5 Saltwater Fish for a 20 Gallon Tank: List for Beginners

beginner friendly list of saltwater fish for a 20 gallon tank

Saltwater aquariums can be a captivating and rewarding hobby for beginners. Choosing the right fish species for a 20-gallon tank is crucial. In this article, we have compiled a list of five saltwater fish that are perfect for beginners.

These fish, including the Yellow Watchman Goby, Clownfish, Pajama Cardinalfish, Firefish, and Royal Gramma, offer a diverse range of colors, patterns, and behaviors that will undoubtedly add life and vibrancy to your tank.

However, it is essential to consider the temperament, dietary needs, and compatibility of each species to ensure a harmonious and thriving aquarium environment.

So, let's dive in and explore these fascinating saltwater fish options together.

Key Takeaways

  • The Yellow Watchman Goby, Clownfish, Pajama Cardinalfish, Firefish, and Royal Gramma are all suitable options for a 20-gallon saltwater tank.
  • These fish have peaceful temperaments and are generally easy to care for, making them ideal for beginners.
  • It is important to consider the fish's temperament and diet when choosing which ones to include in the tank.
  • The visual appearance and unique characteristics of these fish, such as vibrant colors and distinct patterns, can add beauty and interest to the aquarium.

Yellow Watchman Goby

bright yellow fish with markings

The Yellow Watchman Goby, a peaceful and brightly colored fish, is an excellent choice for a 20-gallon saltwater tank. This species, known scientifically as Cryptocentrus cinctus, boasts a vibrant yellow body with striking blue and black markings.

As a peaceful fish, it can coexist with a variety of tankmates, making it a suitable choice for community tanks. The Yellow Watchman Goby is a bottom-dwelling fish that forms a symbiotic relationship with pistol shrimp. It feeds on small invertebrates and algae, making it an omnivorous species.

In the aquarium, it can be fed a variety of commercially available foods, including frozen brine shrimp, mysis shrimp, and pellets. The Yellow Watchman Goby's feeding habits are quite fascinating to observe, as it sifts through the sand searching for food.


Continuing our exploration of suitable saltwater fish for a 20-gallon tank, let us now turn our attention to the captivating and popular species known as Clownfish.

Clownfish, also known as anemonefish, are renowned for their vibrant orange bodies adorned with distinctive white stripes. These small fish, with a maximum size of four inches (10 cm), are a delightful addition to any tank.

They have a peaceful temperament and are best kept in small groups or with other Clownfish species. Clownfish have a unique symbiotic relationship with anemones, often seeking refuge among their tentacles.

When choosing suitable tankmates for Clownfish, it is important to consider their compatibility with the anemone. Some suitable options include gobies, dottybacks, and damselfish.

Providing a suitable environment with proper tankmates will ensure the Clownfish thrives and adds a touch of brilliance to your saltwater tank.

Pajama Cardinalfish

colorful tropical fish species

Pajama Cardinalfish, a fascinating and visually striking species, is an excellent choice for a 20-gallon saltwater tank. Here are some key characteristics of this remarkable fish:

  1. Breeding Behavior: Pajama Cardinalfish can display aggression during breeding. It is essential to provide ample hiding places to mitigate any potential conflicts between mating pairs.
  2. Nocturnal Habits: These fish are primarily active during nighttime. They exhibit an intriguing behavior of wiggly swimming, adding a unique touch to the tank's ambiance.
  3. Peaceful Temperament: Pajama Cardinalfish generally have a peaceful demeanor. However, it is essential to monitor their interactions with tank mates to ensure compatibility.
  4. Colorful and Patterned: Pajama Cardinalfish showcase a stunning array of colors and patterns. Their vibrant appearance brings a captivating visual element to any aquarium.

With their captivating breeding behavior and nocturnal habits, Pajama Cardinalfish are an exciting addition to a 20-gallon saltwater tank. Their peaceful temperament and visually striking appearance make them an ideal choice for beginners seeking innovation and beauty in their aquatic setup.


Firefish, also known as Nemateleotris magnifica, is a vibrant and captivating species that can make a stunning addition to a 20-gallon saltwater tank. This small fish, reaching around three inches (7.62 cm) in size, has vibrant colors and an elongated body.

Firefish are peaceful in temperament but can be shy and hide in rockwork. When it comes to feeding habits, Firefish are carnivores and prefer small live foods. They have a keen appetite for small invertebrates and zooplankton.

As for tank mates, Firefish are generally compatible with other peaceful fish that won't compete for food or harass them. Some suitable options include Clownfish, Yellow Watchman Goby, and Pajama Cardinalfish. However, it is always essential to research and consider the specific needs and compatibility of potential tank mates before introducing them to the aquarium.

Royal Gramma

vibrantly colored reef fish

The Royal Gramma, scientifically known as Gramma loreto, is a visually striking saltwater fish that can be a captivating addition to a 20-gallon tank. Here are some key points about the Royal Gramma:

  1. Unique colors and temperament: The Royal Gramma features a purple front body and a yellow back, making it a visually appealing fish in any aquarium. It has a peaceful temperament overall, but can display territorial aggression towards similar-looking fish.
  2. Compatibility with other species: When introducing a Royal Gramma to a tank with other fish, it is important to consider their compatibility. Avoid adding fish that have similar coloration or body shape, as the Royal Gramma may exhibit territorial behavior towards them.
  3. Proper introduction: To introduce a Royal Gramma to a tank with other fish, it is recommended to acclimate them slowly. Gradually introduce the Royal Gramma to the tank, allowing it to explore its new surroundings and establish its territory.
  4. Monitoring behavior: Keep a close eye on the Royal Gramma's behavior after introducing it to the tank. If any signs of aggression or territorial behavior are observed, it may be necessary to separate the fish or rearrange the tank layout to provide more hiding spots and territories.

Frequently Asked Questions

Can the Yellow Watchman Goby and Clownfish Be Kept Together in the Same Tank?

The Yellow Watchman Goby and Clownfish can be kept together in the same tank. It is important to provide a suitable environment with plenty of hiding spots. Pajama Cardinalfish should be fed a diet consisting of meaty foods for optimal health.

How Often Should I Feed the Pajama Cardinalfish and What Type of Food Is Best for Them?

The feeding frequency for pajama cardinalfish should be 2-3 times a day, with small meaty foods like brine shrimp or mysis shrimp. Ideal tank mates for pajama cardinalfish include peaceful and non-aggressive species that won't compete for food or territory.

Are Firefish and Royal Gramma Compatible With Other Fish Species in a 20-Gallon Tank?

Firefish and Royal Gramma can be compatible with other fish species in a 20-gallon tank, but careful consideration is needed. Ideal tankmates for Firefish include peaceful and non-aggressive species, while Royal Gramma may exhibit territorial behavior towards similar-looking fish.

Do Any of These Fish Require a Specific Water Temperature or Ph Level?

The fish listed, such as the Clownfish, Yellow Watchman Goby, Pajama Cardinalfish, Firefish, and Royal Gramma, do not have specific water temperature or pH level requirements. However, it is important to maintain stable and appropriate conditions for the overall health of the fish.

Are There Any Specific Tank Decorations or Hiding Spots That These Fish Prefer?

Tank decorations for saltwater fish are important for creating a visually appealing and stimulating environment. Hiding spots, such as caves or rockwork, are crucial for providing security and reducing stress for these fish.


In conclusion, selecting the right saltwater fish species for a 20-gallon tank is crucial for beginners. Considering factors such as temperament, diet, and compatibility with other species is essential for creating a visually appealing and harmonious aquarium.

The Yellow Watchman Goby, Clownfish, Pajama Cardinalfish, Firefish, and Royal Gramma are popular choices that offer vibrant colors and unique characteristics.

With proper research and understanding of these fish species, beginners can successfully embark on their saltwater tank journey.