Ontogeny of a threatened freshwater minnow: Implications for conservation

Investigating the ontogeny of threatened freshwater fishes is vital for designing future conservation actions that will increase the potential of species' persistence. This study provides a detailed description of the early life stages of a threatened freshwater fish species, the Evrotas minnow Pelasgus laconicus, which occupies aquatic ecosystems with extreme seasonal hydrological variation. The study of the embryonic and juvenile stages was conducted in vivo using light microscopy from eggs obtained from acclimatized wild spawners at 20 ± 1°C. Fertilized eggs were spherical and transparent with a mean diameter of 1.24 ± 0.06 mm and the average length of free embryos at hatching was 3.85 mm NL (notochord length). The main morphological changes observed are related to the absorption of the yolk, the increase and distribution of the melanophores and the sequential development of the fins. In conclusion, the Evrotas minnow was identified as a multiple spawner, exhibiting a protracted reproductive period (March to August), a particularly short egg-hatching period (5–6 days), a short free embryo stage and a rapid onset of exogenous feeding (2 days). The conservation implications of our study, such as safety stock creation, population reintroduction, conservation of fish refugia and breeding habitats and beaver dam analogues, are discussed.