Bioenergetic cost of cryptobiosis in fish: Rainbow trout Oncorhynchus mykiss infected with Cryptobia salmositica and with an attenuated live vaccine

Food consumption, dry weight and energy gain, energy concentration and gross conversion efficiency were measured in 4 groups of juvenile rainbow trout Oncorhynchus mykiss over a 14 wk study period. The infected group, each fish inoculated with 2000 pathogenic Cryptobia salmositica, showed significant reduction of all of these factors and were anemic during acute cryptobiosis when compared to the control group. A third group fed an amount of food equivalent to that fed to the infected group (pair-fed) displayed energetic relationships similar to those of the control group except for gross conversion efficiency, which was slightly higher. Each fish in the last group was inoculated with 20000 attenuated live C. salmositica and the group was not significantly different from the control group throughout the 14 wk period. These vaccinated fish had very low parasitemia and were resistant to the disease when challenged with the pathogen. Fish that recover from cryptobiosis are immune but at considerable bioenergetic cost whereas vaccination serves as an effective control with little bioenergetic cost to the host.