Elevated salinities may enhance the recovery of hydrated heat-shocked Artemia franciscana cysts (International Study on Artemia. LXV)

Hydrated encysted embryos of the crustacean Artemia franciscana Kellogg 1906 were incubated at 42degreesC and 44degreesC for 48 h at elevated salinities. They exhibited better recovery when incubation took place in a high salinity environment. The recovery and/or protection by salinity of A. franciscana encysted embryos depend on the severity of the heat shock. Cysts heat shocked at 44degreesC and different salinity media (35, 50 and 70 ppt), upon return to optimal conditions, gave similar hatching percentages of less than 5\%. When heat shock took place at 80 ppt, a significant increase in hatching was observed (i.e. from 5\% to 22\%). Concentration of glycerol and translocation of a major protein of about 26 kD (p26) in Artemia encysted embryos were studied to reveal the potential protective role of these two factors against elevated temperatures. Increased glycerol levels were scored when cysts were incubated in elevated salinities within the first 4 h and prior to heat shock treatment (i.e. a 38 \% and 49 \% increase at the salinities of 70 ppt and 80 ppt, respectively). SDS-PAGE of proteins extracted from control and heat-shocked cysts suggested that the intracellular translocation of p26 was enhanced as the salinity increased. It is proposed that salinity-dependent heat shock seems to be at least partly responsible for i) the significant increase of glycerol and ii) the degree of translocation of p26, a suspected molecular chaperone described previously. These two factors along with others may contribute to the better recovery of heat-shocked Artemia encysted embryos. This phenomenon, which may be attributed to increased thermostability of proteins, is reflected as different cyst hatching ability.