In this study, a flow-cytometric cell cycle analysis method to assess instantaneous growth rate of whole larvae of the Australian barramundi Lates calcarifer was developed and validated. High-resolution DNA measurements of either fresh, frozen or RNAlater-preserved larvae (gap0gap1, G0G1, coefficient of variation (c.v.) < 3, 4 and 5%, respectively) enabled the deconvolution of the DNA histogram and assignment of the proportion of nuclei into cell cycle compartments G0G1, S (DNA synthesis) and G2M (Gap2Mitosis). This technique can be also used for individual fish tissues such as brain, liver, fin and muscle. For the first time, the combined proportion of replicating nuclei (into S and G2M phases) of whole fish larvae and absolute growth rate in length (mm day-1) has been correlated in commercial aquaculture conditions. Fast growing L. calcarifer larvae had an overall hyperplasia advantage as indicated by a greater proportion of cells in the S+G2M phase compared with slow growing larvae, which might explain the increasing differences in size during culture. In a fasting trial, larvae ceased growth while maintaining the constant initial rates of cell division throughout a 6 day period. For a highly fed fast growing control group, cell division rates significantly increased after day 4. Flow-cytometric cell cycle analysis of whole fish larvae may provide fish biologists and aquaculturists with a better understanding of how cell division rates influence early growth in natural and artificial environments.
