General characteristics of killifishes

Killifishes are small, commercially unimportant, fish native to all continents except for Australia and both polar regions. Although they are widely distributed all over the world, their incidence is rather localized and only rarely can they be described as common fish. Most of them are fish of small habitats (marshes, ponds, creeks, etc.) and, consequently, of small populations, although a limited number of species expand into large habitats such as rivers, lakes, or even seas and oceans. Many killifishes occupy temporary habitats with exceedingly variable climate. They are ideal aquarium fish for their small size, attractive colouration, easy maintenance and very interesting biology, particularly in annual species.

CONTENTS OF THE CHAPTER systematics of killifishes term killifish in this project morphology of killifishes body shape principal body shapes of killifishes size colouration and brilliance colour patterns of killifishes intraspecific variability of colouration and aquarium forms sexual dimorphism and dicolorism, differential maturation

Systematics of killifishes

TERM KILLIFISH IN THIS PROJECT

ACCORDING TO THE LATEST CLASSIFICATION OF FISHES (Eschmeyer, 2002, Huber, 2007), the killifishes belong to the class ACTINOPTERYGII (=Osteichthyes, =Fishes) and order CYPRINODONTIFORMES. This order is divided into 10 families: Aplocheilidae, Nothobranchiidae (subfamilies Nothobranchiinae and Epiplateinae), Rivulidae (subfamilies Rivulinae, Cynolebiinae and Kryptolebiinae), Fundulidae, Profundulidae, Goodeidae (subfamily Empetrichthyinae), Valenciidae, Cyprinodontidae (subfamilies Cyprinodontinae and Cubanichthyinae), Anablepsidae (subfamiliy Oxyogonectinae), Poecilidae (subfamilies Poecilinae and Aplocheilichthyinae). This publication includes also order Beloniformes with family Adrianichthyidae and subfamily Oryziinae with genus Oryzias because species of this genus are very often kept by killifish fans. The scientific name of the order Cyprinodontiformes comes from the Greek "kyprinos" (i.e., a carp-like) and "odont" (a tooth) and it means - the toothcarps. Their teeth are conical except for herbivorous species which have flat and triangular teeth. Killifishes have a cylindrical body with a conical head, relatively large eyes and an upturned mouth. All fins have only soft rays, and the adipose fin is generally absent. The dorsal fin is placed far back on the body and the lateral line is only present on the head. They have a very characteristic sexual dimorphism and dicolorism.

TERM KILLIFISH: in this project, and generally in the aquarium practice, includes only a fragment of the families and subfamilies of the order CYPRINODONTIFORMES, namely: all species of the families: Aplocheilidae, Profundulidae, Fundulidae, Valenciidae and Cyprinodontidae; only the subfamily Empetrichthyinae of the family Goodeidae, only the subfamily Oxyzygonectinae of the family Anablepidae, only the subfamily Oryziinae of the family Adrianichthyidae, only 1 species - Tomeurus gracilis of the subfamily Poeciliinae. SYSTEM OF KILLIFISHES The term killifish includes as many as 77 genera and 840 species and subspecies (valid to - March 21, 2007. There are more than 2 800 populations and aquarium strains of killifishes kept in captivity. TABLE OF GENERA

Morphology of killifishes

BODY SHAPE

There are two principal body shapes of killifishes: type Cyprinodon and type Aplocheilichthys. TYPE CYPRINODON: typical carp-like body, slightly compressed laterally, with the back highly arched and the dorsal fin located far back on the body. They inhabit mid- or bottom-layers of a habitat where they usually form temporary or permanent territories. Several species are omnivorous, although most of the Cyprinodon-like fishes are herbivorous. Typical genera are Cyprinodon and Nothobranchius; a thicker variation is the type Cynolebias with typical genera: Cynolebias, Austrolebias and Simpsonichthys.

TYPE APLOCHEILICHTHYS: slender, cylindrical body, with a flat back and the dorsal fin placed far back on the body. The head is rather pointed. They live preferentially at or near the surface of water or in mid-layers of habitats, form schools and feed mainly on terrestrial insects which have fallen onto the water surface, or on crustaceans. Typical genera: Aplocheilichthys, Aplocheilus and Epiplatys. A thicker variation with a slightly rounded head is the type Rivulus. The species of this type of body may be found at the surface of water (Rivulus) but more often in mid- or bottom-layers of habitats (e.g., Aphyosemion and Fundulopanchax), and feed mainly on aquatic insects and their larvae.

Principal body shapes of killifishes

SIZE
Killifishes are fish of small habitats and small size. Most of the species grow up to 10 cm [4 in]. The small size is the principal precondition for life in temporary water bodies where the fish have only limited time to grow and reproduce (a few weeks or months). The smallest species of killifishes are usually about 2 cm [3/4 in] (Fluviphylax obscurus, F. pygmaeus, F. simplex, F. zonatus and Plesiolebias lacerda), while the largest, probably extinct, Orestias cuvieri grew up to 27 cm [10 3/4 in]. The largest recent killifishes are Orestias pentlandii (23.5 cm [9 1/2 in]) and Austrolebias elongatus (22 cm [8 3/4 in]).	The size of killifishes in captivity is sometimes larger than that in their natural habitats. There are two explanations for this phenomenon: 1. the fish in captivity receive plenty of food, are more healthy, and not so active as in natural conditions, which may result in the excessive growth. 2. on the other hand, the top sized specimens may be excellently adapted to their natural habitats so that they are never, or only exceptionally, collected in the field, because they are best hidden and not easy to catch. For this reason, it is recommended to add 20 - 30 % to the measurements made on wild preserved material to get the correct estimation of the maximal size of the species.
COLOURATION AND BRILLIANCE
Many killifishes are brightly coloured and are amongst the most attractive aquarium pets. Although their colour patterns are very variable, in general we can distinguish 4 types: TYPES OF COLOUR PATTERNS: Type I: rather achromatic, dull species with hardly more than one colour. The main component of the colouration is a brilliance, mostly silver (e.g., Cyprinodon or Fundulus), sometimes attractively blue (e.g., Procatopus). The typical example of the Cyprinodon-like body shape is genus Cyprinodon and of the Aplocheilichthys-like body shape - genus Fundulus. Type II: vertical dark bars on the body represent the adaptation of fish to vegetated pools with plenty of aquatic and terrestrial plants. The typical example of the Cyprinodon-like body shape is genus Austrolebias and of the Aplocheilichthys-like body shape - Epiplatys. Type III: medium attractive species, generally of brown, yellow and orange colours. For instance, genera - Simpsonichthys and Nematolebias of the Cyprinodon-like body type, or Rivulus of the group of the Aplocheilichthys-like body shape. Type IV: the most brilliantly coloured, very attractive species that are reminiscent of the gorgeous colouration of the coral reef marine fishes. The main colours are red, blue and green. The Cyprinodon-like group represents genus Nothobranchius while the Aplocheilichthys-like group consists of the very popular genera, such as - Aphyosemion, Fundulopanchax, Callopanchax or Scriptaphyosemion.	STABILITY OF COLOURATION: while in many fish the colour patterns and the intensity of colouration correspond more or less to the momentary mood of a specimen, in killifishes this phenomenon occurs only rarely. The exception to this is, e.g., Nothobranchius patrizii which has an intensity of colouration of the caudal fin reflecting the momentary mood of the fish. Also a spawning colouration, known in many fish, is rather exceptional in killifishes because most of them have no distinct spawning season and the adult specimens spawn usually every day. Killifishes with the distinctive spawning season are, e.g., genus Cyprinodon. Also a nocturnal colouration occurs only exceptionally in killifishes. Most of the killifishes become pale at night, and only a few species show the characteristic nocturnal colouration (e.g., some species of genus Epiplatys). BRILLIANCE: is a characteristic for many killifishes. Fishes with the colour pattern type I have the brilliance as the principal colouration, while other killifishes reflect their metallic colours according to the angle of light. For this reason, we recommend to illuminate the killifish tanks from the front. Many killifish fans shine a pocket lamp on their fish from the front to see their metallic brilliance. The intensity of reflection depends on various factors. The first is the intensity of light: the fish raised in tanks with a strong light develop more metallic brilliance than those raised in dark tanks. The second factor is a slime: the more slime - the less brilliance. For instance, when moved from one tank to another, the killifishes lose their metallic brilliance, for some time, probably because of the increase in production of the slime as result of the stressful stimulus. The total brilliance is also affected by the amount of oxygen present in water: the more oxygen - the less brilliance.