Zoogoneticus tequila 

The Tequila Goodeid, or Tequila splitfin, is a critically endangered livebearer named for the Tequila volcano near Guadalajara in central Mexico. Unique among live bearing fishes, the goodeids take an almost mammalian approach to reproduction. Rather than the typical approach - of hatching their eggs internally immediately prior to birth, the way guppies, swordtails, platies and other livebearers do - the goodeids nourish developing embryos via something very much like a placenta/umbilical cord arrangement. There are even two species of goodeid (from southern Texas) which are still egg layers.
These are occasionally aggressive, hardy fish which face extinction only because of human activity- habitat destruction and pollution.

 ^^fry, born Jan 4, 2011
 ^^pair, male to the right
 ^^newly pregnant female
^^pregnant female, close to due date
 ^^fry, born Jan 4, 2011 (just shy of 2 months at time of posting)
 ^^courting pair
 ^^courting pair
^^courting males darken considerably -almost to black in some areas- enhancing fin markings and eye rings. Both male and females repeat a side-to-side jerk of their heads.

^^same pair,  3 months later, colour change reversed. Females also darken with mood.

^^ This recently rescaped aquarium has different sized caves built in.