When it comes time to stock a new marine reef tank, a fish-only-with-live-rock tank or a specialized marine biotope (coral reef lagoon, reef face, reef cave, etc.), domestic aquarists are most often predisposed to go with Indo-Pacific fishes, corals and invertebrates. But by pigeonholing their livestock selections to fit the "Coral Triangle" model (and why wouldn't they, as the majority of aquarium fishes and corals come from there?), they do a disservice to the many beautiful reef fishes and invertebrates in their own backyard: the western Atlantic, particularly the Caribbean. Not only are these animals colorful, but they offer interesting life histories, unique behaviors and undergo much less shipping stress (they don't have to go as far or as long from their home to yours).
The next time you set up an aquarium, give a Caribbean biotope tank a whirl. The goal with a biotope is to capture the essence of a particular place, be it a Pacific reef lagoon or a Caribbean patch reef, by housing corals, reef fishes, invertebrates, macroalgaes, etc., that would normally be found in close proximity in the wild. A beautiful, readily available and inexpensive fish that would fit into just such a biotope would be the sergeant major (Abudefduf saxatilis).
Difficulty: These damselfish quickly adapt to home aquaria, and their care requirements make them easy to maintain.
Hardiness: If kept in a well-maintained aquarium with an absence of bullies, and plenty of live rock and coral for hiding places and to help create visual breaks, these fish thrive in a reef aquarium setting.
Physical description: Their common moniker comes from the five vertical black stripes (sometimes a faint sixth stripe is visible) on their white and yellow (dorsally) flanks reminiscent of a U.S. Army sergeant major's six-striped insignia. Their color fades with age, and most of the yellow coloration eventually dissipates. Sergeant majors grow to 6 inches as adults, and if keeping several, need a big tank with plenty of swimming room. Their narrow, rounded, laterally compressed body type makes them speedy swimmers. They also have a black spot at the base of the pectorals.
These fish are omnipresent on Caribbean coral reefs but range throughout the western Atlantic, north to Canada (thank the warm Gulf Stream for this) and south to Uruguay. They also turn up in the equatorial waters of the eastern Atlantic, off the coast of West Africa. Adults are most often out in the open on shallow coral reefs and are often found in large feeding groups, which can number in the hundreds; juveniles hang out in small shoals near overhangs, caves and shipwrecks.
When stocking these fish, go online for information on what Caribbean fishes will handle their "business" with these semi-aggressive, territorial damsels. One sergeant major is probably appropriate for most smaller-sized reef tanks (less than 50 gallons); more can obviously be kept in larger setups replete with lots of visual barriers and other fishes that will push back if a sergeant starts drilling its tankmates. Conspecifics, smaller and peaceful fishes will potentially be bullied. Corals are safe from these omnivores, but they chomp on small crustaceans, small anemones and small fishes.
Interestingly, they were first called Abudefduf saxatilis by famous Swedish taxonomist Carl Linnaeus. Abudefduf translates to "father," which is an unfaltering salute to the species' bossy modus operandi.
A minimum tank size of 20 gallons is recommended for a single specimen. For small groups, you'll want at least a 50 gallon, preferably larger if keeping other fish as well. Keep these temperamental beauties with other large, pugnacious fishes. Avoid natural predators of these fish, including some wrasses and groupers in the families Labridae and Serranidae, respectively.
Besides the usual good filtration and a balanced diet of meaty foods (Mysis and brine shrimp), commercial diets for herbivores (Spirulina) and flaked foods, they will also graze on a good crop of in-tank algae for their nutritional needs.
Sergeant major tank parameters incude a water temperature between 72 and 78 degrees Fahrenheit, dKH of around 10, pH of 8.2 and a specific gravity of 1.025.
Special note: One interesting thing about these fish is their ability to camouflage themselves in two ways. They appear to blend in with the brightly illuminated surface when viewed from underneath; when viewed from above, they have a darker, broken-up form that perfectly blends into the reef.