Stress in juvenile grouper Epinephelus marginatus (Lowe, 1834) transported at different stocking densities
Fish health and well-being are negatively affected during transport, stress responses are species-specific, so this study aimed to assess the stress response to transport of juvenile grouper Epinephelus marginatus at different stocking densities, through hematological markers. For this, after 24h of fasting, groupers juveniles were transported in 27 plastic bags for 8h at 28, 45 and 64g / L. Upon arrival, they were transferred to 18 recovery tanks (300L) where they were kept for 24 hours. Water samples were collected before and after transport and dissolved oxygen, temperature, pH, alkalinity and carbon dioxide were analyzed. Blood samples (n = 9) were performed before packaging (pre-transport), and at each stocking density, on arrival (0h),2 and 24h after transport (3 fish / repetition). Blood was analyzed on the i-Stat clinical analyzer for measurement of glucose levels, partial pressure of O2 (pO2), partial pressure of CO2 (pCO2), pH in the blood and bicarbonate (HCO3-). Plasma cortisol was analyzed using the electrochemiluminescence method. In addition, blood extensions were prepared for differential leukocyte count and neutrophil to lymphocyte ratio (N / L). The pH and oxygen levels dissolved in the water gradually decreased, while the CO2 concentrations increased with increasing storage densities. PCO2, pH, and HCO3- showed an increase in fish from all treatments, when compared to pre-transport values. Blood glucose was elevated only at the highest transport density.Plasma cortisol and pO2 were not influenced by the increase in transport density. Transport had a marked effect on the proportion of leukocytes evidenced in the fish sampled in all treatments at the end of transport, which showed changes both in the proportion of leukocytes (lymphopenia and neutrophilia) and in the N / L ratio. Lymphopenia lasted up to 2 hours after transport, in the highest tested densities. The leukocyte profile is a cheap and fast technique, which has been shown to be sensitive and effective for monitoring the stress response in this species. Both the reestablishment of hematological parameters in 2 hours and its stabilization in 24 hours of post-transport recovery, as well as the fact that there was no mortality show the species tolerance to the transport methodology employed.Therefore, as the profitability of the live fish transport systems is based on high stocking densities, it is suggested that the density of 64g / L is ideal for the transport of groupers in closed systems for up to 8h.