Effects of epitheliocystis on serum lysozyme activity and osmoregulation in cultured juvenile striped trumpeter, Latris lineata (Forster)

Cultured juvenile striped trumpeter, Latris lineata (Forster), were sampled at two time points in spring (68 fish) and autumn (48 fish) to assess the prevalence and severity of epitheliocystis and associated physiological impacts. Prevalence of epitheliocystis was 49.2% in spring and 100% in autumn. Fish sampled in spring had low mean density of epitheliocystis induced cysts at 0.39±0.08 per cm2 whereas those fish sampled in autumn had significantly higher mean cyst density at 134.93±15.81 (pb0.05). The mean diameter of cysts did not differ and itwas 47.9±3.41 ìmin spring and 50.7±0.50 ìmin autumn. The cystswere positioned at the tips or along lamellae. Host response was affected by the severity of infection. Histological examination revealed little host response in striped trumpeter with low densities of cysts; however proliferative responses, including lamellar fusion due to epithelial hyperplasia and inflammation, were present in fish that had higher cyst densities. Serum osmolality and lysozyme activity were positively correlated with the densities of cysts in juvenile striped trumpeter (pb0.001). Furthermore, the osmolality and lysozyme activity of infected striped trumpeter were significantly elevated compared with the non-infected striped trumpeter (pb0.05). Histological examination revealed the absence of chloride cells at the base of the gill lamellae in the vicinity of the cysts, which may explain the elevation of osmolality in the individuals affected by epitheliocystis. However, the counts of chloride cells in the interlamellar areas did not differ between the fish with high and normal osmolality (p>0.05). This study describes the first case of epitheliocystis in striped trumpeter and reports associated physiological effects.