Temperature effects on immune response and hematological parameters of channel catfish Ictalurus punctatus vaccinated with live theronts of Ichthyophthirius multifiliis

This study evaluated the influence of temperature on the immune responses and hematological parameters in channel catfish Ictalurus punctatus immunized via intraperitoneal injection with live theronts of Ichthyophthirius multifiliis. Fish were distributed in 18 aquaria and received 9 treatments: 4 groups of fish were vaccinated with live theronts and maintained at constant temperature 15 degrees C, 20 degrees C, 25 degrees C and 30 degrees C: 3 groups of fish vaccinated and subjected to cycling temperature regime from 15-25 degrees C, 20-25 degrees C and 20-30 degrees C, changed 5 degrees C each day; 2 groups of fish were not vaccinated and served as controls at 25 degrees C, one with Ich challenge and the other without challenge. Non vaccinated fish and those vaccinated at 15 degrees C or 15-25 degrees C did not show anti-Ich antibodies in the serum 14 and 21 days post-immunization. The antibody levels were significantly higher from fish vaccinated at 25 degrees C, 30 degrees C, 20-25 degrees C and 20-30 degrees C compared to fish at 15 degrees C, 20 degrees C and 15-25 degrees C both 14 and 21 days post-immunization. At constant water temperature, fish vaccinated at 15 degrees C showed significantly higher mortality rate (67.8%, P < 0.05) than those vaccinated at 20 degrees C, 25 degrees C, and 30 degrees C (0-10.7% mortalities). At cycling water temperature, fish vaccinated at 15-25 degrees C showed significantly higher mortality rate (67.8%) than those vaccinated at 20-25 degrees C and 20-30 degrees C (P < 0.05). Twenty days after immunization fish vaccinated at 30 degrees C and 20-30 degrees C showed significant increase in the red blood cells, white blood cells, thrombocytes and monocytes. Six days after challenge with I. mutifiliis theronts the fish showed decreased white blood cells, thrombocytes and monocytes. This study suggests that vaccinated catfish were severely impacted by low temperature, either at 15 degrees C constant temperature or at 15-25 degrees C cycling temperature. The fish showed no anti-Ich antibodies and suffered high mortality similar to non vaccinated control fish. (C) 2011 Elsevier Ltd. All rights reserved.