That Fish Blog – Aquarium Advice and Information

Hello, Frank Indiviglio here.  Please see Part I of this article for information on the natural history of the clownfishes and their close relatives, the damselfishes.  Today we’ll take a look at the most popularly kept of the clownfishes, the beautifully-colored Percula clownfish, Amphiprion ocellaris.

Even before being skyrocketed to fame by the movie Finding Nemo, the Percula was an aquarium favorite, and one of the most widely-recognized marine fishes in the world.  Its brilliant orange and white coloration and seemingly “comic” mode of swimming endears it to all. 

Natural History

Hailing from the Indo-Pacific region (western Pacific and eastern Indian Oceans, including the Great Barrier Reef), this clownfish reaches a length of 3.2 inches in captivity; wild specimens are reported to exceed 4 inches in length, but captive bred animals are generally smaller.

Observations of free living Percula clowns indicate that they usually colonize magnificent sea anemones, Heteractis magnifica.  I have not read any research indicating that the various clownfishes seek out host anemones based upon their ability to survive within a particular species (please see Part I), but such would certainly be interesting to investigate.  Please note: Maldive Clownfishes are pictured here with a Magnificent Sea Anemone.

Clownfishes in the Aquarium

Like all clownfishes, the Percula is territorial and quite protective of the anemone in which it lives.  Generally only one mated pair can be maintained in an aquarium, unless it is very large and well stocked with coral and other sight barriers. 

Percula Clowns are omnivorous, and accept a wide variety of dry, frozen and live foods.   A mix of vegetable-based and meaty items should be provided.

Fortunately, captive bred specimens are readily available.  If considering a Percula Clownfish, please be sure to select a captive bred animal. 

The Anemone-Clownfish Relationship

Percula clowns do fine in captivity without an anemone in which to live, but not so
in the wild….there, clownfishes deprived of an anemone’s protection are quickly consumed by predators.  However, they are at their best when displayed with a living anemone, and when kept so will reveal a great many of their interesting interactions with these invertebrates (please see Part I of this article for further information).

The keeping of live sea anemones differs somewhat from fish-keeping.  For further information, please see the following articles on our blog: Unusual Invertebrates for marine Aquariums and Anemone Movement: Common Aquarium Questions .

Further Reading

Please check out the book I’ve written on marine and fresh water aquariums: The Everything Aquarium Book.

You can learn about clownfish natural history here.

Please write in with your questions and comments. 

Thanks, until next time,

Frank Indiviglio

Hello, Frank Indiviglio here.  It takes some doing to stand out among the catfishes, a group that contains some of the most bizarre creatures on earth.  Yet the Electric Catfish (Malapterurus electricus) does this quite admirably.  Indeed, this species is so unique that it and the small mouth electric catfish (M. macrostoma) are alone classified in the family Malapteruridae.

Characteristics and Cautions

The Electric Catfish has a number of qualities that would seem to mitigate against its popularity, but catfish enthusiasts, myself included, seem drawn to “unlovable” beasts.  It is no beauty, and is impossible to house with any species other than its own – tank mates that are not shocked to death are eaten!  Fortunately, it is immune to its own unique defense system.

In all seriousness, however, this fish is not for beginners.  It may reach 3 feet in length, and when disturbed emits electrical charges that are, at 400 volts, strong enough to stun adults (the strength of its charges increases with size, but even a 3 inch specimen can make itself felt).  Obviously, it is imperative that children and mentally challenged persons be kept away from electric catfishes.

Natural History

The Electric Catfish inhabits slower-moving portions of the Nile, Niger and other river systems in Central and West Africa.  The small mouth Electric Catfish is confined to the Congo River Basin and rarely appears in the pet trade. 

This species captures its prey, mainly other fishes, by releasing short bursts of electricity.  Electrical impulses are also used for defense, but do not assist in navigation (as is the case for the knife fishes). A unique pectoral muscle that surrounds most of the body generates the electrical discharges.

Pairs form during the breeding season, and the eggs are laid in a self dug or confiscated hole below a sunken log or rock. Little else is known of its reproductive behavior.

Captive Care

Despite, or perhaps because of, their formidable defenses, electric catfishes make most responsive pets. Owners invariably describe them as alert and quick to respond to one’s presence (in such cases, feed but don’t “pet” them!).  They soon abandon their nocturnal ways where food is involved.

Plan for a large, well-covered tank, as these stout fishes may reach 35 inches in length.  They seem to be fish specialists, but will also take all manner of other meaty foods, carnivore pellets, prawn, earthworms, insects, crayfishes and just about any other small animal.  Long term captives rarely discharge electricity during routine tank maintenance, but they should none-the-less be treated with respect and caution.

Captives do best under low light and in moderately soft water at 76-78 F and 6.5-7.5 in pH.  A suitably powerful filtration system is essential, as are regular water changes.  Electric catfishes prefer sluggish waters in the wild, and do not abide strong currents in captivity.  Albinos are sometimes available.

Research Potential

The Electric Catfish is yet another relatively common, hardy fish about which we know very little.  Documenting their breeding behavior would be a most interesting and useful endeavor…please consider it if your resources allow.

A New Exhibit

I recently obtained a nice group of Electric Catfishes and helped set up an exhibit for them in the new African Underwater Adventure display at the Maritime Aquariumin Norwalk, Ct.  Please visit if you have a chance.

Further Reading

You can read more about the Electric Catfish at Fishbase.

Please write in with your questions and comments. 

Thanks, until next time,

 Frank Indiviglio

Hello, Frank Indiviglio here. Damselfishes and Clownfishes are closely related, with all 325+ species being classified in the Family Pomacentridae. Among the most numerous and conspicuous fish on tropical coral reefs, a number make hardy marine aquarium inhabitants.

Range and Habitat

Damselfishes and Clownfishes are found throughout the world’s tropical and semitropical seas, with the greatest diversity occurring in the Indo-Pacific Region, especially off Australia; relatively few occur in the Atlantic and Eastern Pacific Oceans. They occupy a startling variety of habitats, with many species restricted to specific depths or specific areas of wave action. Several species can even enter brackish waters.

Identification in both the wild and pet trade is sometimes difficult, as their colors often vary from individual to individual; different populations of the same species may also exhibit unique color patterns.

Clownfishes and Sea Anemones

Clownfishes (aka anemonefishes) are well-known for their habit of living in close association with an invertebrate that is also an aquarium favorite, the sea anemone. Usually home to just one pair of clown fish, the host anemone forms the basis of their territory, and they rarely stray far from it.

Surviving Among Deadly Tentacles

Clownfishes were long thought to be immune to the anemone’s stinging tentacles, as they shelter right among them without being harmed (other small fishes would be killed if they attempted to do this). We now know, however, that the clownfish’s secret is not immunity at all, but an even more amazing adaptation.

Anemone tentacles fire their sting-bearing cells (nematocysts) upon contact with any organism that they come in contact with. The tentacles are coated with mucus which inhibits them from stinging one another. It seems that the clownfish secretes mucus which mimics that covering the tentacles of the anemone. Therefore, the anemone simply does not recognize the clownfish as prey, or even as a distinct organism!

In return for the protection offered by its host, the clownfish consumes parasites that might harm the anemone. By swimming about and fanning its fins, the clownfish may also increase the flow of oxygenated water through the anemone’s tentacles and about its base.

Do Anemones and Clownfishes “Need” One Another?

Aquarists often question whether clownfishes and anemones can survive without one other. It appears that the relationship might the best be described as “commensal”. By this we mean that each derives benefits from living in close association with the other, but they are not strictly limited to that situation.

The vast majority of anemones live without clownfishes. Clownfishes, however, seem somewhat more dependent upon the relationship. While they will live quite well “on their own” in the aquarium, experiments in the wild have shown that clownfishes without anemone hosts are quickly eaten by larger fishes.

Further Reading

The Florida Museum of Natural History has posted an interesting article and video on clownfishes here.

Next time we’ll take a closer look at the damselfishes and a favorite aquarium clownfish.

Please write in with your questions and comments.

Thanks, until next time,

Frank Indiviglio

Amphiprion sandaracinos image referenced from wikipedia and originally posted by Bricktop

Hello, Frank Indiviglio here.  This Southeast Asian fish’s slender, 3-inch- long body belies its reputation as a fearsome combatant.  However, in betting parlors from Thailand to the Sunda Islands, matches between male wrestling halfbeaks (Dermogenys pusilla/pusillus) rival those featuring the better-known bettas (Betta splendens) in popularity.  In contrast to bettas, battling halfbeaks rarely inflict any serious damage…other than to the billfolds of losing gamblers!

Description and Habitat

Halfbeaks sport a startling adaptation to surface feeding…their immobile lower jaw is more than twice the length of the upper.  This, along with their subtle beauty – a silvery body highlighted by hints of blue and green – renders them a most unique addition to one’s collection. 

Halfbeaks inhabit estuaries and other areas of fluctuating salinity, and, while sometimes kept in fresh water, are at their best in brackish water aquariums. 

Feeding Wrestling Halfbeaks

Halfbeaks are highly specialized surface feeders and rarely if ever swim to lower depths in the aquarium. They tend to be picky feeders and prefer tiny live invertebrates such as mosquito larva, brine shrimps, fruit flies and Daphnia. Chopped blackworms may be taken, but these sink quickly and so must usually be offered via forceps (tedious but effective!). 

Halfbeaks may be habituated to flake and frozen foods, but the progeny of such fishes rarely reproduce, most likely due to a nutritional deficiency.

The Halfbeak Aquarium

While visiting pet stores and aquariums in Japan, where halfbeaks are more commonly kept than in the USA, I was surprised to find that multiple males were often housed together.  I learned that males will co-exist in large, well planted aquariums if emergent and surface-dwelling plants are grown as sight barriers.  Watching the threat displays and interactions in such aquariums was most interesting, and cast these little fellows in a new light for me.

A unique habitat preference and feeding style dictates that halfbeaks be kept in long, shallow aquariums and, with few exceptions, in single-species groups.

Breeding Halfbeaks

Wrestling Halfbeaks are live bearers, with healthy females giving birth every 30 days or so; males may be distinguished by a bright red blotch located in front of the dorsal fin. 

Unfortunately, adults are quite cannibalistic, and the fry rarely survive.  Breeding traps are not recommended, as the birthing process takes several days and females become stressed by long confinement in small areas.  Thickly-planted aquariums, with much of the vegetation at the surface, offer the best chance of success. 

Further Reading

Detailed information on the natural history of these and related fishes is posted at ZipCodeZoo.com.

A book I’ve written, The Everything Aquarium Book, addresses the care of brackish water fishes in detail.

Please write in with your questions and comments. 

Thanks, until next time,

Frank Indiviglio

Halfbeaks image referenced from wikipedia and originally posted by Neale Monks
 

Hello, Frank Indiviglio here. Plankton forms the base of the food chains in all the world’s fresh and marine waters. Comprised of innumerable species of tiny, often microscopic plants and animals, plankton is a very useful but overlooked food source for tiny fish fry, filter-feeding invertebrates and seahorses, pipefishes and other small live food specialists.

Collecting Plankton

Marine waters are undoubtedly the best sources of plankton for seahorses and such creatures, but do not hesitate to try fresh water plankton as well. Just bear in mind that fresh water creatures will perish rapidly in salt water, so don’t overload your tank.

Available through biological supply houses, plankton nets are the most effective means of harvesting this valuable food. Don’t forget to examine your catch with a hand lens or microscope – you won’t believe your eyes!

Using Plankton

When rearing Atlantic seahorse fry at the Staten Island Zoo, I often towed a plankton net behind a boat and by hand from a dock. My efforts were rewarded with an amorphous glob of “organic material”, but the seahorses sure knew what to do with it!  Their reactions were much more vigorous than when presented with their standard meal of brine shrimp, and they grew rapidly.  I have also noticed that northern pipefishes immediately begin feeding when fresh seawater is added to their aquarium…I usually cannot see anything that looks like food, but they do!

I consider plankton to be nearly indispensible for seahorse and pipefish fry, and for adult dwarf seahorses and similar species. But nearly all small fishes and invertebrates, including fresh water species, will eagerly accept plankton as well.  Its use will greatly improve your chances of success with a number of delicate organisms.

Useful Products

Fortunately, “plankton substitutes” are available for those unable to collect their own. “Reef Bugs” are living microbes that are eagerly accepted by corals and other invertebrates. A wide range of other foods for filter feeding invertebrates helps simplify the keeping of these fascinating creatures.

Newly hatched brine shrimp, while not a complete diet for seahorses and pipe fishes, may be nutritionally improved through the use of Artemia food.

Further Reading

The Monterey Bay Aquarium has posted an interesting article on plankton collecting here.

Please write in with your questions and comments.