Related FAQs: Four-Eyes,

Related Articles: Livebearing Fishes by Bob Fenner,  Poeciliids: Guppies, Platies, Swordtails, Mollies by Neale Monks, Brackish Water Fishes, Cyprinodontiform Fishes,

/The Conscientious Brackish Water Aquarist

By Bob Fenner

Female and male Anableps anableps at the Steinhart Aquarium

male and female shown above

Anableps dowi Gill 1861, the Pacific Four Eye. Pacific; Southwestern Mexico to Nicaragua. To almost nine inches in length. Brackish to marine. Temp. 24-28 C. Upper body is dark brown, below is a yellow band, with brown under this.

Anableps microlepis Muller & Troschel 1844, Foureyes. South American; Trinidad, Venezuela to the Amazon Delta. To a foot in length. Has two narrow bands bordering yellow area in-between along body.

Jenynsia spp.

Livebearers

Oxyzygonectes

To 12 cm. Egglayer

Excerpted From:   So you think livebearers are boring? There's more to livebearers than guppies. Neale Monks looks at some of the interesting and unusual livebearers available to aquarists by Neale Monks

The Anablepidae 

Starting our review of the livebearers alphabetically, the four-eyed fishes of the genus Anableps certainly qualify as being decidedly un-boring fish. In fact, it would be hard to find more interesting aquarium fish. Their most celebrated features are their eyes, which are each divided into two lobes, one for seeing above the waterline, and the other below. This specialisation presumably allows them to hunt for food and avoid predators at the same time, and these fish are certainly nervous, jumpy fish that take a long time to settle into aquarium life. 

The other famous oddity is that these fish aren't just male or female; they're 'right-handed' or 'left-handed' as well. Females have a covering, called a foricula, over the genital opening that is hinged on either the left or the right hand side of the opening. If the foricula is hinged on the right, the genital opening is only clear on the left, and vice versa. Males have a gonopodium, a modified anal fin, that delivers sperm to the female, and again, it either bends to the left or to the right. A male with a gonopodium that bends to the right can only mate with a female that has its genital opening open on the left, and left-handed males can only mate with females that are open to the right. 

In terms of aquarium care, four-eyed fish are quite demanding. The first issue is size: these are big fish, getting to around 25-30 cm in length. Females are usually a bit bigger than the males, but if you want to breed these fish, you're going to need to keep at least half a dozen specimens just to make sure you get compatible males and females. Consequently, a big aquarium with plenty of filtration is essential. Complicating things somewhat is the need these fish have for 'resting' places. In the wild, these fish beach themselves on sandbanks, but in aquaria, large, smooth stones or flat pieces of slate will work perfectly well. Arrange these so that they form a ledge a just far enough under the waterline that the fish can rest with just their eyes protruding. Finally, these are brackish water fish, and do not do well when kept in completely fresh water. The exact saltiness of the water isn't critical, but a specific gravity between 1.005 and 1.010 will do nicely. 

Despite being livebearers, breeding these fish isn't especially easy. As with some of the other oddball livebearers, the tricky bit is making sure the female doesn't miscarry. Providing optimal water conditions and a stress-free environment is half of the battle here, but keeping her in good conditions by providing plenty of live and frozen foods is just as important. The baby fish are born after a gestation period of about three months, and they are about 5 cm in length, easily big enough to small brine shrimp, daphnia, bloodworms, and other small foods. The parents aren't especially cannibalistic, but removing them to a separate maturing tank is a good idea, if only so that you can ensure that the baby fish get plenty of food.