The killifish of the genus of Nothobranchius – small annual fishes from the savannahs of East Africa– are real record-breakers. Their extremely short life is connected with the fastest sexual maturation of all vertebrates. This significant discovery by scientists from the Institute of Vertebrate Biology of the ASCR in Brno has now been published in the international journal EvoDevo as a component of its articles on life in extreme conditions (see the abstract). The investigation of killifishes living in savannah pools created during the seasonal monsoon rains.
They hence must grow and manage to reproduce before their pool dries up again.
An extreme environment often leads to extreme adaptation for survival and successful
reproduction. “These killifish can grow as much as 23 % of their size daily,” says Mgr. Radim
Blažek, Ph.D., from the Institute of Vertebrate Biology of the ASCR. One of the studied species,
N. kadleci, began to reproduce already at an age of 17 days at a size of only 31 mm, the
related species
N. furzeri only one day later. After reaching sexual maturity, they reproduce daily and the
fish eggs can hatch already after 15 days. That means that an entire generation could take place in
a single month – which makes these killifish not only the vertebrates with the fastest adolescence
but also with the shortest generational length among all of the vertebrates.
When the pools in the savannah dry up, the fish eggs survive to the next period of rain in the dry mud as embryos in the dormant
stage, resistant to drying out. When new rains come, they hatch and give rise to a new generation
of killifish. In the laboratory it is possible to significantly accelerate their embryonic
development and skip the long dormant stage. However, also in nature some embryos skip the dormant
stage of development and are able to hatch already in 2–3 weeks. These embryos are ready to hatch
in case the original pool dries up quickly, but with additional rain is again filled with
water.
Long-lived animals on the contrary have a lot of time for everything. For example, the olm (Proteus anguinus), with a size comparable to killifish, which is a small aquatic salamander inhabiting safe and cold cave systems in the Balkans, lives and more than a hundred years and puberty it lasts for 16 years. On the other hand, also other vertebrates than the killifish are known for their rapid sexual maturation. Tropical marine fish, the goby genus Schindleria, already mature in 23 days. However, when compared to killifish, their ontogenetic development is very rapid and they retain many larval characteristics - basically they look like small fish larvae with developed and functional gonads. Conversely, killifish look like typical fishes, with all their fins and internal organs. For instance, the females of the house mice, especially some strains bred in the laboratory, also mature very quickly.
“We already knew about the rapid adolescence of the killifish of the genus Nothobranchius, and we assumed that some species could mature as early as at 4 weeks of age. The period of 17 days, however, was breathtaking,” Radim Blažek added. “Moreover, it is not an artefact of breeding in aquariums. In nature, fish grow even faster than in captivity and it is likely that under favourable conditions they mature even earlier.”
Contact:
Doc. RNDr. Martin Reichard, Ph.D., ÚBO of the ASCR, Brno (team leader); e-mail:
reichard@ivb.cz, tel.: +420 775 097 426
Prepared by: The Institute of Vertebrate Biology of the ASCR and the Department of Media
Communication of the Head Office of the ASCR
5 Sep 2013
