The effects of net-chasing training on survival and growth are related to stocking density in the freshwater prawn Macrobrachium rosenbergii

Low-intensity net-chasing training produces moderate stress that improves the culturing of prawns. Optimizing stocking density is considered one of the most crucial factors in aquaculture. The effects that net-chasing training can provide under changes in stocking density are still not fully understood. The purpose of this study was to evaluate the interactive effects of stocking density and net-chasing training on the culture performance of the freshwater prawn Macrobrachium rosenbergii through analyses of behavioral and physiological changes. Animals were stocked at 40, 80, and 120 individuals m⁻² and cultured under no-training and 25%-exhausted training for 45 days. The growth and survival indicators including organ loss of dead animals, the behavioral indicators including time spent on fighting, swimming, walking, and stationary, and physiological indices of pleopod and second pereiopod muscles were observed and measured. The results showed that high stocking density reduced the survival rate due to the increased behavioral activities of fighting and cannibalism. The increased frequency of swimming and fighting elevated the activities of enzymes involved in aerobic metabolism in pleopod muscles and anaerobic metabolism of second pereiopod muscles, and consequently lower growth occurred due to greater energy expenditure in these muscles. The 25%-exhausted chasing enhanced survival rates and growth rates at a density of 80 individual m⁻² due to the reduced frequencies of fighting and swimming. Locomotor behaviors were not regulated by net chasing when M. rosenbergii were reared at densities of 40 or 120 individuals m⁻². Net-chased M. rosenbergii at a density of 120 individuals m⁻² still showed low levels of growth rates and survival rates, and most of the dead prawns had lost pleopods, pereiopods, or uropods. These findings indicate that the net-chasing effects on survival and growth vary according to rearing density. Net-chasing training improved the survival and growth of M. rosenbergii only when the animals were reared at appropriate density levels such as 80 individuals m⁻².