Gonapodasmius spp

From Fish
A yellowish sack in the muscle of red sea bream
Parasite worm of G. okushimai
G. okushimai collected from red sea bream
Parasite eggs of G. okushimai.

Gonapodasmius spp are a didymozoid fluke parasite of marine fishes worldwide, that affects the trunk muscles[1].

Clinical sign

No external signs are usually evident. A yellowish amorphous or elliptical sack (a few cm) is observed in the trunk muscle. Yellow filamentous parasite is folded inside the sack.


The parasite encysts on the primary lamellae of the gills. Histological sections usually reveal larvae primarily embedded underneath the gill epithelium and eggs of the parasite are often distributed in other organs such as gill epithelium, heart and macrophage centers in the head kidney. Pathological changes and host response are seen mainly on gill lamellae, e.g. reduction and destruction of secondary lamellae.

Since this parasite is not infectious to human, it is harmless in food hygiene[2].


  1. Ishii, N. (1935) Studies on the family Didymozooidae (Monticelli, 1988). Jap J Zool 6:279-335
  2. Nakajima, K., K. Sugiyama and S. Egusa (1974) A trematode, Gonapodasmius okushimai Ishii, found in the muscle of red sea bream, Pagrosomus major. Fish Pathol 8:175-176