Rapid growth, early maturation and short generation time in African annual fishes

Abstract

Background: Extreme environmental conditions can give rise to extreme adaptations. We document growth, sexual maturation and fecundity in two species of African annual fish inhabiting temporary savanna pools.

Results: Nothobranchius kadleci started to reproduce at the age of 17 days and size of 31 mm and Nothobranchius furzeri at 18 days and 32 mm. All four study populations demonstrated rapid growth rates of up to 2.72 mm/day (23.4% of their total length). Both species may produce diapausing embryos or embryos that are able to hatch in as few as 15 days, resulting in a minimum generation time as short as only one month. Incubation on the surface of damp peat moss results in high embryo survival (73%) and a high proportion of rapidly developing embryos (58%) that skip diapauses and hatch in less than 30 days. We further demonstrated that rapid growth and maturation do not compromise subsequent fecundity.

Conclusions: Our data suggest that both species have the most rapid sexual maturation and minimum generation time of any vertebrate species, and that rapid maturity does not involve paedogenesis.

Figure 1

Study species and their typical habitat. (A) Typical habitat of the study species: a shallow savanna depression filled with water during the rainy season in Chefu region. (B) Male Nothobranchius kadleci. (C) Male Nothobranchius furzeri. (D) Female Nothobranchius kadleci.

Figure 2

Growth rates of all study populations. Growth rates of the males and females for each of the four study populations of N. furzeri (A: NF222 Chefu, B: NF121 Limpopo) and N. kadleci: C: NK91 Save, D: NK430 Pungwe), with indication of the period between the onset of nuptial coloration in males and attainment of sexual maturity in both sexes (gray columns). For NF222, total length data from an adjacent population NF220 (N = 3 males, 7 females) collected in the wild are added for comparison.

Figure 3

Embryo survival and development during the first 30 days. (A) Proportion of embryos surviving on different developmental substrates visualized by Kaplan-Meier estimate. Sample size for each category is given in parentheses. (B) Proportion of embryos hatched at a given time when incubated on different substrates visualized by Kaplan-Meier estimate. The number of embryos surviving the experimental period for each category is given in parentheses.