: Semi-Aggressive

SCHOOLING: Rainbow Sharks do best kept individually as they can be highly territorial. Bala Sharks, however, prefer to be in groups of 5 or more.

COMMUNITY: Rainbow Sharks are boisterous and territorial, doing best with large semi-aggressive fish. Avoid similar looking fish such as loaches, botias, and Chinese Algae Eaters. Bala Sharks prefer to be in schools but may chase or prey on smaller fish.

NATURAL DIET: Small insects and crustaceans.

FOOD: High quality tropical fish flakes and frozen fish food occasionally

Large Bichir

SIZE: Up to 24"

LIFESPAN: 10-15 years, potentially longer in ideal conditions

EXAMPLES: Dinosaur Bichir (Polypterus senegalus)

TANK SIZE: 125+ gallon

WATER TEMP: 75-82° F (24-28° C)

HABITAT: Natural gravel and a few ornaments/rocks.

BEHAVIOR: Semi-Aggressive.

SCHOOLING: They will do well as a single bichir in the aquarium.

COMMUNITY: Bichirs do well with peaceful or semi-aggressive fish too large to fit in their mouths.

NATURAL DIET: Insects, crustaceans, small fish.

FOOD: High quality tropical fish flakes as a juvenile then pellets as an adult. Frozen fish food occasionally

Loaches & Botias

SIZE: Up to 12" for clown loaches, 4-6” for the others

LIFESPAN: 6-10 years, potentially longer in ideal conditions

EXAMPLES: Clown Loach (Chromobotia macracanthus), Kuhli Loach (Pangio oblonga), Yo-Yo Botia (Botia almorhae)

TANK SIZE: 20+ gallon

WATER TEMP: 76-80° F (25-26° C)

HABITAT: Natural sand and a few ornaments/rocks. Lots of live plants are preferred.

BEHAVIOR: Semi-Aggressive.

SCHOOLING: Loaches and botias prefer large schools of 12 or more.

COMMUNITY: Loaches and botias do well with most community fish and many semi-aggressive fish. They prefer a sand tank to allow them to dig and may prey on snails.

NATURAL DIET: Insects and crustaceans.

FOOD: High quality sinking pellets and frozen fish food occasionally

Semi-Aggressive Algae Eater

SIZE: Up to 11"

LIFESPAN: 8-10 years, potentially longer in ideal conditions

EXAMPLES: Chinese Algae Eater (Gyrinocheilus aymonieri)

TANK SIZE: 50+ gallon

WATER TEMP: 72-79° F (22-26° C)

HABITAT: Natural gravel and a few ornaments/rocks.

BEHAVIOR: Semi-Aggressive

SCHOOLING: These fish do well as an individual specimen in a semi-aggressive aquarium or with large community fish. They do not tolerate smaller, similar looking fish such as loaches, freshwater sharks, or other algae eaters. In a large enough aquarium, groups of 6 or more can show fascinating community behaviors.

COMMUNITY: Will do well in a large semi-aggressive aquarium or in a large community aquarium with similarly sized fish.

NATURAL DIET: Algae, small crustaceans, and insect larvae

FOOD: Available algae, appropriately sized sinking vegetable-based pellets, and blanched vegetables (broccoli, cucumber, zucchini, and leafy greens).

Rainbowfish

SIZE: 4"

LIFESPAN: 5-8 years, potentially longer in ideal conditions

EXAMPLES: Boesemani Rainbowfish (Melanotaenia boesemani), Australian Rainbowfish (Melanotaenia fluviatilis), Turquoise Rainbowfish (Melanotaenia lacustris)

TANK SIZE: 29+ gallon

WATER TEMP: 75-82° F (24-28° C)

HABITAT: Natural gravel or sand and a few ornaments/rocks. Lots of live plants are preferred.

BEHAVIOR: Semi-Aggressive.

SCHOOLING: Yes, groups of 6 or more preferred.

COMMUNITY: Rainbowfish do well with most community fish and some semi-aggressive fish. They prefer heavily planted tank with calm tank mates.

NATURAL DIET: Insects and crustaceans.

FOOD: High quality tropical fish flakes and frozen fish food occasionally

How do I set up a semi-aggressive fish aquarium?

Typical Community Fish Aquarium:

Glass or acrylic tank
Hood or tank cover with light
Thermometer
Substrate: Gravel or sand
Décor for hiding and enrichment
Live or artificial plants
Heater
Filter

Setup Steps:

Choose your equipment: Select an appropriately sized tank, substrate, décor, heater, and filter. A PetSmart associate can help guide your selections.
Prepare your space: Place the aquarium on a flat, stable surface that can support its full weight - water weighs 8.3 pounds per gallon.
Rinse and place décor: Rinse all substrate and decorations with tap water (never soap), then add to the tank.
Add water and conditioner: Fill with tap water and use a water conditioner to remove chlorine and chloramines. If your home uses a water softener, use a tap source that bypasses it.
Install and test equipment: Set up the heater, filter, and thermometer per manufacturer instructions. Add the hood and lighting and set lights on a 12-hour cycle using a timer for consistency.
Let the tank stabilize: Run the system for at least 24 hours to ensure all equipment works and the water temperature is stable.
Begin cycling the tank: Add a beneficial bacteria starter and introduce just a few hardy fish to start, or follow a fishless cycling process to reduce stress.
Monitor water quality daily: During cycling, test water regularly. Perform a water change if ammonia or nitrite is above 0 ppm or if nitrate exceeds 20 ppm. Always add water conditioner after each change.
Add fish gradually: Once your tank is cycled and stable, add compatible fish slowly and monitor for any signs of illness or stress.
Quarantine new additions: To protect your established aquarium, quarantine new fish for 30 days in a separate, cycled setup.

Learn more about fish-less cycling in Setting Up an Aquarium.

When should I test my water quality?

Fish are sluggish, near the bottom of the tank
Fish are at the top, breaking the water to breathe
Fish are not eating
Sudden behavior changes in your fish
Water is cloudy
Water smells funny

PetSmart offers free water quality testing and one of our knowledgeable associates can help you get your system balanced.

When should I contact a veterinarian?

Contact an aquatic veterinarian if you notice the following signs:

Unusual swimming pattern
Thinness or decreased appetite
Abdominal swelling
Inflamed or discolored skin/fins
Fins clamped to sides of body
Scraping body on rocks (flashing)
Visible signs of illness or recent fish loss

If your fish show any of the signs above, we recommend using the “Find a Fish Vet” tool at fishvets.org or wavma.org to locate a qualified aquatic veterinarian in your area.

Shopping Checklist

What will I need for my semi-aggressive fish?

Aquarium sized appropriately for the species and number of fish, (10-20+ gallon) with stand
Aquarium top/hood with light fixture
Natural aquarium gravel or sand & gravel vacuum
Tank décor like driftwood or ornaments
Live or artificial plants
Aquarium heater and thermometer
Aquarium filter sized for your tank
Water testing kit or strips
Water conditioner/dechlorinator
Beneficial bacteria starter
Algae cleaning pad or scraper
Species-appropriate pellets or flakes and frozen fish food

Ready to learn more?

This guide is a great starting place, but we encourage you to do more research on the individual species that you are keeping so that you can be as successful as possible with your aquarium!

Related guides:

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The PetSmart Promise: If your pet becomes ill during the initial 14-day period, or if you’re not satisfied for any reason, PetSmart will gladly replace the pet or refund the purchase price.

Safety tips for you and your pet:
1. ALL ANIMALS can potentially carry viral, bacterial, fungal, and parasitic diseases contagious to humans. 2. Thoroughly wash your hands with warm, soapy water before and after contact with any pet or its habitat. 3. Adults should assist children with hand washing after contact with a pet, its habitat or aquarium water. 4. Always add a dechlorinator or water conditioner and bacteria starter to tap water before adding it to the aquarium. 5. Do not use soaps or detergents to clean aquarium or decor, since they are toxic to fish. For more information, visit petsmart.com, cdc.gov/healthypets, or contact your veterinarian.

This care guide contains general information for the proper care of your pet, but is not comprehensive and is not a substitute for veterinary advice or care. PETSMART and VET ASSURED are trademarks of PetSmart Home Office, Inc. © 2025 PetSmart. All rights reserved.}

Semi-Aggressive Fish Care Guide

In this Article

Bold and Boisterous

Semi-Agressive Fish Types

Angelfish

Barbs

Dwarf Cichlids

Gourami

Freshwater Sharks

Large Bichir

Loaches & Botias

Semi-Aggressive Algae Eater

Rainbowfish

How do I set up a semi-aggressive fish aquarium?

Shopping Checklist

In this Article