How many fish? Around 1" per 2 gallons in a well-established (mature) fish only tank - after a year - has been quoted as a preferred maximum. Where fish and invertebrates are together, the number of fish should be far less, as their wastes could be problematical for the invertebrates if heavy. Much also depends on the tank's capability to clean itself and this reflects back to the filtration and water management capabilities once more. However, there is also the problem of compatibility to be considered - that's inter-fish compatibility, not the strain on your finances!

Not all fish get on well together, not even those from the same species. Some won't even tolerate other fish that share the same colouration. Of course, the fishkeeper will rule out keeping fishes that have extreme differences in size and will also understand, ahead of purchase, what demands the fish will make in respect of diet; like freshwater fish there are diverse tastes to satisfy - carnivores, herbivores and omnivores, plus those fish that like bite-sized chunks, those that eat only microscopic sized particles - and those that will eat your treasured corals and sponges.

Incidentally, some of the more exotic species of Angelfish and Butterflyfish have such very specialised diets in the wild that they do not make very good aquarium subjects, unless their dietary needs can be met.

Add to those choice problems the fact that there are fish that use mimicry of colour patterns to achieve less sociable activities and you will realise that any advance information is well worth having, before you buy!

Invertebrates fall into two categories - those that get around and those that don't.
Again, some of the mobile ones can be predatory and some of the sedentary ones can sting, so there's caution to be exercised during selection here too.

With all its natural benefits, it is often overlooked that although living rock may well bring beautiful surface growths with it, it can also have hidden dangers; maybe a predatory Mantis Shrimp will crawl out of the rock some weeks later and set about your other tank inhabitants. Bristleworms, too, are likely to be stowaways in the rock along with small Crabs.

Like fish, not all invertebrates get on with each other - make sure you site them in the aquarium with sufficient 'security space' between them. Many sedentary invertebrates (corals, for example) require specific lighting to devlop properly (see Lighting).
Feeding invertebrates is not much of a problem: some may require the odd tidbit once a week - or a brief squirt of liquid food - but most get their nourishment direct from the water - juices from frozen foods, for example.

Add regular top-ups of trace elements to keep invertebrates nourished; calcium is vitally important so that the shells of crabs and shrimps can develop and hard corals are also equally dependent on calcium for their continuing good health.

Marine fish and invertebrates are well catered for as far as food is concerned; most of the well-known aquatic manufacturers have produced flake, granular or liquid foods (many in carnivore, herbivore or omnivore formats) suitable for marine aquarium use. Additionally, dealers' freezer cabinets are well-stocked with frozen foods from natural sources. Here, as in all aquarium management circles, the rule is never to overfeed. Some fishes may take a little time to acclimatise to 'processed foods' but generally pangs of hunger eventually bring them round.

What Size Aquarium?
Water Preparation
Filtration Systems
Setting-up and Running-In
Water Condition Management
Useful Hints

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Last updated March 10, 2002