Trust me, one of the primary ways to pick good fish is knowing which fish NOT to pick. I recently saw this type of list on another site, and found it so beneficial I thought I would start one here. The list includes fish/invert species NOT for the beginner; in many cases not for any average home aquarium, due to various demands which must be met in order to keep them healthy and happy. If you have had success with one, by all means share your knowledge with others, but understand; the purpose is not to limit your choices as a marine aquarist, only rather to expand your success, and to observe good stewardship of the natural reefs by leaving some animals where they belong. By learning which species to avoid, hobbyists will reduce demand for them and also reduce the chances of outright bans on all wild imported species. Surely I have forgotten something here; I will edit/update this from time to time. That said, here goes...
Marine Species NOT for the Beginner:
1. Sharks and Rays (Nurse, Bluespot Ray, etc.)
Although usually hardy, most of these juveniles soon prove to be mega-polluting beasts that easily overwhelm all but the largest of home systems sporting heavy skimmers and high turnover rates. Possible exceptions: Family Hemiscyllidae; the Bamboo/Epaulettes, but even then requiring massive systems and heavy filtration/organic export for long term success.
2. Large Moray Eels (Gymnothorax spp.)
Often sold by the LFS as adorable juveniles, some species easily attain 2 meters or more and most are expert fish killers, sporting flexible jaws capable of swallowing fish far larger than the width of their heads. You have been warned; if hungry, even the popular snowflake at 45 cm can gulp a good sized fish in three blinks of your eye. There are several very good exceptions (i.e. Gymnomuranea zebra) which are more peaceful and remain small, but identifying the various "Misc. Green, Brown Atlantic Eels" staring at you from the bottom row in the LFS is your responsibility. KNOW what you are buying/creating demand for. If in doubt, read. If still in doubt, don't. Morays grow quickly my friend, and the fish you purchased at 25 cm will eventually double/triple it's size, taxing your system far more than you think.
3. Ribbon Eels (Blue, Black Rhinomuraena quaesita)
Truly gorgeous, always available and... don't buy one. With a 95 plus percent mortality rate you will support demand for many thousands which are stripped from the sea only to die in a matter of weeks.
4. Small Groups of Aggressive Damsels
Surprised? Although often used for cycling/toxin testing, an identical group of these toughies usually ends up being the first headache for the beginner; one will dominate the others to the point of death or stress related disease/pathogen infestation, which leads to medications, which leads to...you get the idea. Want a damsel? Get one (1).
Although a few are considered hardy, beginners will do best to leave all of these in the LFS. Many species may nibble/eat prepared foods but thrive only on coral/inverts, all are highly susceptible to Cryptocaryon, Amyloodinium, etc.
6. Cleaner Wrasses (Labroides spp.)
Removing them from Hawaiian waters is illegal since 1996 for good reason; most survive only a few weeks in captivity. Why do they continue to be sold? Because aquarists continue to purchase them. I have known some who have had these adapt and thrive, but thousands have died for every one that survived. Symbiotic friends of the reefs, cleaner wrasses provide a specialized purpose in a limited service area; I have personally watched mantas, sharks and others literally line up/circle the wagons and wait for the service this little fish provides, and they return to the same spot year after year. Please don't spoil the fun.
7. Parrotfishes (Family Scaridae)
Fantastic colors, dismal survival record; see those specialized teeth? Scarids are best left on the reefs they love to chomp.
8. Mandarin Dragonets (Synchiropus picturatus, S. splendidus)
Sometimes called Psychedelics, gobies, scooters etc, they are not gobies, but in fact a beautiful and fascinating species that most often starve to death due to slow behavior and demand for continuous live foods. This is not an impossible species (some have good success providing the right care) just specialized beyond the realm of most hobbyists. Established pod colony or not, you would likely never purchase another one if you could see the millions which have died while in better care than you can provide. I have seen these wild in the lagoons in Micronesia; they are stunning in nature and deserve better than to slowly starve in our glass box...not for beginners or most aquarists for that matter.
9. Regal Angelfish (Pygoplites diacanthus)
Maybe the biologist who named Diacanthus was trying to tell us something (Diacanthus will DIE). Fenner writes; "one of the worst survival records of all marine angels." During my dives in the pacific, these were the most plentiful of all angels seen; perhaps this explains why they are still collected/imported. Beauty beyond compare, but not for your tank.
10. Rock Beauty Angelfish (Holacanthus tricolor)
Sadly, over 50 percent die within the first 30 days. Like diacanthus above, even apparent robust specimens which readily feed on prepared foods often suddenly die. Not impossible to keep, but not for beginners...as a diver and lover of Florida fauna, I implore you; leave them on the reef. There are others in the Holocanthus group which will bring you far more joy.
11. Other Angelfish and Tangs
Although some species are very hardy and adapt well under good care, in my opinion this group as a whole should be reserved for established tanks with at least 6-12 months growth of green micro algae or, even better, some live rock and the experience to go with it. Some species are highly susceptible to head and lateral line erosion (HLLE) without proper diet and proper organic export equipment/protocol.
12. Longnose Filefish (Oxymonacanthus longirostris)
Often called Orange Spot Filefish, obligate coral polyp feeder. Sadly, still frequently offered in LFS, should not be purchased or sold; most aquarists do not offer live coral buffets.
13. Seahorses and Pipefishes
Like the dragonets, these are not impossible...only greatly misunderstood and inappropriately sold to unwary beginners, who sadly drop them in a community tank with fast-moving damsels and tangs and offer them flake food. Special animals often require special care and suitable environments; please research your charges.
14. Boxfish, Cowfish, Long Horns (Ostraciidae, Lactoria)
Fascinating, beautiful yet deadly, some can easily wipe out your entire fish population when they suddenly release killer toxins into the water column.
15. Frogfish, Groupers and other Predators
Usually hardy but, surprise! Your clownfish just disappeared. Plan accordingly. As a beginner, it's imperative to research your choices BEFORE you purchase.
16. Moorish Idol (Zanclus canescens)
Should not be purchased or sold due to its terrible mortality rate in captive systems. Highly susceptible to shipping damage/stress (including copper treatments). Notice I did not say it is impossible, it CAN be kept with proper selection/space/care, but consider how many will die to bring you the rare one that adapts and most will agree with me it should be avoided unless they are inconsiderate of the world's reefs.
17. Pinnate Batfish (Platax Pinnatus)
Sadly, another hard-to-resist beauty, best left in the ocean. With an almost 100 percent mortality rate, it rarely feeds/thrives in captivity. Its two cousins on the other hand, the Orbic (P. orbicularis) and Tiara Bats (P. tiara) are very hardy/wonderful pets, but quickly reach their true spadefish proportions of 40x40 cm or more, and they will heavily tax a small system as they do it.
Although a few species are maintainable with correct lighting/water quality, millions have wasted away in aquaria; most live only a few weeks or months under a beginner's care; even advanced hobbyists are now backing off many species, due to increased awareness of the symbiotic/longevity/sparse population of wild specimens and the dismal mortality of captives. Many of these are still gladly sold to unsuspecting/ignorant hobbyists with no clue about lighting/water movement/feeding requirements, etc. Which leads us to...
19. Filter Feeding Invertebrates & Corals
Sponges, sea fans, sea pens, gorgonians, other Cnidaria, soft, stony etc., all specialty feeders requiring far greater care/water quality/hardware/experience than the beginner can afford. Although certainly maintainable in a reef system, most serve no more purpose in the beginner's marine tank than a starved, temporary splash of color, reducing our hobby to the level of the dried animal curios in the trinket trade. Many corals require more dollars in just lighting than most beginners have invested in their entire system! Beautiful and fascinating, these are for your NEXT tank, after a year or so with marine fish experience. Indeed, many aquarists are satisfied to avoid them completely, with so many hardy fish species and better quality artificial corals to choose from. Even the base line encrusting inverts on live rock can pose a problem for the novice who has a parasitic infestation with no quarantine tank or experience with medications. For the beginner who must have these, I would suggest trying it "sans fish" for a while to greatly reduce the associated complications that can easily arise.
Probably the ideal beginner's invertebrate, some can still pose a problem for beginners, so choose with caution. The mantis shrimp, while hardy enough, is a deadly assassin (read: terminator), requiring a tank of its own. Crabs with large claws have them for a reason. Even the largest of shrimps can pose a problem for a small, weak or struggling fish. Like other inverts, all are sensitive/killed by even a trace amount of metal in the water, including copper cures required to kill those pesty pathogens like cryptocaryon (marine ich), so plan accordingly.
21. Blue Starfish (Linckia sp.)
Over 90 percent mortality in captive systems, usually due to shipping damage. While diving in Palau, some of my most vivid memories were formed from these dazzling echidnoderms in shallow water, sunlight dappling on the brilliant blue...makes you appreciate these in a different way, and encourage beginners to avoid them.
22. Sea Apple, Cucumbers (Pseudocolochirus tricolor, P. violaceus)
Brilliant coloration makes them sad targets for beginners; they can and do poison entire systems overnight when subjected to stress, including getting sucked into an overflow or powerhead intake.
The king of the invertebrate world, highly intelligent/fascinating but, sadly, very problematic. Beginners who are not prepared will find them far too delicate, aggressive and short lived, requiring a specimen tank (isolation) and an absolutely escape-proof (sealed) lid. Even in the wild, octopus have a short life span...usually 12-18 months. Both males and females die shortly after breeding (females last long enough to tend the eggs).
24. Other Molluscs
Nudibranchs, clams, scallops, oysters, etc., more specialty feeders for the list. I remember at 16 years of age, seeing my first gorgeous nudibranch in the LFS...colors beyond compare. How could a beginner resist such a jewel? How many have purhcased them like me, only to see them slowly starve due to lack of knowledge and a proper environment?
With many hardy species available, like certain wrasses, clowns, chromis, hawkfishes, some of the dottybacks, smaller triggers, certain tangs, gobies, even smaller groupers and predators, etc., the beginner will have no problem stocking the successful marine aquarium while avoiding the ones on this list. Although not all of that last group I just mentioned are necessarily compatible in the same tank, and some will outgrow the small display and eventually need to be moved, they will individually provide hours of fascination and years of success when given proper care and carefully chosen tankmates. Of course, beginners would do well to start with tank raised animals for a while, before risking wild caught options; although sad to lose, captive-bred fish losses will not negatively impact our living reefs.
Just because they are silent, small and submerged, delicate marine fish and inverts are somehow removed from the mainstream of pet life...how long would an industry last if it continued to sell puppies which starved to death because they required live food that could only be obtained in a remote location of the world? As thousands, even millions of puppies died of starvation, there would be a public outcry so loud it would force a solution...even if it meant the total ban of puppy sales. Although abstract, you see my point; if we do not increase knowledge in our hobby, others will increase restrictions on it. As more and more advances are made and research is documented, perhaps some of the species above will be easily maintained by beginners; it is my sincere hope that until such a time, we all share this information for the benefit of the hobby and the fascinating animals of the sea.