Orestias ascotanensis Parenti 1984 (Pisces; Cyprinodontiformes), larval adaptations to extreme conditions in high Andes

Orestias ascotanensis Parenti is a critically endangered endemic species of the Chilean high Andean systems, found only in the springs of the Ascotán saltpan. Considering the importance of reproduction and early life history stages in population persistence in fishes, understanding these is essential for successful conservation efforts. We studied the larval development of O. ascotanensis under controlled temperature and photoperiod conditions. A total of 50 O. ascotanensis specimens were captured during 2014 and 2015 and moved to the laboratory to be kept under controlled conditions and diet. Females were subjected to hormone therapy using Ovaprim® to induce oviposition, which was followed by artificial fertilization under dry conditions. Water temperature was maintained at 20 °C (± 1 °C), conductivity values oscillated in the interval of 2800–3600 µS/cm3, and the photoperiod was established as 16:8 (light hours:dark hours). The larvae hatched within 14 to 18 days. Three larval stages were established: (i) flexion larva with yolk sac, (ii) flexion larva, and (iii) post-flexion larva. The newly hatched larvae were highly prepared for the free-living stage and they absorbed the yolk sac in 5–7 days. The intense pigmentation of O. ascotanensis eggs and larvae and the high degree of development at hatching may represent adaptations to extreme conditions, such as high levels of solar radiation and significant changes in daytime temperatures. A range of anthropogenic activities have caused the contraction and degradation of the habitat of O. ascotanensis, producing serious concern regarding the conservation status of the species.