Scanning electron microscopic studies on nematode parasite Hysterothylacium gadi (Müller, 1776) infecting Nemipterus japonicus fish (Japanese threadfin bream) (Bloch, 1791) of the Red Sea, Egypt

Abstract

This study was carried out to detect the parasites affecting Japanese threadfin bream (Nemipterus japonicus). A total of 150 specimens collected from Gulf of Suez- Red Sea in Egypt from November 2016 to April 2017. Specimens were subjected to clinical, postmortem and parasitological examinations for detection of nematode parasites. The clinical examination showed no pathognomic clinical abnormalities on the external body surface except abdominal distension. Postmortem examination revealed excessive mucus secretion and swelling in intestine. Only the endoparasite Hysterothylacium gadi (Muller, 1776) (Nematoda: Anisakidae) was recorded in the intestine and stomach of examined fish. The prevalence rate was 54.7% and the intensity of the infection ranged 1-3 worms per fish. The morphological characteristics of this species were described in details using light and scanning electron microscopy. The results showed that females are larger than males. It is also shown that the cephalic region provided with three hexagonal-shaped lips separated from each other by three prominent interlabium; ventrolateral lips somewhat smaller. Dorsal lip provided on its surface with two double papillae, whereas both ventrolateral lips with one papilla and one small papilla. Interlabila are conical and their base is wider than length (Figs. 1&4). The worm was characterized by a broad lateral alae starting immediately below lips gradually narrowing posterioly and extending as narrow alae along whole body. A groove like structure is seen in the ventral surface of the body (Fig. 9). The tail is conical and tail tips of both sexes provided with numerous conical spines and the male has equal spicules.