torsdag den 3. januar 2013

Fish Spotlight: Heterandria formosa - AKA least killifish, mosqu or midget livebearer

Hello all,
Once in a while you find that one of the fish you keep turns out to be a favourite although there is no good reason for this. The small Heterandria formosa is just such a fish. Unremarkable in colour, not a really good swimmer, and as small as you are likely to find any fish to be, it still is surprisingly lovable.

 So whats to love? Well, for one thing it breeds remarkably easily. As with guppies, it will keep throwing out babies (the smallest slivers that are barely visible). But it is also very, very, undemanding as it can tolerate temperatures from 5 to 30 degrees.
It is also just plain weird.
Size-wise, the male is less than half the size of the female.
The female will give birth to between one and three baies every three days or so, the only livebearer to do so, which is due to how the eggs mature. At our house it is sometimes referred to as the "rapist", the large 'genital' that is almost half the size of the male, can be swung around and used to perform "swim-by-rapes". The male can literally impregnate the female from afar. And will do so often and at every opportunity. As a consequence studies have shown that the female has developed an ability to eject semen from her body, but (gets weirder and weirder) also the ability to only do so with semen from fish that are too genetically close to her (i.e. 'brothers').

I've found them to unpecky eaters (they will eat anything they can get in their mouth) and will not, generally, eat their own offspring.
Easy, somehow adorable, fish. Highly recommended for small, possible low tech (i.e. no heater and filter) aquariums.

This is what Wikepedia has to offer:
Heterandria formosa (known as the least killifish, mosqu or midget livebearer) is a species of livebearing fish within the family Poeciliidae. This is the same family that includes familiar aquarium fishes such as guppies and mollies. H. formosa is not as commonly kept in aquaria as these species. H. formosa is one of the smallest fish in the world (7th smallest as of 1991), and is the smallest fish found in North America. Despite the common name "least killifish", it belongs to the family Poeciliidae and not to one of the killifish families.
Heterandria formosa is the only member of its genus to be found in the United States. Its range covers southeastern United States, from South Carolina south to Georgia and Florida, and through the Florida Gulf Coast to Louisiana. It is one of the few aquarium fishes to come from North America.
H. formosa lives primarily in vegetated, slow moving or standing freshwater but also occurs in brackish waters. 
Heterandria formosa is one of the smallest fish and smallest vertebrates known to science. Males grow to about 2 centimeters (0.8 inches), while females grow a little larger, to about 3 centimeters (1.2 inches).
The fish is generally an olive color, with a dark horizontal stripe through the center of the body. There is also a dark spot on the dorsal fin and females also have a dark spot on their anal fin. Like most poeciliids, males' anal fins are modified into a gonopodium that is used for impregnating females during mating.
 Like most poeciliids, H. formosa is a livebearer. The male uses his modified anal fin, or gonopodium, to deliver sperm to the female. The fertilized eggs grow within the female until they hatch, and the young are released free swimming. H. formosa has a unique breeding strategy even among livebearers. Rather than all the young being released at once, as many as 40 fry are released over a 10 to 14 day period, but occasionally over a longer period.

All the best,

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