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Freshwater Semi-Aggressive Fish Care Sheet

Developed with and approved by a qualified veterinarian.

freshwater semi aggressive care sheet

This care sheet covers a variety of freshwater semi-aggressive community fish species, including:

  • Barbs
  • Black skirt and serpae tetra
  • Redtail and rainbow sharks
  • Gold and opaline gourami
  • Dwarf cockatoo cichlid
  • Ram cichlids
  • Large loaches



Semi-aggressive fish species such as the black skirt and serpae tetras, gold and opaline gourmais, and barbs should not be kept with other fish with long, flowing fins. Some semi-aggressive species are schooling fish and will reduce aggression when kept in odd-numbered schools of five or more. Additionally, many species of semi-aggressive species will do well in community environments with fish who have similar temperaments and personalities.


Typical appearance and behavior

  • Most semi-aggressive species will spend most of their time in the middle to lower levels of the aquarium
  • Schooling species feel more comfortable in schools of five or more of the same species; odd numbers are recommended to prevent pairing
  • Due to their territorial behavior, species like redtail and rainbow sharks do best individually unless a mated pair
  • Although cichlids, dwarf cockatoo and ram cichlids are best kept with semi-aggressive community species instead of more-aggressive cichlid species



Care Difficulty Beginner, intermediate or advanced, depending on the species
Average Life Span Depends on species
Average Adult Size 1 1/2-8 inches long, depending on the species
Diet Omnivore or carnivore, depending on the species
Minimum Habitat Size 10+ gallons, depending on the species
Water Temperature 72-82°F



Habitat size

Keep in an appropriate size aquarium based on the species selected, which can range from 10 gallons for smaller species to a much larger aquarium for a school of semi-aggressive species. 


Building your habitat

Water health -

  • Provide proper filtration to ensure optimal water quality to help maintain health. Slow to moderate water circulation should be provided to mimic water currents and high oxygen levels found in various semi-aggressive fish’s natural habitat. Stable water quality (pH, ammonia, nitrate, nitrite) and water temperature are critical to the health of aquatic life. If you are unsure of your water quality, bring a sample to Petco for free testing
  • An aquatic heater should be used to stabilize water temperature, ensuring it does not fluctuate more than 2 degrees in either direction in a 24-hour period
  • Many semi-aggressive species will benefit from the addition of freshwater salt to the aquarium; the specific gravity should be kept at 1.004. Always research your species-specific needs before adding freshwater aquarium salt. Do not allow specific gravity to fluctuate more than 0.001 in either direction in a 24-hour period


Décor- Provide plenty of space for swimming and hiding places, as well as plants, rocks or décor for hiding



A well-balanced freshwater semi-aggressive fish diet consists of:

  • Pellets, flakes, frozen or freeze-dried food
  • Treats, including bloodworms or brine shrimp (frozen or live)


Things to remember when feeding your freshwater semi-aggressive fish:

  • Feed small amounts one to two times a day, no more than fish will eat in 1-2 minutes
  • Thaw frozen food before feeding


Freshwater semi-aggressive species care

Maintaining great water quality with regular water changes and adequate filtration is important to help keep your freshwater semi-aggressive species healthy

  • Daily: Check filter, water temperature and other equipment
  • Weekly: Test water quality at least once a week
  • Weekly to monthly: Change 10 to 25% of the total volume of water every two to four weeks or as needed; change filter media monthly

Avoid overcrowded conditions, which are a major cause of stress and disease


Where to buy semi-aggressive fish

Various semi-aggressive species are available for purchase at Petco online and in store; availability varies by location. If visiting your local Pet Care Center location, please call ahead to check availability.




Tank mates

Compatible with:

  • Barbs
  • Ram cichlids
  • Catfish
  • Plecostomus
  • Dwarf cockatoo cichlids
  • Large gouramis
  • Silver dollars
  • Larger loaches



Signs of a healthy fish

  • Eats vigorously
  • Clear eyes
  • Swims actively
  • Regular breathing
  • Bright, even coloring
  • Free of parasites or disease



Red flags (If you notice any of these signs, contact your local aquatic specialist or aquatic veterinarian.)

  • Loss of color
  • Spots or fungus on body or mouth
  • Erratic swimming
  • Labored breathing
  • Elevated scales
  • Frayed fins
  • Weight loss
  • Bloating
  • Cloudy eyes or pop-eye
  • Loss of appetite


Common health issues

Health Issue Symptoms or Causes Suggested Action
Health IssueFin rot Symptoms or CausesFrayed or disintegrating fins; the base of the fins usually reddens. Suggested ActionImprove water quality; consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueIch Symptoms or CausesWhite spots appear on fins and body; fish rubs against hard objects or swims erratically. Suggested ActionTreat entire aquarium with a commercial parasite remedy and improve water quality; freshwater or saltwater (depending on specific gravity being kept at) dips can help dislodge the parasites; consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueFungus Symptoms or CausesWhite, cottony growth and/or discoloration of the eyes. Suggested ActionQuarantine fish; use a commercial antifungal remedy as directed; consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueBacterial infections Symptoms or CausesCloudy eyes, open sores and/or reddening of the skin. Suggested ActionImprove water quality; add freshwater aquarium salt; use a commercial antibacterial remedy as directed; consult your local aquatic specialist or aquatic veterinarian for treatment
Health IssueCottonmouth or columnaris Symptoms or CausesCottony white growths along the body and/or gills, frayed fins and gills turn brown and necrotic in late stages; caused by bacterial infection. Suggested ActionQuarantine fish; improve water quality; lower aquarium temperature to 72°F to deter bacteria from growing; medicate as directed; consult your local aquatic specialist or aquatic veterinarian for treatment.



  • Why are they called semi-aggressive fish? Semi-aggressive fish can be territorial and may chase and nip at the fins of more timid species.
  • What semi-aggressive fish can be housed together? Semi-aggressive community fish species such as barbs, large gouramis, serpae tetras and ram cichlids will do well together in an aquarium.


Additional care sheets


Notes and resources

Ask a Pet Care Center associate about Petco's selection of products available for the care and happiness of your new pet. All products carry a 100% money-back guarantee.

Because all aquatic life are potential carriers of infectious diseases, such as  atypical mycobacterium and salmonella, always wash your hands before and after handling your aquatic life and/or habitat contents to help prevent the potential spread of diseases.

Pregnant women, children under the age of 5, senior citizens and people with weakened immune systems should contact their physician before purchasing and/or caring for aquatic life and should consider not having aquatic life as a pet.

Go to the Centers for Disease Control at for more information about aquatic life and disease.


The information on this Care Sheet is not a substitute for veterinary care. If you need additional information, please contact your veterinarian as appropriate.