Cryptosporidium molnari n. sp. (Apicomplexa: Cryptosporidiidae) infecting two marine fish species,Sparus aurata L. and Dicentrarchus labrax L

Cryptosporidium molnari n. sp. is described from two teleost fish, the gilthead sea bream (Sparus aurata L.) and the European sea bass (Dicentrarchus labrax L.). The parasite was found mainly in the stomach epithelium and seldom in the intestine. Oocysts were almost spherical, with four naked sporozoites and a prominent residuum, and measured 3.23-5.45 x 3.02-5.04 (mean 4.72 x 4.47) microm in the type host, gilthead sea bream (shape index 1-1.17, mean 1.05). Sporulation was endogenous, as fully sporulated oocysts were found within the fish, both in the stomach epithelium and lumen, and in faeces. Oocysts and other stages of C. molnari fit most of the diagnostic features of the genus Cryptosporidium, but differ from hitherto described species, including piscine ones. All stages were located within a host contributed parasitophorous vacuole lined by a double host microvillar membrane. Merogonial and gamogonial stages appeared in the typical extracytoplasmic position, whereas oogonial and sporogonial stages were located deeply within the epithelium. Ultrastructural features, including the characteristic contact zone of the parasite with the host epithelial surface, were mostly coincident with those of other Cryptosporidium spp. Mitochondria were found in dividing meronts, merozoites, microgamonts and sporozoites. Pathological effects were more evident in gilthead sea bream, which also exhibited a clearly higher prevalence (24.4 versus 4.64% in sea bass). External clinical signs, consisting of whitish faeces, abdominal swelling and ascites, were rarely observed, in contrast with important histopathological damage. The wide zones of epithelium invaded by oogonial and sporogonial stages appeared necrotic, with abundant cell debris, and sloughing of epithelial cells, which detached to the lumen. No inflammation reaction was observed and the cellular reaction was limited to the cells involved in the engulfing of intraepithelial stages and debris, probably macrophages.