This is not my own list but just a guideline that I found on the net.
Good Beginner Fish
Angelfish
Coral Beauty Angelfish [Centropyge bispinosus] (probably the hardiest of all the dwarf angels but they can nibble on corals and clams)
Half Black Angelfish [Centropyge vroliki] (see Coral Beauty)
Pygmy/Cherub Angelfish [Centropyge argi] (see Coral Beauty but
consider that they are often meaner, the same goes for most other similar shaped Pygmy Angels)
*Angels can be a little prone to disease but are otherwise pretty hardy if given a good diet
Blennies
Bicolor Blenny [Ecsenius bicolor] (great little fish with lots of personality that can help with algae problems, only problem is they're know to sometimes take a liking to munching on corals and clams, procede with caution)
Tail Spot Blenny [Ecsenius stigmatura] (in most cases probably a better choice all around than the Bicolor Blenny, though they aren't quite as boisterous which can be a good or bad thing depending on your perspective, less commonly available)
Linear Blenny [Ecsenius lineatus] (see above)
Cardinalfish
Pajama/Spotted/Orange Lined Cadinalfish [Sphaeramia nematoptera most common] (peaceful, disease resistant, and hardy, Cardinalfish in general are good choices just be a little more leary of Bangaii Cardinals that are new to captivity and red nocturnal varieties)
Clownfish/Chromis/Damselfish
Tank Raised Clownfish [Amphiprion sp.] (percula and ocellaris stay smaller and are les aggressive, Skunk clowns can be more peaceful as well, Maroon clowns tend to be the meanest, and all the others usually fall somewhere in between)
Green Chromis [Chromis viridis] (very peaceful and will school, but it is becoming pretty clear that in smaller schools they will sometimes pick the weakest member of the group off one by one, perhaps larger schools of 6+ in larger aquariums would eliminate that possibility)
Yellowtail Damselfish [Chrysiptera parasema] (can be aggressive but not quite as mean as most other Damselfish, add them as one of your last fish)
*In general Damsels are very hardy but the majority of them get far too mean to be considered good inhabitants in most tanks
Gobies/Dartfish
Firefish [Nemateleotris decora/magnifica] (great reef fish, just be weary when keeping in groups as they can turn on one another, singles or mated pairs are you best bet, they have been known to jump but it's not a big problem)
Scissortail Goby/Dartfish [Ptereleotris evides] (almost identical to Firefish in care)
Yellow Watchman Goby [Cryptocentrus cinctus] (tough as nails, very comical, peaceful, but a little shy and require some sand to burrow in, make sure your rocks are stacked securely)
Pink Spotted Watchman [Cryptocentrus leptocephalus] (see Yellow Watchman)
Gold/Blue Neon Goby (peaceful and often avilable as tank raised, keep as mated pairs or singles unless you have a large aquarium)
Hector's Goby [Amblyeleotris hectori] (similar to Rainford's but seem to accept prepared foods more often, just make sure they're eating before purchase and keep them with more peaceful fish, they will also sift food from your sandbed and tidy it up so it's best to have a sandbed)
Pseudochromis/Basslets
Royal Gramma [Gramma loreto] (kept singly they are peaceful, but the biggest drawback is their shyness, provide plenty of overhangs, they may also do best in aquariums with a little less intense lighting)
Pseudochromis [springeri/fridmani/flavivertex/aldabraensis] (very hardy and disease resistant, however can get quite mean, they are fairly well behaved as long as they're the last fish added and you avoid similar size/shape fish, frequently available as tank raised)
Pseudochromis sankeyi (same as above except far more peaceful)
Tangs/Foxfaces
Zebrasoma sp. [Yellow, Purple, Scopas, Sailfin] (these are the hardiest of the tangs in my opinion, still not great beginner fish, but if you must have a Tang these are the best choices, be sure to provide plenty of green stuff for them to graze on and feed them often to stay plump, as a basic guideline it's best to keep these in 75 gal. or larger aquariums with the consideration that they might outgrow those down the road, they can get mean so make them later additions)
Foxfaces/Rabbitfish [Siganus vulpinus is the most common] (these fish can get quite large so be sure to research if your tank is large enough to house one, they're great at algae control, more disease resistant than their cousins the Tang, and generally more peaceful, also keep in mind their dorsal spines are mildly venomous)
Wrasses
Six/Four Line Wrasse (can get mean much like the Pseudochromis, but also requires a sandbed to borrow in, sometimes these will consume undesirable flatworms)
Fish To Be Avoided::
Fish that have incredibly low survivability in aquaria or are totally unsuitable for most home aquaria.
Moorish Idol (Zanclus cornutus): A few success stories, but miniscule amounts live long, difficult feeder, mystery deaths, and even when accepting prepared foods often slowly starve
Rock Beauty Angelfish (Holacanthus tricolor): Nearly impossible to meet the dietary needs in home aquaria
Multi-Barred Angelfish (Centropyge multifasciatus): They don't adapt to aquarium life well, rarely eat, and are very secretive, though not fatal, they also seem particularly prone to Lymphocystis
Venustus Angelfish (Centropyge venustus): See the Multi-Barred Angelfish above
Butterflyfishes (Chaetodon spp.): Many problem feeders in the group and most are corallivore that are almost guaranteed to starve to death in aquaria, do a lot of research before purchasing any butterflyfish
Clown Tang (Acanthurus lineatus): VERY ich prone and a finicky eater, horrible survival rates, when they do live they are terribly aggressive and often take over a tank
Twinspot Goby (Signogobius ocellatus): Terrible survival rates in captivity, rarely accept prepared foods or survive long even when they do
Clown Sweetlips (Plectorhinchus chaetodonoides): Difficult feeders and rarely adapt to aquarium life, should you manage to get one to live they get quite large
Oriental Sweetlips (Plectorhinchus orientalis): See Clown Sweetlips, in general this can be repeated for most species in the genus Diagramma and Plectorhinchus
Pinnatus Batfish (Platax pinnatus): Gorgeous fish when young, very very few success stories, diet, disease, and stress from aquarium life are big issues
Tiger Tiera Batfish (Platax batavianus): See Pinnatus Batfish above
Orange Spotted Filefish (Oxymonacanthus longirostris): Specialized coral polyp feeder and almost never accepts prepared foods
Ribbon Eel (Rhinomuraena quaesita): Rarely eat in captivity and are excellent escape artists
Snake Eels & Garden Eels (various genera): Difficult feeders that require specialty tanks
Tamarin Wrasses (Anampses spp.): Very poor shippers and need tanks with their special needs in mind, even then they often starve to death, their best chance is often a large established reef aquarium with large amounts of live rock, peaceful fish, and something to prevent their escape from jumping
Leopard Wrasses (Macropharyngodon spp.): See Tamarin Wrasses above, but there are more success stories, both these and the Anampses are boderline being in this area of the list and the next section
Pencil Wrasses (Pseodojuloides spp.): Very sensitive, they almost always die in transit so you don't see them very often if ever in the trade
Parrotfishes (Family Scaridae): Very specialized feeders on mostly dead (some live) coral skeletons and the algae and organisms associated with them, they adapt poorly to aquarium life in almost all regards
Tilefishes (Family Malacanthidae): VERY timid and must be kept in a covered aquarium with lots of space and docile tankmates, in general they just don't adapt to aquarium life
Cartilaginous Fishes (Sharks, Rays, Skates): With very few exceptions, unless you own a massive aquarium that is several hundred gallons stay away
Grunts (Family Haemulidae): Rarely adapt well to aquarium life and should probably only be considered in a large species tank
Jacks (Family Carangidae): See Grunts above
Drums (Family Sciaenidae): Poor shippers, being very shy and fragile they rarely live long after being collected
Trumpetfish (Aulostomus spp.): Too large and too specialized for 99.9% of the aquarists out there, also poor shippers
Remoras (Family Echeneidae): Unless you have a large Shark or Whale in your backyard oceanarium it's probably best to stay away
Leopard Blenny (Exallias brevis): Specialized coral feeders that rarely live long in captivity
Chambered Nautilus (Nautilus pompilius): Though technically not a fish, there are a plethora of reasons to leave them in the ocean, simply not suited for typical aquarium life
Fish Best Left For Experienced Or Knowledgable Hobbyists:
Finicky nature, parasite prone, specialty feeders, require specialty tanks, or threatened species
Anthias (family Anthiinae): Require a good amount of swimming room, peaceful tankmates, and frequent feedings, often unhealthy and starving by the time they make it to dealers tanks, some almost require special tanks with their needs in mind and others often refuse to eat and starve quickly in aquaria, do plenty of research before purchasing any Anthias
Teira Batfish (Platax teira): Can be very hardy once acclimated but there can be problems feeding, they stress easily, are disease prone, and will also outgrow most aquaria
Majestic, Blueface(Pomacanthus Euxiphipops spp.): Can be hardy once acclimated to aquarium life and eating well, that's often easier said than done though, larger juvenilles are often the best way to go with these fish as tiny specimens are quite fragile and large specimens have the hardest time adapting to aquarium life, this is true for many large angelfish
Regal Angelfish (Pygoplites diacanthus): A problem feeder, specimens from the Philippines and Indonesia rarely make it long in captivity, Red Sea Specimens tend to be hardier and more willing to accept prepared foods partially due to collection and holding techniques, the more recent trend to keep this fish in reef aquariums helps with survivability
Bandit Angelfish (Holacanthus arcuatus AKA Apolemichthys arcuatus): Very similar to the Rock Beauty above but with a much smaller sample, at their price you'll probably do your research, if you don't you'll most likely learn an expensive lesson
Bicolor Angelfish (Centropyge bicolor): Concerns with drugs used in collection and frequent unwillingness to accept prepared foods, also one of the more common coral nippers
Heralds's or Yellow Angelfish (Centropyge heraldi): Often collected with the use of drugs, be very wary of newly collected specimens, this can be true with many Centropyge but seems especially problematic here
Lemonpeel Angelfish (Centropyge flavissima): See Herald's angelfish above
Potter's Angelfish (Centropyge potteri): Mixed results with this one with a lot of mystery deaths early in captivity, if they've been eating and active at the fish store for a few weeks they usually end up being quite hardy
Golden Pygmy Angelfish (Centropyge aurantius): Adapts poorly to aquarium life, only attempt if you find a healthy specimen and have a larger reef aquarium containing less boisterous fish with a lot of rock to graze on
Swallowtail Angelfishes (Genicanthus spp.): Can be hardy once acclimated, but lots of problem specimens due to the depths they are collected at, take extra special care in examining and observing them before purchase
Angelfish in General (Centropyge, Chaetodontoplus, Apolemichthys, etc. spp.): Just a general note, Angelfish are among the more common fish collected using cyanide, so paying particularly close attention to their behavior and appearance before purchase is advised
Butterflyfishes (Chaetodon spp.): Very few are suited for a reef tank or a beginner hobbyist, do your research
Copperband Butterflyfish (Chelmon rostratus): Like the Regal Angelfish, this one has gone from nearly impossible to having some success with the popularity of them being kept in reef tanks, even then, longevity is questionable
Garibaldi Damselfish (Hypsypops rubicunda): Typically will not do well longterm in tropical conditions, if they do live long that cute little fish turns into a large territotial nightmare
Trunkfish, Boxfish, and Cowfish (various genera): Most are rather sensitive and can release toxins when stressed or dying
Clown/Gumdrop Gobies (Gobiodon spp.): Poor shipper, once established can be a good surviver with less boisterous fish, will nip "SPS" corals
Catalina gobies (Lythrypnus dalli): Not a tropical species and will not live long in the temperature of the average marine aquarium
Mandarin "Gobies" and Scooter "Blennies" AKA Dragonets (family Callionymidae): Require large amounts of live food, quite often starve to death, providing larger tanks (50+ gallons) with large amounts of live rock and little competition for food has proved successful, do not treat with copper medications
Radiata Lionfish (Pterois radiata): Tough to acclimate to aquarium life and foods, more sensitive than others in the genus
Fu manchu Lionfish & Dwarf Zebra Lionfish (Dendrochirus spp.): All the dwarf Lions require tanks with their needs in mind, these two also seem very sensitive, very shy, are poor shippers, and can be particularly difficult to ween onto aquarium foods
Anglerfishes and Frogfishes (Order Lophiiformes/Antennariiformes): Most get very large and can consume fish nearly their own size, often will only consume live foods which is troublesome since feeder fish are rarely nutritious enough longtern
Achilles, Powder Brown, Powder Blue, and Gold Rim Tangs (Acanthurus spp.): Ich prone and fairly sensitive to water conditions, they also require large amounts of swimming room, very risky to consider one without quarantine
Bristletooth Tangs (Ctenochaetus spp.): Ich prone, some of the hardier tangs once established but can starve when detritus and algae aren't available in decent supply, so overly "clean" aquariums are not a good choice, the Chevron is probably the least hardy of the genus and can be particularly difficult
Seahorses, Seadragons, Pipefish (Family Syngnathidae): Need quiet species tanks and large quantities of nutritious live food, wild caught specimens ship poorly and have high mortality rates, tank raised seahorses are often already accepting prepared foods and are much better candidates for aquarium life, they still need a tank with their needs in mind though
Hawkfishes ( Family Cirrhitidae): Hardy fish but they are notorious jumpers, be very careful with ornamental shrimp, crabs, and small fish
Porcupine Pufferfish (Family Diodontidae): Can be hardy but some are very disease and parasite prone, most require large fish only aquariums
Fairy and Flasher Wrasses (Paracheilinus and Cirrilabrus spp.): Require peaceful tankmates and do best in reef aquariums, they stress easily and the first few weeks in captivity will often make or break their longevity, known jumpers
Lawnmower Blenny (Salarias fasciatus): Will sometimes not accept prepared foods and will starve to death in tanks without a natural algae food source
Diamond, Golden Head, Sleeper Gobies (Valenciennea spp.): Sometimes starve to death even when accepting prepared foods, tanks with large sandbeds containing lots of food will help as will frequent feedings when they will eat, mated pairs may help as well
Courtjester/Rainford's and Hector's Goby (Amblygobius spp.): Often will not accept prepared foods, need established tanks with a fine sandbed full of life
Fourline Cleaner Wrasse (Larabicus quadrilineatus): A cleaner when small, but are coralivores as they enter adulthood so are not good reef aquarium inhabitants, some of the Tubelip Wrasses are know for a similar behavior and rarely live long in captivity
Cephalopods, Octopi, Cuttlefish, Squid (Class Cephalopoda): Not fish, but including them here because of their intelligence compared to the dumb lumps of goo that are most invertebrates, the Nautilus from above is in this group as well, these must have species tanks and require a lot of research before attempting them
Fish That Require Huge Aquariums (200 gallons or more):
Cartilaginous Fishes (Sharks, Rays, Skates): Require tanks much larger than 200 gal. and should just be left out of home aquaria, Nurse sharks can grow to 14ft. long!, repeating this one so it sinks in
Groupers & Seabass (various genera): Especially take note of the cute little Panther Groupers commonly offered in the trade as they can attain over 2' in length
Snappers (Family Lutjanidae): Those little Red Emperor Snappers seen in the trade get over 3' long
Unicorn Tangs (Naso spp.): They will even outgrow common size aquariums such as 125 gal. and 180 gal.
Moray Eels (Family Muraenidae): Do your research as many are not suitable for home aquariums
Squirrel and Soldierfish (Family Holocentridae): Some of these are borderline, do your research
Batfish and Spadefish (Family Ephippidae): Probably best left to public aquaria
Twinspot Wrasse (Coris aygula): Take special note of this one as they're often offered as small attractive juveniles, they get very large and very mean, up to 4' long
Red Coris Wrasse (Coris gaimard & Coris frerei): Sold as tiny juvenilles they can grow up to be 2' beasts, beware the size of most Coris wrasses, though the common Yellow Coris Wrasse is actually a smaller fish from not in the genus Coris but belonging to the genus Halichoeres
Dragon Wrasse (Novaculichthys taeniourus): Offered as very small juvenilles they grow to be about a foot long and are known to flip aquarium decorations and rocks when adults
Flounder (Paralichthys spp.): Rarely suitable for aquarium life, also becoming increasingly rare due to overfishing as a food fish
Tassled filefish (Chaetoderma pencilligera): Often offered when cute and tiny but grow quite large
Angelfish (various genera): When purchasing any angelfish that isn't Centropyge be sure to check their ultimate size, take special note of the French, Gray, Blue, and Queen which are often offered as small juvenilles ang will outgrow most aquariums
Triggerfish (various genera): Most will be fine in large aquariums of around 100 gallons, but there are a few that would be unsuitable for all but the largest home aquariums, do research on their ultimate size and temprament before a purchase is made
Venomous and/or Toxic Species:
Stonefishes (Synanceia spp.): Believed to be the most venomous fish in the world
Scorpionfishes/Rockfishes (various genera): Rhinopias has gained in popularity recently
Toadfish (family Batrachoididae)
Lionfish (various genera)
Rabbitfishes/Foxfaces (Siganus and a sub-genus Lo)
Coral Catfish (Plotosus lineatus): These also get up to a foot long and become more solitary as they grow
Blue Ring Octopus (Hapalochlaena spp.)
Fang Blennies (Meiacanthus spp.): Venomous bites that can be painful
Flower Urchins (Toxopneustes pileolus): Rare in the trade, but outside the trade there are reported deaths from this species
Black Longspined Sea Urchins (Diadema spp.): Can inflict painful wounds, some debate exists whether or not they are really venomous, but it's wise to handle all urchins with care
Cone Shells (Conus spp.): Rarely encountered in the aquarium trade, can be deadly
Stingrays (familly Dasyatidae): Many have venom associated with the spike on the tail which they use in self defense, fatalities are very rare
Sea Snakes (various genera I know you're not going to try to add one to your reef aquarium, but included for good measure
Box Jellyfish (Chironex fleckeri): Quite deadly but of no concern to aquarists
Extremely Aggressive Species:
Undulated Triggerfish (Balistapus undulatus): Perhaps the meanest aquarium fish available and one to avoid unless you don't mind having a large aquarium with one fish
Queen Triggerfish (Balistes vetula): Not quite as bad as the Undulated, but pretty close and what they lack by comparison in aggression they more than make up for in size
Clown Triggerfish (Balistoides conspicillum): Pretty similar in demeanor to the above two
Blueline Triggerfish (Pseudobalistes fuscus): Not so bad when young, but a beast once it grows, probably the least aggressive of the four triggers mentioned
Passer Angelfish (Holacanthus passer): Probably the meanest of all Angelfish, some of the larger Angels may look like delicate beauties, but some can be quite aggressive
Damselfish (family Pomacentridae): They're not all bad, but ounce for ounce some of them are the meanest fish around, think long and hard about adding them as some of your first specimens
Maroon Clownfish (Premnas biaculeatus): Females get quite large and they can take over medium size tanks, they're also probably the least tolerant of other clown species
Sohal Tang (Acanthurus sohal): Much hardier than the Clown Tang but just about as mean, probably best to keep them as the lone Tang, and if you must keep one in a community reef tank make it your last fish addition
Bicolor Pseudochromis (Pseudochromis paccagnellae) A lot of Pseudochromis get a bad wrap, but this isn't one of those cases, very nasty fish, P. porphyreus, P. diadema, and P. aldabraensis are others to be weary of.
Taken From: http://www.reefsome.com/articles/A-list-of-difficult-fish-to-keep
http://www.reefsome.com/articles/A-List-of-good-beginner-fish
Good Beginner Fish
Angelfish
Coral Beauty Angelfish [Centropyge bispinosus] (probably the hardiest of all the dwarf angels but they can nibble on corals and clams)
Half Black Angelfish [Centropyge vroliki] (see Coral Beauty)
Pygmy/Cherub Angelfish [Centropyge argi] (see Coral Beauty but
consider that they are often meaner, the same goes for most other similar shaped Pygmy Angels)
*Angels can be a little prone to disease but are otherwise pretty hardy if given a good diet
Blennies
Bicolor Blenny [Ecsenius bicolor] (great little fish with lots of personality that can help with algae problems, only problem is they're know to sometimes take a liking to munching on corals and clams, procede with caution)
Tail Spot Blenny [Ecsenius stigmatura] (in most cases probably a better choice all around than the Bicolor Blenny, though they aren't quite as boisterous which can be a good or bad thing depending on your perspective, less commonly available)
Linear Blenny [Ecsenius lineatus] (see above)
Cardinalfish
Pajama/Spotted/Orange Lined Cadinalfish [Sphaeramia nematoptera most common] (peaceful, disease resistant, and hardy, Cardinalfish in general are good choices just be a little more leary of Bangaii Cardinals that are new to captivity and red nocturnal varieties)
Clownfish/Chromis/Damselfish
Tank Raised Clownfish [Amphiprion sp.] (percula and ocellaris stay smaller and are les aggressive, Skunk clowns can be more peaceful as well, Maroon clowns tend to be the meanest, and all the others usually fall somewhere in between)
Green Chromis [Chromis viridis] (very peaceful and will school, but it is becoming pretty clear that in smaller schools they will sometimes pick the weakest member of the group off one by one, perhaps larger schools of 6+ in larger aquariums would eliminate that possibility)
Yellowtail Damselfish [Chrysiptera parasema] (can be aggressive but not quite as mean as most other Damselfish, add them as one of your last fish)
*In general Damsels are very hardy but the majority of them get far too mean to be considered good inhabitants in most tanks
Gobies/Dartfish
Firefish [Nemateleotris decora/magnifica] (great reef fish, just be weary when keeping in groups as they can turn on one another, singles or mated pairs are you best bet, they have been known to jump but it's not a big problem)
Scissortail Goby/Dartfish [Ptereleotris evides] (almost identical to Firefish in care)
Yellow Watchman Goby [Cryptocentrus cinctus] (tough as nails, very comical, peaceful, but a little shy and require some sand to burrow in, make sure your rocks are stacked securely)
Pink Spotted Watchman [Cryptocentrus leptocephalus] (see Yellow Watchman)
Gold/Blue Neon Goby (peaceful and often avilable as tank raised, keep as mated pairs or singles unless you have a large aquarium)
Hector's Goby [Amblyeleotris hectori] (similar to Rainford's but seem to accept prepared foods more often, just make sure they're eating before purchase and keep them with more peaceful fish, they will also sift food from your sandbed and tidy it up so it's best to have a sandbed)
Pseudochromis/Basslets
Royal Gramma [Gramma loreto] (kept singly they are peaceful, but the biggest drawback is their shyness, provide plenty of overhangs, they may also do best in aquariums with a little less intense lighting)
Pseudochromis [springeri/fridmani/flavivertex/aldabraensis] (very hardy and disease resistant, however can get quite mean, they are fairly well behaved as long as they're the last fish added and you avoid similar size/shape fish, frequently available as tank raised)
Pseudochromis sankeyi (same as above except far more peaceful)
Tangs/Foxfaces
Zebrasoma sp. [Yellow, Purple, Scopas, Sailfin] (these are the hardiest of the tangs in my opinion, still not great beginner fish, but if you must have a Tang these are the best choices, be sure to provide plenty of green stuff for them to graze on and feed them often to stay plump, as a basic guideline it's best to keep these in 75 gal. or larger aquariums with the consideration that they might outgrow those down the road, they can get mean so make them later additions)
Foxfaces/Rabbitfish [Siganus vulpinus is the most common] (these fish can get quite large so be sure to research if your tank is large enough to house one, they're great at algae control, more disease resistant than their cousins the Tang, and generally more peaceful, also keep in mind their dorsal spines are mildly venomous)
Wrasses
Six/Four Line Wrasse (can get mean much like the Pseudochromis, but also requires a sandbed to borrow in, sometimes these will consume undesirable flatworms)
Fish To Be Avoided::
Fish that have incredibly low survivability in aquaria or are totally unsuitable for most home aquaria.
Moorish Idol (Zanclus cornutus): A few success stories, but miniscule amounts live long, difficult feeder, mystery deaths, and even when accepting prepared foods often slowly starve
Rock Beauty Angelfish (Holacanthus tricolor): Nearly impossible to meet the dietary needs in home aquaria
Multi-Barred Angelfish (Centropyge multifasciatus): They don't adapt to aquarium life well, rarely eat, and are very secretive, though not fatal, they also seem particularly prone to Lymphocystis
Venustus Angelfish (Centropyge venustus): See the Multi-Barred Angelfish above
Butterflyfishes (Chaetodon spp.): Many problem feeders in the group and most are corallivore that are almost guaranteed to starve to death in aquaria, do a lot of research before purchasing any butterflyfish
Clown Tang (Acanthurus lineatus): VERY ich prone and a finicky eater, horrible survival rates, when they do live they are terribly aggressive and often take over a tank
Twinspot Goby (Signogobius ocellatus): Terrible survival rates in captivity, rarely accept prepared foods or survive long even when they do
Clown Sweetlips (Plectorhinchus chaetodonoides): Difficult feeders and rarely adapt to aquarium life, should you manage to get one to live they get quite large
Oriental Sweetlips (Plectorhinchus orientalis): See Clown Sweetlips, in general this can be repeated for most species in the genus Diagramma and Plectorhinchus
Pinnatus Batfish (Platax pinnatus): Gorgeous fish when young, very very few success stories, diet, disease, and stress from aquarium life are big issues
Tiger Tiera Batfish (Platax batavianus): See Pinnatus Batfish above
Orange Spotted Filefish (Oxymonacanthus longirostris): Specialized coral polyp feeder and almost never accepts prepared foods
Ribbon Eel (Rhinomuraena quaesita): Rarely eat in captivity and are excellent escape artists
Snake Eels & Garden Eels (various genera): Difficult feeders that require specialty tanks
Tamarin Wrasses (Anampses spp.): Very poor shippers and need tanks with their special needs in mind, even then they often starve to death, their best chance is often a large established reef aquarium with large amounts of live rock, peaceful fish, and something to prevent their escape from jumping
Leopard Wrasses (Macropharyngodon spp.): See Tamarin Wrasses above, but there are more success stories, both these and the Anampses are boderline being in this area of the list and the next section
Pencil Wrasses (Pseodojuloides spp.): Very sensitive, they almost always die in transit so you don't see them very often if ever in the trade
Parrotfishes (Family Scaridae): Very specialized feeders on mostly dead (some live) coral skeletons and the algae and organisms associated with them, they adapt poorly to aquarium life in almost all regards
Tilefishes (Family Malacanthidae): VERY timid and must be kept in a covered aquarium with lots of space and docile tankmates, in general they just don't adapt to aquarium life
Cartilaginous Fishes (Sharks, Rays, Skates): With very few exceptions, unless you own a massive aquarium that is several hundred gallons stay away
Grunts (Family Haemulidae): Rarely adapt well to aquarium life and should probably only be considered in a large species tank
Jacks (Family Carangidae): See Grunts above
Drums (Family Sciaenidae): Poor shippers, being very shy and fragile they rarely live long after being collected
Trumpetfish (Aulostomus spp.): Too large and too specialized for 99.9% of the aquarists out there, also poor shippers
Remoras (Family Echeneidae): Unless you have a large Shark or Whale in your backyard oceanarium it's probably best to stay away
Leopard Blenny (Exallias brevis): Specialized coral feeders that rarely live long in captivity
Chambered Nautilus (Nautilus pompilius): Though technically not a fish, there are a plethora of reasons to leave them in the ocean, simply not suited for typical aquarium life
Fish Best Left For Experienced Or Knowledgable Hobbyists:
Finicky nature, parasite prone, specialty feeders, require specialty tanks, or threatened species
Anthias (family Anthiinae): Require a good amount of swimming room, peaceful tankmates, and frequent feedings, often unhealthy and starving by the time they make it to dealers tanks, some almost require special tanks with their needs in mind and others often refuse to eat and starve quickly in aquaria, do plenty of research before purchasing any Anthias
Teira Batfish (Platax teira): Can be very hardy once acclimated but there can be problems feeding, they stress easily, are disease prone, and will also outgrow most aquaria
Majestic, Blueface(Pomacanthus Euxiphipops spp.): Can be hardy once acclimated to aquarium life and eating well, that's often easier said than done though, larger juvenilles are often the best way to go with these fish as tiny specimens are quite fragile and large specimens have the hardest time adapting to aquarium life, this is true for many large angelfish
Regal Angelfish (Pygoplites diacanthus): A problem feeder, specimens from the Philippines and Indonesia rarely make it long in captivity, Red Sea Specimens tend to be hardier and more willing to accept prepared foods partially due to collection and holding techniques, the more recent trend to keep this fish in reef aquariums helps with survivability
Bandit Angelfish (Holacanthus arcuatus AKA Apolemichthys arcuatus): Very similar to the Rock Beauty above but with a much smaller sample, at their price you'll probably do your research, if you don't you'll most likely learn an expensive lesson
Bicolor Angelfish (Centropyge bicolor): Concerns with drugs used in collection and frequent unwillingness to accept prepared foods, also one of the more common coral nippers
Heralds's or Yellow Angelfish (Centropyge heraldi): Often collected with the use of drugs, be very wary of newly collected specimens, this can be true with many Centropyge but seems especially problematic here
Lemonpeel Angelfish (Centropyge flavissima): See Herald's angelfish above
Potter's Angelfish (Centropyge potteri): Mixed results with this one with a lot of mystery deaths early in captivity, if they've been eating and active at the fish store for a few weeks they usually end up being quite hardy
Golden Pygmy Angelfish (Centropyge aurantius): Adapts poorly to aquarium life, only attempt if you find a healthy specimen and have a larger reef aquarium containing less boisterous fish with a lot of rock to graze on
Swallowtail Angelfishes (Genicanthus spp.): Can be hardy once acclimated, but lots of problem specimens due to the depths they are collected at, take extra special care in examining and observing them before purchase
Angelfish in General (Centropyge, Chaetodontoplus, Apolemichthys, etc. spp.): Just a general note, Angelfish are among the more common fish collected using cyanide, so paying particularly close attention to their behavior and appearance before purchase is advised
Butterflyfishes (Chaetodon spp.): Very few are suited for a reef tank or a beginner hobbyist, do your research
Copperband Butterflyfish (Chelmon rostratus): Like the Regal Angelfish, this one has gone from nearly impossible to having some success with the popularity of them being kept in reef tanks, even then, longevity is questionable
Garibaldi Damselfish (Hypsypops rubicunda): Typically will not do well longterm in tropical conditions, if they do live long that cute little fish turns into a large territotial nightmare
Trunkfish, Boxfish, and Cowfish (various genera): Most are rather sensitive and can release toxins when stressed or dying
Clown/Gumdrop Gobies (Gobiodon spp.): Poor shipper, once established can be a good surviver with less boisterous fish, will nip "SPS" corals
Catalina gobies (Lythrypnus dalli): Not a tropical species and will not live long in the temperature of the average marine aquarium
Mandarin "Gobies" and Scooter "Blennies" AKA Dragonets (family Callionymidae): Require large amounts of live food, quite often starve to death, providing larger tanks (50+ gallons) with large amounts of live rock and little competition for food has proved successful, do not treat with copper medications
Radiata Lionfish (Pterois radiata): Tough to acclimate to aquarium life and foods, more sensitive than others in the genus
Fu manchu Lionfish & Dwarf Zebra Lionfish (Dendrochirus spp.): All the dwarf Lions require tanks with their needs in mind, these two also seem very sensitive, very shy, are poor shippers, and can be particularly difficult to ween onto aquarium foods
Anglerfishes and Frogfishes (Order Lophiiformes/Antennariiformes): Most get very large and can consume fish nearly their own size, often will only consume live foods which is troublesome since feeder fish are rarely nutritious enough longtern
Achilles, Powder Brown, Powder Blue, and Gold Rim Tangs (Acanthurus spp.): Ich prone and fairly sensitive to water conditions, they also require large amounts of swimming room, very risky to consider one without quarantine
Bristletooth Tangs (Ctenochaetus spp.): Ich prone, some of the hardier tangs once established but can starve when detritus and algae aren't available in decent supply, so overly "clean" aquariums are not a good choice, the Chevron is probably the least hardy of the genus and can be particularly difficult
Seahorses, Seadragons, Pipefish (Family Syngnathidae): Need quiet species tanks and large quantities of nutritious live food, wild caught specimens ship poorly and have high mortality rates, tank raised seahorses are often already accepting prepared foods and are much better candidates for aquarium life, they still need a tank with their needs in mind though
Hawkfishes ( Family Cirrhitidae): Hardy fish but they are notorious jumpers, be very careful with ornamental shrimp, crabs, and small fish
Porcupine Pufferfish (Family Diodontidae): Can be hardy but some are very disease and parasite prone, most require large fish only aquariums
Fairy and Flasher Wrasses (Paracheilinus and Cirrilabrus spp.): Require peaceful tankmates and do best in reef aquariums, they stress easily and the first few weeks in captivity will often make or break their longevity, known jumpers
Lawnmower Blenny (Salarias fasciatus): Will sometimes not accept prepared foods and will starve to death in tanks without a natural algae food source
Diamond, Golden Head, Sleeper Gobies (Valenciennea spp.): Sometimes starve to death even when accepting prepared foods, tanks with large sandbeds containing lots of food will help as will frequent feedings when they will eat, mated pairs may help as well
Courtjester/Rainford's and Hector's Goby (Amblygobius spp.): Often will not accept prepared foods, need established tanks with a fine sandbed full of life
Fourline Cleaner Wrasse (Larabicus quadrilineatus): A cleaner when small, but are coralivores as they enter adulthood so are not good reef aquarium inhabitants, some of the Tubelip Wrasses are know for a similar behavior and rarely live long in captivity
Cephalopods, Octopi, Cuttlefish, Squid (Class Cephalopoda): Not fish, but including them here because of their intelligence compared to the dumb lumps of goo that are most invertebrates, the Nautilus from above is in this group as well, these must have species tanks and require a lot of research before attempting them
Fish That Require Huge Aquariums (200 gallons or more):
Cartilaginous Fishes (Sharks, Rays, Skates): Require tanks much larger than 200 gal. and should just be left out of home aquaria, Nurse sharks can grow to 14ft. long!, repeating this one so it sinks in
Groupers & Seabass (various genera): Especially take note of the cute little Panther Groupers commonly offered in the trade as they can attain over 2' in length
Snappers (Family Lutjanidae): Those little Red Emperor Snappers seen in the trade get over 3' long
Unicorn Tangs (Naso spp.): They will even outgrow common size aquariums such as 125 gal. and 180 gal.
Moray Eels (Family Muraenidae): Do your research as many are not suitable for home aquariums
Squirrel and Soldierfish (Family Holocentridae): Some of these are borderline, do your research
Batfish and Spadefish (Family Ephippidae): Probably best left to public aquaria
Twinspot Wrasse (Coris aygula): Take special note of this one as they're often offered as small attractive juveniles, they get very large and very mean, up to 4' long
Red Coris Wrasse (Coris gaimard & Coris frerei): Sold as tiny juvenilles they can grow up to be 2' beasts, beware the size of most Coris wrasses, though the common Yellow Coris Wrasse is actually a smaller fish from not in the genus Coris but belonging to the genus Halichoeres
Dragon Wrasse (Novaculichthys taeniourus): Offered as very small juvenilles they grow to be about a foot long and are known to flip aquarium decorations and rocks when adults
Flounder (Paralichthys spp.): Rarely suitable for aquarium life, also becoming increasingly rare due to overfishing as a food fish
Tassled filefish (Chaetoderma pencilligera): Often offered when cute and tiny but grow quite large
Angelfish (various genera): When purchasing any angelfish that isn't Centropyge be sure to check their ultimate size, take special note of the French, Gray, Blue, and Queen which are often offered as small juvenilles ang will outgrow most aquariums
Triggerfish (various genera): Most will be fine in large aquariums of around 100 gallons, but there are a few that would be unsuitable for all but the largest home aquariums, do research on their ultimate size and temprament before a purchase is made
Venomous and/or Toxic Species:
Stonefishes (Synanceia spp.): Believed to be the most venomous fish in the world
Scorpionfishes/Rockfishes (various genera): Rhinopias has gained in popularity recently
Toadfish (family Batrachoididae)
Lionfish (various genera)
Rabbitfishes/Foxfaces (Siganus and a sub-genus Lo)
Coral Catfish (Plotosus lineatus): These also get up to a foot long and become more solitary as they grow
Blue Ring Octopus (Hapalochlaena spp.)
Fang Blennies (Meiacanthus spp.): Venomous bites that can be painful
Flower Urchins (Toxopneustes pileolus): Rare in the trade, but outside the trade there are reported deaths from this species
Black Longspined Sea Urchins (Diadema spp.): Can inflict painful wounds, some debate exists whether or not they are really venomous, but it's wise to handle all urchins with care
Cone Shells (Conus spp.): Rarely encountered in the aquarium trade, can be deadly
Stingrays (familly Dasyatidae): Many have venom associated with the spike on the tail which they use in self defense, fatalities are very rare
Sea Snakes (various genera I know you're not going to try to add one to your reef aquarium, but included for good measure
Box Jellyfish (Chironex fleckeri): Quite deadly but of no concern to aquarists
Extremely Aggressive Species:
Undulated Triggerfish (Balistapus undulatus): Perhaps the meanest aquarium fish available and one to avoid unless you don't mind having a large aquarium with one fish
Queen Triggerfish (Balistes vetula): Not quite as bad as the Undulated, but pretty close and what they lack by comparison in aggression they more than make up for in size
Clown Triggerfish (Balistoides conspicillum): Pretty similar in demeanor to the above two
Blueline Triggerfish (Pseudobalistes fuscus): Not so bad when young, but a beast once it grows, probably the least aggressive of the four triggers mentioned
Passer Angelfish (Holacanthus passer): Probably the meanest of all Angelfish, some of the larger Angels may look like delicate beauties, but some can be quite aggressive
Damselfish (family Pomacentridae): They're not all bad, but ounce for ounce some of them are the meanest fish around, think long and hard about adding them as some of your first specimens
Maroon Clownfish (Premnas biaculeatus): Females get quite large and they can take over medium size tanks, they're also probably the least tolerant of other clown species
Sohal Tang (Acanthurus sohal): Much hardier than the Clown Tang but just about as mean, probably best to keep them as the lone Tang, and if you must keep one in a community reef tank make it your last fish addition
Bicolor Pseudochromis (Pseudochromis paccagnellae) A lot of Pseudochromis get a bad wrap, but this isn't one of those cases, very nasty fish, P. porphyreus, P. diadema, and P. aldabraensis are others to be weary of.
Taken From: http://www.reefsome.com/articles/A-list-of-difficult-fish-to-keep
http://www.reefsome.com/articles/A-List-of-good-beginner-fish
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