Evaluation of immunological parameters in farmed gilthead sea bream, Sparus aurata L., before and during outbreaks of ‘winter syndrome’

Abstract

In recent years, 'winter syndrome' has caused severe economic losses in many marine farms in southern Europe. This study compared the activity of the immune system in healthy, asymptomatic and diseased gilthead sea bream. Serum protein and immunoglobulin content were evaluated as well as serum complement activity from these groups of fish. Differential leucocyte counts were also determined. Immunological assays were performed to determine intra- and extracellular 'respiratory burst' activity as non-specific immune response parameters. Diseased fish showed a significant reduction in haemolytic activity (90%), and in serum proteins and immunoglobulins in comparison with the other groups. A significant increase in the lymphocyte percentage (50%) and a decrease in the granulocyte percentage (over 70%) was found in asymptomatic fish. Respiratory burst activity was reduced in both the clinical and preclinical stages of the disease, compared with the controls. These observations confirm a severe immunodeficiency in diseased fish but also the presence of a cellular immune dysfunction in fish without clinical signs, before the onset of the disease.

Low-temperature challenges to gilthead sea bream culture: review of cold-induced alterations and ‘Winter Syndrome’

“…A slight abdominal distension, pallor of the gills and corneal opacity may also be noticed. The main lesions observed in necropsy are a pale and friable liver, sometimes haemorrhagic, and a distended gut tract filled with a clear fluid, with a whitish mucous content in the lumen (Bovo et al 1995;Padrós et al 1998;Tort et al 1998b;Contessi et al 2000Contessi et al , 2006Gallardo et al 2003). The main histopathological findings are observed in the liver, pancreas, muscle, intestine and, in some cases, also in the kidney.…”

“…Hepatic changes may vary from incipient steatosis (Contessi et al 2006) to severe fatty degeneration in hepatocytes (Galeotti et al 1999;Padrós et al 1998;Tort et al 1998b;Contessi et al 2000). Atrophy and degeneration of the exocrine pancreatic tissue within the liver or in the perivisceral tissue is also usually reported, and granulocyte infiltration of the pancreatic tissue has been observed (Contessi et al 2006). Granular degeneration and necrosis in white muscle fibres is another very common finding.…”

“…This natural fasting period is particularly severe in northern Mediterranean aquaculture facilities, where it may be prolonged for some months, leading to losses in body weight and a halt in production. Moreover, in recent years noticeable mortalities have been repeatedly recorded in several parts of the Mediterranean during specific winter periods, this being referred to as 'Winter Syndrome' or 'Winter Disease' (Bovo et al 1995;Bilei et al 1996;Bossu et al 1997;Padrós et al 1996;Tort et al 1998a, b;Sarusic 1999;Gallardo et al 2003;Contessi et al 2006). Mortality rates are usually around 7-10% of fish stock, although in some acute cases they may be as high as 80% (Padrós et al 1998), resulting in severe economic losses.…”

Pathological Investigations of Winter-like Disease in Cultured Sea Breams (Sparus aurata)

“…In some outbreaks, mortality rates reached as high as 30-50% and it caused severe economic losses 2,10 . In this study, during the outbreak, approximately two million dead fish were found and it was resulted from serious economic losses in all affected farms.…”

“…It has been reported that WD outbreaks are appeared during the winter seasons and several environmental stress factors such as decrease in salinity and temperature (<13ºC) of sea water influenced the formation of WD 5,8,10,13 . Hepatic steatosis is accentuated in sea bream affected by WD and a polifactorial, metabolic-based pathology which causes high mortality when the water temperature drops below 11-13ºC 2,4 .…”