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Small Marine Fish Care Sheet

Developed with and approved by a qualified veterinarian.

Small Marine Fish

This care sheet covers a variety of small marine fish species, including:   

  • Dwarf angelfish
  • Damsels and chromis, depending on species
  • Dottybacks
  • Dartfish
  • Gobies
  • Blennies
  • Reef-safe wrasse, depending on species 
  • Hawkfish, depending on species 
  • Dragonets
  • Basslets, depending on species
  • Cardinalfish 
  • Jawfish
  • Clownfish, depending on species 



These fish may be small, but some have big personalities. Small marine fish are favorites with many marine aquarists, as they include a wide range of species that can be housed in both smaller and larger aquariums. Some species are suitable for fish-only habitats, while others thrive in reef aquariums. Small marine fish come in a wide range of striking patterns and colors and inhabit different levels of the aquarium.  


Typical appearance and behavior

  • Some species are solitary and territorial
  • Tend to inhabit all levels of the aquarium
  • Some species, like dwarf angels, may eat coral polyps and nip at clam mantles
  • Some may form symbiotic relationships with other marine life such as shrimp, urchins or anemones
  • They come in a vast array of colors and shapes
  • Every species varies in personality, from shy and timid to active and bold
  • Some small marine fish species exhibit behaviors such as jumping and burrowing 



Care Difficuty Beginner to advanced, depending on species
Average Life Span Depends on species
Average Adult Size Depends on species
Diet Omnivore, herbivore or carnivore, depending on species
Minimum Habitat Size 10+ gallons, depending on species
Water Temperature 74-80°F
Specific Gravity 1.020-1.025


Habitat size

A minimum of 10+ gallons is recommended for smaller adult species; however, water conditions can change rapidly in smaller water volumes. A larger aquarium is recommended for schools of small marine fish species and species thatcan reach a moderate adult size.

Building your habitat

  • Water health - Provide proper filtration to ensure optimal water quality to help maintain health. Slow to strong water circulation, based on species, should be provided to mimic water currents found in the small marine 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. The addition of a protein skimmer can aid with maintaining great water quality and high dissolved oxygen levels. 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. The specific gravity should remain stable. Do not allow specific gravity to fluctuate more than 0.001 in either direction in a 24-hour period
  • Décor - Provide rock and décor for hiding places and plenty of room for movement
  • Live rock can provide a natural food source while also enhancing biological filtration
  • Some species of small marine fish are good jumpers; a secure cover is recommended to keep them safe 
  • Some species like to burrow and sift through substrate and will appreciate a smaller grain and softer substrate



A well-balanced small marine fish diet consists of:

  • Commercial algae sheets and wafers
  • Flakes, pellets, frozen,  freeze-dried and live foods

Things to remember when feeding your small marine fish:

  • Feed small amounts 1 to 2 times daily, no more than fish will eat in 1 to 2 minutes; some species may need 2 to 3 feedings per day
  • Some species require algae or algae sheets to be present at all times
  • Thaw frozen food before feeding


Small marine fish care

  • Water care: Maintaining great water quality with regular water changes and adequate filtration is important to help keep your small marine fish healthy
    • Daily: Check filter, water temperature and other equipment
    • Weekly: Test water quality at least once a week
    • Weekly to monthly: Change 10–25% of the total volume of water every 2–4 weeks, or as needed; change filter media monthly
  • Avoid overcrowded conditions, which are a major cause of stress and disease


Where to buy small marine fish

Small marine fish are available for purchase at Petco online and in-store; availability varies by location. If visiting your local location, please call ahead to check availability.




Tank mates

  • Compatible tank mates will vary by species selected; please research individual species for compatibility. Depending on the species, two males may fight with one another and may not accept the addition of another of their own species, unless a mated pair
  • Introduce new inhabitants to the aquarium gradually



Signs of a healthy small marine fish

  • Clear eyes
  • Healthy appetite
  • Bright, even coloring
  • Fins completely intact and undamaged
  • 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 or appetite
  • Spots or fungus on body or mouth
  • Erratic swimming
  • Labored breathing
  • Weight loss
  • Cloudy eyes or pop-eye
  • Bloating
  • Listlessness 


Common marine fish 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 IssueMarine ich or velvet Symptoms or CausesCysts on fins, gills and skin; labored respiration, excess skin mucus or pale skin. Suggested ActionQuarantine fish immediately and use a commercial parasite remedy; complete a water change; freshwater dips can dislodge the parasites; 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; use a commercial antibacterial remedy as directed, consult your local aquatic specialist or aquatic veterinarian for treatment.
Health IssueViral infection (lymphocystis) Symptoms or CausesWhite nodule growths on fins or body. Suggested ActionImprove water quality; consult your local aquatic specialist or aquatic veterinarian for treatment.



  • What are the best beginner saltwater fish? Some great small marine fish species for the first-time marine aquarist are clownfish, chromis, damsels and dottybacks. 


Additional care sheets


Notes and resources

Ask a Pet Care Center partner 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 or habitat contents to help prevent the potential spread of disease.

Pregnant women, children under the age of 5, senior citizens and people with weakened immune systems should contact their physician before purchasing 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.