Are female reproductive status and male morphotypes of the giant freshwater prawn Macrobrachium rosenbergii altered by selection for high growth?

Understanding genetic changes in the hierarchical population structure of the giant freshwater prawn (GFP) Macrobrachium rosenbergii is important to improve productivity and profitability of prawn farming. We examined correlated responses in male morphotype and female reproduction status resulting from a selection programme for high growth in a GFP population undergoing four generations of selection. Two contemporary lines (selection and control) were maintained and produced simultaneously; the selection line was selected for high breeding values for harvest body weight and the control for average breeding values of the population. A total of 21,459 individual prawns were measured for body traits and morphotypes. Individual morphotype was recorded as a binary trait (0 and 1) and were analysed using a generalised threshold mixed model with a logit link function. Correlated genetic changes in three important male morphotypes (small, orange and blue claw males) were significant (p < 0.05- 0.001) only in generation 2010 but not in the last generation (2012). Selection for high growth did not have an adverse effect on reproduction status of females, except that the selection line had a greater proportion of spawned females than the control (p = 0.01). Our results pointed out that selection for high growth may have had both positive and negative impacts on the social population structure of male morphotypes in GFP. Undesired changes in important morphotypes should be taken account of in genetic improvement programmes for GFP in order to minimise social competition effects and increase total biomass and consequently economic returns of the sector.