Cyprinodontiformes vivparos e ovovivparos

Livebearer Cyprinodontiformes

Espcies > Ficha da espcie > Heterandria formosa

Species > Species profile > Heterandria formosa

















Heterandria formosa  Agassiz, 1853

Heterandria formosa
Girard ( ex Agassiz ), 1859

Peixe Mosquito [ Portugus ]

Heterandria [ Portugus ]

Least Killifish [ English ]

Lesser Killifish [ English ]

Geographical distribution :


Photos Disclaimer :

All photographs on this website can't be used without permission. 

Copyright of all photographs belongs to the photographer/author who has taken/created the photograph and may not be used without permission from that person. 

For images permission in accordance with the copyright/licensing/legal use guidelines please e-mail us.

I - Morphology Synopsis ( some meristic characters )

Total absolute lenght

Adult male : 12.4 a 18.6  mm

Adult female : 23.0 a 31.2 mm

Dorsal fin rays : / 6 ( 7 )

Caudal fin rays : / 20 ( 22 )

Scales on lateral line : 26 ( 28 )

Head lenght body lenght ratio ( male ) : 0,20

Head lenght body lenght ratio ( female ) : 0,19

You can find more pictures about these species availabe at the photo gallery.

II - Habitat and Geographical distribution

The Least Killifish can be found in a vast coastal area of South-eastern United States of America from the Atlantic to the Golf of Mexico seaside. There are wild populations reported in North Carolina, Georgia, South Carolina, Florida, Alabama, Mississippi, Louisiana and Texas.

This is the only representative species of its genus found in North America, despite the fact that the closest relative is spread out just up to the Yucatan Peninsula in Mexico, bout 1.500 kilometres away further South.

Except in Florida, where this fish is established from coast to coast, in the rest of the geographical distribution it reach no more than 160 kilometres from the sea into to inland.

Wild populations are referenced from Cape Fear River drainage, in North Carolina, down to Orange River drainage in the State of Texas.

They subsist in areas of sub-tropical to semi-tropical kind of climate.

To understand a little bit of what this means, we will consider subsequently the extreme areas of the geographical distribution as regards a climatologically approach. These two areas will be North Carolina and Florida.

North Carolina has in general a humid, subtropical climate especially at the coastline where our attention is focused in.

Winters are short and mild, while summers are usually hot but temperatures rarely go above 38C ( 100.4F ).

Mean annual temperature ranges 16.9C ( 62.42F ) by the seaside, however differentiation in altitude and closeness to the ocean create significant local variations inside the State territory.

Average January temperatures are around 9C ( 48.2F ), presenting extreme limits between -2C ( 28.4F ) and 21C ( 69.8F ) . Average July temperatures can be around 27C ( 80.6F ), with lower limit around 19C ( 66.2F ) and maximum limit near 37C ( 98.6F ).

Average annual precipitation at the coast line varying between 1120 and 1420 mm.

Especially for the summer period, North Carolina weather perform in response to the Bermuda High pressure system, centred in the mid-Atlantic. Winds from the southwest bring masses of hot humid air over the State.

Water temperature at Cape Fear River can show extremes stuck between 5.3C ( 41.54F ) and 31.9C ( 89.42F ), reaching annual mean between 16.9C ( 62.42F )and 19.8C ( 67.64F ). On these same waters, pH ranges from 3.1 ( at riparian swamps areas ) to 8.3, with mean values around 7.0 to 7.9 on the main river and streams. Median pH expectedly increased from the upper river down into the estuary.

The extremely low pH values found in wetland forest swampy areas result from high concentrations of organic acids profusion.

Florida with a quite mild sunny climate is the Southern tip of this species geographical distribution.

Average annual temperatures range from 18C ( 64.4F ) to 21C ( 69.8F ) in the North, and 23C ( 73.4F ) to 25C ( 77.0F ) in the deep South.

Miami annual mean temperature is 24C ( 75.2F ).

The State highest record, 41C ( 105.8F ), was registered at Monticello on June 29, 1931; the lowest record 19C ( -2.2F ), at Tallahassee on February 13, 1899.

Combined effect of Florida's proximity to the Atlantic and the Gulf of Mexico, together the latitude contribute for the humid sub-tropical and humid semi-tropical climate.

Although high humidity and generally abundant rainfall ( 1200 mm a 1450 mm between June and September ), precipitation can vary greatly from year to year and serious droughts have occurred.

Water temperature registered at State of Florida lakes and rivers can vary from 7C ( 44.6F ) and 39C ( 102.2F ) limits. Typical average water annual temperatures range from 19.6C ( 67.28F ) and 23C ( 73.4F ).

We can found in Northern Florida waters usual limits between 11C ( 51.8F ) and 28.5C ( 83.3F ), average annual around 19.6C ( 67.28F ). In the southern farthest, these values can be flanked by 17C ( 62.26F ) and 32.4C ( 90.32F ), average annual around 23.3C ( 73.94F ).

In States like Mississippi, Louisiana, Texas and South Carolina the Heterandria formosa habitat are somewhere between the panorama of North Carolina and Florida.

In the end of summer as well as the opening of autumn, all these natural regions are located on the way for hurricanes and tropical storms.

The Least Killifish live especially in well vegetated shallow, lentic waters and is known to occur in both fresh and brackish waters, along the borders of creeks, ponds, swamps, and lakes.

Natural most common underwater aquatic plants can be Utricularia purpurea, Myriophyllum laxum, Myriophyllum heterophyllum, Myriophyllum pinnatum, Websteria confervoides, Utricularia floridana, Utricularia amethystina, Utricularia foliosa, Utricularia juncea, Utricularia olivacea, Utricularia simulans, Sagittaria fasciculata, Sagittaria filiformis, Sagittaria graminea, Sagittaria isoetigormis, Sagittaria subulata, Hydrilla verticillata, as well as others.

Although adults can venture in deeper waters, 1 meter is usually an unfathomable limit. For this reason, usually form schools close to the shore where vegetation is denser.

III - Physical-chemistry parameters

Ideal temperature range : 15C ( 59.0F ) - 25C
( 77.0F )

Tolerated limits : 10C (50.0F ) e 30C ( 86.0F )

Survival limits : from 5C ( 41.0F ) to 10C ( 50.0F ) and from 32C ( 89.6F ) to 39C ( 102.2F ), according to population.

Ideal pH : 6 8

Ideal dH : 7 - 23

Maximum salinity : 1,027 ( 36,3 ppt )

Temperature monthly maintenance for this species in captivity ( suggestion ) :

Thermal regime (1) 

Thermal regime (2)

12C ( 53.6F )

15C ( 59.0F )

14C ( 57.2F )

17C ( 62.6F )

17C ( 62.6F )

20C ( 68.0F )

19C ( 66.2F )

22C ( 71.6F )

21C ( 69.8F )

23C ( 73.4F )

23C ( 73.4F )

24C ( 75.2F )

25C ( 77.0F )

25C ( 77.0F )

25C ( 77.0F )

26C ( 78.8F )

24C ( 75.2F )

25C ( 77.0F )

21C ( 69.8F )

23C ( 73.4F )

18C ( 64.4F )

20C ( 68.0F )

15C ( 59.0F )

17C ( 62.6F )

Each one of this table lines report a different month period.

The temperature values are provided only as a reference for captivity maintenance.

Performing on this way your action can be considered reasonable, according with the species known thermal exigencies.

It is sometimes difficult, if not even impossible, to recreate in aquarium the natural conditions, most favourable for the fish biology. The most ideal situation was, if you could be able to provide your fish a daily as well as a weekly temperature variation, like in the wild.

Note about Heterandria formosa : The lower thermal regime (1) is most appropriated to colder region populations, while the higher thermal regime (2), more realistic on domestic aquarium environment, is no doubt more satisfactory for warm demanding populations, similar to those from southern Florida.

For better understanding about perfect environment or to simulate water temperature annual evolution according to natural habitat for this species, please be so kind and have a look to Savannah and Miami graphics at Wild water's temperatures ( all year round ) issue.

IV - Biology and ecology synopsis

Heterandria formosa is, without any hesitation, one of those ideal species to keep in captivity.

In a relatively small area its possible to raise an entire population as well as to carry on with it in good genetic viability for long.

Most of this fish physic and chemical needs are easy to achieve in aquarium. To ensure a most favourable environment you need only to pay a reduced amount of effort and control.

While we cant say that this is a colourful and out of the ordinary bright species, but is quite difficult to avoid a certain sudden passion by these tiny mimetic wonders with a vibrant conduct.

In terms of water chemistry, probably the most significant attention they require is some degree of hardness. Besides that, the Least Killifish accept very well a wide range of pH values, becoming this way a selectable fish for the majority of our tap waters.

One of the most outstanding aspects of their biology is undoubtedly the reproduction subject matter.

Besides deliver fully developed babies this fish is remarkable while the best and most perfect paradigm of superfetation among livebearer Cyprinodontiformes.

Heterandria formosa mothers give birth during a period of several days, but only one or two newborn each time. Most other species produce in a single brood an entire new generation, and all the little fish are release in a single delivery up to several hours long.

By the fact that females can preserve viable active sperm inside their ovaries for a number of months and quite a few broods of embryos developing in different stages, this species can also be regarded as a good illustration of a significant predisposition to multi paternity.

Females kept at a constant little changeable temperature ( very typical in captivity ), will show a stable rhythm of gestations with regular births.

Due to this animals body dimension is quite expectable that a total progeny can produce only as far as about 10 newborn ( but delivered in different days ).

Breeding can be affected in particular by nourishment deficiencies or by water dissolved oxygen availability.

Around the beginning of the XX century, by the start of the aquarium hobby in mass proportions, hobbyists living in industrialised countries with low temperature winters, were limited only to species showing some degree of cold resistance or species from the local fauna.

Later, with the less complex and more accessible tank water heather technologies, tropical small and colourful exotic species become soon the favourites, occupying in a short time the place of the previous cold/temperate water ones.

Nowadays it is unfortunately accepted, in general, that keeping and breeding temperate region fish species turn out to be, more often than not, a difficult assignment, in particular if compared with more easily tropical popular favourites.

While in fact they need a slight coldness during winter, the good news is that, all the ovoviviparous and almost all viviparous Cyprinodontiformes, do tolerate very well the warm up during summer and hang about in good physical shape under the high temperatures of some domestic tanks on this period.

The first big difference between tropical fish and those who come from temperate regions regards the breeding season.

Tropical species generally have no defined seasonality; they breed all year round with intermittent intervals caused by extremely environmental unfavourable conditions.

For species from temperate regions a colder winter interlude as well as simultaneously a larger dark daily period is very important or even fundamental for their biological clock work as it should be.

The Least Killifish doesnt have the need of a photoperiod and thermal intense seasonal distinction, like other northern fish from wintry regions. Populations from the deeper south edge of Florida can be considered more or less tropical fish. Even so, a light change from seasons is essential to keep these fish healthy and allow breeding without problems.

Even concerning the warmest region of its geographical distribution, reproduction is still seasonal and takes place above all between March and October, allowing 2, 3 or even 4 generations each year.

When placed on environments of invariable temperature all year round, the females lives are jeopardized by the severe response to reproductive uninterrupted effort. Baby fish born under such conditions will suffer from that sooner or later. On the other hand, animals that benefit from a breeding interval can recover easily after such procreation demands.

Besides that, as a general rule, gestation under lower temperatures has a tendency to produce fewer embryos by brood, which can represent faster recovery after delivery and no doubt a less demanding procreation effort to mothers.

Under a constant temperature of 25C (77.0F ) very well feed Heterandria formosa mothers can deliver every 4 days a complete brood.

Raising 2C ( 3.6F ) or 3C ( 5.4F ) can be enough to delay such regularity by sudden gestation adjustment to these new tepid conditions. An abrupt raise in 4C ( 7.2F ) or more can take the life of several embryos in a brood.

As hot the water will be as high oxygen consumption will be. We must keep in mind that embryos receive an oxygen supply from mothers on this species.

Delivery work can become more difficult and take longer in high temperatures by the same reason. Also smaller newborn can be expected when gestation is limited by stressful environmental stress.

Extra artificial lightning also produce more fry and reproduction increase even in lower temperatures. The photoperiod must be under strict supervision with this species.

This is also an unexpected example in terms of reproduction. Unlike many other members of the Poeciliidae family, this species is a step ahead in evolution as regards the ovoviviparity. Least Killifish mothers dont give a simple protection body protection to independent eggs developing inside of it. In fact, thanks to a primitive kind of placenta, there must be in effect a certain metabolic relation between the embryos and the female who carry them in gestation.

Otherwise we could not understand why diet and oxygen can pay such evident a roll on the embryonic development and newborn size on release.

In contrast, isnt so obvious why newborn kept at 20C ( 68.0F ) during gestation period can show more tolerance to high temperature limits than those spawn at 26C ( 78.8F ). Quite the opposite, those embryos developed at higher temperatures seam to be more resistant.

More than hobbyists opinion, scientific papers do confirm that larger fry do survive more easily than smaller ones.

Sexual maturity comes around 45 to 65 days and limit longevity in the wild can go from approximately 130 to 170 days. In contrast, in captivity here these fish usually do go quite further than one year extended.

Average gestation period is typically around 5 weeks long.

As several generations can succeed fast in such little time, this species presents a incredible genetic variability among wild populations, ( sometimes even inside the same hydrographical basin ).

This conjuncture can made us think about the high probability of endogamy problems in captivity small populations. You should do your best efforts to keep the largest number of individuals and also invest some profitable effort exchanging frequently fish with other breeders.

Endogamy threat as well as high muti-paternity can be a possible explanation for some aquarium populations sex ratio large disequilibrium propensity.

These are invertivorous animals, so ordinary diet in nature is made a great deal by invertebrates with the proper size to their minuscule oral cavity ( micro invertebrates ). Some times a quantity of vegetal matter is also found in wild fish stomachs.

In captivity, the main concern about the appropriate feeding is no doubt the size of all kinds of the food supplied. Especially little fry and very young ones can die from starvation malnourishment if proper sized feeding is not provided for them.

Adults do accept very well industrial flake food ( keep always in mind to smash it in to small pieces and even powder to the little ones ).

As newborn and very young individuals stay almost always occults inside the dense vegetation refuges, be careful to disseminate a little powder food above those places where they feel safety.

As live or freeze up food it is advisable to use small aquatic invertebrates ( Daphnia, Cyclops, Infusoria, etc ), small new hatched aquatic snails as well as other molluscs, and zooplankton.

From time to time dont disregard green stuff as well too.

V - Complementary notes

This species doesnt present any behaviour problem, which turn these fish has magnificent community tank mate.

Male regular disputes dont harm other fish around, and never result in injuries to the antagonists itself.

Your major concern must be to avoid place this tiny pacific fish together with potential predators or aggressive kind ones who can become a danger to Heterandria formosa own safety. Thats why it is forthrightly better to place them together with peaceful companion too, away from piscivorous invertebrates.

Natural most direct predators are other fish from Centrarchidae and Poeciliidae. Most references do point species like Lepomis gulosus, Lepomis punctatus, Lepomis marginatus, Lepomis microlophus, Lepomis macrochirus, Lepomis miniatus, Lepomis Cyanelus, Lepomis auritus, Lepomis humilis, Lepomis microlophus and Gambusia holbrooki. Other predators also cited are the fish Aphredoderus sayanus ( in particular during night attacks ), besides aquatic insects larvae like the dragonflies Anax junius and Coryphaeschna ingens.

Mainly in the presence of other species in captivity, the Least Killifish reveals to be an inhibited and shy species. Nevertheless, any thank inhabited by this charming fellows is always a party, yet newborn and fry are only visible only after a few days of live, depending how secure they feel to come up to the limits of the dense vegetation where they make use as place of safety.

Be careful with some helpful freshwater shrimps, very valuable in tank cleaning but also very effective predators on Heterandria formosa. Caution and a wary search for some species compatibility will help you to avoid losses by predation.

Although this species is able to stand for low levels of oxygen ( as well as a certain degree of water contamination ), frequent water partial changes will help to preserve hale and hearty fish. In some cases this procedure can represent the difference between a florescent population and sporadic problems.

VI - Threats, protection and present status

This species is officially considered as vulnerable in Georgia, Alabama, Mississippi, Louisiana and is considered in danger in North Carolina.

Environment obliteration, in particular by discharge of a given amount of polluting substances into streams, including human sewage, animal manure, industrial waste water as well as exotic species introduction are the more significant recognized threats.

Even in a developed country like United Sates of America environmental problems keep affecting natural regions of Heterandria formosa in a very significant scale.

Auspiciously, a vast geographical distribution allows many populations to stay free from human press on, most of all in remote wild regions.

One of the main pressure sources is water dissolved oxygen low levels. This stresses fish and can lead to kills if levels fall down too far.

Such contrariety is originated in water contamination with materials including human sewage, animal manure, wood pulp, and debris from forest clear cutting and everyday forest functioning.

Another source of survival problems has a close relation with increase contamination by bacteria, viruses, and protozoan.  Some of these microbes are pathogenic ( cause disease ), and can be introduced by many of the organic noxious waste waters dumped in to the ecosystem by domestic, agriculture and industrial human activities, many described above for causes for water dissolved oxygen low levels.

A different seasonal problem is a consequence from high pluvial peaks, causing turbidity that clouds the water.  A major type of turbidity is dirt, mainly soil that runs off the land during a rainstorm.  This take place especially where there has been any land-disturbing activity, such as timber cutting, agriculture, road building, or most types of human building.

Modern intensive agriculture, especially those cultures when high levels of chemical fertilizers considered as nutrients, pollute the water resources when this products reach subterranean run. Nutrients that contaminate the water consist mainly of nitrogen and phosphorus.

These nutrients will fertilize the algae in lakes and streams, and can cause blooms stimulating an acceleration of the eutrophication process.

Industrial accidents can amplify all of these problems as well as to produce catastrophic proportions in case of chemical substances dumping.

Exceptionally adverse atmospheric conditions can also become a potential resource of environmental problems.

Hurricanes have major impacts on water quality.

When such big storm hits the regions where this species is present in the wild, human civilization pays again an important role on the consequences from it. Usually one of the first consequences is the electric power shutting down.  When this happens, sewage treatment plants and pumping stations cannot carry on and complete their purpose. Untreated or partially treated human sewage is then dumped directly into the ecosystem.

Another major problem concerns contamination from other pollutants and fuel release from devastated facilities.

The heavy rains cause also some waste lagoons to rupture, others to overflow, and some become entirely inundated by floodwaters.

Nonetheless, the Least Killifish isnt yet under a great global concern neither is referenced by the I.U.C.N. Red List.

For further knowledge or information about this please check Livebearer Cyprinodontiformes in the IUCN Red List of Threatened Species.

Other topics available about this species :

Literature cited ( references ) :

Charles F. Baer, 1998. Species-Wide Population Structure in a Southeastern U.S. Freshwater Fish, Heterandria Formosa : Gene Flow and Biogeography.

Evolution, Vol. 52, No. 1 ( February, 1998 ), pp. 183-193.

David Reznick, Heather Callahan and Raymund Llauredo, 1996. Maternal Effects on Offspring Quality in Poeciliid Fishes.

Department of Biology, University of California Riverside, California 92521.

American Zoologist 36(2) ( 1996 ), pp. 147-156.

Joseph Travis
, James A. Farr, Sabine Henrich, Ron T., 1987. Testing Theories of Clutch Overlap with the Reproductive Ecology of Heterandria formosa.

CheongEcology, Vol. 68, No. 3 ( June 1987 ), pp. 611-623

Henrich S., 1988. Variation in offspring sizes of the poeciliid fish Heterandria formosa in relation to fitness.

Oikos. Vol. 51, no. 1 ( 1988 ), pp. 13-18.

Jacob F. Schaefer
, Steven T. Heulett, Terence M. Farrell, 1994. Interactions between Two Poeciliid Fishes ( Gambusia holbrooki and Heterandria formosa ) and Their Prey in a Florida Marsh.

Copeia, Vol. 1994, No. 2 ( May 16, 1994 ), pp. 516-520.

Mark C. Belk, Charles Lydeard, 1994. Effect of Gambusia holbrooki on a Similar-Sized, Syntopic Poeciliid, Heterandria formosa : Competitor or Predator ?

Copeia, Vol. 1994, No. 2 ( May 16, 1994) , pp. 296-302.

Nevin S. Scrimshaw
, 1944. Embryonic Grouwth in the Viviparous Poecilid Heterandria formosa.

Biol Bull 87 ( August 1944 ), pp. 37-51..

We should be extremely gratified and thank you in advance if some one could provide new data about this topic, or even eventually any correction to be made on this document. For this purpose please be so kind and write us.

Optimized for 1024 x 768 resolution

2006 - 2011 All Rights Reserved 

e-mail :

- Data and information authored and produced on this website are in the public domain.

While the content is in the public domain, some pages contain images and material that are copyrighted by others and used here with permission.

Such information is available for private use, study or research. You should obtain permission from the copyright owner for other uses. Please carefully examine all the content and all linked pages for copyright restrictions and to secure the necessary permissions.

Content accuracy and usability of data and information - Every effort is made to provide and maintain accurate, complete, useable, and timely information on this website. However, some data and information accessed through these web pages may, of necessity, be presented prior to final review and confirmation.

These data and information are provided with the understanding that they are not guaranteed to be correct or complete. Users are cautioned to consider carefully the provisional nature of these data and information before using them; such data and information are the singular responsibility of the user.