Groupers in the Home Aquarium

Author: Jim McDavid

We’ve all seen them at one time or another, perhaps on television, at a public aquarium, or even at your local fish store. Beautiful, charismatic, and robust, the groupers of the family Serranidae offer much to those with enough space to accommodate their basic needs. Easy to keep and full of personality, one is hard-pressed to name a more trouble-free, interesting, and rewarding group of fish for the larger home aquarium. One might be right for you!

I’m Interested, Tell Me More!

The family Serranidae is quite large and diverse, with members ranging from a few inches in size to over 9 feet—large enough to swallow a diver! Within the family are several subfamilies. This is a diverse group of fish that includes aquarium favorites such as anthias, basslets, and hamlets.


Here I want to focus on the subfamily Epinephelinae, specifically on the smaller, aquarium-suitable representatives that are easily obtainable in the hobby. The subfamily includes some true monsters that are best left in the ocean, but there are also plenty of species that can be housed in a 200-gallon-plus aquarium, and some are even small enough to make do with slightly smaller accommodations.


The common names of these fishes can be confusing. They are all, regardless of genera, properly called basses. Only members of the genus Epinephelus, Mycteroperca, and a few other genera are generally referred to as groupers by scientists, while members of the genus Cephalopholis are often called hinds. As with all common names, this is purely arbitrary, and the hinds were at one time groupers in good standing. I’ll lump the hinds and groupers together here, as their care, general morphology, and behavior are more or less identical.

Physical Characteristics

These fish are robust, moderately elongate ambush predators with large, voluminous mouths capable of swallowing rather large prey items in relation to their size. Ranging in color from drab to stunningly vibrant, even the less-garish species possess a personality that endears them to many keepers, including yours truly. Often when peering at a grouper in a large marine aquarium, you’ll find it actually looking back at you, as if wondering just exactly what you’re up to!

What Do I Need to Know?

Tank Size

Let’s begin with the tank, which for a prospective grouper keeper is the first limiting factor. It’s very important that the aquarist is realistic when considering buying one of these specimens at his or her local fish store. Though they are stunning animals, they are often victims of classic impulse purchases by aquarists with accommodations that are far too small.

Although most species you’re likely to come across—and definitely all those appropriate for home aquaria—are small by grouper standards, the species I’ll focus on here are still large by aquarium standards and need plenty of room. This is both to provide the needed swimming space and to make sure dissolved nutrients are kept at reasonable levels between water changes.

While small individuals are often offered for sale, they can grow quickly, and you shouldn’t get one thinking you can get a bigger tank down the road. You probably won’t, at least not in time.

As mentioned above, 200 gallons is a good minimum target if one is planning on keeping a grouper with a handful of other appropriate fish, but a few of the smaller species such as C. formosa or E. ongus can live quite comfortably in a 120-gallon or larger community aquarium, whereas larger species such as the lyretail grouper Variola louti, the spotted coral grouper Plectropomus maculatus, and the tomato hind Cephalopholis sonnerati all need accommodations of greater than 300 gallons.

With regard to tanks, larger is always better, especially when tankmates are considered. The aquarist should steer clear of narrow show tanks and look for aquariums with a front-to-back measurement of at least 24 inches for most species.

Social Behavior

While not aggressive by marine fish standards, they can have their moments, especially with other, similarly sized groupers. Make sure to provide plenty of shelters in the form of caves or overhangs. Not only will these fish often select such locations for their home base, but you’ll also find that the fish will be much less shy if it knows it can hide if it wants to. Additionally, out of sight is out of mind with regard to territorial disputes, and plenty of rocks will mitigate aggressive interactions with tankmates.

Keep Track of These Needs

The above requirements, along with the need to provide plenty of swimming space and the average size of these fish, should make the need for a very large tank obvious.

Be realistic with regard to your ability to accommodate the fish at or near its full adult size. A small 3-inch coral hind or miniatus grouper C. miniata is easy to accommodate in a 40-gallon tank, but shortly down the road you’ll have a fish on your hands that has outgrown its quarters and then some.

What About Waste Management?

An ever-important consideration, careful planning in the filtration department is a must with these fish. A small specimen is of no particular concern, and no extra measures need be taken on the part of the aquarist. As it grows, however, it places an increasingly large load on the filtration system, and managing the nitrogen cycle can become a real challenge.

E. hexagonatus

An 11-inch honeycomb grouper E. hexagonatus puts away a considerable amount of food, with a waste output to match! At a single feeding, a fish this size can easily eat two 8-inch squids whole, and a proportional amount of waste is produced as a result.


Unless the system is very large, with a preponderance of live rock, a large protein skimmer, and only a few other fish, you’re going to need supplemental filtration to handle the significant waste produced by these hefty predators. Every tank is different with regard to the bioload it can sustain, but it is likely that the husbandry practices employed to handle the waste loads of say a few damselfish, a sixline wrasse, and a flame angel will not suffice when dealing with a grouper or two and the companions that are likely to be kept with it. Predatory fish are messy, and will place a strain on any system that is not carefully managed.

While live rock and decent water circulation is a good start, I would strongly recommend that the keeper employ a protein skimmer, as well as a means of mechanical filtration such as a large canister filter, or perhaps a large power filter or two, to help with the large amounts of waste produced. Although power filters are not typically used on marine tanks nowadays, they do a fine job of removing particulates and are easily cleaned, and cleaning is something you’ll do often when keeping the fish at or near adult size!

Water Changes

On that note, and perhaps most importantly, regular water changes must be carried out. How much and how often will depend on the bioload and the filtration being employed on the tank in question, and this can range as high as 50 percent every week! Indeed, with regard to the husbandry of these fish, the filtration should be regarded as a stopgap to keep water parameters in line between water changes, rather than the primary means of controlling water quality, as is normally the case with other marine tanks.

Which one do I pick?

The behavior of the various species of groupers, including the hinds of the genus Cephalopholis, are more or less identical, thus an exhaustive description of the various species is pointless here. Your choice will come down to the size of your aquarium, the other fish you wish to keep in the system, and your personal preferences.

Assuming the tank is properly set up and established, and a quarantine tank of suitable size is also ready and waiting, you can start looking for your new pet fish. Groupers are resilient fish and thankfully handle shipping well, so most specimens are still in fine shape by the time they reach your local store. Look for good color, and make sure there are no off-color patches or spots on the skin or fins. Look for pits on the head or behind the eyes, which could be indicative of lateral line erosion. Also, make sure the fish is alert and wary.

A healthy individual is attentive and will look back at you in a way you don’t experience from most other marine fish. The aquarist doesn’t have to be too concerned about the size of the individual he or she is shopping for, as both very young and larger, more mature individuals adapt readily to captivity, but I do recommend that fish no larger than 6 inches be purchased.

The Genus Cephalopholis

The groupers of the genus Cephalopholis are some of the most desirable and commonly available members of the group. Hardy and drop-dead gorgeous, they make perfect residents for a larger marine system. Most species are relatively small, in the 9- to 16-inch range, and all are hardy and easy to keep. There are species available that will be at home in aquariums from as small as 6-feet long and up.

Other Species

Some standout species include the miniatus grouper C. miniata (also known as the coral hind or coral trout), which grows to 18 inches, and the blue-spotted grouper C. argus (also known as the peacock hind), which attains a similar size.

The blue line grouper C. formosa is another species of note. Under 14 inches, it’s one the best species for small tanks in the 135-gallon range.

Among the groupers of the genus Epinephelus are some great choices as well, with E. ongus, the specklefin grouper, being one of the best bets. Topping out at about a foot, this beautiful species is another great choice for a tank of at least 135 gallons. E. hexagonatus and E. merra are similar in size and desirability, if somewhat harder to find.

How do I add one to my tank?

Rearrange Decor

When introducing a grouper into your display (after a six-week quarantine period, of course), it’s a good idea, if practical, to rearrange the decor in order to break up existing territories in the tank. This is especially true if any somewhat aggressive fish are already established in the system, such as an angelfish or triggerfish. It is doubly important if another grouper is already in residence!

This puts all of the fish in a new, uncertain environment, eliminates established territories, and mitigates aggressive territorial responses from the current residents. Introducing the new fish at night after the lights have been out for a time goes further to reduce aggressive interactions. A grouper is often very shy initially, frequently dashing into a cave or crevice, the keeper seeing only glimpses of it for a number of days. Over time it will become bolder, spending more and more time in full view.

Keeping Multiple Groupers

Contrary to what you may have read elsewhere, if the tank is at least in the 180-gallon range, it’s often possible to keep two or more groupers together, even those belonging to the same genus (note: not the same species!) in a single display. By far the best way to accomplish this is to add the fish at the same time. This way the fish in question are again on equal footing, neither has an established territory, and both are somewhat disoriented at suddenly finding themselves in new surroundings. Rearranging the decor as mentioned above will be of help here in regard to dealing with fish already in the system.

If a grouper is already established in the system, it is almost imperative that the newcomer be a bit larger than the resident. The established fish will invariably be irritated at the new arrival in his territory, and will hold the upper hand in the inevitable confrontation. If the newcomer is somewhat larger, he will be less stressed by and better able to cope with the irate behavior of the resident grouper. This displaying, gaping, chasing, and ritualized combat starts out rather intensely by both individuals, and decreases in frequency and severity over a matter of hours. By the next day, both fish are usually over it, and life can proceed as normal.

What About Other Tankmates?

These fish, while far from meek, are more or less on the easy-going side with regard to temperament. While aggression among conspecifics is intense to the point where keeping two of a given species is usually impossible, interspecific aggression is usually minimal, especially where other non-serranids are concerned.

The main concern the aquarist has is selecting companions that will be too large to be swallowed by the grouper. While this might seem a straightforward consideration, these fish can surprise you in this regard, so err on the side of caution when picking tankmates. All members of the subfamily Epinephelinaecan put away a meal at least a third of their own body length, and some species, especially members of the genus Epinephelus, can swallow even bigger meals than that.

When selecting tankmates, keep the likely adult size in mind for all species that you’re considering, as well as the growth rates of all fish concerned. For instance, a lionfish will grow much more quickly than most grouper species. Thus, a juvenile grouper and lionfish of equal sizes living together with no issues will result eventually in the grouper becoming a meal for the lionfish! As with all things in the world of marine aquaria, planning is key.

How Should I Feed My Grouper?

Feeding is one of the best parts of keeping a grouper! These fish are out and out predators, carnivores in full—no algae flakes please! An often-overlooked aspect by lazy keepers, variety in the diet is essential, and every effort should be made on the part of the aquarist to make sure the fish in his care receive a varied array of food offerings. This, more than anything, is the key to a long, disease-free life. Indeed, these fish should enjoy a lifespan of at least 12 to 15 years in captivity.

A visit to the seafood counter at your local grocer will reveal a multitude of choices. Of particular use are scallops, shrimp, and squid, as they are for most hinds already in ready-to-feed, bite-sized morsels. Fish meat such as halibut and snapper can also be utilized.

It should be noted, however, that all predators, be they reptiles, birds, cats, or fish, need whole food items in order to obtain all the nutrients they require, not just meat. In other words, organs, bones, etc., are all part of their natural diet. This means the keeper must offer some kind of complete animal item at least once or twice a week, and these items should be as varied as possible. Possibilities are frozen baitfish of various species, which are often available at bait stores, or whole shrimp and crayfish. Frozen silversides are commonly available at aquarium fish retailers as well. Soak food items in a vitamin supplement a few times a week. Additionally, there are frozen preparations available that are already vitamin fortified, which make excellent food for these fish.

Give Groupers a Try

If you have the space and want the most beautiful, hardy, long-lived, and interesting centerpiece fish around, don’t hesitate to give the groupers a look. Hardy, long-lived, charismatic, and beautiful, a more rewarding marine tank inhabitant is hard to find!

See the full article on TFH Digital