Influence of conditioning diet and spawning frequency on variation in egg diameter for greenlip abalone, Haliotis laevigata

Both nutrient provisioning of eggs during development within the ovary, and egg diameter are believed to be important factors governing the development and survival of invertebrate larvae. The diet of female broodstock and the conditioning regimen are likely to influence these parameters. In this study we examine the effect of broodstock diet (three formulated diets differing in levels of the fatty acid, Arachidonic acid [ARA], and a red seaweed diet) and spawning frequency on egg diameter variability both within a batch of eggs spawned from one female and between batches of eggs. Greenlip abalone broodstock were spawned at the beginning of the experiment and again every 16 wks (1131 degrees C days effective accumulative temperature [EAT]) using commercial hatchery practices. The variability of egg diameter within batches spawned from the same female over three consecutive spawning rounds and within diet treatments was determined. Cytoplasm diameter, vitelline layer and jelly coat thickness of unfertilized eggs were also compared between eggs spawned from individual females and between females. In addition. the relationships between broodstock parameters (weight and shell length) and egg diameter were explored. Eggs spawned from females feeding on a red seaweed diet were smaller than eggs from the low ARA treatment. Depending on spawning frequency, broodstock diet can influence the cytoplasm diameter and jelly coat thickness. No relationship between egg diameter and broodstock parameters was found. However, batches spawned from the same female abalone became more variable over time with a shift in size frequency distribution. Results indicate that the variability of egg diameter within a batch changes from female to female and highlights the importance of selecting successful broodstock for conditioning at commercial hatcheries.