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Use of the Facebook social media network to establish the distribution and prevalence of dusky grouper dermatitis (DGD) in Libyan waters

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In the period 2013-2015, wild dusky grouper, Epinephelus marginatus (Lowe), caught in Libyan coastal waters and ranging in size from 42 to 92 cm in total length, were observed to have distinctive skin lesions of unknown aetiology. Histopathologically, the lesions comprised a multifocal, unilateral or bilateral dermatitis, involving the epidermis, superficial dermis and scale pockets, and sometimes, in severe cases, the hypodermis. Severe lesions had marked epidermal spongiosis progressing to ulceration. Healing was observed in some fish. Bacteria and fungi could be isolated from severe lesions, although they were not seen histopathologically in early-stage lesions. By contrast, metazoan parasite eggs were observed in the dermis and epidermis of some fish with mild and moderate dermatitis. Unidentified gravid digenean trematode parasites carrying similar eggs were also seen within the blood vessels of the deep and superficial dermis. The cause of this distinctive condition, termed dusky grouper dermatitis (DGD), and its potential impact upon already threatened Mediterranean wild dusky grouper populations and upon cultured grouper more widely have yet to be established.
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This chapter discusses the culture of groupers. Groupers are the marine finfish belonging to the subfamily Epinephelinae and they are widely distributed in the tropical and subtropical coastal waters. In Asia, the culture of groupers in floating net cages is normally practiced along sheltered coastal regions and the main species of groupers cultured in Asia are Epinephelus coioides, E. malabaricus and E. lanceolatus. The majority of grouper seeds are obtained from the wild, with some produced in hatcheries. The culture of groupers can be divided into three stages: the hatchery/larval, nursery and the grow-out stage. Different skills are required in each of these three stages of grouper culture to ensure a high survival of healthy groupers. At the hatchery/larval stage, the larvae are maintained in either cement or fiberglass tank with constant moderate aeration. The nursery stage is carried out in ponds, cement or fiberglass tanks as well as net cages, which are kept afloat with styrofoam and plastic carboys in rivers. The grow-out groupers are usually placed in floating net cages, cement tanks or earthen ponds.
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