A new large egg type from the marine live feed calanoid copepod Acartia tonsa (Dana)-Perspectives for selective breeding of designer feed for hatcheries

Mass cultivation of marine copepods as live feed requires predictable and uniform production of a standard product for the end users, the hatcheries. A previously undescribed large egg type, measuring a mean diameter of 106.5 μm, was characterized and compared to normal eggs (82.3 μm) from a continuous culture of Acartia tonsa. The large egg type was significantly larger than the normal eggs, and only 1 large out of approximately 100 000 normal-sized eggs was found. Mean egg densities was 1.34 ± 0.16 g/cm3 and 1.20 ± 0.07 g/cm3 for normal and large eggs, respectively. The hypothesis that large eggs were dormant, as indicated from the relatively low hatching success of 60%, within 48 h, was rejected as no significant difference was found in egg volume-specific respiration rates or histological analysis of the chorion between the two egg types. The nauplii hatched from large eggs were correspondingly large, and the copepods remained large when developing into adulthood. The fact that copepods hatched from large eggs were fertile indicates no chromosomal abnormalities and suggests that this egg type represents the upper tail end of eggs in a classical normal distribution of size vs. frequency. The next generations' eggs were not as large as the ones they originated from suggesting that the rare large eggs represent a maternal effect. The large size eggs do however pose an interesting selection potential for designing large species-specific live feed products in aquaculture.