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Effect of light colour, timing, and duration of light exposure on the hatchability of Artemia spp. (Branchiopoda: Anostraca) eggs

We investigated the effect of illumination on the hatching of eggs of one strain of Artemia franciscana Kellogg, 1906 and two strains of parthenogenetic Artemia (Branchiopoda, Anostraca). The following light parameters were used: colour (red, blue, and white light, having different intensities in the range 22-27 mu mol E/m(2) per s, corresponding with different wavelengths in the range 400-700 nm), and additionally (Experiment I) duration of light exposure (varying between 15 min and continuous light) or (Experiment 2) timing of light exposure (from the 1st to the 13th hour of incubation of eggs for hatching). Continuous darkness was included as negative control. Hatching percentage was determined after 24 and 48 h, and additionally after 72 h in Experiment 2. For all samples a relatively short exposure to light (6 h or less) during the initial hours of incubation maximally triggered the hatching process; I h of light had highest efficiency when given during the 4th hour of incubation of eggs for hatching, and less so when supplied earlier or later. Lower sensitivity was observed for the red light spectral region (600-700 nm), with mostly limited differences between blue (400-500 nm) and white (400-700 nm) light. Differences between samples could be linked to factors such as chorion thickness, pigmentation, storage conditions, diapause status and genotypic differences in general, but to what extent each of these factors contributes to the variability among the strains needs to be studied by analysing a more comprehensive set of samples. The fact that the inter-strain differences observed in our study were only of quantitative nature nevertheless suggests that light triggers hatching in Anemia eggs through a process that is consistent throughout the genus. Our work could contribute to a better understanding of the hatching biology of dormant life stages in Crustacea in general.