Shoaling Saltwater Aquaria Fish

In the article you will find some basic information on Shoaling Saltwater Aquaria Fish.

Two Fish that Readily Shoal in the Saltwater Aquarium

So you want a shoaling fish for your saltwater aquarium, eh? There are many delights associated with having a large aquarium, but keeping a small shoal (or school—more on that later) of fish can be visually stunning. Threadfin cardinalfish and green chromis are among the best, readily available shoaling fish for a large saltwater aquarium.

Shoal or School?

A shoal is the term used to describe a group of fish which swim together. This behavior is all about survival. Shoaling behavior is a means to ward off potential predators and to feed or forage more successfully. Can you call it a “school” of fish? Sure—if you like. Since Anglo-Saxon times, the word has been used interchangeably (and the Irish have even been known to say scule). While there are some generally accepted differences between shoal and school, they are beyond the scope of this article.

Do All Shoaling Fish Shoal in the Saltwater Aquarium?

The problem with shoaling fish in the saltwater aquarium is that certain species that shoal in the wild will fight to the death if placed in anything but the largest public aquarium. Yellow tangs are a good example. This most common of saltwater aquarium fish shoals in large numbers in the wild, but more than one adult in a home saltwater aquarium can cause serious problems. Therefore it is not advisable to try to recreate that shoal of fish you saw on your recent dive or in that picture of a natural reef without first doing a little more research.

Threadfin Cardinal

One excellent shoaling family of fishes for the saltwater aquarium is the family Apogonidae, better known as the cardinalfishes. In particular, the threadfin cardinalfish (Zoramia leptacantha) is an easy-to-keep, readily available and relatively inexpensive cardinalfish species that will readily shoal in a saltwater aquarium. You may also see them sold as longspine cardinalfish or glass cardinalfish.

The threadfin cardinalfish, with its pronounced dorsal fin, is an almost transparent yellowish-white fish with metallic blue and orange accents on the anterior part of its body and head. They grow to about two and one half inches and are indigenous to the Indo-Pacific and the Red Sea.

In the wild, the threadfin cardinalfish will shoal with other species over branching corals such as porites (both (Porites cylindrica and P. andrewsi are cited in Fishbase). While they are a nocturnal fish, threadfin cardinalfish will readily adjust to being active during the day. Threadfin cardinalfish (as with most shoaling fish) should be introduced in odd numbers of five or more individuals to the saltwater aquarium at the same time. They are a generally peaceful fish and are best in a non-aggressive reef tank or FOWLR system.

Green Chromis

Another outstanding shoaling marine fish for the saltwater aquarium is the green chromis (Chromis viridis). This is a damselfish (family Pomacentridae) that, while under some lighting will appear a dullish blue green, is actually an incredibly showy fish under most quality aquarium lighting. As the shoal shifts and turns, the flashes of metallic aqua-marine add life and beauty to almost any community reef tank or FOWLR system.

In addition to their remarkable coloration, green chromis act as a so-called “dithering fish” known to entice shy fish out into the open. The green chromis is less aggressive than the sometimes flashier blue chromis. Growing to three inches, they shoal around thickets of branching Acropora coral in the wild and in the large saltwater aquarium. It is best to add them in uneven numbers, at the same time and with at least five to seven individuals.

The threadfin cardinalfish and the green chromis both make excellent shoaling fish for the large saltwater aquarium. The threadfin cardinalfish can usually be found for between $10 and $15 each, while the green chromis is generally under $5 each.