Seawater incubated embryos of a freshwater Aplocheilus lineatus (Aplocheilidae; Cyprinodontiformes) support the dispersal hypothesis of killifish intercontinental distribution.

BACKGROUND

Aplocheiloid killifishes (Cyprinodontiformes, Aplocheiloidei) inhabiting Africa, America, and South Asia are unique in that embryos of annual species are capable of entering a state of diapause and becoming extremely stress resistant. Distribution of aplocheiloids is a biogeographical enigma: how freshwater fish managed to cross long-distance oceanic barriers to become intercontinentally distributed? As a hypothesis, we proposed their embryos to be a dispersal stage. To test it, we compared embryonal development in seawater and freshwater incubated eggs of Aplocheilus lineatus from the Aplocheilidae family, an early-diverging aplocheiloid non-annual clade with the intercontinental disjunct distribution across Madagascar and India separated by an ocean.

RESULTS

Seawater incubated A. lineatus embryos were revealed to be salt tolerant and able: (i) to delay hatching and prolong embryonic period, (ii) to retard embryonic development and growth, and (iii) to reduce consumption of endogenous food reserves.

CONCLUSIONS

Revealed developmental traits in principle may favor long-distance transoceanic trips of embryos. Given eggs in aplocheilids are adhesive and can readily attach to plant debris, rafting seems to be possible as a mechanism of oceanic dispersal. It is not excluded that a similar mechanism was used by some other freshwater fish clades with intercontinental distribution (e.g., cichlids).