Combined effect of temperature and salinity on hatching characteristics of three fairy shrimp species (Crustacea: Anostraca)

The combined effects of temperature and salinity on hatching performance of three anostracan species, Phallocryptus spinosa, Branchinecta orientalis and Streptocephalus torvicornis from East and West Azerbaijan, Iran, were studied. The cysts were kept for 10 days at seven different temperatures (12, 15, 18, 21, 24, 27 and 30 degrees C) and four salinity conditions (0, 5, 10, and 15 gL(-1)), and the effects of the resulting 28 experimental conditions on hatching patterns (duration of pre-hatching period, hatching percentage at first day of hatching, cumulative hatching success) were examined. Results were tested by ANOVA and multiple regression was applied to generate contour models by polynomial equation. The hatching performance in all species was significantly affected by temperature and salinity. Based on contour plot analysis, maximum hatching for P. spinosa, B. orientalis and S. torvicornis cysts was registered at temperatures 19-25 degrees C, 18-23 degrees C and 16-20 degrees C, respectively, within the same salinity range of 0-1 gL(-1). The highest cumulative hatching success among the species was observed in P. spinosa at the combination of 24 degrees C and 0gL(-1) (88. 98%). No hatching was observed for eggs of S. torvicornis and B. orientalis incubated at lower (<15 degrees C) and higher (>27 degrees C) temperature, respectively. The pre-hatching period was prolonged with increase in salinity and decrease in temperature and was highest in P. spinosa (7.7 days at 12 degrees C and 15 gL(-1) salinity). High hatching success was observed over wide ranges of temperature and salinity in P. spinosa eggs which demonstrates one of the possible mechanisms responsible for the wide distribution of this species.