Antibodies against Discocotyle sagittata (Monogenea) in farmed trout

Abstract

Discocotyle sagittata is a monogenean parasite infecting freshwater salmonid fishes with a wide distribution in the northern hemisphere (Williams & Jones 1994). In common with other monogeneans (Thoney & Hargis 1991), D. sagittata occurs at low prevalence and intensity in wild fish, but can reach pathogenic levels of infection in farmed fishes. Temperature is the main abiotic factor affecting its development, which is virtually arrested with water temperatures <10C (Gannicott & Tinsley 1997, 1998a,b). This results in clear annual transmission cycles: no infections occur during the winter, while transmission is continuous during the summer and until late autumn. Knowledge of D. sagittata biology enabled the establishment of a dependable experimental infection system (Rubio-Godoy & Tinsley 2002). In laboratory trials, rainbow trout were partially protected against controlled challenges following immunisation with D. sagittata extracts, and a significant negative correlation was found between antibody levels and parasite numbers recovered from immunised fish (Rubio-Godoy et al. 2003). This study aimed to determine whether infection under farm conditions induced the production of specific antiparasite antibodies.