Livestock Selection and Compatibility

Every animal needs the system to give it the right water, light, flow, food and room. Check those first: what the animal needs, where in the system it would live, what it eats and what might eat it, and how big it gets as an adult. An animal that doesn't fit the system won't do well however healthy it was when bought.

Planning which animals belong in which system is Module 36. This module is about choosing the animal itself and keeping the animals in a system from harming each other.

A healthy fish holds its fins open, has clear eyes, breathes normally and swims actively. Ask to see it eat: healthy fish respond eagerly to food. Walk away from white spots, a fine gold dust on the body, ragged fins, sores or cloudy eyes. If one fish in a tank is sick, treat every fish in that tank as exposed, even the ones that look fine.

Ask whether it was captive-bred or wild-caught, when it arrived, and whether it's had problems with tankmates. A fish that arrived days ago may still be stressed from shipping; one that's been in the shop at least a week with no signs of illness is a safer choice. For corals, look for receding tissue, bite marks and pests (Module 23). A carpet anemone shouldn't be deflating and reinflating often or showing a gaping mouth (Module 29); clams are covered in Module 28.

Captive-bred fish have grown up on aquarium foods and haven't been through capture and long shipping chains, and they're usually calmer in a tank. Wild-caught fish may take time to accept aquarium foods and arrive more stressed. Many species are only available wild-caught, and corals are often grown from fragments in captivity.

Captive-bred doesn't mean free of disease. A pathogen already present in a breeder's stock comes with every animal from it. Either way, every new animal is watched closely and gets into stable, mature water fast (Module 23).

Carpet anemones are predators: most fish will eventually be eaten by one, except their symbiotic clownfish and anemone shrimp. Most triggerfish are aggressive carnivores that eat smaller fish and invertebrates and grow large.

Predation can be slow. A fish that ignores small shrimp today may eat them as it grows, and an animal that disappears at night may have been eaten. Pump and overflow intakes are a danger to anemones too, so cover them (Module 22).

Large angelfish aren't reef safe, and butterflyfish that feed on coral eat coral polyps. Dwarf angelfish are debated: they may nip fleshy LPS corals and clam mantles. Some wrasses kill small fish and invertebrates, dottybacks may eat small shrimp, and adult tangs may eat crustaceans just after they molt. Larger, more aggressive damselfish can be a problem too.

Treat "reef safe" as a starting point, not a promise. Behavior varies between individual fish and with how well they're fed. In a system built around clams and anemones, any fish that might nip a mantle or eat an anemone is a risk to the main animals.

Marine fish are peaceful, semi-aggressive or aggressive, and many defend territory or compete for food in a confined tank. Add the most peaceful fish first and the most aggressive last: an aggressive fish added early claims the whole tank. Tangs and large angelfish usually go in last. Tangs may not get along with their own kind.

Rearranging the rock before adding a new fish breaks up established territories, so residents spend their time reclaiming space instead of chasing the newcomer. Hiding places and enough food reduce fighting. Flared fins and posturing are warning signs before a fight, and a new fish that hides and won't eat may be under attack.

In the wild, A. ocellaris lives in H. magnifica, S. gigantea and S. mertensii, and A. percula in H. magnifica, S. gigantea and H. crispa. Some clownfish are specialists with one host; others, such as A. clarkii, live with many. Juvenile A. ocellaris grow better with a natural host than with an unnatural one or none.

In an aquarium, clownfish may host other things, including anemones that aren't natural hosts. A carpet anemone that hosts clownfish still eats other fish. Clownfish defend their anemone against other fish, so plan the system around the pair and its host (Module 29).

Many LPS corals have long sweeper tentacles that can reach 15 cm (6 inches) or more and kill whatever they touch, so keep them well away from other corals. Many also fight with chemicals (section 9). Placing animals by light and flow is in Module 22.

Anemones move, and a moving anemone stings what it touches. Once an S. gigantea is established in a system, a new anemone never goes into that system's water (Module 23).

Allelopathy is chemical warfare. Animals fixed in one place can't chase competitors away, so many of them, particularly soft corals, release toxins into the water to keep neighbors from encroaching and to discourage predators. Leather corals such as Sarcophyton, Sinularia, Lobophytum and Lemnalia are well known for it; the chemicals include terpenoids. In the ocean they're diluted; in a closed system they build up.

Affected animals may show nothing, stay closed, stop growing, lose tissue or die, while the animal releasing the chemicals looks perfectly healthy. Suspect allelopathy when a system mixes soft and stony corals, when trouble starts after a new arrival, or when the animals suffering sit downstream of a known culprit. Fresh activated carbon, Poly-Filter and water changes remove the chemicals; carbon is used up and has to be replaced (Module 17). Give known culprits space and place them so the flow doesn't carry their chemicals straight onto sensitive animals. When choosing an animal, its tendency for chemical warfare matters as much as its size and care.

Anemones can do it too. In IMARCS experience, S. haddoni carpet anemones can be highly allelopathic toward each other, but not consistently: sometimes the effect is obvious and sometimes it isn't, and sometimes separating them clearly helps the health of both while other times it makes no difference. Why isn't known. The signs are an anemone that never fully inflates and deflates in cycles, looking irritated rather than limp; a limp anemone points to a bacterial infection instead (Module 29). Watch carpet anemones kept together, and be ready to separate them if either shows these signs.

Choose by the size an animal reaches as an adult, not its size in the shop. Territorial fish need enough space to hold a territory; tangs need large systems. Every animal adds to the system's load, and the system has a limit (Module 36).

A system that's comfortable today can be crowded in a year as animals grow. When that happens, something has to move, so plan the numbers with growth in mind.

Add new animals slowly, one at a time, with the most aggressive fish last. Every new animal is acclimated in its own container and rinsed through two buckets of the destination system's water (Module 23). Watch for the first days: whether it eats, whether it's being chased, and whether it's harming anything.

A nipped clam mantle: look for angelfish or other nippers. A small fish missing: check the carpet anemone and other predators. A new fish hiding and not eating: a territorial fish may be attacking it; rearrange rock or move one of them. Coral receding next to a neighbor: sweeper tentacles; move them apart. Stony corals closing after a soft coral arrives: suspect allelopathy; fresh carbon, Poly-Filter and a water change, and move the culprit. Removing the aggressor or moving an animal to a system it fits is often the only fix.