Study of the gill health status of farmed sea bass (Dicentrarchus labrax L., 1758) using different tools

•Gill health status in culture sea bass•Determination of histopathological gill changes by a semi-quantitative system•Gill parasites

Sea bass (Dicentrarchus labrax L., 1758) is one of the most cultured fish in Southern European countries. Recently, particular emphasis has been placed in culture fish welfare. Several tools have been used to determine the health status and welfare condition of fish populations. As gills are a very sensitive organ that is exposed to many traumatic factors faced by cultured fish we investigated the gill health status of farmed table size sea bass. Fulton's condition factor (CF), hepatic somatic index (HSI), haematocrit and gill histopathology were used as tools to determine the health gill status of farmed sea bass (n = 30). Histological changes were assessed according to the semi-quantitative system proposed by Bernet et al. (1999). Hypertrophy and hyperplasia of the epithelial and mucous cells, lymphocytes and mast cells/eosinophilic granular cells (EGCs) infiltration (branchitis), hyperaemia and necrosis of gill tissue were observed. More than 50% of the specimens presented severe histological gill alterations. Individuals of the monogenean Diplectanum aequans, the copepod Caligus minimus and not identified copepodite and calimus stages were detected on the gills but these parasites cannot be considered the only factor that affected gill integrity.