Light and scanning electron microscope observations of the digenean intestinal parasite Acanthostomum spiniceps Looss 1896 (Cryptogonimidae) from the catfish Bagrus bajad and B. docmak

Abstract

Fishes of the River Nile are a promising source of animal protein. The catfishes Bagrus bajad Fabricius 1775 and Bagrus docmak Fabricius 1775 are economically important with well-marketable size and use in fish farming. Digenean parasites cause severe damage to the gut tissue of their fish hosts. There are still some questions regarding the taxonomical features of the genus Acanthostomum Looss 1899. The present study has revealed new morphological features that confirmed the identity of the collected worms as Acanthostomum spiniceps Looss 1896 and aided in elucidating the possible functions of different internal organs and surface features. A long-stemmed excretory bladder was detected but there was no evidence of gonotyl. The circumoral spines (28–30) were detected in the early juvenile stage and adult. The ventral sucker has no tegumental folds in juveniles or crescent-shaped tegumental folds in adults but possesses two overlapping lips. In both juveniles and adults, the oral sucker with the associated circumoral spines assumed retracted, and protracted positions reflecting its highest movement activity. Elongation of the anterior region and partial emergence of the oral cavity in living juveniles and adults were described. The possible functions of the forebody glands and the posterior body openings near the anal pores were discussed. Large, non-ciliated, dome-shaped, and small ciliated, button-like papillae were concentrated on the body surface, particularly the oral and ventral suckers. The tegument possesses densely arranged single-pointed and scale-like spines that gradually decrease in size and number as they proceed posteriorly.