# Freshwater Aquarium Fish: Best Species and Care Guide Freshwater aquarium fish are captive animals that depend entirely on the water you provide, and the single most common reason they get sick or die is poor water quality and rushed stocking. The best beginner species are hardy, widely bred, and tolerant of a range of conditions, but no fish survives an uncycled filter. Before you buy a single fish, you need a cycled tank, a test kit for ammonia and nitrite, and a plan for temperature, pH, and tank mates. This guide covers the nitrogen cycle, the water chemistry thresholds that matter most, species profiles with adult size, minimum tank volume, temperature, pH, diet, and temperament, plus a compatibility table you can act on today. It focuses on tropical and subtropical freshwater species kept in indoor aquariums. Goldfish are coldwater fish and are covered here only to explain why they should not be mixed with tropical species. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## At a Glance: Your First 30 Days 1. Set up the tank, filter, heater, and substrate. Fill with dechlorinated water. 2. Start the nitrogen cycle before adding fish. Dose ammonia or use a fishless cycling method and test daily. 3. Wait until ammonia and nitrite read zero and nitrate is rising. This typically takes several weeks. 4. Add a small number of hardy fish, not a full community at once. 5. Test ammonia and nitrite every day for the first two weeks after stocking. 6. Do a partial water change if ammonia or nitrite rises above zero. 7. Add new species in small groups, spaced weeks apart, with a quarantine period if possible. 8. Match every species to your tank volume, temperature, and pH before purchase. ## Why Water Quality Comes Before Species Choice Most fish keepers choose fish first and water second. That order causes most of the problems. A fish can tolerate a slightly wrong pH far better than it can tolerate ammonia or nitrite in the water. According to the Merck Veterinary Manual, poor water quality is a leading contributor to disease in pet fish, and the World Aquatic Veterinary Medical Association (WAVMA) emphasizes that water quality testing and husbandry review are the foundation of aquatic animal health. A review of husbandry mistakes in ornamental fish found that problems commonly stem from insufficient water quality, inadequate feeding, poor equipment, and inappropriate social structure [1]. Clinical signs in these cases are usually not specific, which means a sick fish often looks "just off" rather than showing a clear diagnosis. Another review of husbandry-related diseases in ornamental fish makes the same point: most common fish problems can be avoided or treated once proper freshwater husbandry is understood [2]. The practical takeaway is that you manage water first, then fish. Species selection is a matching exercise against the water you can reliably provide. ## The Nitrogen Cycle Explained for New Owners The nitrogen cycle is the process by which beneficial bacteria convert toxic fish waste into less harmful compounds. Fish excrete ammonia through their gills and urine. Uneaten food and waste also break down into ammonia. Ammonia is toxic. A group of bacteria (including Nitrosomonas) converts ammonia into nitrite, which is also toxic. A second group (including Nitrospira) converts nitrite into nitrate, which is much less toxic and is removed by water changes and by plants. A study of freshwater aquarium systems found that nitrifying bacteria such as Nitrosomonas and Nitrospira are central to nutrient cycling and water quality regulation, and that loss of these nitrifiers coincided with fish health problems [3]. In that study, the most severe microbial imbalance occurred alongside a bloom of Pseudomonas and concurrent fish health issues, while healthier exhibits maintained more balanced microbial communities with lower pathogen loads [3]. Routine husbandry such as partial water changes and substrate cleaning coincided with improved microbial balance [3]. This is why the cycle matters. You are not just adding water. You are cultivating a bacterial filter. ### Cycling a New Tank Cycling means growing the bacterial colonies that process ammonia and nitrite. A new tank has almost none of these bacteria. Cycling takes weeks, not days. You can cycle without fish by dosing a source of ammonia and testing until ammonia and nitrite return to zero and nitrate appears. You can also cycle with a very small number of hardy fish, but this exposes those fish to ammonia and nitrite, so it requires daily testing and frequent water changes. ### Stocking Is Not the Same as Cycling Cycling establishes the bacterial capacity of the filter. Stocking is the act of adding fish, and it must be done gradually. The bacteria population grows to match the waste produced. If you add too many fish at once, the bacteria cannot keep up, ammonia rises, and fish get sick. Add fish in small groups, spaced at least a week or two apart, so the filter can adjust. This distinction between cycling and stocking is one of the most important concepts for a new owner. ## Ammonia and Nitrite: The Thresholds That Matter Ammonia and nitrite should read zero in a healthy, cycled aquarium. Any detectable ammonia or nitrite is a warning that the filter is not keeping up, that you overfed, that you overstocked, or that the filter failed. The Merck Veterinary Manual lists ammonia and nitrite toxicity as a primary cause of acute illness in aquarium fish, and WAVMA guidance treats routine water testing as essential. When ammonia or nitrite is present, act immediately: - Stop feeding for 24 to 48 hours. - Do a partial water change with temperature-matched, dechlorinated water. - Test again after the water change. - Check the filter for clogs or a stopped impeller. - Reduce stocking if the problem keeps returning. Do not add more fish while ammonia or nitrite is detectable. Do not assume a water conditioner removes ammonia permanently. Most only detoxify it temporarily, and the underlying filter problem remains. ## Choosing the Right Tank Size
Goldfish swimming in a planted freshwater aquarium tank
A properly sized, well-maintained tank is the foundation of freshwater fish care. Image: AJ Gray, CC0, via Wikimedia Commons.
Tank volume drives everything else. A larger volume dilutes waste, holds temperature more steadily, and gives you more room to correct mistakes. Small tanks are harder, not easier, for beginners because a small volume changes chemistry quickly. Use the minimum tank volumes in the species profiles and compatibility table as a floor, not a target. If you want a community tank, add up the needs of every species and choose the largest tank you can reasonably maintain. Surface area matters for oxygen exchange, so a long tank is often better than a tall one of the same volume. ## Essential Equipment and Selection Criteria - Filter: Choose a filter rated for at least your tank volume, and prefer one with biological media that supports nitrifying bacteria. The filter is the home of your nitrogen cycle. - Heater: Required for tropical species. Choose one with a thermostat and a wattage appropriate to your tank volume and room temperature. - Thermometer: Verify the heater is holding the target temperature. - Test kit: You need ammonia, nitrite, nitrate, and pH testing. Liquid reagent kits are generally more accurate than strips. - Water conditioner: Removes chlorine and chloramine from tap water. - Substrate: Gravel or sand, matched to the species. Bottom dwellers such as Corydoras prefer smooth sand. - Lighting: Supports plants and helps you observe fish. Match the light period to avoid algae problems. - Lid: Many species jump. A lid also reduces evaporation. Tap water quality varies. A study of tap water in a major rice-producing region found that water properties were not stable across the year and that rearing fish in that tap water negatively affected growth and reproduction [4]. The lesson is not that tap water is bad. It is that you should test your own source water and know its baseline before you rely on it. ## Feeding Freshwater Aquarium Fish Diet type matters as much as water chemistry. Fish are broadly omnivores, carnivores, or herbivores, and feeding the wrong type causes nutritional problems and worsens water quality. A study of different fish feeds found that feed quality affected both growth performance and water nutrient concentrations, and that better-quality feed produced better growth with less impact on water quality [5]. Overfeeding is a common mistake that raises ammonia and nitrate. Feed only what the fish consume in a few minutes, once or twice daily. Remove uneaten food. Match the food to the species: herbivores need plant matter, carnivores need protein-rich foods, and omnivores need a mix. ## Disease Prevention and Biosecurity Most disease in home aquariums is preventable through husbandry. Transport stress and handling are recognized challenges in ornamental fish husbandry, and disease outbreaks remain a major cause of loss [6]. Proper husbandry and biosecurity, including a disease detection plan, are essential to monitor and prevent outbreaks [7]. Quarantine new fish before adding them to a display tank. This limits the spread of infectious disease. Emerging infectious diseases in ornamental fish include goldfish herpesvirus, koi herpesvirus, carp edema virus, Edwardsiella species, and Francisella, and many of these affect a range of species rather than one [7]. Some fish diseases are zoonotic, meaning they can spread to people. Nontuberculous mycobacteria are common chronic bacterial pathogens in ornamental fish and carry zoonotic potential [8]. A survey of aquarium fish found Mycobacterium marinum as the most common nontuberculous mycobacterium isolated, and it is potentially dangerous to both fish and humans [9]. Wash your hands after handling fish, water, or equipment, and never clean aquarium equipment in a kitchen sink or with household dish soap. Parasites also travel with the trade. A study of pindani cichlids found the monogenean Cichlidogyrus tilapiae in fish from aquarium shops, the first report of this genus in India, showing how parasites move with ornamental fish [10]. This is another reason to quarantine. ## Species Profiles Each profile lists adult size in centimeters, minimum tank volume in liters, temperature range in degrees Celsius, pH range, diet type, and temperament. These are general husbandry targets. Individual fish vary, and stressed or sick fish behave differently. ### Guppy (Poecilia reticulata) - Adult size: 3 to 6 cm, females larger - Minimum tank volume: 40 L - Temperature: 22 to 28 degrees C - pH: 6.8 to 7.8 - Diet: Omnivore - Temperament: Peaceful, active Guppies are hardy, colorful, and breed readily, which makes them a common first fish. They are sexually dimorphic, and females are larger and less colorful than males. A study of guppies found that increased temperature raised prey consumption in both sexes and that females consumed disproportionately more prey than males [11]. This reflects their active metabolism and appetite. Guppies do best in groups with more females than males to reduce harassment. They are community-safe with other peaceful species. ### Neon Tetra (Paracheirodon innesi) - Adult size: 3 to 4 cm - Minimum tank volume: 40 L - Temperature: 20 to 26 degrees C - pH: 6.0 to 7.0 - Diet: Omnivore, accepts small foods - Temperament: Peaceful, schooling Neon tetras are schooling fish and should be kept in groups of at least six. They are sensitive to sudden changes in water chemistry, so acclimate them slowly and keep conditions stable. They are community-safe with other small, peaceful species but may be eaten by larger fish. ### Zebra Danio (Danio rerio) - Adult size: 4 to 5 cm - Minimum tank volume: 40 L - Temperature: 18 to 24 degrees C - pH: 6.5 to 7.5 - Diet: Omnivore - Temperament: Peaceful, active Zebra danios are fast, hardy, and tolerate cooler temperatures than many tropical species. They are a good choice for a beginner community tank. As a species, zebrafish are also widely used in research, and studies have shown that water source and quality can affect their growth and reproduction [4]. Keep them in groups and provide swimming space. ### Betta (Betta splendens) - Adult size: 6 to 7 cm - Minimum tank volume: 20 L - Temperature: 24 to 28 degrees C - pH: 6.5 to 7.5 - Diet: Carnivore, accepts protein-rich prepared foods - Temperament: Males territorial toward other males Bettas are often kept alone, and a single male in a properly heated and filtered tank is a reasonable setup. They are not community-safe with other bettas or with fin-nipping species. They can be kept with some peaceful tank mates in a larger tank, but temperament varies by individual. Bettas need warm water and should not be kept in unheated bowls. ### Common Goldfish and Fancy Goldfish (Carassius auratus) - Adult size: 15 to 30 cm, larger for common goldfish - Minimum tank volume: 75 L for one fancy goldfish, more for common goldfish - Temperature: 10 to 22 degrees C - pH: 6.5 to 8.0 - Diet: Omnivore - Temperament: Peaceful but messy Goldfish are coldwater fish. They should not be mixed with tropical species because their temperature requirements are different. Keeping a goldfish at tropical temperatures stresses it, and keeping tropical fish at goldfish temperatures stresses them. Goldfish also produce a large amount of waste relative to their size, so they need strong filtration and generous water changes. Goldfish herpesvirus is a recognized emerging infectious disease of ornamental fish [7]. ### Corydoras Catfish (Corydoras species) - Adult size: 4 to 7 cm depending on species - Minimum tank volume: 60 L - Temperature: 22 to 26 degrees C - pH: 6.5 to 7.5 - Diet: Omnivore, bottom feeder - Temperament: Peaceful, schooling Corydoras are bottom-dwelling schooling fish and should be kept in groups of at least six. They need smooth substrate to protect their barbels. They are community-safe with peaceful midwater species. ### Platy (Xiphophorus maculatus) - Adult size: 4 to 6 cm - Minimum tank volume: 40 L - Temperature: 20 to 26 degrees C - pH: 7.0 to 8.2 - Diet: Omnivore, benefits from plant matter - Temperament: Peaceful Platies are hardy livebearers that tolerate a range of conditions, including slightly hard, alkaline water. They are community-safe and breed readily. Provide plant matter in the diet. ### Mollies (Poecilia species) - Adult size: 5 to 10 cm depending on species - Minimum tank volume: 60 L - Temperature: 24 to 28 degrees C - pH: 7.0 to 8.5 - Diet: Omnivore, benefits from plant matter - Temperament: Peaceful, occasionally nippy Mollies do best in harder, alkaline water. They are community-safe with other peaceful species but can be nippy in small tanks. They breed readily. ### Angelfish (Pterophyllum scalare) - Adult size: 15 cm - Minimum tank volume: 110 L - Temperature: 24 to 28 degrees C - pH: 6.0 to 7.5 - Diet: Omnivore - Temperament: Semi-aggressive, territorial when breeding Angelfish are cichlids and need a taller tank because of their body shape. They can be kept in community tanks but may eat small fish such as neon tetras. They are prone to nontuberculous mycobacteria infections, and a study of diseased freshwater angelfish isolated Mycobacterium chelonae, M. fortuitum, M. gordonae, M. intracellulare, and M. peregrinum, all of which have been reported in human patients [8]. This reinforces the need for good husbandry and hand hygiene. ### Pindani (Chindongo socolofi) - Adult size: 10 to 12 cm - Minimum tank volume: 150 L - Temperature: 24 to 28 degrees C - pH: 7.8 to 8.6 - Diet: Omnivore, benefits from plant matter - Temperament: Semi-aggressive, territorial Pindani are Lake Malawi cichlids and need hard, alkaline water and a large tank with rockwork. They are not community-safe with peaceful species. They are popular in the ornamental trade, and a study found them carrying the monogenean parasite Cichlidogyrus tilapiae in aquarium shops [10]. Quarantine is important for this species. ### Malabar Dwarf Puffer (Carinotetraodon travancoricus) - Adult size: 2 to 3 cm - Minimum tank volume: 40 L - Temperature: 24 to 28 degrees C - pH: 6.5 to 7.5 - Diet: Carnivore, live and frozen foods - Temperament: Semi-aggressive, nippy The Malabar dwarf puffer is the smallest known pufferfish and is popular in the international aquarium trade [12]. It is a batch spawner that releases one to five eggs per day, with low fecundity, and its reproductive behavior is unusual in captivity [12]. It is not community-safe with small, slow, or long-finned fish because it nips fins. It needs live or frozen foods such as Artemia nauplii, moina, and bloodworm [12]. ### Cherry Shrimp (Neocaridina davidi) - Adult size: 2 to 3 cm - Minimum tank volume: 20 L - Temperature: 20 to 26 degrees C - pH: 6.5 to 7.5 - Diet: Omnivore, grazer - Temperament: Peaceful Cherry shrimp are freshwater invertebrates, not fish, but they are common in freshwater aquariums and worth including because they affect compatibility. The genus Neocaridina includes species that have been introduced outside their native range through the aquarium trade [13]. They are peaceful and community-safe with small, non-predatory fish, but larger fish will eat them. ## Compatibility Table | Species | Minimum Tank (L) | Temperature (C) | pH | Diet | Community-Safe | |--|--|--|--|--|--| | Guppy | 40 | 22 to 28 | 6.8 to 7.8 | Omnivore | Yes | | Neon Tetra | 40 | 20 to 26 | 6.0 to 7.0 | Omnivore | Yes, with small peaceful fish | | Zebra Danio | 40 | 18 to 24 | 6.5 to 7.5 | Omnivore | Yes | | Betta (single male) | 20 | 24 to 28 | 6.5 to 7.5 | Carnivore | No, keep alone or with careful tank mates | | Goldfish | 75 plus | 10 to 22 | 6.5 to 8.0 | Omnivore | No, coldwater only | | Corydoras | 60 | 22 to 26 | 6.5 to 7.5 | Omnivore | Yes | | Platy | 40 | 20 to 26 | 7.0 to 8.2 | Omnivore | Yes | | Molly | 60 | 24 to 28 | 7.0 to 8.5 | Omnivore | Yes, with peaceful fish | | Angelfish | 110 | 24 to 28 | 6.0 to 7.5 | Omnivore | Caution, eats small fish | | Pindani | 150 | 24 to 28 | 7.8 to 8.6 | Omnivore | No, aggressive | | Malabar Dwarf Puffer | 40 | 24 to 28 | 6.5 to 7.5 | Carnivore | No, nips fins | | Cherry Shrimp | 20 | 20 to 26 | 6.5 to 7.5 | Omnivore | Yes, with small fish | ## Building a Community Tank Step by Step 1. Decide on your water. Test your tap water for pH and hardness. Choose species that match it rather than fighting it. 2. Choose a tank volume that fits the largest species on your list, then add a margin. 3. Cycle the filter completely before adding fish. 4. Add the hardiest species first, in a small group. 5. Test ammonia and nitrite daily for two weeks. 6. Add the next species after two to four weeks, quarantining if possible. 7. Keep a written log of temperature, pH, and test results. 8. Do partial water changes on a schedule, not only when something looks wrong. ## Common Mistakes - Adding fish to an uncycled tank. - Stocking too many fish at once. - Overfeeding. - Mixing goldfish with tropical species. - Buying fish before checking tank volume and temperature. - Skipping quarantine. - Using soap or household cleaners on aquarium equipment. - Ignoring ammonia and nitrite readings because the fish look fine. ## Troubleshooting Common Problems Cloudy water in a new tank is often a bacterial bloom during cycling. Test ammonia and nitrite and wait. Cloudy water in an established tank often follows overfeeding or a filter disturbance. Fish gasping at the surface suggests low oxygen or ammonia toxicity. Test the water and increase surface movement. Fish hiding, losing color, or refusing food suggests stress. Check temperature, pH, ammonia, and nitrite. Check for aggression from tank mates. Fin damage suggests fin nipping or bacterial infection. Review tank mates and water quality. ## Welfare and Safety Points - Provide a tank large enough for the adult size of every species. - Keep temperature and pH within the species range. - Test water regularly. - Quarantine new arrivals. - Wash your hands after contact with aquarium water. - Do not release aquarium fish or plants into the wild. Non-native fish introductions are driven largely by the aquarium trade, and established non-native fish species now number in the thousands worldwide [14]. Released fish can survive, spread, and carry parasites and disease [14]. ## Limitations and When to Contact a Veterinarian This guide covers general husbandry. Individual fish, tanks, and water sources vary, and a veterinarian with aquatic animal experience should evaluate any sick fish. Contact a veterinarian if you see any of the following: - Ammonia or nitrite remains detectable after repeated water changes. - Fish show ulcers, open wounds, or exophthalmia (bulging eyes). - Fish show lethargy, loss of appetite, or weight loss that does not improve. - Multiple fish die within a short period. - You see white spots, fuzzy growths, or red streaks on the body or fins. - A fish stops eating and hides for more than a few days. - You handle fish frequently and develop skin lesions on your hands or arms. A veterinarian can examine fish, review water quality records, and recommend treatment. The Merck Veterinary Manual and WAVMA both note that water quality and husbandry review are central to diagnosing aquatic animal disease. Bring your water test results and a description of your setup to the appointment. ## Frequently Asked Questions ### How long does it take to cycle a new aquarium? Cycling typically takes several weeks. It is complete when ammonia and nitrite read zero and nitrate is rising. Test daily and do not add fish until the cycle is stable. ### Can I add all my fish at once? No. Add fish in small groups spaced weeks apart so the filter bacteria can adjust to the increasing waste load. ### What ammonia level is safe for fish? Ammonia should read zero. Any detectable ammonia means the filter is not keeping up and you should act immediately with a water change and reduced feeding. ### Why can't I keep goldfish with tropical fish? Goldfish are coldwater fish with a temperature range of about 10 to 22 degrees C. Tropical species need warmer water. Mixing them stresses both. ### Do I need a heater? You need a heater for tropical species. Goldfish and some danios tolerate cooler water, but most community fish need a stable tropical temperature. ### How often should I change the water? A common schedule is a partial water change every one to two weeks. The exact frequency depends on tank volume, stocking, and test results. ### Are bettas community fish? A single male betta is usually kept alone. Some individuals tolerate peaceful tank mates in a larger tank, but temperament varies and fin-nipping species should be avoided. ### Can fish diseases spread to people? Yes. Nontuberculous mycobacteria, including Mycobacterium marinum, can infect people who handle fish and aquariums [9][8]. Wash your hands after contact with aquarium water and equipment. ## Related Articles - [Freshwater Fish Species Selection for Aquaculture: Climate, Market, and System Fit](/knowledge/animal-farming/aquaculture/freshwater-fish-species-selection-aquaculture-climate-market-system-fit) - [How to Set Up a Freshwater Aquarium for Beginners](/knowledge/veterinary-medicine/aquarium-fish-care/aquarium-setup-beginners) - [Coral Reef Fish: Species Selection and Compatibility for Marine Aquariums](/knowledge/veterinary-medicine/marine-aquatics/coral-reef-fish-species-selection-and-compatibility-for-marine-aquariums) - [Ich Treatment for Freshwater Fish](/knowledge/veterinary-medicine/aquarium-fish-care/ich-treatment-freshwater-fish) - [Freshwater Fish Hatchery Management](/knowledge/animal-farming/aquaculture/freshwater-fish-hatchery-management) - [Tetra Fish Care: Species Guide, Tank Setup, and Feeding](/knowledge/veterinary-medicine/aquarium-fish-care/tetra-fish-care-species-guide-tank-setup-and-feeding) - [Parrotfish: Species, Diet, and Reef Aquarium Needs](/knowledge/veterinary-medicine/aquarium-fish-care/parrotfish-species-diet-and-reef-aquarium-needs) - [Do Fish Sleep? Fish Rest and Activity Cycles](/knowledge/veterinary-medicine/behavior/do-fish-sleep-fish-rest-and-activity-cycles) - [Water Conditioner for Fish Tank: How and When to Use](/knowledge/veterinary-medicine/aquarium-fish-care/water-conditioner-for-fish-tank-how-and-when-to-use) ## Sources 1. [[Mistakes in general husbandry of ornamental fish].](https://pubmed.ncbi.nlm.nih.gov/11314467/) 2. [Husbandry and husbandry-related diseases of ornamental fish.](https://pubmed.ncbi.nlm.nih.gov/11228686/) 3. [Temporal microbiome dynamics and fish health-associated dysbiosis in freshwater aquarium systems: a case study from River Wonders Singapore.](https://pubmed.ncbi.nlm.nih.gov/42245514/) 4. [Water properties and quality of the largest rice production region in Japan and their influence on the reproduction of zebrafish.](https://pubmed.ncbi.nlm.nih.gov/38400980/) 5. [Effect of different fish feeds on water quality and growth of crucian carp (Carassius carassius) in the presence and absence of prometryn.](https://pubmed.ncbi.nlm.nih.gov/34678629/) 6. [Sustainable Ornamental Fish Aquaculture: The Implication of Microbial Feed Additives.](https://pubmed.ncbi.nlm.nih.gov/37238012/) 7. [Updates on Selected Emerging Infectious Diseases of Ornamental Fish.](https://pubmed.ncbi.nlm.nih.gov/32327045/) 8. [Isolation of potential zoonotic Mycobacterium spp. from diseased freshwater angelfish (Pterophyllum scalare) from an aquarium.](https://pubmed.ncbi.nlm.nih.gov/35674600/) 9. [Isolation and identification of non-tuberculous mycobacteria from aquarium fish in Ilam, Iran.](https://pubmed.ncbi.nlm.nih.gov/39253556/) 10. [Monogeneans on exotic Indian freshwater fish. 8. Co-translocation of Cichlidogyrus tilapiae (Monogenea, Dactylogyridae) with pindani Chindongo socolofi (Cichliformes, Cichlidae): first report of this parasite genus in India within aquarium trade facilities.](https://pubmed.ncbi.nlm.nih.gov/40729558/) 11. [Intraspecific variation in the functional responses of an invasive tropical freshwater fish under increasing temperature regimes.](https://pubmed.ncbi.nlm.nih.gov/39558026/) 12. [Embryonic development of the world's smallest puffer fish, Carinotetraodon travancoricus - a threatened freshwater fish of the Western Ghats Biodiversity Hotspot.](https://pubmed.ncbi.nlm.nih.gov/39344425/) 13. [Integrative Taxonomy Reveals Freshwater Shrimp Diversity (Decapoda: Atyidae: Neocaridina) from Kyushu and Southern Honshu of Japan, with a Discussion on Introduced Species.](https://pubmed.ncbi.nlm.nih.gov/39659496/) 14. [A Global Account of Established Non-Native Fish Species.](https://pubmed.ncbi.nlm.nih.gov/40855738/)