That Fish Blog – Aquarium Advice and Information

Hey Fish Blog Followers! There are lots of different types of freshwater communities created by hobbyists. Some people choose a peaceful community of tetras and other small docile fish, while others opt for a tank populated with predators or other territorial species, often a fine balance between tolerance and aggression. Many aquariums are somewhere in between, referred to as semi-aggressive communities, which often include fish such as barbs, gouramis, large tetras and others that fit into the category.  Today I wanted to give a small introduction to several popular species of fish often purchased for these aquariums that may interest you.
 

Not Exactly Maneaters

Some of the most popular fish for the freshwater semi-aggressive community are the cyprinids known as sharks. These are not the cartilaginous carnivores as featured in movies or the Discovery Channel. These fish are found primarily in the waters of Southeast Asia and Thailand. There are several species that are often imported for use in the aquarium trade, and several species also referred to as sharks that are less common in the trade. Though from several different genera, these fish all have in common the pointed heads and large, curved dorsal fins that give them their misleading common names.

Though these fish lack teeth, as a general rule they are considered semi-aggressive, if not for the sizes they attain, then for the territoriality they often express as they mature. They are generally not suitable for tanks under 55 gallons (some not less than a 75 to 100 gallon tank) and should only be mixed with fish that can stand up to the potential for chasing and harassment that sharks can dish out (especially to their own kind). Smaller fish may eventually be seen as a snack as the fish grow. Sharks make bold and interesting additions to freshwater semi-aggressive communities, as long as the tank is of adequate size and the conditions in the tank suit their needs. Suitable tank mates for most include fish like barbs, catfish, large tetras, and other fish of similar temperament.

If you are considering the addition of a shark to your community, there are several things to keep in mind. As far as the set-up goes (besides having an adequately sized aquarium) be sure that you provide plenty of cover like wood, plants or rock formations so these fish can hide and fell secure when they feel the need. A tightly fitting lid is also highly recommended as they tend to be terrific jumpers, especially if startled. Most common sharks prefer well-aerated, clean water with temps between 74 and 81 degrees (F) and a pH maintained between 6.5 and 7.5. Sharks do not tend to be finicky eaters, readily accepting flakes, pellets and frozen, freeze-dried or live treats like bloodworms, tubiflex, glass worms, plankton, brine shrimp or other meaty tidbits.

Popular Species

There are several species of freshwater shark, and variants of these species, regularly available on the market that may be candidates for your semi-aggressive community.

Bala Sharks (Balantiocheilus melanopterus), also called Tricolor Sharks, are a popular variety with silvery scales and bold black edges on the fins and tail. Though attractive, this species tends to be rather skittish unless kept in small groups. These fish tend to be more shy and docile than many of the other sharks. Reaching a length of between 13 and 15 inches potentially, this species is best left to aquarists with tanks of at least 75 gallons or more for a single specimen, much larger if they are to be kept in the security of a small group.

Rainbow Sharks (Epalzeorhynchos frenatus) may be the best choice for most hobbyists, despite their tendency to become territorial and increasingly aggressive as they mature. Also known as the Ruby Shark or the Red-Finned Shark, this species grows to only about 6 inches and bears bright red fins that are quite attractive. Several variants have also been selectively bred to make things even more interesting, such as albinos and white-finned. These sharks should be kept as a single specimen in the community as they do not tend to tolerate others of their kind in the confines of an aquarium. Red-tail Sharks (Labeo bicolor) are similar in size and behavior to Rainbow Sharks, but lack the red fins and display a velvety black body and a red tail.

Other types of freshwater sharks include Black Sharks, Iridescent Sharks, Colombian Sharks, and others that are even more uncommonly seen in the trade. For various reasons, these species are typically not suitable for the average semi-aggressive community, and careful consideration should be taken before purchasing these species.

Black Sharks are attractive, but they grow rather quickly to about 30 inches in length, too large for most home aquariums. Iridescent Sharks are actually a type of catfish that also quickly grows from a 2 inch juvenile to lengths nearing 4 feet, another that should not be considered for the average home aquarium. Colombian Sharks are sleek and active catfish too, rounding out at about 10 inches, with huge appetites and a preference for brackish to marine conditions as they mature.

Thanks, hope this information is helpful!

Patty

Hello, Frank Indiviglio here.  As a child, I constantly combed the pet stores of the Bronx and Manhattan in search of the odd catfishes, lungfishes and eels I so favored.  I distinctly recall first coming upon some creatures labeled as “rubber eels”, and realizing that I was looking at something special – I just didn’t know exactly what!  The blue-gray “fish” were indeed quite rubbery in texture and did look like eels, yet something was “off”.  In time, I learned that these odd beasts were amphibians, specifically aquatic or River Cauca Caecilians, Tylphlonectes natans.

Natural History

Today, so many years later, you can still find these caecilians being sold as rubber eels.  The River Cauca caecilian is one of the few aquatic members of this little studied amphibian order (the Gymnophiona), and, even now, is the only one to regularly appear in the trade, or even in zoos.  They are found only within the drainages of 2 rivers systems in northern Columbia and northwestern Venezuela, and little is known of their lives in the wild.

Aquatic Caecilians in the Aquarium

River Cauca Caecilians are quite hardy when given proper care, and may even surprise you with young, which are born alive and have external gills.  I’ve bred them in a well-filtered (undergravel) 20 gallon aquarium at a pH of 7 and temperature of 76 F, but one experienced keeper advises that they fare better in acidic water, and recommends sphagnum moss as a substrate.  They may reach 24 inches in length, but most top out at 12-16 inches.

Caecilians are quite shy at first, and must be provided with subdued lighting and artificial caves, PVC pipes, live plants and the like as shelter.  Those I’ve kept have become quite bold after a time, leaving their hideouts by day when scenting the earthworms, blackworms and prawn that are their favorite foods.  A few individuals learned to take frozen foods and shrimp pellets, but live food is definitely preferable.

Fish keeping experience will serve you well in caring for these fascinating amphibians…with so much still unknown about them, I hope that more aquarists take up the challenge!

Further Reading

You can read more about this and other caecilians here.

Please write in with your questions and comments. 

Thanks, until next time,

Frank Indiviglio

Tylphlonectes natans image referenced from wikipedia and originally posted by Christophe cagé

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