The Effect of Biomass Density, Salinity, and Substrate on Transport Survival of Juvenile Freshwater Prawns Macrobrachium rosenbergii in Continuously Oxygenated, Vented Containers

Abstract

During the stocking of grow-out ponds, juvenile prawns are usually transported from regional nurseries by truck in vented tanks. Hauling stress and associated delayed mortality have been implicated as potential causes of low pond survival. An experiment was conducted to evaluate the effects of biomass density, substrate, and salinity on water quality and transport survival of juvenile freshwater prawns Macrobrachium rosenbergii. The trial was designed as a 3 × 2 × 2 factorial and evaluated three biomass densities (10, 20, and 30 g/L), the presence or absence of added substrate (plastic mesh to provide a 200% increase in surface area), and the presence or absence of added salt (0‰ or 6‰). Model transport tanks were 15-L, open styrofoam containers aerated with pure oxygen and compressed air. Water quality analyses were performed prior to stocking. After 24 h, water quality analyses were again conducted and all prawns were removed, designated as alive or dead, weighed, and counted. After 24 h of simulated transport, three-way analysis of variance indicated no significant interactions (P > 0.05) between the main effects of density, substrate, or salinity for prawn survival or water quality. When the main effects were analyzed separately, survival was significantly influenced by density. Survival was significantly lower (P < 0.05) in the high-density treatment (30 g/L: 89% survival) than in the medium- (20-g/L) and low-density (10-g/L) treatments, which were not significantly different (P > 0.05) and averaged 95% survival overall. Total ammonia nitrogen and un-ionized ammonia nitrogen concentrations significantly increased (P < 0.05) as biomass density increased. The addition of salt to the transport water did not significantly affect survival (P > 0.05) but did result in a significant decrease (P < 0.05) in both pH and un-ionized ammonia nitrogen. Added substrate had no significant (P > 0.05) impact on any measured variable. These data indicate that good survival can be achieved at a biomass density of 20 g/L and that increased salinity appears to reduce the buildup of toxic metabolites. The addition of substrate to the transport tank appears to provide no benefit.