Yield characteristics of the prawn Macrobrachium rosenbergii in temperate zone aquaculture

Yield characteristics of the freshwater prawn Macrobrachium rosenbergii are examined in both commercial and experimental ponds during the first pilot growth trial in Israel. Because of the temperate climate, production is restricted to 6 or 7 summer months. Given a minimal commercial size of 30 gm, conditions were found in which the majority of animals can be brought to this size in a single growth season. Total biomass is linearly related to density up to over 1,500 kg/ha. Density is found to be a major factor affecting the size of males and females whose growth characteristics contribute differently to yield. Males of harvestable size are restricted in their growth at higher density, resulting in lowered mean weight. Even in high densities reported in this study nearly all the potentially harvestable males achieve minimum market weight, while the rest of the male population cannot be brought to market size in even the most favorable conditions. The contribution of females to yield is precarious since female sizes are relatively uniform and their average weight may be above, close to or below market size. Conditions are described in which well over 80% of the females achieve market size, but at densities too low to secure profitable yield. The effects of late season selective harvest reveal no dramatic effect on yield. Nevertheless, selective harvest seems to enable continued growth in densely populated ponds. We conclude that combined stocking of larger animals, with early selective harvest, reducing density dependence during final growout, could prove useful in attaining commercial yields.