Reef safe is a distinction used in the saltwater aquarium hobby to indicate that a fish or invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

 is safe to add to a reef aquarium

Reef aquarium

A reef aquarium or reef tank is an marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the coral reef environment...

. There is no fish that is completely reef safe. Every fish that is commonly listed as reef safe are species that usually do not readily consume small fish or invertebrates. Fish listed as reef safe also do not bother fellow fish unless in some cases, for instance tangs, they do not get along with conspecifics and sometimes fish with similar color or body shape. Every fish has a personality, is different, and, in some cases, are opportunistic feeders. Tangs, which by most accounts are reef safe, may in adulthood eat some crustaceans shortly after they molt. Many larger predatory fish, for instance eel

Eel

Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...

s and pufferfish

Pufferfish

Tetraodontidae is a family of primarily marine and estuarine fish of the Tetraodontiformes order. The family includes many familiar species which are variously called pufferfish, balloonfish, blowfish, bubblefish, globefish, swellfish, toadfish, toadies, honey toads, sugar toads, and sea squab...

, will adapt very well to a reef tank and will be problem-free as long as they have sizable tankmates and no crustaceans. Some aquarists have also had success in keeping smaller fish with predatory ones in reef tanks by adding the smaller fish at night, sometimes with newly rearranged rockwork.

Reef safe fish

Anthias

Anthiinae

Perhaps the quintessential "reef fish," anthias make up a sizeable portion of the population of pink, orange and yellow fishes seen swarming in most coral reef photography and film...

Basslet

Basslet

The basslets are a small family, Grammatidae, of fishes in the order Perciformes. The twelve members are all small fish of the western Atlantic, typically no more than 10 cm in length. Several species are colorful and popular for marine aquaria...

s
Blennies: Excludes fang blennies. A few species will nip at polyps and giant clam

Giant clam

The giant clam, Tridacna gigas , is the largest living bivalve mollusc. T. gigas is one of the most endangered clam species. It was mentioned as early as 1825 in scientific reports...

 mantles.
Cardinalfish
Chromis

Chromis

Chromis is a genus of fish in the family Pomacentridae. While the term Damselfish describes a group of marine fish larger than just one genus, most damselfish are in the genus Chromis...

Clownfish

Clownfish

Clownfish or anemonefish are fishes from the subfamily Amphiprioninae in the family Pomacentridae. Twenty-eight species are recognized, one in the genus Premnas, while the remaining are in the genus Amphiprion. In the wild they all form symbiotic mutualisms with sea anemones...

: Excludes the maroon clown which can grow very aggressive and territorial.
Damsel

Pomacentridae

Pomacentridae are a family of perciform fish, comprising the damselfishes and clownfishes. They are primarily marine, while a few species inhabit freshwater and brackish environments . They are noted for their hardy constitutions and territoriality...

s: Excludes larger, more aggressive Dascyllus varieties.
Dwarf angelfish

Centropyge

Centropyge is a genus of marine angelfishes. The genus is the largest within the Pomacanthid family, comprising over 30 described species. Species in this group do not exceed 15 cm in length and live in haremic structures with one dominant male and multiple females...

: Dwarf angelfish in a reef setting has been heavily debated.
Dottyback

Dottyback

The dottybacks are a family, Pseudochromidae, of fishes in the order Perciformes. Around 100 species belong to this family.They are found in the tropical and subtropical Indo-Pacific, where they inhabit coral reefs. They are brightly coloured fish, often showing striking sexual dimorphism. They are...

s: They may consume small shrimp and can be highly aggressive.
Dragonet

Dragonet

Dragonets are small, perciform, marine fish of the diverse family Callionymidae . Found mainly in the tropical waters of the western Indo-Pacific, the family contains approximately 186 species in 18 genera. The Draconettidae may be considered a sister family, whose members are very much alike,...

s
Foxface

Rabbitfish

Rabbitfishes or spinefoots are perciform fishes in the family Siganidae. The 28 species are in a single genus, Siganus. In some now obsolete classifications, the species having prominent face stripes—colloquially called foxfaces–are in the genus Lo. Other species like the Masked...

: Foxface and rabbitfish will occasionally eat certain corals if underfed.
Gobies

Goby

The gobies form the family Gobiidae, which is one of the largest families of fish, with more than 2,000 species in more than 200 genera. Most are relatively small, typically less than 10 cm in length...

Jawfish
Pipefish

Pipefish

Pipefishes or pipe-fishes are a subfamily of small fishes, which, together with the seahorses, form the family Syngnathidae.-Anatomy:...

: They can be killed by stinging corals and anemones.
Pseudochromis

Pseudochromis

Pseudochromis is a genus of dottybacks with around 70 described species.- Species :* Pseudochromis aldabraensis - Orange dottyback* Pseudochromis alticaudex* Pseudochromis andamanensis- Andaman dottyback* Pseudochromis aureolineatus...

: They may consume small shrimp and can be highly aggressive.
Seahorse

Seahorse

Seahorses compose the fish genus Hippocampus within the family Syngnathidae, in order Syngnathiformes. Syngnathidae also includes the pipefishes. "Hippocampus" comes from the Ancient Greek hippos meaning "horse" and kampos meaning “sea monster”.There are nearly 50 species of seahorse...

s: They can be killed by stinging corals and anemones.
Tangs
Wrasse

Wrasse

The wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 82 genera, which are divided into nine subgroups or tribes....

: There are both reef safe wrasses and ones that are notorious for killing small fish and invertebrates.
Planktivorous Triggerfish

Triggerfish

Triggerfishes are about 40 species of often brightly colored fishes of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacific...

: With caution.

Melichthys

Melichthys

Melichthys is a genus in the triggerfish family .- Species :*Melichthys indicus : Indian triggerfish*Melichthys niger : Black triggerfish*Melichthys vidua : Pinktail triggerfish...

spp.

Xanthichthys spp.

Odonus spp.

Reef safe invertebrates

Coral

Coral

Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

s (Class Anthozoa): There are aggressive types of coral which have sweeper tenticles that can burn other corals. These may require specific placement in an aquarium.
Crab

Crab

True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...

s: Specifically small hermit crab

Hermit crab

Hermit crabs are decapod crustaceans of the superfamily Paguroidea. Most of the 1100 species possess an asymmetrical abdomen which is concealed in an empty gastropod shell that is carried around by the hermit crab.-Description:...

s, anemone crabs, emerald mithrax crab

Emerald Crab

Mithraculus sculptus, the green clinging crab or emerald crab is a species of crab used as pets in marine house aquariums. They are dark green colored, and can sometimes be aggressive. The species is found in tropical waters in the Caribbean Sea....

s and strawberry crab

Strawberry crab

The strawberry crab, Hawaiian strawberry crab or red boxing crab, Neoliomera pubescens, is a small, bright pink crab found in the Indo-Pacific region, including around Hawaii, French Polynesia and Mauritius. It has small white bumps on the main shell and whitish claws. Adults reach about across....

s.
Fan worms (Suborder Sabellida)
Giant clam

Giant clam

The giant clam, Tridacna gigas , is the largest living bivalve mollusc. T. gigas is one of the most endangered clam species. It was mentioned as early as 1825 in scientific reports...

s
Scallop

Scallop

A scallop is a marine bivalve mollusk of the family Pectinidae. Scallops are a cosmopolitan family, found in all of the world's oceans. Many scallops are highly prized as a food source...

s
Sea anemone

Sea anemone

Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...

s (Order Actiniaria): Anemones, especially carpet anemones can eat fish and burn corals to death requiring specific placement for specimens in an aquarium.
Sea cucumbers
Sea fan

Sea fan

A gorgonian, also known as sea whip or sea fan, is an order of sessile colonial cnidarian found throughout the oceans of the world, especially in the tropics and subtropics. Gorgonians are similar to the sea pen, another soft coral. Individual tiny polyps form colonies that are normally erect,...

s
Sea slug

Nudibranch

A nudibranch is a member of what is now a taxonomic clade, and what was previously a suborder, of soft-bodied, marine gastropod mollusks which shed their shell after their larval stage. They are noted for their often extraordinary colors and striking forms...

s
Sea squirts: See Tunicates
Starfish / Sea stars: There are many starfish which are not reef safe like crown-of-thorns starfish

Crown-of-thorns starfish

The crown-of-thorns starfish is a large nocturnal sea star that preys upon coral polyps. The crown-of-thorns receives its name from venomous thorn-like spines that cover its body. It is endemic to tropical coral reefs in the Red Sea, the Indian Ocean, and the Pacific Ocean...

 and chocolate chip sea star

Protoreaster nodosus

Protoreaster nodosus is a species of sea star found in the warm, shallow waters of the Indo-Pacific region. Also known as "horned" or "Chocolate Chip" sea stars, they possess rows of spines or "horns"; black conical points arranged in a single row, radially on the dorsal side, which may erode and...

.
Shrimp

Shrimp

Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

s: Peppermint shrimps, cleaner shrimps, pistol shrimps, anemone shrimps and blood red fire shrimp

Lysmata debelius

Lysmata debelius is a species of cleaner shrimp indigenous to the Indo-Pacific. It is popular in the aquarium trade, where it is known as the fire shrimp, blood shrimp or scarlet cleaner shrimp.-Taxonomy:...

s are better choices since the commonly available banded coral shrimp

Stenopus hispidus

Stenopus hispidus is a shrimp-like decapod crustacean belonging to the infraorder Stenopodidea. Common names include banded coral shrimp and banded cleaner shrimp.-Distribution:...

 can kill fish, and the mantis shrimp

Mantis shrimp

Mantis shrimp or stomatopods are marine crustaceans, the members of the order Stomatopoda. They are neither shrimp nor mantids, but receive their name purely from the physical resemblance to both the terrestrial praying mantis and the shrimp. They may reach in length, although exceptional cases of...

 will kill and eat most animals in a tank.
Snail

Snail

Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

s: Some snails are parasitic but are rarely, if ever, offered in the saltwater aquaria trade.
Sponges
Tunicate

Tunicate

Tunicates, also known as urochordates, are members of the subphylum Tunicata, previously known as Urochordata, a group of underwater saclike filter feeders with incurrent and excurrent siphons that is classified within the phylum Chordata. While most tunicates live on the ocean floor, others such...

s

Unsafe fish

Non-dwarf Angelfish: This includes any of the larger angelfish.
Non-planktivorous Butterflyfish

Butterflyfish

The butterflyfish are a group of conspicuous tropical marine fish of the family Chaetodontidae; the bannerfish and coralfish are also included in this group. Found mostly on the reefs of the Atlantic, Indian and Pacific Oceans, there are approximately 120 species in 10 genera...

: Eat mainly or exclusively coral polyps
Non-planktivorous Triggerfish

Triggerfish

Triggerfishes are about 40 species of often brightly colored fishes of the family Balistidae. Often marked by lines and spots, they inhabit tropical and subtropical oceans throughout the world, with the greatest species richness in the Indo-Pacific...

: This includes most triggerfish. Most triggerfish are highly aggressive carnivores that will eat many smaller fish and invertebrates in an aquarium. They also grow to be quite large.

Unsafe invertebrates

Sea apple

Sea apple

Sea apple is a common name for the colorful and somewhat round sea cucumbers of the genera Paracucumaria and Pseudocolochirus, found primarily in Indo-Pacific waters. Sea apples are filter feeders with tentacles, ovate bodies, and tube-like feet. They can release their internal organs or a toxin...

s: Currently short-lived in aquaria. They release a highy-toxic substance at death, decimating the aquarium.