Saltwater fish

More than 4,000 species of saltwater fish are thought to inhabit the world’s coral reefs. Reefs occupy less than 1% of ocean surface area, but provide the habitat for more than a quarter of all saltwater fish species.

colorful saltwater fish

In the home aquarium, saltwater fish add color, flash and personality to any tank. Selecting the best fish for your marine aquarium is a decision based on a couple of important factors:

  • How new your tank is—fish suited for the living conditions of a newly set up marine aquarium are called starter fish. Suitable starter fish should be hardy, vibrant and peaceful.
  • Do you have coral? Many saltwater fish species nip at or even eat coral you would commonly keep in your aquarium. If you plan to keep corals with your fish, you will have to limit your choices to reef safe fish
  • Compatibility with other fish species—As a general rule, most big fish will eat almost any smaller fish that will fit inside its mouth. But even similarly sized saltwater fish may not be compatible. Check out this compatibility chart to see if the fish you are thinking about are compatible with each other.

Cycle your tank before adding saltwater fish

Everyone has their own opinion about what fish to add to a new saltwater fish tank. One of the biggest problems with new tanks is a phenomenon called New Tank Syndrome—essentially, new tanks are unstable and oftentimes fish added to a new tank perish quickly—because the environment is too harsh. The most important thing you can when setting up your new saltwater fish tank is to allow for the time to properly cycle the marine aquarium.

Cycling a marine aquarium is the process of establishing the biological filter. Adding saltwater fish (sometimes called starter fish) to a marine aquarium before the tank has completed cycling is one of the most common mistakes hobbyists make. The best way to cycle a marine aquarium is with the fishless cycling method.

Set up a quarantine tank to prevent the spread of parasites and disease


image by Hilary Kladke

It may seem like a hassle to set up a quarantine tank, but it is probably the most important thing you can do to ensure the long-term health and success of the saltwater fish in your aquarium. Parasites like saltwater ich and marine velvet spread rapidly in a marine aquarium and can be a nightmare to treat in a reef tank. The best medicine is prevention. The best way to prevent the problem is by setting up a quarantine tank.

Acclimate before adding fish to a marine aquarium

From the moment the saltwater fish is put in the plastic bag for the trek home to your marine aquarium, the water inside that bag begins to degrade and the temperature begins to change. Depending on the quality of the water when the fish was packed for transportation and the time it takes for the fish to reach your home, the water parameters inside the bag (temperature, pH, ammonia concentration) may be significantly different from the water in your tank. To avoid shocking (and potentially killing) your saltwater fish, you need to acclimate the fish to the new marine aquarium conditions. One of the most effective ways to acclimate saltwater fish is with the drip method.


There are a few things you should consider when feeding your saltwater fish:

  • It is better to feed your fish small portions 2-3 times a day than to feed a large portion once a day
  • Uneaten food will decay and deteriorate the water quality in your marine aquarium
  • Understand the nutritional requirements and feeding preferences for the fish species in your aquarium and try to meet those needs with a varied diet of high quality foods
    • Herbivorous fish like tangs and surgeonfish need seaweed in their diets
    • Certain angelfish species require sponges and other reef-based foods and do better when feed a varied diet
    • Many butterflyfish species eat coral polyps and nearly impossible to keep in a saltwater fish tank
    • Saltwater fish that are reluctant to eat in your aquarium can often be coaxed into eating with frozen foods (instead of dry flakes or pellets) or live foods like brine shrimp or black worms
    • You can easily make your own fish food using frozen seafood ingredients

Diseases of saltwater sail fin tang saltwater fish from New England Aquariumfish

Disease and parasitic infections are a major reason why aquarists can become frustrated with and leave the saltwater aquarium hobby. Infestations of marine velvet or saltwater ich can ransack the fish in a marine aquarium. Once inside your tank, eliminating parasites can be a major hassle.

Common saltwater fish diseases/parasitic infections are:

  • Saltwater ich—a parasitic infection that looks like tiny white dots that attach to the fins, scales and gills of your saltwater fish
  • Marine velvet—an infection caused by a single-celled parasite known as a dinoflagellate. Marine velvet looks like tiny specks of gold on the fins and scales of your fish. Affected fish will show signs of stress and rapid breathing. This is a very serious and deadly parasite
  • Brooklynella—a disease caused by a protozoan. One of the most obvious symptoms will be excessive production of mucus on the skin of an infected fish.
  • Black ich—is a worm infection that looks like tiny black dots. Surgeonfish and tangs are commonly affected by this disease
  • Fin rot—is the deterioration of the fins and is caused by a bacteria. Fin rot is often made worse by poor water conditions and can be treated with water changes and an antibiotic to kill the problem bacteria.
  • Pop eye—also caused by a bacteria, pop eye shows up as swelling or cloudiness of the eyes. Pop eye can also be treated by an antibiotic
  • Head and lateral line erosion (HLLE)—is also called hole-in-the-head disease and appears as holes/sores on the head and lateral line of your saltwater fish. HLLE appears to have both a viral and nutritional component that causes the condition. There is a link between HLLE and use of activated carbon in the tank. Don’t miss this article, it is a MUST READ.

A great place to learn about what the different diseases look like is here.

If you are looking for a good book on the topic, check out Fish Disease Diagnosis and Treatment, by Edward J. Noga, it provides a very nice overview of the common (and uncommon) diseases, parasites and treatments.

Breeding saltwater fish

popular saltwater fish

Neon Gobies: A popular saltwater fish-image by tiswango

Breeding saltwater fish is truly my passion. I have been fortunate enough to breed the Banggai Cardinalfish, Neon Goby and Common Clownfish—but there are countless other species that will readily breed in the marine aquarium. Breeding saltwater fish, in my experience, is similar to breeding freshwater fish. It is important to have healthy, mature broodstock (the fish you want to be the parents), and to feed them with highly nutritious foods. It’s almost like you need to ‘fatten up your fish’ to get them ready to breed. The three hardest parts about breeding are:

  • Patience—the fish will breed in their own good time. Most of the fish commonly sold in fish stores and online are juvenile or young-adult fish—and it takes time for them to become mature enough to breed.
  • Caring for the offspring—Freshwater fish emerge from their eggs as fry—fully formed, baby fish. Most saltwater fish, on the other hand, hatch from their eggs as larvae and require a fair amount of care and feeding even before they reach the stage of small fry. To illustrate this point—let’s think about butterflies and birds. When birds lay eggs, a baby bird emerges from the egg—it grows up, and flies out of the nest. That is what freshwater fish are like. Marine fishes, on the other hand, are more like butterflies—and their babies are like caterpillars—they have a larval phase and must undergo a metamorphosis before they turn into little fish first.
  • Culture your own food–a lot of the art of breeding has to do with growing the right foods. You need to know the basics of culturing your own food, like phytoplankton, rotifers, copepods and brine shrimp.

Feeding and caring for your larval fish is the hardest part of breeding saltwater fish. Still, when that hard work pays off and you have a tank of tiny fish, it is totally worth it.

breeder's guide to saltwater fishesThe best online source for information about breeding saltwater fish is MOFIB, a forum of people dedicated to breeding. You will find an awesome amount of information there.

The best book you can buy about breeding is Matthew Wittenrich’s book, The Complete Illustrated Breeder’s Guide to Marine Aquarium Fishes. Matthew does a great job covering the generalities of breeding as well as specific accounts on a species by species basis.

The science of captive-breeding is continually advancing. Read about breakthroughs for four more species.

Written by Albert B. Ulrich III. Follow me on  and Twitter

Other information about saltwater fish

Here are some other interesting articles about saltwater fish that you might enjoy:

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