Creating a compatible community of marine fish

With a terrific diversity of colour and form, marine fishes are some of the most popular of aquatic pets but require careful handling to avoid potential problems.

One of the most convenient aspects of keeping marines is the fact that unlike many tropical freshwater fish, which differ in their environmental requirements, most marine species are found in similar conditions in the wild.

This means that fishes that would be oceans apart in the wild state may be kept alongside one another in the aquarium, providing factors such as territorial and dietary requirements are taken into account.

Unlike freshwater fish, marine species likely to be kept in the aquarium are almost always aggressively territorial. This means that individuals of the same species are as likely to fight in an aquarium as they would in the wild, unless already paired or of the correct sizes/sexes to do so. Such territorial aggression is the limiting factor to population density in the wild and is the reason that young fish are the best choice for the aquarium as their collection has little impact on healthy reef fish populations. An increasingly large number of fishes are now captive bred and as well as being hardier and less stressed than their wild counterparts they tend to be less aggressive.

When deciding on which fish to keep in your aquarium, a number of factors are important:

- Will this fish eat invertebrate or fish tank mates?

- Will this fish bully or be harassed by other inhabitants?

- Will this fish outgrow the set-up in question?

- Is this fish suitable for aquarium life?

Although other factors may be of concern, these are the most significant and can be seen to be behind most unsuccessful attempts to introduce new fish.

Many popular fish make use of the most numerous food resource found in their natural habitat- marine invertebrates. Some are very unselective feeders and will sample most organisms including shrimps, anemones and corals. Such species are usually easy to feed but are never suitable for reef tanks. Other fishes are superbly adapted to feed on smaller fish and will swallow most suitable individuals they encounter- as with freshwater predators. These fish are often available as very young individuals and find their way into community tanks, where the other tank mates eventually become lunch as they grow! 

A common mistake is to add territorial species such as Damselfishes to new tanks due to their tolerance of pollution as the system matures during the early stages. This results in difficulties adding less aggressive specimens to the Damsel's territory- something that would not be tolerated in the wild and is not welcomed in the artificial reef in your aquarium. A better way to mature any marine tank is to add liverock to support the biological loading and introduce the least aggressive specimen first, once water quality permits. More aggressive individuals can then be added last and can generally establish a territory alongside established fish with far less disruption. Homework during the early stages can determine the order in which your community should be established. Due to the territorial nature of reef fish, avoid putting species with similar colouration or markings together in the same tank, as they will normally clash over living space. Members of closely related species can also be poor choices as they are likely to require identical niches and fight as much as two individuals of the same species. Another combination prone to problems is mixing of species with the same feeding pattern- some Tangs and Blennies for example can be aggressive towards other algae-eating fish.

Many commonly available marine fish will grow to large sizes and may be bought by the unwary before outgrowing home aquaria. Dragon, Clown and Twinspot wrasses (Novaculichthys and Coris) are often seen as tiny juveniles that may grow far larger than 30cm and become very disruptive. Lionfish (Pterois) are capable of growing equally large and eating a wide range of tankmates, even the 'Dwarf' lionfish (Dendrochirus) can grow to 20cm but favours a diet of crustaceans. Panther or Polkadot groupers (Chromileptes) attain 60cm or more in common with many other frequently seen members of this group.

Size is not the only limiting factor to successfully maintaining marine fish, as in the right set-up many of these large fish can be successfully kept and will live a long and healthy life. More problematic are the species adapted to diets that cannot be duplicated in captivity - such as coral-eating Butterflyfish (Chaetodon), Filefish (Oxymonacanthus) and Blennies (Exalias), or those whose requirements are poorly understood such as Sweetlips (Plectorhinchus), some Batfish (Platax) and Goatfishes (Parupeneus). Such fish should be avoided as they are unsuitable for aquarium life and should not be removed from the wild.

Another group which deserves mention are those species such as Dragonets (Synchiropus) that can only be maintained when nutrition issues are solved. These fish need to be kept in established aquaria with healthy populations of amphipods and copepods to enable natural foraging behaviour. Similarly, Seahorses (Hippocampus) are difficult and time-consuming fishes to feed and should not be housed with species that will out compete them at feeding time. Due to pressure on wild populations only captive-bred Seahorses should be selected. Cleaner wrasses (Labroides) are also difficult to keep and only suitable for aquariums housing communities of large fish more commonly seen in public facilities. Their removal from reefs also damages the health of wild fish. Neon gobies (Gobiosoma) are an excellent alternative and captive-bred specimens are the most commonly available. 

In brief, a well-selected community of fish should consist of a variety of colour and pattern, with similar levels of aggression and adult sizes. Individuals should be added in increasing order of aggression and species should be researched before selection to ensure suitability. All fish should be feeding and healthy before purchase and although not essential, a quarantine tank can be a very useful resource in ensuring a long and healthy life for your aquatic pets. Tempting though it may be, never buy unhealthy livestock out of sympathy as it merely rewards poor husbandry by the supplier concerned. Maidenhead Aquatics only select top quality captive bred or net-caught stock from sustainable sources and I urge all marine keepers to do the same.