Culture of fish food organisms

Unit 4 - Copepods

4.5.1.Use of resting eggs
Many temperate copepods produce resting eggs as a common life-cycle strategy to survive adverse environmental conditions. Resting eggs can tolerate drying at 25°C or freezing down to - 25°C and that they are able to resist low temperatures (3-5°C) for as long as 9 to 15 months. These characteristics make the eggs very attractive as inoculum for copepod cultures. Samples of sediments rich in resting eggs can be stored in a refrigerator at 2-4°C for several months. When needed, the sediment containing the resting eggs is brought in suspension and sieved through 150 μm and 60 μm sieves. The resting eggs is then immersed in the disinfectant, (i.e. FAM-30 or Buffodine); surface-disinfection being needed to eliminate contaminating epibiotic micro-organisms. After disinfection, the eggs are then washed with 0.2 μm filtered sterile seawater and transferred to disinfected culture tanks or stored under dark, dry and cool conditions. Before starting the surface-disinfection procedure attention must be paid to the physiological type of resting eggs. Some marine calanoids are able to produce two kinds of resting eggs, i.e. subitanous and diapause eggs. Since subitanous eggs only have a thin vitelline coat covering the plasma membrane, they are more susceptive to disinfectants than the diapause eggs which are enveloped by a complex four-layer structure.