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

Abstract

The dusky grouper Epinephelus marginatus (Lowe) is an ecologically and commercially important fish species of the Atlantic and Mediterranean coastal rocky habitats. Despite records of didymozoid infections in several grouper species, the identification and pathogenesis of these parasites in E. marginatus are lacking. The aim of this study is to characterize the didymozoids of E. marginatus, particularly their mechanisms of infection and histopathological features. Dusky groupers (n = 205) were caught off Majorca Island (western Mediterranean Sea) and examined for parasites. Of the fish sampled, 45% were infected with white and yellow didymozoid capsules and brown nodules, found on the gills and pseudobranchs. Parasite abundance had a strong positive relationship with the fish length; only fish larger than 20 cm were infected, suggesting infection via consumption of an intermediate host, for which E. marginatus size was a limiting factor. The capsules contained two convoluted viable adult trematodes, identified as Didymodiclinus sp., in close contact with host capillary vessels, with no evidence of the tissue inflammatory response. Conversely, nodules containing degraded parasites were surrounded by an intense inflammatory infiltrate. The findings suggest that Didymodiclinus sp. have the potential to evade the host's immune system by inhibiting the inflammatory response.

Parasite Fauna of the Dusky Grouper (Epinephelus marginatus, Lowe 1834) from the Central Mediterranean Sea

“…A possible explanation for the positive correlation between fish size and presence of Didymodiclinus sp. and P. jordanoi once again falls on the diet of E. marginatus as, being young fish, they are unable to prey on intermediate hosts of these parasites, e.g., mollusks and other fish; this strong positive relationship between parasite abundance and fish size has previously been reported by Polinas et al [ 18 ].…”

“…Although this is the first report of Didymodiclinus sp. from the central Mediterranean Sea, the presence of this species had previously been reported in an E. marginatus specimen caught off Majorca Island (Western Mediterranean Sea) [ 18 ].…”

“…Prosorhynchus caudovatus and P. temensis showed the highest rate of infection compared to the other parasite species found, also according to analysis of the size classes ( Figure 2 ). According to species descriptions by Yamaguti [ 19 ] and Polinas et al (2018) [ 18 ], three flukes identified as Didymodiclinus sp., Pseudoempleurosoma sp. and Megalocotyle hexacantha were found in gills ( Figure 3 a).…”

“…More recently, helminthological investigations on marine fish throughout the Mediterranean Sea reported adult philometrid nematodes in gonads of E. marginatus [ 17 ]. Polinas and co-authors [ 18 ] reported white and yellow didymozoid capsules and brown nodules on the gills and pseudobranchs of E. marginatus from the western Mediterranean Sea. Widespread occurrence of parasite infections in dusky grouper populations highlights the need for further research into the parasite fauna and infection mechanisms.…”

Morphological and molecular study of Didymodiclinus marginati n. sp. (Trematoda: Didymozoidae) gill parasite of Epinephelus marginatus from the central and western Mediterranean Sea

“…(1994) reported similar findings on dusky grouper from the Adriatic Sea, with the uncertain attribution to the genera between Gonapodasmius (Ishii, 1935) and Indoglomeritrema (Madhavi and Hanumantha, 1983). Thus, the same parasitological lesions were observed on E. marginatus from several localities of the western Mediterranean Sea (Panebianco et al ., 1995; Azzurro et al ., 2002; Polinas et al ., 2018). Recently, De Benedetto et al .…”