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The Big Picture – Marine Aquarium Giants

Hello again everyone! Craig here again, and in my last blog I talked about some of the biggest of the freshwater fish to be kept in home aquariums. In this blog, I will go over some of the big saltwater fish found in the hobby. Without a doubt, there are very large fish that call the sea their home. Some of these mammoth fish are being kept by hobbyists. With all the challenges of keeping a marine tank in tip-top condition, adding a giant fish to the mix can present dedicated fish keepers some challenges.

Honeycomb MorayLarge fish can be intimidating not only for their size, but their ferocious looks, too. Moray Eels are certainly some of the most intimidating. Their snake-like bodies and gaping mouths often cause people to get squeamish. One species, Gymnothorax favagineus, the Honeycomb Moray, is one of the most beautiful. Also known as the Tessellated Moray, this is one impressive fish. Able to reach a size of over 6 feet in length in the wild, this is definitely a giant. Boasting a beautiful white body with black splotches, there are few morays that are as attractive. In some individuals the dorsal takes on a yellow hue.  Read More »

Eels In The Home Aquarium

Jason TschudyPlease welcome our newest contributor, marine biologist in-training  Jason Tschudy with a little insight on some marine eels.

Eels.  Beautiful creatures that inspire fascination in many, fear in others, in many cases, a little of both.  These mysterious creatures make for a great focal point in a display aquarium.  There are quite a few species sold for the aquarium trade, but some are better suited for the aquarium than others.

Take the Snowflake Moray (Echidna nebulosa) for example.  It is one of the most attractive and readily available eels in the hobby.  These eels will eat crustaceans and small fish, and they can grow to about 36″ in length. The Snowflake Moray can generally be kept with other fish, things of moderate size like lionfish and angels won’t have a problem living with a Snowflake Moray. 


The Black Edged Moray (Gymnothorax saxicola) is another smaller species that can be a good fit for many aquariums.  It has diet and behavior similar to the Snowflake, and as with any eel it can get a bit aggressive when food is present.  They can be kept in a reef tank, but may predate any crustaceans in the tank. 

For those who like to go all out and have some extra cash lying around, the Dragon Moray (Enchelycore pardalis) is the eel for you.  They are considered the “holy grail” of eels by many aquarium enthusiasts.  They are extremely attractive, but pretty rare to the hobby.  These eels eat fish, but will happily eat shrimp, clam, and other foods in the aquarium too.  They grow to about 36 inches, so they’ll need a large tank, a nice cave to hide in, and a clean, well-maintained tank.

Generally a 75 gallon tank is big enough for the smaller species, but a larger tank is always recommended.  Most of the common eels found for the aquarium will grow between two and four feet long, though there are some, like the Green Moray (up to 8 ft) that can reach several feet. Larger species should only be housed in the largest of tanks, and it is important to know as much as you can about the species you’re considering –  how big a species can get, how much space it needs, dietary needs, and to be prepared before considering an eel for the home aquarium.

Introducing Moray Eels (Superorder Elapomorpha, Order Anguilliformes, Family Muraenidae): Natural History and Basic Care


More than 200 species of moray eels, all classified within the Family Muraenidae, have been described.  Like the familiar American eel, morays are considered to be true eels of the Order Anguilliformes.  The Superorder to which all eels belong, Elapomorpha, contains over 800 species, including the decidedly “un-eel like” tarpon.

Natural History

Although usually associated with tropical and subtropical habitats, a number occur in temperate seas, and several enter brackish and fresh water on occasion.  Ranging in size from the red-faced eel (Monopenchelys acuta), which reaches only 8 inches in length, to the 12.5 foot long giant green moray (Strophidon sathete), all share a similar body pattern and habits.  The latterly flattened body allows them access to the narrow caves and crevices that form their home base.  Many spend their entire lives within close proximity to a favored shelter, leaving only to mate and foraging nearby.

Some Interesting Facts

Morays can reach quite high densities in suitable habitats, accounting for nearly 50% of the carnivore biomass on some reefs off Hawaii.  Although nowhere considered a delicacy, moray eels are eaten on occasion, and instances of fatal poisoning (ciguatera) have been reported in the Philippines.  A number have unusual life histories…the leaf-nosed moray (Rhinomuraena quaesita) begins life as a dark blue-and-yellow colored male and later transforms into a black-and-yellow female.

Diet and Feeding

Moray eels are carnivorous, and in captivity will readily accept frozen silversides , sand eels , clams  and other fish, crustaceans and mollusks.  Local seafood markets are wonderful shopping grounds for the moray owner – be sure to try mussels, conch and various marine fishes.

Well-fed eels will coexist with smaller fish, but there is always the possibility of predation.  On the other hand, morays are not quick feeders, and indeed can be rather shy about this, so one must take care that they are getting enough food if they are housed with large, aggressive fishes.


Moray eels are, like all their relatives, master escape artists.  If this occurs, be sure to move the animal back and forth in the aquarium once it is replaced, so that water is forced through the gills, and treat it with Stress Coat Marine to help replace the skin’s slime coat.

Even small morays are equipped with needle-sharp teeth, and they are not shy about using them in defense or if they mistake your finger for a tasty food item.  The resulting wound almost always becomes infected, and large animals can cause permanent damage.  These are definitely not fish for homes with children.


Well cared for specimens can reach impressive ages in captivity.  A huge green moray I worked with at the Staten Island Zoo is still going strong at age 30+.

Snowflake Moray, Echidna nebulosa

Brilliantly patterned in black and white, this Indo-Pacific native averages 24 (rarely to 40) inches in length and makes an ideal first choice for one new to keeping moray eels.  Many individuals become quite tame, reaching out from their lairs to accept food offered on feeding tongs.

They are, like other members of their family, slow feeders, and so are best individually-fed if kept in a community aquarium.  Snowflakes readily accept all manner of frozen or fresh marine foods such as shrimp, clams and fish.  Like all morays, they will not thrive unless provided with a secure retreat.

Other Commonly-Available Moray Eels

The girdled moray (Echidna polyzona) hails from the Red Sea and Indo-Pacific and its small size (to 35 inches) suits it well as an aquarium subject.  It has a relatively small head ….food item size should be adjusted accordingly.

The attractively patterned reticulated or leopard moray (Gymnothorax tesselatus) also appears in the pet trade.  Pale reticulations on a dark background lend it a spectacular appearance, but it reaches 5 feet in length and is therefore suited only to large, very well-secured tanks.

Please write in with your comments and questions.  Thanks, until next time, Frank Indiviglio.

You can learn more about moray eels at:


Understanding Marine and Freshwater Fish Behavior – nocturnal and diurnal activity

Please welcome back Frank Indiviglio with another interesting article.

Studying fish behavior is both a fascinating and very practical endeavor for the fish keeper. In addition to opening one’s eyes to the amazing diversity of fish lifestyles and behavioral adaptations, research concerning your pets’ natural behaviors will also lead to much greater success in keeping and breeding them.

The primary motivation behind animal behavior is survival – breeding, finding a suitable environment, obtaining food and avoiding predators (yes, human behavior often seems to break this rule!). Of course, even the best-designed aquarium is a poor mimic of nature, and so captive fishes must modify their behaviors – sometimes so much so that the actual purpose or function of what the fishes are doing will be lost on us. However, with experience, you should be able to see the relationship that the captive behavior has to its natural counterpart.

A wonderful aspect of the study of fish behavior is that it will provide a lifetime of surprises – there is far too much for any one person to know, and new facts emerge, quite literally, on a daily basis. With careful observation and research, you may well be able to discover sTiger Oscaromething new. Today I will focus on just one facet of behavior – the time at which fishes are active, and how this affects their welfare in the aquarium.

When selecting fishes for your aquarium, it is important to consider whether they are diurnal (active by day), nocturnal (active by night) or crepuscular (active in the dim light of evening and early morning). This will affect both your enjoyment of your pets and the composition of species that you might wish to include in the aquarium.

Nocturnal fishes such as the fire eel, Mastacembelus eyrthrotaenia, and other freshwater eels, need a place to hide during the daytime. If denied this, they may become stressed and will languish in captivity. However, eels, catfishes and other species that barely move by day change radically at night, and may engage in a surprising degree of activity. These nighttime wanderings may disturb diurnal fishes and prevent them from resting properly, thereby impairing their health.

Unlike the alwSnowflake Moray Eelays “ready-to eat” oscar, Astronotus ocellatus, and other Cichlids, nocturnal fishes often appear placid by day and morph into quite aggressive predators only as night falls. For example, octopuses, snowflake moray eels, Echidna nebulous, and similar species are usually quite content to spend the day secluded in a favorite retreat – easily tricking the novice into believing that they are compatible with their tank-mates. At nighttime, however, they undergo quite a change, and will quickly devour smaller neighbors.

Many diurnal fishes, such as the princess parrot fish, Scarus taeniopterus, and related species, swim about actively in daylight but secrete themselves within caves at night. Again, if you see them only during the day, you may miss such points and fail to provide for their needs (shelter-sleeping species become stressed if forced to remain in the open at night).
Red Anglerfish
Please bear in mind also that many nocturnal fishes will not feed during the day. Some, including most catfishes and moray eels, will forego their nocturnal habits once they adjust to captivity. Many, however, (i.e. the fossil catfish, Heteropneustes fossilis) remain strictly nocturnal even after years in captivity, and must be fed at night if they are to thrive.

Just as nocturnal species may unsettle diurnal fishes at night, actively swimming fish (by day or night) may stress species that are largely sessile (fish which move about only occasionally). Most typical “sit and wait predators,” such as the various anglerfishes, will be greatly disturbed if forced to remain in close proximity to vigorous, mobile species (also, bottom-feeding predators usually do not obtain enough food when kept with surface-feeding fishes).

The best way to observe nocturnal fishes, and to see how diurnal fishes behave at night, is by utilizing a bulb designed specifically for nighttime aquarium viewing. Be sure to invest in such bulbs, as they will open up an entirely new world of fascinating observations and learning opportunities for you. If you plan to focus on nocturnal fishes, you may wish to consider a complete reverse light cycle, in the manner of zoo exhibits for nocturnal creatures. If a dimly lit room is available, you can leave the night-viewing bulbs on during the day, and give the fishes their “daytime” at night. This may give you more time to observe your nocturnal fishes – unless, of course, you are yourself “nocturnal”! I have been able to learn a great deal about a number of animals, both at home and while working at zoos, in this manner. Be sure to research your fishes’ natural history so that you can provide a day/night cycle of the proper length.

I’ll explore other aspects of fish behavior in future articles – until then, please write in with your observations and questions. Thanks, Frank.

An interesting article concerning the effect of light on fish activity is posted at:http://www2.hawaii.edu/~delbeek/delb12.html

Thanks Frank,

Until Next Time,