Intensity scale of side effects in European sea bass (Dicentrarchus labrax) post intraperitoneal injection with commercial oil-adjuvanted vaccines

Abstract

Intraperitoneal (i.p.) injection vaccination is considered effective to protect European sea bass (Dicentrarchus labrax) from economically important diseases. Water-based as well as oil-adjuvanted vaccine formulations are being widely used. The oil adjuvants used to potentiate antigen effects lead to higher and more prolonged immune response but also to chronic peritoneal inflammatory reactions, regarded as adverse or side-effects. During a three-year field study conducted throughout Greek mariculture, the intra-abdominal lesions were assessed on fish sampled prior to, and at different times post i.p. injection with different oil-adjuvanted vaccine formulations. The scope was to create a macroscopic side-effect intensity scale for sea bass in line with those applicable to salmonids (Salmo salar, Oncorhynchus mykiss) and cod (Gadus morhua). The diversity of lesions observed ranged from none (presumably non-injected; score 0) to widespread, strong adhesions with granuloma, pigmented or not (score 6). The occurrence of small nodules apparently containing vaccine remains, encapsulated by layers of connective tissue is described. The proposed scoring system is described and illustrated, intended to guide farm staff to evaluate the intensity of post-injection vaccination side-effects by necropsy on site.