The effects of CO.sub.2 level and temperature on embryos and free embryos of the Patagonian pejerrey Odontesthes hatcheri

Climate Change includes an increase of both the concentration of atmospheric CO.sub.2 and of global temperature. Embryos (= eggs) of Odontesthes hatcheri were collected in spring-summer from the littoral of Lake Morenito (Andes of Argentina). Embryos and free embryos were exposed to different temperatures (within a currently natural thermal range) and CO.sub.2 levels (obtained by bubbling lake water with gaseous CO.sub.2). High temperature and high CO.sub.2 led to low embryonic survival. Embryonic abnormalities were observed. Incidence of colorless blood cells and delayed dorsal pigmentation increased significantly at high CO.sub.2 level. Free embryo survival decreased with time, being particularly low at high CO.sub.2 level. Free embryo body shape also signaled the effects of high CO.sub.2. The combined effect of temperature and CO.sub.2 was additive. As temperature and atmospheric pCO.sub.2 increasing continues, the best survival at hatching observed in our experiments (50-60%, pH 7.5, 14 °C) will deteriorate (< 20% at 18 °C and pH 7.0). These Climate Change-related results and the fact that the species is already threatened by translocated species suggest a fragile situation. Spatial variation of temperature and pCO.sub.2 led us to reconsider the suitability of shallow littoral vegetated areas of the lakes as anti-predatory refuges for fish early life periods.