Marine Fish Compatibility

For anyone starting a new marine aquarium the first question is what are good beginner fish. Fortunately, there are a lot of marine fish that are relatively easy to keep when several guidelines are followed. First the fish selected should be healthy and feeding when they are added to the tank. Second they should be acclimated slowly and carefully, preferably by first adding them to a quarantine tank before they are added to the display tank. Lastly, they should be matched in terms of size and temperament with the other fish with which they are going to be housed. Good beginner fish are often thought to be those that can tolerate poor water conditions or wide variations in a tank’s conditions, which are often the hallmark of a new tank. There are fish that fall into this category, but over the long term they are usually too aggressive to be kept in the confines of a small tank with other fish. It is far better to set up a tank properly using the latest and best methodology and then adding fish of similar dispositions.

As mentioned above one of the critical aspects of putting a group of fish together is to choose fish of similar size and temperaments. Fish can be grouped into three general categories: docile, aggressive and predatory and they should be kept with fish of similar dispositions. These can then also be expanded further to include size. When selecting fish to start in a tank they should be matched for both size and disposition. It is not however a hard and fast rule, as it is possible to mix fish with one type of disposition with those from another if care is taken. The size consideration is just as critical in that if a large or even moderately sized fish from the predatory group is mixed with a small fish from the docile or even the aggressive group, the smaller fish will usually end up as food.

Some of the fish in the docile group would include small sized clownfish, firefish, gobies, cardinalfish, assessors, marine betas, flasher wrasses and blennies. Aggressive fish would include angelfish, tangs, rabbitfish, hawkfish, hogfish, most wrasses and dottybacks. Predators would include groupers, lionfish, triggerfish, snappers, and moray eels. There are exceptions within every group usually based on size such as the orchid dottyback (Pseudochromis fridmani) would probably fall in the docile group due to its small size, while the Tomato or Maroon Clownfish would probably be considered in the aggressive group. So these groupings should be more of a guideline rather than the only way to do things. Also there are variations within the species itself. There have been reports of blennies that have attacked and killed anything put in their tanks as well as angelfish that have harassed and killed groupers.


Damselfishes (Pomacentridae) These are generally considered the best beginner’s fish as they are hardy, inexpensive and colorful. Unfortunately they are highly territorial and very aggressive. In small or medium tanks they will claim the entire tank as their own and harass any fish that enter their domain. For these reasons they may not be the best choice for small beginner’s tanks, although they do quite well in larger tanks when they are housed with other aggressive fish. Exceptions to this are the Yellowtail blue damsel and the Green chromis both of which can be considered on the docile end of the scale and can be housed in schools.

Anemonefish (Amphiprion) The clownfish and especially the percula clown are the fish that get more people interested in the hobby than any other. They are best kept alone or in known male-female pairs. They can be kept with or without an anemone and they should housed only one pair to a tank. Most are docile to moderately aggressive, with the exceptions being the larger types, which can be very aggressive especially if an anemone is present. Prone to Brooklynella infections and parasitic worms they should be quarantined before being placed in a display tank.

Gobies (Gobiidae) The gobies are a very diverse group with the largest number of species of any fish group. They inhabit virtually every niche of the reef from the spines of a sea urchin to the tentacles of some jellyfish. They are a small bottom-oriented group that displays little aggression except toward other similar looking relatives. They require adequate hiding places and good water quality.

Blennies (Blennidae) Blennies usually sit on aquarium décor and can be aggressive to other small bottom dwelling fish. Most feed by grazing algae from the rocks and stay fairly small. Only one should be kept in a tank, as they can be aggressive towards other blennies.

Firefish These small elongated fish are good for a passive community. They are extremely hardy, colorful and eat most small meaty foods. They are prone to jumping from the tank, so their tank should be covered. They also have a tendency to fight with members of their own species and with other gobies and firefish if inadequate hiding places and cover are not provided.

Dwarf Angelfish (Centropyge) The dwarf angelfish are generally small colorful individuals that do well when housed singly in a tank. They can also be kept as pairs if they can be sexed or obtained as pairs but they may fight to the death if two males are housed together. They should be fed a diet high in plant material and they do better if some algae is present in their tank.

Cardinalfish (Apogonidae) Moe than 170 species, many of which are nocturnal. They are extremely hardy and non-aggressive although they will swallow anything that fits in their mouth. They need caves and other hiding places in order to thrive. Should be fed small plankton like foods.

Angelfish (Pomacanthidae) The angelfish group includes some of the most stunning of all marine fish. Unfortunately most of the species are suitable only for the more experienced fishkeeper. Do best when acquired small and allowed to acclimate to their new surroundings gradually. Need a diet high in plant material to which some sponge is added for some species. Most of the species require larger tanks as they grow large and can become quite aggressive.

Marine Bettas and Assessors (Plesiopsidae) Both species are extremely disease resistant and not aggressive. Good choices for the passive aquaria although the betta may eat crustaceans including cleaner shrimp. They are extremely cryptic so hiding places are essential for their well-being. Marine Bettas also consume bristleworms so they also offer this benefit.

Dottybacks (Pseudochromidae) Hardy and often very colorful these elongate fish can also be very aggressive. One specimen per tank unless it’s very large and plenty of hiding places can be provided. They are prone to color loss unless a varied high quality diet is provided. Commercial propagation of many of these species is now being achieved with their being some diminution of the aggressive qualities a result.

Wrasses (Labridae) This is a very diverse family (over 600 species) with the large members being very aggressive. The larger fish will eat their smaller tankmates so care should be taken when choosing tankmates. For passive community tanks flasher (Paracheilinus) and fairy (Cirrhilabrus) wrasses make good tankmates as long as their need for almost constant feeding with plankton is met.

Surgeonfish (Acanthuridae) These flatly compressed fish contain some of the most frequently kept fish. They require large tanks with lots of swimming space and can be aggressive to other members of their species if their tank is not large enough. They require lots of plant material in their diet and are prone to lateral line disease if their dietary requirements are not met. The also have a very thin mucous coat on their body so they are prone to ick and other parasitic infections after shipping so they should be quarantined before being placed in their final home.

Rabbitfish (Siganidae) Similar in shape to the surgeonfish these fish have poisonous hollow dorsal spines, which they use for protection. They can deliver a painful sting if they are touched. They require lots of swimming space and are herbivores like the surgeonfish. They can be housed in groups or schools in large tanks.

Lionfish (Scorpaenidae) These fish are predatory, but are rarely aggressive to each other. The dorsal spines are venomous and while their stings are rarely fatal they can be quite painful and require medical attention. They should be fed only once or twice per week with chunks of white fleshed fish once they have been weaned from live food. Otherwise they have a tendency to develop fatty livers and die.

Groupers (Serenade) Most are very hardy and some species are aggressive to large tankmates. They will eat or attempt to eat fish that are up to ¾ of their length so care should be taken when selecting tankmates. They are not overly active and spend much of their time sitting in a cave or hiding place so this should be taken into consideration when selecting tankmates. They also grow quite rapidly from the small individuals that are usually available so they can rapidly outgrow most tanks.

Triggerfish (Balistidae) These fish are popular due to their striking colors, interesting behaviors and their resilience to poor water quality and disease. Their dispositions vary from combative to compliant. They are in general one of the more aggressive and territorial fish so they should almost always be the last fish introduced into a tank. They will eat almost anything and will do so with vigor so they should not be housed with any passive non-aggressive feeders.

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