2) Diseases normally occur in the cultured fish compared to wild fish due to several factors. One of it is the population density in which the cultured fish commonly has a higher population density which will allow the disease to spread more easily due to the increasing contact between the infected and uninfected fishes. Furthermore, the high density of the cultured fish in unnatural surrounding which is not their natural habitat will lead to even more stressful condition as crowded density will cause the increase of competition for resources and lead to aggression that can injure them. Besides, cultured fish with high population density can also lead to poor water flow and quality which increases the pathogen concentration in their holding system. Higher pathogen concentration contributes to immunocompromised state in the fish. As a result, these stressors combine with immunocompromised condition make them more susceptible to diseases. In comparison to the cultured fish, the wild fish have a lower population density in their natural habitat and the pathogens from infected fish can be washed away or diluted by the water flow or probably will not have chances of contact with the healthy fish at all.

a)      What is aquaculture?

Aquaculture is the cultivation and harvesting of plants and animals in water (Saunders, 2007). Aquaculture refers to the breeding, rearing, and harvesting of plants and animals in all types of water environments including ponds, rivers, lakes and the ocean. Aquaculture produces foodfish, sportfish, baitfish, ornamental fish, crustaceans, mollusks, algae, sea vegetables and fish eggs. Aquaculture includes the production of seafood from hatchery fish and shellfish which are grown to market size in ponds, tanks, cages or raceways and also includes the production of ornamental fish for the aquarium trade, and growing plant species used in range of food, pharmaceutical, nutritional and biotechnology products.

b)     Why diseases normally occur in the cultured fish compared to wild fish?

Diseases normally occur in the cultured fish compared to wild fish because of few factors. Firstly, for the cultured fish, usually the area provided was small with the maintenance of  large number of fish crowded together will provides an environment conducive for the development and spread of diseases. In this crowded, relatively unnatural environment, fish are stresses and more susceptible to disease. To be compared with the wild fish whose can swim freely in their natural environment with plenty of spaces will not easily get stressed which will lead to disease. Second is the water environment for cultured fish is usually limited water flow which will facilitate the spread of pathogens within crowded populations. To be compared with the wild fish, the population densities of wild fish are comparatively low and the concentration of pathogens from an infected fish is rapidly diluted in the environment thus lowing the probability to be infected with diseases. 

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Question :
A)Aquaculture is aqua farming where the breeding, rearing, harvesting of aquatic organisms such as fish,crustaceans, molluscs, aquatic plants. It involves cultivating freshwater and saltwater populations under controlled conditions and it is different with commercial fishing that are harvesting of wild fish.

B)Diseases normally occur in the cultured fish compared to wild fish because the cultured fish are raised in the close quarters and pens in oceans with mixed unnatural diets means diseases can spread quickly and pathogen can spread like wild-fire. Concentrated antibiotics, pesticides and other drugs are commonly used to fight diseases and common parasite to fish farms could destroy ecosystem and other living organisms and transmit disease.