A robust flow-cytometric protocol for assessing growth rate of hatchery-reared barramundi Lates calcarifer larvae

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 (gap0-gap1, G(0) -G(1), 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 G(0) -G(1), S (DNA synthesis) and G(2) -M (Gap2-Mitosis). 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 G(2) -M 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+G(2) -M 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.