The effect of food type and quantity on egg production and nucleic acid content of Acartia sinjiensis

Both food type and quantity have a strong effect on the egg production, RNA:DNA ratio and RNA content of the copepod Acartia sinjiensis. Copepods were fed limiting (150μgCl⁻¹) and non-limiting (1500μgCl⁻¹) concentrations of Tetraselmis chuii (Prasinophyceae), Pavlova salina and Isochrysis aff. galbana (Prymnesiophyceae), and Chaetoceros muelleri (Bacillariophyceae). Saturation of copepod egg production was estimated for Tetraselmis and Pavlova offered in a wide range of concentrations (0-1500μgCl⁻¹). Under non-limiting food conditions, A. sinjiensis produced more eggs when fed Tetraselmis (mean 17.6 eggs female⁻¹ day⁻¹ -efd) and Pavlova (14.2 efd), and produced fewer eggs when fed Isochrysis (9 efd) and Chaetoceros (7.6 efd). RNA:DNA ratio (mean 7) and individual RNA content (mean 2μg RNA ind⁻¹) were significantly higher in females fed abundant Tetraselmis in comparison to the other algae. Under food-limiting conditions, A. sinjiensis could still produce eggs when fed Pavlova (3.3 efd) and Tetraselmis (1.7 efd), but failed to produce eggs when fed Isochrysis and Chaetoceros. In food-limited females RNA:DNA ratios and individual RNA content were variable and lower than animals fed non-limiting algae concentrations. The saturation of egg production was 714μgCl⁻¹ for Tetraselmis and 509μgCl⁻¹ for Pavlova. The relationship of RNA:DNA ratio and food concentration followed a similar function to egg production, with a saturation level of 509μgCl⁻¹ for Tetraselmis. Egg production was positively correlated with female size only in animals fed Tetraselmis at 1500μgCl⁻¹; all other algae and food concentrations were uncorrelated with female size. Of the algal species tested, Tetraselmis and Pavlova are candidate algae for use in A. sinjiensis culture. Egg production saturates around 500μgCl⁻¹, as is the case in other Acartia species. Both RNA:DNA ratio and RNA content of the females were sensitive to different food type and concentration, and have the potential to be used as an alternative method for the identification of optimal food for use in Acartia culture. These observations have important implications for the understanding of the dynamics and productivity of this species in coastal environments of tropical Australia, and also its potential use in aquaculture and ecotoxicology.