Parasitic castration of Eurhomalea lenticularis (Bivalvia: Veneridae) by a digenetic trematode: quantitative histological analysis

Abstract

The clam Eurhomalea lenticularis may be parasitized by digenean trematodes of the family Plagiorchidae, specifically in the gonads (parasitic castration). A quantitative histological analysis of the parasitized gonads demonstrated a significant decrease in gonadal area, in the size of individual acini, and in the numbers of differentiated germ cells compared to unparasitized clams. Castration may be caused by mechanical compression due to trematode sporocyst growth. However, the uniform loss of germ cells in areas without sporocysts suggests that a more generalized mechanism is responsible. We suggest that parasitic castration has a primary effect on the host's neuroendocrine and gametogenic systems that regulate gamete production. KEY WORDS: Bivalve mollusc · Parasitic castration · Histological analysis · Eurhomalea lenticularis · Digenea · Trematode · Central Chile Resale or republication not permitted without written consent of the publisherDis Aquat Org 59: [151][152][153][154][155][156][157][158] 2004 of alteration in the neuroendocrinological system of the clam, we quantified the variation between germ cell number in the presence and absence of sporocysts. MATERIALS AND METHODSSample processing and histology. To determine the prevalence of the parasite, a total of 1702 clams was obtained from June 1995 to February 1998 by diving on a natural bank located at El Algarrobo inlet, central Chile (33°20' S, 71°40' W). They were transported live to the laboratory, and at least 1 random sample of 30 clams was processed each month (1034 in total; the remaining clams were dissected and observed under the stereoscopic microscope to determine the presence of the parasite) using routine histological techniques (Gabe 1968). After 1 h fixation in Bouin Hollande fluid to harden the tissues, serial transverse sections, 5 mm thick, were made of the visceral mass containing the gonad. After fixation in fresh fixative for 48 h, the thick sections were washed in tap water for 24 h, dehydrated in graded ascending concentrations of ethanol to 100%, cleared in butanol and embedded in Paraplast Plus (Oxford ® ). Histological sections of 5 µm thickness were made at different levels through the tissue at 300 µm intervals, deparaffinized, and rehydrated in a decreasing series of ethanol concentrations, and stained by a trichrome staining method. Briefly, the sections were stained in Harris hematoxylin solution for 75 s and rinsed in running tap water for 10 min, followed by a quick rinse in distilled water. Next, they were stained with a mixture of 0.5% Erythrosin-0.5% Orange G for 30 min, and quickly rinsed in distilled water. They were immersed in 0.5% phosphotungstic acid for 10 min, and again quickly rinsed in distilled water. Finally, they were stained in 1% Aniline blue for 75 s and immediately dehydrated in 3 consecutive baths of 95% ethanol followed by 3 baths in 100% ethanol (Arteta trichrome stain; López et al. 1982). After clearing in xylenes, the slides were coverslipped using Canada balsam (López et al. 1982...

Parasite Induced Summer Mortality in the Cockle Cerastoderma edule by the Trematode Gymnophallus choledochus

“…In addition to mortality, G. choledochus seems to castrate its host since no gonad structures could be observed in infected individuals. Such parasite induced castration was also observed in other parasite-bivalve associations (Coustau et al, 1993;Silva et al, 2002;Valderrama et al, 2004). Hence, the infected part of the local adult cockle population is probably no longer reproducing.…”

Report of pathogens and parasites in Perumytilus purpuratus from San Jorge Bay, Antofagasta, Chile

“…In South America, studies of parasites and diseases of bivalves are scarce (CaceresMartinez & Vasquez-Yeomans 2008), even though they are important and necessary. In Chile, major contribution about presence of parasites in molluscs have been recorded by Oliva (1984Oliva ( , 1992, Oliva et al (1986Oliva et al ( , 1999Oliva et al ( , 2010, Franjola & Gallardo (1991), Gallardo et al (1992), Oliva & Vega (1994), García-Tello et al (2002), Valderrama et al (2004), and pathogens by Lohrmann et al (2002), Lohrmann (2009), Campalans & Lohrmann (2009. However, the knowledge of pathogens and parasites in marine organisms inhabiting San Jorge Bay (Antofagasta) and the majority of the Chilean coast remains largely unknown.…”

Pathology survey of the short-neck clam Ruditapes philippinarum occurring on sandy tidal flats along the coast of Ariake Bay, Kyushu, Japan

“…Cake (1977) reported that cestode infections also cause physiological stress, resulting in a negative effect on the reproduction of marine mollusks. Such failure of the host's reproduction is caused by deprivation of essential nutrients, impacts on the host's natural endocrine system, and genetic modulation (Crews and Yoshino, 1989;Valderrama et al, 2004;Rice et al, 2006). Similarly, we found that trematodes, together with cestode infections, cause severe tissue damage in the gonads.…”