Ulcerative dermatitis in wild dusky grouper Epinephelus marginatus (Lowe) from Libyan waters

Abstract

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.

A novel use of social media to evaluate the occurrence of skin lesions affecting wild dusky grouper, Epinephelus marginatus (Lowe, 1834), in Libyan coastal waters

“…When the morphology of the skin lesions in the pictures posted on Facebook is compared with the DGD skin lesions described in Rizgalla et al . (), there are close similarities in their gross morphologies, potentially indicative of common pathology/aetiology. Further similarities between the two data sets reside in the size of fish that are affected by lesions, that is 42 cm+ TL in Rizgalla et al .…”

“…Further similarities between the two data sets reside in the size of fish that are affected by lesions, that is 42 cm+ TL in Rizgalla et al . () and >40 cm TL from the images posted on Facebook. In both cases, the only species that appears to be affected is dusky grouper and observed lesions were present on landed fish throughout the year.…”

“…While the DGD lesions are often severe, these do not appear to impair feeding (Rizgalla et al . ) or normal swimming behaviour (video footage posted on Facebook).…”

“…The observed skin lesions are of unknown aetiology and were classified according to their gross and histopathological presentation into either mild, moderate or severe dermatitis (Rizgalla et al . ).…”

Ecological and histopathological aspects of Didymodiclinus sp. (Trematoda: Didymozoidae) parasite of the dusky grouper, Epinephelus marginatus (Osteichthyes: Serranidae), from the western Mediterranean Sea

“…Natural outbreaks associated with gnathiid isopod larvae have been observed in wild and captive E. marginatus (Genc, ; Marino et al., ). Recently, skin lesions and dermatitis, most likely associated with tissue parasites, have been observed in dusky groupers from the Libyan coast (Rizgalla et al., ). White capsules, tightly attached to the gills, pseudobranchs and orobranchial cavity, have been reported on wild dusky groupers in the Adriatic Sea (Canestri‐Trotti, Fioravanti, Patarnello & Restani, ) and eastern Atlantic Ocean (Gijón‐Botella & López‐Román, ), as well as on captive specimens in public aquaria and aquaculture facilities (Padrós, personal observation).…”