engleski

"Winter disease" in Cage Cultured Sea Bream (Sparus aurata

Croatia, as a Mediterranean country has 20 years long tradition of mariculture and the total amount of produced fish is now about 1700 tons per year. Basically, there are two main fish species that are cultivated on the Croatian coast; sea bass (Dicentrarchus labrax) and the sea bream (Sparus aurata). Several years ago marine fish farmers along the Adriatic coast intensified a cultivation of sea bream at their farms. At the same time, high mortalities of sea bream at the different fish farms occurred during the winter months. The mortality syndrome was related to extreme water temperature drop. All attempts to discover the exact causative agent of the disease failed and therefore the phenomena was denominated as "winter disease". The outbreaks occurred when the water temperature was below 9-10oC, and persisted during the winter months until May when the water temperature increased to 18oC. The mortalities were low but constant and they could reach the 30 %. The same syndrome was observed and described in all Mediterranean region with cultivation of sea bream. Some authors associated the disease with viruses, bacteria Pseudomonas anguillseptica and the myxosporean parasite in the intestine wall, Myxidium leei. In this paper we tried to describe our observation of the "winter disease" during several past years. On the external pathoanatomical examination no noticeable lesions were observed at the affected fish and they had just slightly distended abdomen due to increased amount of liquid in the body cavity. The stomach and the gut were enlarged and filled with serous liquid to which some fibrinous precipitate was admixed. A general rool finding it was a prominent paleness of liver ranging in color from light gray to white yellowish. However, the size of the liver varied drastically from almost double shrinked to double larger than normal. Bacteriological examinations of liver, kidney and spleen were negative. On histopathological examination micro and macro-vacuolar fatty degeneration of liver were seen. Inflammatory changes were repeatedly absent. The results of our investigation indicate that "winter disease" in the sea bream is metabolic disease with multifactorial etiology including malnutrition caused whether by incorrect feeding, physiological imbalance caused by abrupt lowering of environmental temperature. Different infectious agents (virus, bacteria, and parasites) could act as secondary or opportunistic invaders.

sea bream; mariculture; winter diseases; etiology

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