These are not recommended for a marine invertebrate tank, as they attack other species, such as sponges. Starfish are in fact either carnivorous, gripping their prey with their long arms that emerge from a central disc, or microphages, in which case they feed on small organisms on the bed. The ophiuroids, sometimes called brittle-stars and closely related to starfish, have articulated arms which allow them to move around quite quickly. These arms, like those of the starfish, can regenerate themselves if they break off.


These are pieces of rock or fragments of dead coral (madreporites), that are bound together by calcareous rocks or various pieces of debris from invertebrates. They

Somespecies of sea urchins with varyingsizes of prickles can be found in marine aquariums.
Madreporites Seastar

Compatibility and incompatibility between fish and invertebrates

Total incompatibility with all invertebrates

Triggers (Balistidae), snappers (Lutjanidae), murenas (Murenidae), groupers - except Anthias (Serranidse), wrasses {Labridae), porcupine fish (Diodontidae), puffers (Tetraodontidae and Canthigasteridae), scorpions {Scorpenidae), zebras (Plectorhynchidae), other fish longer than 10-15 cm with a lively nature.

Incompatibility with worms, crustaceans, mollusks, echinoderms

Predatory fish from other groups, such as squirrel fish, soldier fish (Holocentridae) and bat-fish (Ephippids).

Incompatibility with sponges and Coelenterates

Butterfly fish (Chaetonidae), angelfish {Pomacanthidae).

Compatibility with practically all invertebrates

Anthias (Serranidae), sea horses (Syngnathidae), hawks (Cirrhitidae), Opistognotidae, lime fish {Monacanthidae), mandarin fish (Cailionymidae), cardinals (Apogonidae) - except with small shrimps, rockets (Plesiopidae) - except with crustaceans, Grammtdae, and Pseudochromis, Blenniidae, Pomacentrids, small tangs (Acanthuridae). This amounts to more than 20 species, generally under 10 cm in length, easy to acclimatize.

An aquarist does not in fact reconstitute a biotope in an invertebrate tank, since it unites species which do not necessarily live together in a natural setting. Common sense will make it possible to obtain satisfactory results, pleasing to the eye, in which fish and invertebrates live together in harmony.

are sometimes removed from their natural setting and sold commercially. "Live rocks" harbor various organisms: bacteria, algae, sponges, small Coelenterates, and sometimes even small crustaceans, hidden in crevices. They can therefore be considered as living pieces of decor which contribute to the equilibrium of the aquarium. If, before sale, they have been suitably transported, cared for, and housed, then they are worth acquiring, despite their high price, as they permit the introduction of a variety of beneficial organisms into the aquarium, in the most "natural" way possible.

Another option is to collect these types of rock yourself, off the shores of Florida, for example. Organisms capable of surviving in a tropical tank grow there in summer, when the water temperature is higher. There is always a chance, however, of introducing an undesirable organism or of finding that some residents of the "live rock" deteriorate and die, with an ensuing risk of pollution. It is therefore best to proceed with caution and isolate the rock in a quarantine aquarium.


Invertebrates cannot cohabit with just any fish, for a number of reasons. The first is that they are liable to become prey for carnivorous fish. Coelenterates are completely incompatible with angelfish (Pomacanthids), for example. Secondly, some lively and active fish, of over 10-15 cm in length, can jostle and disturb invertebrates in the aquarium. Furthermore, the bigger and more active a fish, the more it excretes nitrogenous substances, leading to the accumulation of nitrates (NO3-), which are harmful to invertebrates. It is therefore best to avoid the presence of this type of fish. Too many fish produce the same result and the same degree of harm for invertebrates. Finally, there is another problem when a sick fish has to be treated, particularly with substances containing metals, which are toxic for most invertebrates. Remember that it is always preferable to nurse a fish in a hospital aquarium.

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