Marine Fish

There are two main types of marine aquarium, one being a relatively sterile environment to keep fish, with no invertebrates, other than possibly some of the few very hardy species that will survive in such a setting. This is generally known as a “fish-only” aquarium. The other is a “reef tank”, which houses both compatible fish and invertebrates, to form a miniature representation of a coral reef. In this discussion it is the “fish-only” scenario being covered.

A fish-only marine aquarium scene with coral ornaments as decor.

A fish-only marine aquarium scene with coral ornaments as decor.


Marine fish have been kept in captivity for many years now, but it is the home marine aquarium that has really become so hugely popular worldwide today. No longer the preserve of the larger public aquariums and institutions, the spectacular beauty of a marine aquarium can be within the domain of most interested would-be fishkeepers. At the outset of the domestic marine fish hobby, many years ago, the required equipment was either in very limited supply and range, or even unobtainable. Often it was necessary to adapt and modify what was on offer for the established freshwater aquarium hobby. The situation today is totally changed, with a vast range of products on offer, enabling the most sophisticated set-up to be created for keeping the fascinating marine reef fishes from tropical seas. However, we at The Goldfish Bowl believe that a false impression has been generated that much, if not all, of this equipment in its variety is totally necessary in order to be able to maintain a successful marine aquarium. The fact is that with proper care and following a chosen method of maintenance, a relatively simple set-up can deliver very successful results.

n example of a tropical marine aquarium with cured coral skeleton decorations and no live invertebrates.

An example of a tropical marine aquarium with cured coral skeleton decorations and no live invertebrates.


Good water chemistry is what every tropical marine aquarium demands. Good filtration, assisted by the aquarium keeper’s close control on feeding, making regular part-water changes, not over-populating the aquarium, etc, will ensure the correct balance to maintain that all-important requisite of perfect water chemistry. For maximum efficiency the water in the aquarium needs to turn-over via the filters a few times every hour, passing through selected filter media with which the canister bodies will be charged. One outside fitting power-filter – as large as is necessary – might be sufficient, but two working at opposite ends of the tank will be far better. The sparkling clarity of the water is obvious to see, but there is more important work going on inside those filters. Also, another option is a sump-based system, which works as if it is a large canister filter and allows the use of different chambers complete with different media, all depending on stocking levels and size. You can also use this sump – which sits below the tank – as a means of hiding all your equipment so the visual impact on the aquarium is minimal. The nitrobacter colonising the filter media play an essential part in the proper balance of the nitrification process, and it takes time for this natural, living bacteria to form and multiply. The newly set up aquarium does not have this bacteria, and it must be nurtured from scratch. This may be achieved with starter colonies introduced at the outset to get things moving, or by putting in very few tough fish known to be nitrite-resistant, able to live happily through the period of volatile chemistry the water will pass through during the maturing process. How long does it take for this process to build up to a satisfactory level? There in no neat answer to that question, as it all depends on factors that will vary from aquarium to aquarium. Things could settle down reasonably within a couple of weeks (rarely!), or take up to six weeks (a fair average) for a manageable stage to be reached. But FULL maturity will, in all probability, take up to one year. Discuss this matter with your knowledgeable shop staff to get a full understanding of its impact and importance.

If you choose to go ahead with a basic marine aquarium and accept the need for you to give it the time and attention it will require, you will need to address the matter of putting together the other equipment you will need. A choice of lighting, available in a range of spectrums, will need to be made. LED options are the most popular now and WiFi systems are also popular, allowing you to change the spectrum of your lights with a tap on the phone.

Another tough decision – decide what kind of background you will want. These are available in plain colours or reef scene photographic form. However, some people prefer to have an aquarium which they can see from both sides. A choice of substrate material is available, coral “gravel” being the most popular of these.
The “sea water” is usually made up from reverse osmosis water, into which special salt mixes with an impressive number of trace elements in their make-up are added. Even those aquarium keepers living at the seaside are advised to use this artificial sea water, as its quality is known, whereas natural sea water taken from the ocean can bring all manner of pathogens into the aquarium if used untreated. A refractometer is the most accurate way to determine when the correct salinity level has been reached.

Selecting the fish for the aquarium must be done with great care. Not all will live peacefully together and advice about their temperament and any special needs should be obtained before making purchases. Observe the particular fish you intend to buy, and make sure there are no marks, blemishes, or outward signs of damage. Ask for the fish in that aquarium to be fed, and be sure the one you have lined up to possibly buy is feeding confidently. Check the respiration rate by looking closely as the movement of the gill plates. There should be a steady beat, and not an accelerated rate. If it is not a bottom-dwelling fish watch to see that is does not hug the bottom uncharacteristically. Conversely, if it is not a surface swimmer watch it carefully should it be seen spending much of its time at the surface. Do not hesitate to ask the shop staff how long that particular fish has been in stock. Be especially wary if it is a new arrival, and check out the above points even more scrupulously. If is it a wild caught fish, as most are, these points are particularly pertinent. Aquarium bred marine fish are becoming increasingly available, and provide some protection against unseen problems which wild-caught fish may harbour. Buying cheaply from a dubious source is not cheap! Have confidence in the shop where you buy your stock, and use their expertise to guide you through the beginnings of your marine fish hobby.

The Goldfish Bowl offers a free water-check service, so you can bring in a small water sample and have it checked while you wait for certain conditions. Handy test kits are available for you to make your own tests, if you prefer. However you choose to do it, making regular tests of the water chemistry during the early days of the marine aquarium after setting up is crucial. You NEED to know what is happening to the aquarium water in order to monitor its progress towards maturity. Even after attaining full maturity and everything appears to be going on well, it is advisable to make occasional water checks to be sure all is truly well.
A comprehensive range of frozen foods is available from most good aquarium shops that sell marine fish, and these foods should be stocked in variety. Some marine fish will favour certain foods that others might shun altogether, so the offering of some variety is quite important. The best quality flake foods may also be used regularly, and most marine fish will accept these quite readily once they have settled down to aquarium life. Small, active fish, or otherwise voracious feeders, will need to be fed little and often, just as most other kinds of aquarium fish. Some more sedentary species will want nothing more than a good meal every other day.