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The Wrestling Halfbeak – a Tiny Brackish Water Warrior

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

Archerfish – Aquatic Snipers

Patty here. archerfishOften brackish fish are a hard sell to people on the market to start an aquarium.  Fish appropriate for brackish systems don’t tend to be as colorful or as easy to mix in communities as many other types of fish, or so many think.  But though these fish are often banished to a remote corner of the fish shop, and often seem too complicated to keep, there is one fish in particular that may be the one to convince you to try your hand at a brackish system.

Archerfish are a common offering in the trade, but their brackish classification and simple beauty may keep them hidden from the view mainstream aquarium enthusiasts.  They are native to India, Southeast Asia, Australia and other countries of the western Pacific.  They prowl through estuaries and mangroves mostly, but may be found upstream in full freshwater or on reefs periodically.

The Banded Archerfish (Toxotes joculatrix), the species commonly offered in the trade, is modestly colored with a tan-grey dorsal area and a pale silvery-white body.  Bold black markings camouflage them from prey and predator above.  They have a compressed body with a flat area from the dorsal fin to the mouth which allows them to move along just under the surface of the water. The mouth is angled upwards.

The most fascinating thing about Archers is their unique and famed ability to shoot their prey.  These fish are skilled predators that are able to snipe insects from branches and foliage 3-5 feet above the surface.  The fish shoots several droplets of water, quickly correcting any error in trajectory and aim to knock prey from the safety of the canopy to the water’s surface where the fish devours its meal.  They may also leap from the water to catch prey that is within reach or dine on small shrimp and fish in the water, but in the wild they commonly swim in groups of “shooting parties”, working together to pick off unsuspecting bugs. With the right set up, you can witness this behavior in your own living room!

This species can reach a max size of up to 12 inches in the wild, so habitat size is the first thing to consider.  They can be expected to reach about 8-10 inches in captivity, and the minimum size aquarium is 55 gallons.  Larger, deeper tanks are better!  Though juveniles may tolerate freshwater environments for some time, as the fish mature a brackish level of 1-2 percent will be necessary (roughly 8-15 teaspoons of aquarium salt per 10 gallons).  The ideal set-up is one that allows for plenty of room to swim and terrestrial areas or areas of open air (like a large tank filled half or 3 quarters full/paludarium set-up) to make the fish happy and allow for a great show! 

You can furnish the tank with salt tolerant vegitation both in terrestrial areas and submerged, driftwood, root wood, rock, and sand or fine gravel.  Good filtration is a must! Though the fish are hardy, they like clean water like that where they are found in the wild.  Once in their new home these fish will quickly resume normal hunting activities, and a batch of live crickets will make for some sport.  These fish will also eat frozen and freeze-dried foods.  Other fish can also be housed with archers as long as they are tolerant of brackish conditions, large enough not to be considered prey, and not overly boisterous.

Algae and Plants for Brackish Water Aquariums – Part II: Adapting Freshwater Plants to Brackish Aquariums

Hello, Frank Indiviglio here.

Please see Part I of this article for information concerning typical brackish water plants and algae.

A number of well-known freshwater aquarium plants adjust quite nicely to brackish water.  Given the great variety of species that are available, I’m sure many others will be found.

Experimenting With Freshwater Plants

If you are of a mind to experiment, first research various natural habitats, keeping an eye out for plants that thrive along coastlines, estuaries and in other such situations….these might be exposed to salt water during floods or at high tide.  In general, freshwater plants with waxy leaf and stem coverings make the best prospects with which to begin.

Bear in mind that the change from fresh to brackish water is an extreme one, and can easily shock your plants.  Treat them as you would a new, delicate fish and increase their exposure to brackish water gradually.  For untested species, you might consider dripping brackish water into the plant’s tank via a section of airline tubing during the acclimatization period.

Anachris (Egeria) densa

Much favored by freshwater aquarists and a standby for grammar school science experiments, Anachris is very hardy and highly recommended for use in brackish tanks.  Most agree that it is the most likely of all freshwater plants to thrive in this foreign environment.

Anachris grows well as a rooted or floating plant and, in strong light, can add an inch or more a day to its length.  Cuttings taken anywhere along the stem will grow into new plants.

Temple Plant, Hygrophila corymbosa

This most attractive of aquarium plants does very well in brackish water, but is considered a delicacy by snails, hermit crabs and many fishes.  It and related species, which are native to South and Southeast Asia, can be propagated from cuttings and grow best under bright lights.

Cabomba aquatica

Another popular freshwater plant, this South American native has delicate leaves which cannot withstand the attentions of herbivorous fishes and invertebrates.  However, when housed with halfbeaks, mudskippers and others that will not molest it, Cabomba makes a fine addition to the brackish aquarium.

Aquatic Grasses – Sagittaria and Vallisneria

Sagittaria, relatively impervious to salt water damage and unpalatable to most organisms, is one of the best freshwater plants to use in brackish systems.  The widely-available grass Vallisneria does very well also, even under subdued lighting, but is considered a tasty food by many aquatic animals.

Hornwort, Ceratophyllum demersum

Reaching 10 feet or more in length in the wild and equally at home in cold and warm water, this hardy survivor is an excellent candidate for brackish water tanks.  It can get by in dimly-lit aquariums, but in such situations its foliage will pale considerably.

Water Sprite, Ceratopteris thalicroide

Even in such an unnatural environment as brackish water, this plant will grow quite vigorously if kept warm and under bright lights.  It can be maintained either floating or rooted, and in different situations will develop rounded, bulky or fern-like leaves.  Water sprite’s prodigious rate of growth often compensates for the attentions of plant-eaters.

Chain Swordplant, Echinodorus tenellus

This attractive plant spreads rapidly via runners (hence the “chain” portion of its name) and is fully grown at 4 inches in height.  As is true for its larger relatives, the chain sword requires warm water and a well-lit environment.

Further Reading

Anachris (Egeria) densa is widely introduced in the USA and elsewhere.  The University of California has posted an interesting account of its natural and unnatural history at http://ucce.ucdavis.edu/datastore/detailreport.cfm?surveynumber=182&usernumber=43.


Please write in with your questions or to relate your own experiments with aquatic plants.  Thanks, until next time, Frank Indiviglio.

Algae and Plants for Brackish Water Aquariums

Hello, Frank Indiviglio here.

The culture of live algae and plants in brackish aquariums has not been given much attention, and few plants native to estuaries and similar environments are commercially available.  However, as with fresh water tanks, live plants add a whole new dimension to aquarium-keeping, and are extremely interesting in their own right.

In brackish exhibits at the Bronx Zoo and in my own tanks, I have experimented with several varieties of algae and plants.  In addition to mangroves, Java ferns and other such estuarine-adapted species, a surprising number of plants and algae that are typically thought of as either “marine” or “fresh water” can be acclimated to brackish environments.  Following are a few of my favorites.


Plants and algae should be introduced carefully to a brackish water aquarium…treat them as you would a fish or invertebrate.  Particularly as concerns fresh-water plants, sudden changes in pH can wreck havoc with osmotic pressure, causing cell rupture and the death of the specimen.

Marine Algae

Marine algae are commonly referred to as “seaweeds”, but they are in actuality not true plants.  Single or multi-celled, algae lack roots, stems and leaves, but have evolved equivalent structures. For example, holdfasts act as roots in anchoring them to the substrate, but do not absorb nutrients…that role is taken on by the leaf-like portions of the organism.

Caulerpa prolifera

This is the most commonly-available marine algae.  It ranges from Florida and the Caribbean southward, and is commercially cultivated.  Caulerpa spreads via rhizomes, or runners, and, although a true marine algae, it adjusts well to brackish environments.

Like all algae, Caulerpa may leak fluids when pruned, so be sure to clip only a tiny amount at a time if trimming is necessary.  Related species, with rounded, pointed or fern-like shapes, are sometimes seen in the trade.

Other Types of Marine Algae

A number of other types of marine algae are sometimes available.  While not as well-suited to a brackish water existence as Caulerpa, several will adjust if care is taken in the acclimatization process.

I and colleagues have had varying degrees of success with sea cactus (Udotea flabellum), Codiacea spp., mermaid’s cup (Acetabularia spp.), mermaid’s shaving brush (Penicillus capitatus) and several types of red algae.

Brackish Water Plants

Java Fern, Microsorium pteropus

To my knowledge, the Java fern is the only true brackish water aquatic plant that is regularly available to aquarists.  In well-lit tanks it will proliferate rapidly.  A number of fishes favor Java fern leaves as food, but its rapid growth rate can accommodate this in many cases.

Red Mangrove Seedlings, Rhizophora mangle

Mangrove seedlings, or propagules, are semi-aquatic, with the roots usually submerged and the plant itself growing above water.  The red mangrove is often sold in the trade and is commercially propagated in Florida, where it also occurs naturally.  Red mangroves are extremely wide-ranging, being found along coastlines in many of the world’s tropical and subtropical regions.  At home in estuaries, salt marshes and along river mouths, they are adapted to fluctuating salinity levels, and fare well in brackish water aquariums.

Mangroves can be planted in mud or wedged into limestone, and, because of their semi-terrestrial nature, are best kept in aquariums housing mudskippers, fiddler crabs and other creatures that utilize both land and water areas.  They excrete salt on the surface of their leaves…this should be washed away with fresh water every few days.

Mangroves often grow slowly in the aquarium, and stay at a manageable size for some time.  There are a few techniques for dealing with tall plants…please write in if you would like further information.

Eelgrass, Zostera marina

Eelgrass is one of the only true plants to live an aquatic existence in marine environments.  It is not commonly kept in aquariums.  I have had mixed success with it, but have observed healthy stands in commercial aquariums (if you are interested in this plant, please write in and I’ll make some inquiries to public aquarium contacts).

Eelgrass populations have plummeted in the northeastern USA and elsewhere, and I encourage those with an interest to work with this plant (please note that collection is prohibited in California and elsewhere).  An incredible assortment of unique fishes and invertebrates, such as pipefishes, dwarf seahorses and eelgrass-shaped amphipods, are always found in association with eelgrass beds.

I commonly observe eelgrass in estuaries, lagoons and other brackish habitats, and it thrives in true marine water as well.

Next time I’ll discuss some of the many fresh water plants that can be acclimated to brackish conditions.  Please write in with your questions and comments.  Thanks, until next time, Frank Indiviglio.

Brackish environments are home to many fascinating fishes and invertebrates that do well in aquariums.  Please see my article on Mudskippers  for a look at one of the most unusual.

Mudskippers – blurring the line between amphibian and fish


Please welcome back Frank Indiviglio to That Fish Blog.
Those with an interest in unique aquarium fishes need look no further than the mudskipper. These odd little creatures seem to straddle the line between fishes and amphibians, leaving the water for long periods of time to chase insects across mudflats and even climbing up onto tree trunks.

Mudskippers, the largest species of which reach a length of 12 inches, inhabit tidal flats, river mouths and mangrove swamps in East Africa, Southeast Asia, Australia, and along the Red Sea.

The mudskippers are unusual in having highly modified pectoral, pelvic and anal fins that enable them to move about quite well on land – they can even leap (“skip”) about very rapidly. In addition, the fused pectoral fins form a suction disc that allows these little acrobats to climb up onto mangrove roots and tree trunks. The eyes are situated at the top of the head and are, for a fish, quite movable.

Gill covers tightly seal the gill chambers, and water stored there keeps the gills moist and provides oxygen to the fish as it scuttles about on land. Mudskippers also absorb moisture from the damp mud upon which they usually travel when out of water. Although it is tempting to think of mudskippers as representing an early stage in the development of amphibians, the creature that gave rise to frogs and salamanders was more like the Australian lungfish, Neoceratodus fosteri, in appearance and in its method of breathing (utilizing primitive lungs).

The most commonly available mudskipper in the pet trade is Periopthalmus barbarus, a fairly hardy species that reaches a length of 6 inches. Like all mudskippers, it hails from brackish water areas.

Mudskippers are fairly tolerant in their salinity requirements, and will do well under typical brackish water aquarium conditions (salinity of 1.005-1.015) and temperatures of 75 – 80F. They require a “beach” area, which can be a separate, drainable plastic container within the main aquarium or designed as small islands fashioned from non-toxic tree roots, coral heads and rocks. The popular “aqua-terrariums” now on the market make excellent mudskipper homes as well. Remember to keep the water shallow, or to provide easy access to land, as they are poor swimmers (not something you usually worry about when keeping fish!).

Most mudskippers do well in captivity if provided with a suitable habitat. Males, however – distinguished by their large dorsal fins and bright colors – are very territorial, and dominant specimens will make life miserable for others, so plan your group and space accordingly.

Although they prey upon live invertebrates such as crabs and insects in the wild, mudskippers adjust well to frozen foods such as prawn and clams. I also provide a vegetable-based frozen food from time to time, and find they accept this readily as well. Their food should be placed on land, as most species will not feed while submerged. Mudskippers are especially fond of live crickets, small shrimp and other such foods, and these should form a large portion of their diet. Their acrobatics when chasing live food – they often flip over in their excitement – never fail to delight me.

Brackish water community tanks containing mudskippers and fiddler crabs make fascinating exhibits. The interactions between the crabs and mudskippers (assuming they are properly matched in size!) go on all day long. If you establish a deep water area (mudskippers will do okay as long as they can exit the water easily) you can add such fascinating fishes as four-eyed fish, Anableps spp., scats, Scatophagus argus and rubrifus, monos, Monodactylus argenteus, and, of course, the amazing archer fish, Toxotes chatareus. In fact, archer fish are at their best in an aquarium containing a land area because in such they can show off their incredible ability to knock crickets from land into water. Somehow compensating for the refraction of light through water, archerfish eject streams of water at insects (best observed by placing crickets on branches positioned over the water’s surface), hitting them unerringly and thus securing a meal. They will also aim water at your eye movements, so be careful!
I’ll cover the creation of such aquariums in future articles. Until then, please share your observations and write in with your questions. Thanks, Frank.

For more information on establishing aquariums for brackish water fish, please see the article Brackish Water Basics, posted on on February 26, 2008: