According to FAO (2008), the world fisheries production by capture and aquaculture has reached 142 million metric tons which this number shows the increasing of about 26 million metric tons from the fish production in 2007. FAO reported that the scale of fish capturing has reached the maximum level and it was counted that about 77% of the fishing region in the world has now classified as fully exploited. As this scenario might cause the decreasing of new fish sources, the fishing industry will face some problems to fulfill the demand of this protein source around the world (Meryl 2007). As a result, the fisheries industry has now actively develop the aquaculture industry to make sure that the production of this protein source will meet the
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However, the most concerned problem is the declining of the total fish produced. According to Rimmer et al. (1994), two factors that affect the decreasing of L. calcarifer production in aspect of quality and quantity are disease and malnutrition. Larvae of this fish that face the malnutrition problems will show physical symptoms such as pale, less active, poor appetite thus cause death. The high content of unsaturated fatty acid is so important in L. calcarifer diet or the lack of this unsaturated fat will cause the larvae resistance against disease decrease thus decreasing the larvae survival rate and growth (Wattanabe et al. 1989). In aspect of disease, the changes in environment might influence the defense mechanism of fish toward the pathogens infection. The type of diseases and their agents are different according to the fish aquaculture sites which might contribute by the environment factors such as water quality and temperature.
In the previous study reported by Magnadottir (2006), invertebrate are identify to have only an innate immunity as their defense mechanism while both innate and acquired immunity are closely related in vertebrate where the innate immunity will activate their acquired immunity. However, the innate immune mechanism of fish is identified to be more effective to destroy pathogens compared to its sluggish acquired immunity. This scenario also has become another factor explaining why L. calcarifer is easily attacked