Bacteria Isolated From Diseased Wild and Farmed Marine Fish in Greece

Abstract

World production of sea bream and sea bass farming has been rising over time. The total production of gilthead sea bream (Sparus aurata L.) and European sea bass (Dicentrarchus labrax, L.) in Europe has been increased. These marine fish species have high economic value in the aquaculture industry. More specifically, the total production of 92,310 tonnes in 1999 amounted to 175,196 tonnes in 2006, representing an average annual growth rate of 9.6%. Greece is the country with the largest production of euryhaline fish (sea bream and sea bass) between Mediterranean countries. In 2008, Greece held its largest production (130,000 tonnes of which 95,000 tonnes sea bass and sea bream). Climatic and geomorphologic conditions of Greece promoting the cultivation of euryhaline fish, grants and projects given by the European Union, the decline of fish stocks and the restrictions have been imposed last yeas in fishing, contributed significantly in the development of the industry of fish farming. Today the industry fully covers the needs of the Greek market and most of the quantity is exported to foreign markets, the main destination countries Italy, Spain, France, England and Portugal. Currently, additional species have entered in the farming, belonging mainly to the family Sparidae, such as Puntazzo pntazzo, Diplodus sargus, Lithognathus mormyrus, Pagrus pagrus, Pagellus erythrinus and Dentex dentex. Bacterial diseases of fish origin have become one of the major agents of economical losses since the beginning of marine farming (Kubota & Takakuwa, 1963; Anderson & Conroy, 1970). The development of intensive marine fish farming in the form of the concentration of large quantities of biomass in a relatively small volume water leads-under certain conditions (combination of factors) – to the emergence of diseases which lead to losses in the population. The occurrence of a disease can lead to death or symptoms both refer to deviation from the normal structure or function of the host (Hedrick, 1998). Most diseases of farmed fish originate from wild populations. The close contact between farmed and wild fish results in exchange of pathogens. The clinical symptoms caused by any pathogen depend on the type of host, age of the fish and stage of disease (acute, chronic, subclinical form). Moreover, in some cases, there is no correlation between internal and external injuries. In fact, systemic diseases (eg. pasteurellosis) with high mortality rates, causing internal damage to infected fish, but often have a healthy appearance. Conversely, other diseases with relatively low mortality cause significant physical damage, including ulcers, necrosis, exophthalmos, making the fish unfit for the market.The diseases, the number and