Stress response in transport of juvenile cobia Rachycentron canadum using the anesthetic benzocaine

This experiment evaluated the efficacy of benzocaine to reduce stress response during transport of juvenile cobia. Fish (30 g) were packed in bags and transported for 8 h (stocking density = 10 g [L.sup.-1]). Three concentrations of benzocaine were evaluated: 0, 2, and 6 mg [L.sup.-1]. Blood samples were taken for glucose and hematocrit before transportation, and then at 0, 2, 24, and 48 h after. Water quality parameters were verified. No mortality was observed. Total ammonia nitrogen was higher (2.46 mg [L.sup.-1]) and pH was lower (6.92) at 2 mg benzocaine [L.sup.-1]. There was an increase in blood glucose for all treatments on arrival, and it was higher for those exposed to benzocaine at 6 mg [L.sup.-1], although at 48 h they were all similar. The hematocrit did not differ among treatments. The results suggest: 1) the density 10 g [L.sup.-1] is considered safe for juvenile cobia transport; 2) benzocaine did not mitigate stress response on cobia during transport, therefore its use is not recommended for this purpose. Keywords: Rachycentron canadum, Rachycentridae, anesthesia, physiology, hematology, water quality, marine fish. En este experimento se evaluo la eficiencia de la benzocaina para reducir la respuesta al estres durante el transporte de juveniles de cobia. Los peces de 30 g se almacenaron en bolsas y se transportaron durante 8 h (densidad de almacenaje = 10 g [L.sup.-1]). Se evaluaron tres concentraciones de benzocaina: 0, 2 y 6 mg [L.sup.-1]. Se tomaron muestras de sangre para glucosa y hematocrito antes del transporte y despues de 0, 2, 24 y 48 h. Se verificaron los parametros de calidad de agua. No se observo mortalidades. La concentracion de amoniaco total fue alta (2,46 [mL.sup.-1]) y el pH fue bajo (6,92) a 2 mg de benzocaina [L.sup.-1]. Al termino del transporte se determino un aumento de glucosa en la sangre en todos los tratamientos, siendo mayor en los peces expuestos a 6 mg de benzocaina [L.sup.-1], aunque a las 48 h todos fueron similares. El hematocrito no mostro diferencias entre los tratamientos. Los resultados sugieren que: 1) la densidad de10 g [L.sup.-1] es segura para el transporte de juveniles de cobia; y 2) la benzocaina no redujo la respuesta de estres en cobia durante el transporte, por lo tanto no se recomienda su uso para este proposito. Palabras clave: Rachycentron canadum, Rachycentridae, anestesia, fisiologia, hematologia, calidad del agua, peces marinos.