That Fish Blog – Aquarium Advice and Information

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
 

I’d like to take time to welcome Frank Indiviglio to That Fish Blog. Frank is a former Bronx Zoo Zoologist, author and conservationist who’s worked with everything from fish to elephants. He’ll share his unique insights and work with various species on here, as well as the newly created That Reptile Blog & That Avian Blog. Welcome Frank!

Today I would like to pass along some interesting facts concerning fish you may be familiar with. I’ll focus mostly on aquarium trade species, with a few others added for good measure. I’ll add to the list in future articles. Enjoy, and please share your own store of unusual facts with us.

Finding a mate in the dark, featureless expanses of the deep sea poses quite a difficulty. Male benthic anglerfishes, such as Ceratias uranoscopus and related species, solve this dilemma by biting onto the first female they encounter. Thereafter, the male’s internal organs degenerate and he remains fused, by his mouth, to the female – surviving on nutrients circulating in her blood and periodically releasing sperm to fertilize her eggs!

Unique among the world’s fishes, male sticklebacks (small fishes of the family Gasterosteidae that inhabit marine, brackish and fresh waters), use kidney secretions to glue plant materials together when constructing their enclosed, bird-like nests. This behavior, along with their zealous protection of the eggs, helped spur the development of the aquarium hobby in Europe in the 1700s.

Cichlids found in Africa’s Lake Malawi are among the most enthusiastic of nest builders. Although measuring but 6 inches in length, males of one species create circular sand mounds that can exceed 3 feet in diameter, while another excavates 10 foot wide pits. Up to 50,000 such structures may be constructed in the same general area by a displaying group, or “lek” of males.

Marine damselfish, such as Stegastes nigricans, are unique in practicing a form of underwater “farming”. Pairs form territories around beds of marine algae (“seaweed”) and drive off fishes, shrimp, crabs and other creatures that show interest in this favored food.

Clownfish, such as the commonly kept percula clownfish, Amphiprion percula (or its cousin, the false percula, A. ocellaris, of “Nemo” fame) live unharmed among the tentacles of sea anemones — marine invertebrates that sting and consume other similarly-sized fishes. Anemone tentacles respond with a sting upon contact with any alien body, but are prevented from stinging themselves by chemicals in the mucous that they secrete. The clownfish, it seems, produces the same chemical in its own mucous and hence is not recognized as food.

Fishes lack external ears but do have inner ears that pick up the water pressure changes which accompany sounds. Aided by the Webarian Apparatus, an organ that connects the
inner ear to pressure-sensitive gas in the swim bladder, species such as carp and goldfish hear quite well and can communicate through vocalizations (perhaps it is not so odd to talk to your pet after all!).

Among the animals that are kept by people for their fighting abilities, none are as small as brackish-water fishes known as wrestling halfbeaks, Dermogenys pusilla. These thin, 3 inch-long warriors are the subject of staged matches in betting parlors throughout Thailand and Malaysia. Fights rarely result in injury, except to the wallets of losing bettors!

Despite popular belief, koi, Cyprinus carpio and goldfish, Carassius auratus, are not closely related. Goldfish, the first of any fish to be domesticated, were first kept by the Chinese over 2,000 years ago. Koi (the word means “carp” in the Japanese language) originated in the Black Sea area and arrived in Japan as a food source. They were first bred for domestic traits in Nigata, in northeastern Japan, in the 1820’s.

Ichthyologists discover new facts about fish on a near-daily basis. You can read articles about their findings at:
http://sciencedailey.com/

Thanks Frank,

Until Next Time,

Dave