12 Marine Fish That Should Never Be Kept in Home Aquariums

Written By

Mathew Abraham

Updated on

Mathew Abraham

Meet Mathew, Cat Dad and Animal Advocate! Mathew is the editor at PawDown, overseeing content strategy and quality. He's in charge of carefully curating the best pet stories, tips, and advice for you.

 A Lion Fish swimming freely
churananngm/PixaBay

Keeping a marine aquarium is a fascinating way to bring a slice of the ocean into your home, but not every fish belongs in your tank. Some species, due to their size, specialized diets, or aggressive behavior, are better left in their natural habitats. Attempting to house these challenging marine creatures can harm both the fish and your aquarium ecosystem. Let’s discover twelve marine fishes that should never be kept in home aquariums and learn why they’re best admired from afar.

Boxfish

Closeup of a Boxfish
Efraimstochter/PixaBay

Boxfish are unique creatures with a striking, box-like shape, but they come with significant challenges for aquarium enthusiasts. They are very sensitive to stress, and when stressed, they secrete a toxic mucus that can harm or even kill other fish in the tank. Their fragility also makes them prone to injury, especially in smaller or less stable tanks. Additionally, they require large spaces to thrive, and their specialized diet is hard to maintain in typical home setups. For these reasons, boxfish are not ideal for most home aquariums.

Harlequin Sweetlips

Harlequin Sweetlips
By Jens Petersen, CC BY 2.5/Wikimedia Commons

While the Harlequin Sweetlips is undeniably one of the most colorful and eye-catching fish, it’s not the easiest to keep. These fish require very large tanks with plenty of swimming space, and their carnivorous diet can be difficult to replicate in a home aquarium. They grow quickly and can become too large for smaller tanks. Their unique dietary and space needs make them more suitable for public aquariums or professional hobbyists with ample resources and experience.

Batfish

Batfishes
makabera/PixaBay

Batfish, known for their broad, unique fins, are a sight to behold, but their needs go beyond the capacity of most home aquariums. They need deep, expansive tanks to accommodate their large bodies and unique swimming patterns. These fish also grow quickly and can become too large for smaller setups. With their specific care requirements and tendencies to become territorial, batfish require expert care, and without the right environment, they can suffer. Hence, they’re not well-suited for average home aquariums.

Maroon Clownfish

A Maroon Clownfish
By Bernard DUPONT, CC BY-SA 2.0/Wikimedia Commons

While clownfish are beloved in the aquarium world, the Maroon Clownfish stands out for its aggressive tendencies, especially in smaller or overcrowded tanks. Their territorial nature makes them difficult to house with other fish, and they are known to chase away even larger species. If not given proper space or early socialization, they can become dominant bullies in a tank. This makes them less ideal for a community tank setup, especially for first-time aquarium owners.

Lionfish

A Lionfish
Russell_Yan/PixaBay

The Lionfish is famous for its striking appearance, but it’s also infamous for its venomous spines and its demanding care requirements. These fish are best kept by experienced aquarists who can provide them with ample space, a controlled diet, and an environment that mimics their natural habitat. While visually stunning, Lionfish can pose a serious risk to other tankmates and even the aquarium keeper if not handled properly. Due to these factors, they are not ideal for most home aquariums.

Moorish Idol

A Moorish Idol
Magda Ehlers/Pexels

The Moorish Idol, often mistaken for an easy-to-care-for species due to its beautiful and unique appearance, is actually one of the most challenging fish to care for. These fish require a very specific diet, including coral-based foods and a pristine tank environment, making them hard to keep in home aquariums. They are also highly sensitive to changes in water quality and can be susceptible to stress. Their specialized needs make them best suited for advanced aquarists with experience in maintaining delicate species.

Tangs

 A Blue Tang
kjschroeder/PixaBay

Tangs are popular for their vibrant colors and active swimming, but they require very large tanks to thrive. Some tang species can grow up to 12 inches or more and need plenty of open swimming space. Without this, they can become stressed and prone to health issues. Additionally, they have specific dietary needs, including a variety of algae and fresh greens, which can be difficult to provide consistently in a home aquarium. For these reasons, tangs are not a good fit for smaller or beginner aquariums.

Triggerfish

A Triggerfish
MatMoisich/PixaBay

Triggerfish are known for their aggressive and territorial nature, which makes them unsuitable for most home aquariums. They can become hostile towards other tankmates and are capable of damaging aquarium decorations and even the tank itself. Their behavior can be unpredictable, making them difficult to house in a peaceful community tank. Only experienced aquarists with knowledge of managing aggressive species should attempt to keep triggerfish in a home aquarium.

Napoleon Wrasse

A Napoleon Wrasse
Derek Keats/Pexels

The Napoleon Wrasse, one of the largest species of wrasse, requires a vast, spacious aquarium to accommodate its size and active swimming habits. These fish also have specialized dietary needs and require a diet rich in crustaceans and mollusks. Furthermore, they are prone to health issues in smaller, unstable environments, making them ill-suited for most home aquariums. Their large size and complex needs make them a better fit for experienced aquarists with access to large tanks.

Angelfish

A Blueface Angelfish
PixaBay

Angelfish are highly prized for their beauty and grace, but they are not always compatible with reef tanks. Some species can damage or consume delicate corals and invertebrates, making them a risk in a reef aquarium setup. Additionally, their size and territorial nature can cause issues when housed with smaller or more docile species. Angelfish require an experienced hand to maintain a balanced, peaceful tank environment, making them less suitable for novice aquarists.

Pufferfish

A Pufferfish
Alfie Sta/Pexels

Pufferfish are adorable but tricky. They can be quite territorial and aggressive, especially towards other fish in a confined space. Their teeth continue to grow throughout their lives, which requires special care and attention to their diet and tank setup. They can also be a hazard to tankmates, as they often bite or chase other fish, making them more suited to a species-only tank. Due to these behaviors and their large tank requirements, puffers are not ideal for most home aquariums.

Damselfish

A Damselfish
DavidClode/PixaBay

Damselfish, though hardy and colorful, can be extremely aggressive, especially towards other fish and even tankmates of the same species. They are known to establish strong territories and become possessive over their space, which can lead to constant bickering and harm in a shared tank. Once they settle in, they are difficult to remove, as they are highly territorial. Due to their aggression, they are best kept in species-only tanks or with other aggressive species.

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