Part #1

Choosing fish can create a seemingly illicit desire, a lust for something you know you cannot or should not have. These are the fish that come with stipulations and plenty of baggage, the fish that look way cooler than they are to actually keep as a pet for most hobbyists.

#10 Predators or Aggressive Fish

Fish that eat other fish will often harass tankmates to no end or at least make them a quick meal should the opportunity arise. These are the most common "types" of marine predator fish you might see available in the aquarium trade and should only be left to those hobbyists willing to put forth the extra effort necessary to keep these aggressive fish thriving in an aquarium.

  • Sharks & Rays
  • Eels
  • Lionfish
  • Triggerfish
  • Grouper
  • Anglerfish/Frogfish

#9 Angelfish

With the exception of the smaller "dwarf" angels of the centropyge genus, angelfish are not a great choice for first-time saltwater tank owners. Many of them eat coral, will grow quite large, and can be somewhat sensitive. There are always exceptions to the rule but for the most part, stay away from Angelfish if you plan to keep corals in the aquarium. 

#8 Cowfish

While cowfish are super cute and have quite the personality, they can actually grow up to 20" long in the wild.  Ultimately, they will require a much larger aquarium of 250+ gallons to live a long healthy life in captivity.  

#7 Pufferfish

Pufferfish are quite an iconic reef animal but pose a problem in an aquarium if you plan to keep corals and invertebrates.  Most species of puffers will eat corals and possibly invertebrates like shrimp, mollusks, and snails. The maximum size really does vary depending on the exact species of puffer and many will grow large.  Large enough to require an aquarium of 100+ gallons.

#6 Tangs

While tangs are very popular fish to keep inside a saltwater aquarium, they do have some specific requirements that should be considered.  All tangs can grow large and are built to swim fast, so that means they need a large tank to feel comfortable. They are semi-aggressive, especially toward other tangs, and grow a sharp scalpel at the base of their tail that can dole out some harmful damage. 

Part #2

#5 Seahorses & Pipefish

These are quite tempting for many of us because they are just so darn unique. Many of you already know what a seahorse is and their slender relatives, the pipefish, also fall into this category. While we have learned quite a bit about the necessary husbandry for keeping seahorses and pipefish in captivity in the last 20 years, they still require some serious dedication and are not suitable for addition into a mixed reef aquarium.

First and foremost, these fish are very susceptible to stress and disease. They are not great swimmers and do not compete for food so a dedicated, species-specific type aquarium is always best. Many species also prefer cooler water temperatures around 70° F meaning you will probably need a chiller to keep them happy. Diseases are another threat that is always a threat to any aquarium but in this case, Seahorses are particularly susceptible because they can bring infections into the aquarium that are not as common in other types of fish. 

#4 Anthias

Anthias are a beautiful group of fish that are quite popular in reef aquaria but come with some baggage.  They are often expensive because they are highly susceptible to stress and generally do not acclimate very well into aquariums. Keeping a small group of Anthias can help to reduce some of that stress but acclimating them can be tough regardless. The next big hurdle is feeding them properly because anthias are high-energy fish that require multiple feedings throughout the day. You will need to feed them high-quality foods at least 4 to 5 times per day which can pose a problem for a typical tank owner.  Not only does this create additional waste and nutrients in the system, but you must also be available to supply that food every single day. 

#3 Dragonet

Dragonets are right up there with clownfish in terms of being iconic, they boast some absolutely stunning coloration and have quirky personalities that make us quickly fall in love. That said, they have very specialized diets with tiny mouths designed to hunt the smallest prey. They naturally hunt the benthic zone for small crustaceans like copepods and they do this all day long.  In an aquarium, it can be difficult to maintain a sufficient population of this live food source to sustain a dragonet, and manually feeding them 3 to 5 times per day becomes quite a chore.

It is possible to train these fish to accept frozen foods, but still must be done quite often. Furthermore, you need to be sure the food reaches the shy dragonet that hangs out on the bottom; in many cases, tankmates will gobble up the food before the dragonet can get to it. Using a long feeding tube that channels food to the bottom and training fish to feed in a particular area of the tank is quite often the best approach.

The good news is there are captive-bred dragonets available these days which are much better candidates for an aquarium. They will eat frozen foods and small pellets in many cases and are already adapted to life in an aquarium.  As long as you can commit to feeding them multiple times per day, the captive-bred specimens are always best. 

#2 Copperband Butterflyfish

Another showstopper, the Copperband Butterfly is a beautiful fish but is also a very particular eater. "Finicky" is the word most often used to describe them. Just like a dragonet, they have specialized diets and need to be fed often to stay healthy. So even if you are lucky enough to get a copperband that decides to eat in your tank, you must supply food up to 5 times per day or more. 

#1 Moorish Idol

You might recognize this fish from that popular animated movie about a juvenile clownfish that lands himself inside an aquarium alongside a host of charismatic tankmates. In the movie, Nemo's tankmate "Gill" is modeled after a Moorish Idol which is an unfortunate representation because these fish are at the very top of the list in terms of bad choices for an aquarium.

Moorish Idols have a less than 1% survival rate in captivity because they are extremely picky eaters. "Finicky" isn't even appropriate here because no matter what kind of food you serve up, the Moorish Idol will likely not eat. We really have yet to 100% figure out exactly why they are just not able to adapt to life in an aquarium, but it's obvious they most often fall victim to starvation. Really the only documented success has been in large, heavily stocked, and very well-established aquariums with sufficient natural foods the fish can find on its own.