ARK - Arizona Rivulin Keepers

The Scheel Letters, No. 41

As a rule, related fish have many traits in common: the closer the relationship, the more common traits. Breeders of tropical fish use this when trying to breed aquarium fish that previously have not bred in captivity. Aquarists therefore may need information on the relationship within the group of fish they keep.

Killies belong to the order Cyprinodontiformes (Cyprinodontes) or Microcyprini. The origin of the members of this order seems to be somewhat obscure. Very often the toothcarps which is the popular name for the fish in this order are considered as relatives of some of the pike-like fish (order Esociformes), in particular of the rare Umbra which lives in freshwaters in Southeast Europe and the USA. Other zoologists consider the toothcarps as direct descendents of some old herring-like fish (the extinct suborder Leptolepoidei which lived between upper Triassic and middle Cretaceous, that is to say 100-200 million years before our time) in the order of Clupeiformes. Also the garfish relatives (order Beloniformes) are often placed in some connection with the toothcarps. The best known aquarium fish from this order are the Dermogenys, but also the common garfish and the flying fish belong to this order. Besides this, the very small order of Phallostethiformes have been placed near the toothcarps (Berg a.o.) but also near the order Mugiliformes. The Phallostethiformes are only known by a small number of aquarists. The few species live in freshwater and are generally very small. They look very much like toothcarps, but some of the species have two dorsal fins (the anterior one is very small, but it has spines instead of rays). Tek's "minute Oryzias" may belong to this order (see previous pages). The Mugiliformes contain several good aquarium fishes: the rainbowfish (Melanotaenia), Celebes rainbowfish (Telmatherina) and Bedotia species from Madagascar. Wickler (Zoologischer Anzeiger 1959) considered these questions and proposed the following figure as a question:

(figure missing)

The order Cyprinodontiformes normally is divided into 2 suborders: Amblyopsidei (blind cave toothcarps) and Cyprinodontoidei or Poecilioidei (proper toothcarps). Amblyopsoidei only contain a few species within one family, the Amblyopsidae restricted to the USA. Berg names 4 genera: Chologaster, Typichthys, Trogichthys and Amblyopsis. There is or has been a fifth genus: Forbesichthys. Only in Chologaster do some species have normal eyes (C. cornutus) and live in ditches and pools. This species has been imported as an aquarium fish - slender Fundulus-like fish, 15 cm, with 3 thin and dark longitudinal stripes on sides. In C. papiliferus however, the eyes are somewhat degenerated. In the species Typlichthys, the eyes have no rods and cones on the retina, but still the nerves run from the retina to the brain. In Amblyopsis also the pupil is closed. In Troglichthys, one finds the maximum of eye degeneration. A. spelaeus from Ohio-Kentucky has been imported as an aquarium fish to Germany as early as 1899. The shape of this blind fish is like C. cornutus and the other species. 13 cm. It does not like any shaking in the tank, probably because other sensitive organs are highly developed. All species are ovoviviparous, that will say that eggs develop within the female. They hatch at once when they come out into the water. The anal fin of the males does not change into a gonopodium. How eggs are fertilized, I do not know.

Cyprinodontoidei often is divided into 2 or more superfamilies. Sometimes zoologists consider 2 superfamilies: one containing the oviparous (egg laying) and another containing the viviparous (live bearers). I use Niolski's division: