Use of salt during transportation of air breathing pirarucu juveniles ( Arapaima gigas) in plastic bags

Abstract

The farming of the Amazonian air breathing fish, Arapaima gigas, has been growing substantially over the last decade in Brazil and other South American countries. Previous study demonstrated that transportation of pirarucu juvenile in plastic bags is a suitable procedure, although it stimulated some stress responses. Therefore the objective of this study was to investigate the addition of salt as a stress mitigator in pirarucu juveniles during transportation in plastic bags. Fish were reared for a month in earthen pond and held in 3 indoor 2000-L depuration tanks for 24 h to allow complete gastrointestinal evacuation, then placed in 30-L polyethylene bags with 10 L of water at a density of 12 fish/bag (40 g/L) with different table salt (NaCl, 97%) concentrations in the water: 0, 1, 3, 5 g/L (3 replicates each concentration). Transportation took 3 h and afterwards fish were transferred to 1-m 3 floating cages installed inside an earth pond for recovery. Fish stress responses were evaluated before, during and after transportation procedure, and the analyses performed were: cortisol, glucose, lactate, haematrocrit and waterborne net Na +, Cl −, K +, and Ca 2+ fluxes. No mortality was recorded in any treatment during transportation and recovery periods. Cortisol exhibited an increase after transport with 1 g salt/L and at 24 h after transportation for all treatments showing a latency period in their response. Glucose exhibited a similar pattern for all treatments with a significant increase before and after transportation, returning to basal levels in 24 h. Lactate concentrations increased before transportation and after transportation, presenting a significant decrease in all treatments. Addition of salt in the transport water increased Na +, Cl − and Ca 2+ net fluxes in pirarucu. Using salt during pirarucu juvenile transportation should be avoided since there is no reduction on stress responses and causes osmoregulatory disturbances.