Impact of parasitism by nematodes on gonadal anatomy of Pagellus erythrinus (L.)
Nematode larvae (stages 3 and 4) infect various marine teleost fish. 297 specimens of Pagellus erythrinus (Teleostei: Sparidae) from the east coast of Algeria were examined for their parasitic nematodes between November 2015 and April 2017. Five nematode species were collected and identified: Hysterothylacium aduncum (Rudolphi, 1802), H. fabri (Rudolphi, 1819), H. sp., Cucullanus cirratus Müller, 1777 and Philometra filiformis (Stossich, 1896). Among them, three species (H. fabri, C. cirratus and P. filiformis) are reported for the first time in the study area. These parasites infect the peritoneal cavity and ovaries of the parasitized fishes. Nematodes infect Pagellus erythrinus at a high rate (prevalence = 73.19%; mean intensity = 7.23 parasites per infected fish). Philometra filiformis infects particularly the ovarian parenchyma (prevalence = 5.72% and mean intensity = 1.29 parasites per infected host). Our statistical results show a significant difference between the infection rates depending on the host sex. Macroscopic examination reveals more consistency of parasitized ovarian parenchyma. The histological examination shows different histological damages caused by P. filiformis. This worm induces nearly total replacement of the gonadic parenchyma and lesions. Therefore, the reproductive capacity of the fish, which has a high commercial interest, may be affected when a great number of oocytes are degenerated by this worm.