top of page
koi fish in pond

Tropical Freshwater Fish Care Guide


Keeping Tropical Freshwater Fish as Pets

Freshwater fish are the most popular pets in the United States, with an estimated 140 million individuals currently living in homes across the country.


Historically, it has been difficult for concerned fishkeepers to find medical care for their finned friends, leaving owners with limited options when their pet falls ill. Luckily, a growing number of veterinarians, including our doctors at Long Island Bird and Exotics Veterinary Clinic, are now offering services for aquatic patients as well.


At LIBEVC we provide full service veterinary care for aquatic patients including routine examinations, water testing, husbandry consults, bacterial, viral and infectious disease testing, prescription medication, imaging and surgery.

exotic pet freshwater fish
Care Taking

How To Care for Freshwater Fish

Keep in mind that this guide is meant to provide a broad overview of the care requirements for tropical freshwater species, but should not be considered universally applicable for all species listed above. Every species has their own housing and environmental requirements which can be further discussed with your fish veterinarian.

The Importance of Water Quality

The single most important aspect of maintaining a healthy aquarium and happy fish is water quality. Like the air we breathe, the water a fish swims in has a direct impact on their overall health. Poor water quality is the leading cause of disease in pet fish so it is imperative that caretakers monitor water parameters closely to ensure levels remain safe.

3 Steps to Maintaining Good Water Quality

  • Cycle your aquarium - Ideally, aquariums should be fully cycled before introducing any live animals. Ensure the filter and bacteria colony are capable of handling the volume of waste produced by your fish.

  • Perform regular water changes - water changes are necessary, even if all water test results fall within an acceptable reference range. 10-50% of the aquarium water should be replaced by fresh, conditioned water once per week, though more frequent changes may be necessary depending on your aquarium’s stocking density and water chemistry parameters.

  • Test your water - Test your water regularly. In a cycled tank, water chemistry values, including ammonia, nitrite, nitrate, pH, KH and GH should be tested at least once per week with a liquid water test kit. Write these values down along with the date to track your water quality over time.

Housing for Freshwater Fish

Providing the Right Environment for Your Species

Whether it's a goldfish, guppy, a fish from the tetra species or a long finned oscar, every species has its own set of environmental requirements such as preferred water parameters, aquarium size, and access to various types of enrichment. Before purchasing an aquatic friend ensure that you will be able to provide your species with appropriate living conditions for all stages of their life.


The Aquarium

Aquarium Size and Shape

The configuration of a tank can have a significant impact on its housing capacity. Tall tanks with low ratios of surface area to water volume are harder to clean and manage than a tank of equal volume with more surface area. We recommend choosing a horizontal, rectangular tank to maximize surface area.

The size of your aquarium can also have a significant impact on the welfare of your fish. Appropriate aquarium sizes are determined specifically by species, though we strongly advise against anything under 5 gallons, even for small, solitary fish such as bettas.

Aquarium Placement

Established aquariums can be difficult to relocate so some thought should go into the location of the aquarium in your home. The aquarium should be placed on a level, sturdy surface strong enough to support the weight of the aquarium once filled. Aquariums over 5 gallons are often too heavy for commercial furniture and should be placed on an aquarium stand or an industrial shelving unit. The aquarium should be kept out of direct sunlight and away from radiators and air conditioners to avoid extreme temperature fluctuations.


Supplemental lighting is usually not necessary for the health of your fish provided the location of the aquarium receives sufficient ambient light during the day, however many fishkeepers choose to use an overhead aquarium light for better visibility or when the aquarium contains live plants. There are many different types of aquarium lights to choose from but not all lights are appropriate for every aquarium. Contact your veterinarian for help determining the best kind of lighting to keep your aquarium and fish happy and healthy.


All aquariums, no matter the size, must be equipped with a form of filtration. The most common filters found in home aquaria are sponge filters, hang-on-the-back filters and canister filters. Generally, we do not recommend purchasing commercial aquariums with built-in filtration as we have found it can be extremely difficult to clean properly.

A consultation with your aquatic vet can help in the determination of which filtration system is best for your fishes’ needs.

Environmental Enrichment

It is imperative for all captive animals to have access to an environment providing both mental and physical stimulation as well as enable the animal to make choices and exert control over their surroundings.


It is common for aquarists to use plants (both real and fake) to create more naturalistic environments for the aquarium inhabitants. If you are not ready or able to introduce live plants into the aquarium we recommend purchasing a variety of soft fabric plants for your fish to interact with. If you decide to purchase living plants be sure to check that they are compatible with your aquarium set-up and water parameters.


Structures such as large rocks, caves, tunnels and other aquarium safe decorations are not only visually appealing, but also provide coverage and variety for your fish. Decorations should be tailored to your fishes’ needs and behaviors. It is imperative to consider safety before adding anything to your aquarium. Safe decor is sturdy and solid, with no holes or fissures that could trap your fish were they to attempt to swim through. Decor should be inert (i.e. should not dissolve in water) and painted decor must be sealed prior to introducing it into the aquarium. Unfortunately, many commercial aquarium decorations are hazardous to aquarium fish despite being marketed as “fish safe” and must be modified before introducing them to the aquarium or simply avoided altogether in favor of stone and ceramic. Contact us for recommendations on selecting appropriate aquarium decor for your fish.


Aquarium substrate refers to the material used to cover the bottom of an aquarium tank. Popular substrates include gravel, sand, river stones, argonite, crushed coral and aquarium soil. While substrate is sometimes chosen for solely aesthetic purposes it is important to keep in mind that the right kind of substrate can positively affect the quality of the water, environment, and influence the well-being of your fish, thus substrate should be selected carefully.

Substrate is not necessary for all species and some owners may choose to forego substrate entirely in favor of “bare bottom” tanks. This approach is acceptable for species who do not interact with substrate, however species who are naturally inclined to burrow or forage should be provided with appropriate material with which to engage. If you choose to include substrate in your aquarium, ensure that you select an appropriate and safe material for your species and know how to properly clean substrate in order to avoid the buildup of waste. Any course, particulate substrate such as gravel, stones, marbles, crushed coral, etc. Must be larger than the circumference of the fish’s mouth to avoid potentially fatal obstructions. Sand is acceptable for most larger foraging fish provided it is kept clean.

Choosing Tankmates

Prioritizing environmental and social needs

Choosing appropriate tankmates for your fish often proves more challenging than one might expect. Just like any other animal, each species of fish has their own environmental requirements, preferences and patterns of social (or, in some-cases, antisocial) interaction. It is critical to understand the natural history of your species when choosing tankmates.

Multi-species aquariums

When stocking a multi-species or “community” aquarium, it is important to consider both the environmental and social requirements of the species you select. Some species of freshwater fish who share the same environmental requirements are not socially compatible and should not be kept together.

Due to the level of knowledge required to safely and responsibly maintain a community aquarium we do not recommend community tanks for beginner aquarists and emphasize the need for proper research on the needs of each species before deciding to move forward with a community tank. If you are interested in starting a community tank or have questions or concerns about an established community tank be sure to contact your aquatic veterinary specialist for recommendations.

Keeping your Aquarium Clean

Maintaining a clean aquarium environment is crucial to your fishes’ long term health and happiness. A standard aquarium maintenance schedule includes daily spot cleaning (removing feces, uneaten food and detritus), weekly 10-50% water changes, vacuuming substrate with an aquarium siphon, scraping algae from tank surfaces and rinsing decor in tank water and bi-weekly or monthly filter cleaning (rinsing filter components in tank water and scrubbing with aquarium brush if necessary to remove detritus). If a component of the filter media needs to be replaced, do so in increments over a period of weeks so as not to disrupt the nitrogen cycle.


Freshwater Fish Diet and Nutrition

Feeding Freshwater Fish

Proper nutrition is crucial to the health and well-being of all animals, and fish are no exception. Unfortunately, poor nutrition is a common contributing factor to disease in aquarium fish. It is important to know whether your fish is a herbivore, omnivore, carnivore or insectivore and feed them accordingly.

When selecting food, choose a formulated, species-specific diet that provides your fish with an appropriate balance of energy, nutrients, vitamins and minerals as the backbone of your fish's diet. Pellets and crumbles are generally preferred over flakes due to their superior shelf life. Pellets should be soaked in tank water for several minutes prior to feeding. It is also recommended to soak food in a high quality vitamin supplement such as Boyd’s Vita Chem 1-2x per week. Commercial diets designed for a number of common species, including koi, goldfish, bettas, cichlids, plecos and many others are widely available online and in pet stores. Store dry food in a dry, cool place and replace open packages of dry feed every 2 months to ensure freshness.

Formulated diets can be supplemented with live, frozen and cooked foods appropriate for the species. Any live food should be obtained from reputable distributors or cultured at home (brine shrimp, black fly larvae, bloodworms) and fruits and vegetables should be washed thoroughly prior to feeding. Offering your fish a variety of foods is a good way to meet their nutritional needs while also providing a source of enrichment.


Freshwater Fish Behavior

Species Specific Behaviors

As you are well aware of by now, every species of fish have their own set of behaviors unique to them. It is important to get to know your species’ normal behaviors as well as your fishes’ unique behavioral patterns as recognizing deviations from the norm will help alert you that something may not be right.

Fish are similar to other vertebrates in many fundamental ways but their unique physiology can make it difficult for us to accurately interpret their behaviors. Sometimes healthy, natural behaviors such as bubble nesting may appear to us as potential signs of illness while troubling behaviors such as “flashing” can be incorrectly interpreted as play behavior. Always contact your aquatic veterinary expert about unusual behaviors if you are unsure how to interpret them.  

freshwater fish
exotic betta fish

Medical Care for Your Pet Freshwater Fish

Do Fish Need Veterinary Care?

Yes! Just like any other pet, fish should be examined by a veterinarian with experience in aquatic medicine annually or when showing any signs of illness.


Common Fish Health Concerns

  • Bacterial, viral, fungal, protozoa and parasitic infections

  • Organic waste toxicity

  • Heavy metal toxicity

  • Trauma

  • Swim bladder disorders

  • Congenital deformities

  • Reproductive diseases 

  • Nutritional deficiencies

  • Infectious diseases

  • Cancer

Signs of Illness in Freshwater Fish

  • Behavioral changes

  • Difficulty moving and maintaining position in the water column (sinking to the bottom or floating to the top of the tank)

  • Not eating or defecating

  • Weakness

  • Lethargy

  • Flashing (rubbing body against aquarium decor)

  • Clamped fins

  • Twitching or jerking

  • Labored respiration, “piping” (e.g. gasping at the surface)

  • Injuries​
    • Ripped fins

    • Sores

    • Open wounds

  • Skin and scale changes
    • Discoloration

    • Growths

    • Texture changes

    • Increased mucus production

  • Physical changes
    • Bent spine

    • Bulging eye or eyes 

    • Abdominal bloating

    • “Pineconing” (scales raised off body)

Have Questions?

If you have concerns about how to care for your pet fish, feel free to reach out to the professional veterinarian team at Long Island Bird and Exotics Veterinary Clinic.


Read about the other pets we treat.

More Fish Care Tips

bottom of page