Figure 3.3a, b If sampling is made less than or near to 1 hour, cell division may not have occurred even in fertilised eggs and hence it is impossible to distinguish between them (Fig 3.3a). Cell division usually occurs in unfertilised eggs after the 2^nd cleavage of fertilised eggs. When cell division does occur in unfertilised eggs it is clearly asymmetrical (Fig 3.3b). This pattern is easily recognisable at this time and it is why eggs are best sampled between 1 and 1.5 hours after spawning.