Nematopsis marinus n. sp., a new septate gregarine from cultured penaeoid shrimp Litopenaeus vannamei (Boone), in Ecuador

Abstract

The septate gregarine Nematopsis marinus n. sp. (Apicomplexa: Cephaline) heavily infected the midgut of cultured Pacific white shrimp Litopenaeus vannamei (Boone) in Ecuador. It is morphologically similar to other species of the genera Nematopsis, but it can be distinguished from them, by having gamonts with a prominent hemispherical protomerite that contained numerous refractile granules and unusual strong gliding movement. There is evidence that shrimp acquired the infection in the ponds, as larval or postlarval stages do not showed infection. Juveniles and adult shrimp had a prevalence and intensity of infection ranging from 50% to 80% and 10 to > 5000 parasites respectively. When voided from the gut, the gregarine keep alive in seawater. This gregarine have been associated with the marine environment and there are no records of this species in low salinity waters or freshwater. Results suggest that N. marinus could have most of the life cycle of the species within the host L. vannamei.

Fine structure of a septate gregarine trophozoite in the black tiger shrimp Penaeus monodon

“…The morphology of this septate-type gregarine as observed under LM was similar to the gregarine Nematopsis marinus found in Litopenaeus vannamei (Jimenez et al 2002). Both the size and structure under fresh preparation, together with the size and shape of gametocysts as described by the authors, were similar to the gregarine found in the present study, including the association characteristics and striate appearance of the surface of the trophozoite.…”

“…Both the size and structure under fresh preparation, together with the size and shape of gametocysts as described by the authors, were similar to the gregarine found in the present study, including the association characteristics and striate appearance of the surface of the trophozoite. Under LM, the shape and size of the nucleus of N. marinus in the study by Jimenez et al (2002) was similar to that in the present study, although without ultra-structural features for comparison, it is impossible to indicate if the gregarine species in this study is actually N. marinus. Jimenez et al (2002) also reported a longitudinally striated appearance in N. marinus, which could be interpreted as the pellicular folds of the gregarine as observed in our study, but since Jimenez et al (2002) did not include SEM features in their study this cannot be stated with certainty.…”

“…Resale or republication not permitted without written consent of the publisher (Jimenez et al 2002). In the case of P. scolecoides, only immature and mature trophozoites were observed in the midgut lumen of L. vannamei postlarvae, and no gametocysts were found.…”

“…Four genera of gregarines (Nematopsis, Cephalobus, Cephaloidophaidae, and Paraophioidina) have been reported to infect penaeid shrimp (Couch 1978, Lightner 1993, Jones et al 1994, Jimenez et al 2002. Lightly infected shrimp may not show any clinical signs (Couch 1978), but severely infected shrimp may have reduced growth rates and yellow discoloration of the midgut, with perforation and hyperplasia of the midgut epithelium (Lightner 1993(Lightner , 1996.…”

“…The trophozoites are generally divided into septate and nonseptate types, depending on the presence or absence of 'septa' dividing their bodies into different compartments known as the epimerite, protomerite, and deutomerite (Wallace & Taylor 1996). One of the 2 most economically valuable shrimp species, the Pacific white leg shrimp Litopenaeus vannamei, has been reported to be infected both with septate (Nematopsis penaeus, N. vannamei, and N. marinus;Jimenez et al 2002), and non-septate (Paraophioidina scolecoides) gregarines (Jones et al 1994). The differences between septate and non-septate gregarines can be clearly illustrated in N. marinus and P. scolecoides.…”