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10 Hardest Marine Fish to Care For

Melissa cares for a variety of exotic animals and has completed a certificate in veterinary assisting and a bachelor's degree in biology.

Moorish idol

Moorish idol

Are you a first-time marine aquarium owner who finds the wealth of information needed to prevail in this wonderful hobby intimidating? The care of saltwater animals might be more involved than that of freshwater due to the requirement of prepping simulated ocean water (or lugging actual filtered seawater into your home) alone, but most would agree, upon laying eyes on the dazzling colors and unique creatures that can be added, that it is well worth it.

However, not every ocean inhabitant is suitable for the home aquarium. Some fish species, especially when wild-caught, require a large amount of space for their size, feed only on live foods, and are prone to stress that can be instantly lethal. Some are so challenging they are often recommended to be maintained only by professional zoos and aquariums. If you aren't an "advanced" aquarist, you might want to stay away from these species.

1. Moorish Idol

Sadly, the popular movie Finding Nemo may have given the impression that the Moorish idol is a relatively easy and common fish to keep and can do just fine in what looks like a 50-gallon aquarium with plastic plants normally used in freshwater tanks. They closely resemble the more common and much easier to care for black and white butterflyfish, but the Moorish idol is a stunning animal that is extremely hard to maintain because of their significant propensity to quit eating.

This is a common problem in fish that are for "advanced keepers." Moorish idols require a specialized diet that includes sponges (can be found in some commercial preparations) as well as nori, various frozen foods, and live foods like brine shrimp. However, the right foods only go as far as the fish is willing to eat.

The advanced aquarist first needs to be able to identify healthy fish without signs of illness and then treat them for parasites while keeping them in a low-stress environment. Moorish idols also require a lot of swimming space—around five feet of horizontal length minimum—so they are a fish that requires a lot of accommodations!


2. Pipefish

These quirky-looking fish are closely related to seahorses and are sometimes kept with them because of their similar feeding habits. While some seahorse species are now available captive-bred, pipefish are wild-caught and require an experienced fish keeper to encourage this shy animal to eat. For this reason, they are considered to be high-maintenance, although their care will improve once they adapt to aquarium life. A good "beginner" species of pipefish is the Dragonfaced Pipefish.

Pipefish are not strong swimmers and require very little current, in addition to places to hide, and no tank mates that are aggressive feeders. They are often extremely picky, preferring specific live foods such as copepods, brine shrimp, and zooplankton and they should be introduced to a well-established tank with live rock that is teeming with life.


3. Ribbon Eel

Amazingly beautiful as they are adorable, the ribbon eel has easy appeal, but you won't often see people keeping this species for a reason. Ribbon eels are absolutely notorious in their pickiness and often starve to death in captivity. This species, except in the rare circumstances that they've been successfully trained to accept non-live food, often require live fish to get started. They should also be maintained in a well-established tank with plenty of hiding places. Ribbon eel keepers should be highly experienced with fish that are finicky eaters.


4. Achilles Tang

Tangs are popular fish and many of them require general maintenance. The Achilles tang, however, is more demanding, and its "Achilles heel" is that it is prone to stress and a resulting disease called ich and head-and-lateral-line erosion. Like the other fish on this list, they are reluctant to eat in aquariums and have a hard time adapting to life in a tank as they are all wild-caught.

Because this species inhabits an area of the coral reef called the "surge zone", where strong currents create air bubbles with every break, they benefit from a turbulent water flow that helps oxygenate the water. They also need a lot of swimming space to feel comfortable. Once appropriately housed with the right tank mates, space, and a source of food (they are primarily herbivores that eat algae) that it will accept, this species could potentially fare well in the home aquarium.

5. Flashlight Fish

I was amazed when I first saw this fish available for purchase by private owners. I didn't know it was possible to own a fish from depths so deep, they have evolved bodily bioluminescence, just like the extraordinary deep-sea angler fish and viperfish that fascinated us as children. But not so fast, they are sadly ridiculously hard to care for.

Flashlight fish possess a photophore, or lighted organ, under each eye that they may use for communication, prey detection, to confuse predators, and to lure their prey. It has been recommended to acquire flashlight fish that have been recently collected. These fish, when they first arrive, should be acclimated in darkness, and they should have cooler water temperatures (72 to 74 degrees F) to maintain the symbiotic bacteria that fuels their lights.

The photophores can also be permanently damaged if the keeper is unsuccessful at getting the flashlight fish to eat live foods such as Mysis shrimp and mollies. As the fish has already not eaten during its transport, this is critical. If you are successful in keeping the fish stress-free and eating, you'll catch a glimpse of its incredible lights only at night (they will hide during the day) but flashlight fish caretakers believe they are worth the trouble.


6. Stingrays

As an instantly recognizable fish, stingrays are arresting and incredibly cool to have. Blue spot stingrays are one of the more popular species and are beautiful, therefore, of course, they are not are easy keepers. Like so many other fish that are desirable for their beauty and intrigue, they are reluctant to start eating when introduced to aquariums, and even people who've had success with getting them to eat and apparently thrive report that they stop eating "for no reason" and slowly starve.

They require very large aquariums with flat areas of sand and like other difficult to keep fish, should be offered live food as well as meaty pieces of shrimp, scallops, and small crustaceans. If you still really want a stingray, freshwater stingrays are reportedly easier to keep and breed well in captivity.

7. Regal Angelfish

As is in its name, this fish is an obvious beauty with its neon blue stripes and electrifying yellow hues. Therefore, it's no surprise that this species is shy and sensitive, with a preference for live sponges that should be provided with ample live rock in a very large and mature aquarium. Hopefully, once they get started eating algae sheets, clams, Mysis shrimp, and mussels, they can adapt to the home aquarium and live well.


8. Garden Eels

The good news is that these magnificent creatures actually eat in captivity. But here's the bad news: Good luck arranging tank equipment to develop a current so that they can actually eat it. Garden eels are some of the only "reef-safe" eels because they don't eat fish and invertebrates, are extremely sedentary, and won't bother corals. They are colonial eels that sway with the currents in the wild to feed on copepods, fish eggs, prawn eggs, and other small zooplankton.

In the home aquarium, garden eels require a very deep sand bed of at least 8 inches so they can create their burrows. You will also need to rig your aquarium flow so that food is delivered to the eels on a constant basis. With these frequent feeds of meaty foods, you'll also need to maintain excellent filtration to keep your water parameters at the right levels. Once established, garden eels can adapt to aquarium living and readily accept different foods, it's just too bad that the setup they require is nightmarish to deal with.


9. Shrimpfish

Also known as razorfish, shrimpfish are Syngnathiformes along with seahorses and pipefish. Like those fish, shrimpfish are slow eaters, that should be fed small, free-floating crustaceans, baby fish, mosquito larvae, and eventually frozen meaty foods once accepted that must be fed continuously without fouling their water quality. This can be accomplished by a committed aquarist feeding manually or a drip feeder programmed to deliver the feedings, along with some aggressive filtration. This can especially be an issue for people who go on vacations. A mature tank filled with live rock will aid in supplemental feeds for this unique, vertical swimming species.


10. Sharks

Jaws in the home aquarium? Not quite. The most popular shark species that are kept by home aquarists are smaller, bottom-dwelling sharks that resemble catfish. These include "cat sharks", bamboo sharks, short tail nurse sharks, and carpet sharks, and they generally have an adult size around 3 feet long in captivity. Popular choices include the epaulette shark, coral catshark, and speckled carpet shark.

Some very adventurous keepers might attempt very large species like larger nurse sharks, Wobbegongs, Port Jackson sharks, and even blacktip reef sharks, the latter which resembles a layperson's idea of a shark, but these species can easily outgrow even huge home aquariums. The larger shark species are considered "advanced" by their size alone, and they will require some advanced tank maintenance to keep such a large aquarium running (some keepers use enormous tubs to accommodate the largest sharks). The tank, in addition to being long, should also be wide enough to accommodate their mode of swimming. They also require frequent feedings of fresh, meaty foods when active.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Melissa A Smith