Type and ultrastructure ofDidymocystis wedliandKoellikerioides intestinalis(Digenea, Didymozoidae) cysts in captive Atlantic bluefin tuna (Thunnus thynnusLinnaeus, 1758)

Abstract

Tissue encapsulation, one of the most common tissue reactions to invading parasites, is the hallmark sign of didymozoid (Digenea, Didymozoidae) infections in fish. Investigated were the types of intermediate filaments and ultrastructure of the connective tissue capsule elicited by the presence of didymozoids in the gills and intestine of Atlantic bluefin tuna (Thunnus thynnus Linnaeus, 1758). The evaluation was done performing TEM microscopy of two tissue-embedded didymozoid species, along with monoclonal antibodies labeling (anti-fish collagen type I, anti-human cytokeratin, anti-vimentin antibodies). Ultrastructure of Didymocystis wedli (Ariola, 1902) (prevalence = 61.75%, abundance = 28.91) encapsulated in gill filaments and Koellikerioides intestinalis (Yamaguti, 1970) (prevalence = 54.65%, abundance = 10.96) in the intestinal submucosa showed that the thin parasitic hindbody tegumentum was directly embedded in layers of connective tissue bands. Only a few cellular elements (lymphocytes, fibroblasts and fibrocytes) infiltrated the connective tissue capsule, which differed between the two didymozoid species in thickness, not in the type of filaments expressed. Cysts showed positive reaction to extracellular collagen as well as appearing positive for the cytoskeletal intermediate filaments vimentin and cytokeratin.

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

“…An increase in mucous cells and epithelium hyperplasia was observed in pseudobranchs and gill filaments, in response to both viable and degraded parasites. Similar host responses have been reported for the didymozoid gill infections in other groupers, as well as in the Atlantic bluefin tuna, Thunnus thynnus (Abdul‐Salam & Sreelatha, ; Cruz‐Lacierda et al., ; Mladineo & Bočina, ). The gill and pseudobranch immune responses are considered non‐specific and can be caused by many aetiological agents (Bullard & Overstreet, ).…”

“…The mechanism by which this happens is still under researched. It is generally accepted that, at some point of maturation, eggs are released in the external environment after capsule rupture or other traumatic mechanisms (Mladineo & Bočina, ), and it is believed that the inflammatory response could help the egg release (Abdul‐Salam & Sreelatha, ). This mechanism has also been observed in other trematodes, such as Schistosoma sp., where the egg‐derived ribonuclease Omega‐1 is thought to activate inflammation required for egg to cross through host tissues, to reach the external environment (Fitzsimmons et al., ; Hewitson, Grainger & Maizels, ).…”

Expression analysis of the Atlantic bluefin tuna (Thunnus thynnus) pro-inflammatory cytokines, IL-1β, TNFα1 and TNFα2 in response to parasites Pseudocycnus appendiculatus (Copepoda) and Didymosulcus katsuwonicola (Digenea)

“…siphonostomatoid copepod Pseudocycnus appendiculatus are both gill parasites frequently parasitizing tuna, whose populations conspicuously decline during the farming cycle [3]. Whereas the former is encysted in a connective-tissue capsule that apparently enables its sequestration from host immune response [5], copepod causes more intense host reaction prone to secondary bacterial infections [6].…”