Occurrence of Echeneibothrium 

 (Platyhelminthes, Cestoda) in the 

 calico scallop Argopecten gibbus 

 from North Carolina 



Lynda S. Singhas 



Terry L. West 



William G. Ambrose Jr. 



Department of Biology. East Carolina University 

 Greenville, North Carolina 27858 



Scallops are known hosts for larval 

 parasites (Cheng 1967). Nematode 

 and trematode parasites have been 

 described in the calico scallop 

 Argopecten gibbus, a bivalve native 

 to the Atlantic coast (Cummins et 

 al. 1981). Larval cestodes of the 

 genera Parachristianella , Tyloceph- 

 alum, Rhinebothrium, and Poly- 

 cephala have also been described in 

 Argopecten irradians populations 

 from the Gulf of Mexico (Cake 1977). 

 During the course of a study de- 

 scribing gametogenesis and repro- 

 ductive periodicity in the North 

 Carolina population of A. gibbus, a 

 larval cestode was found in speci- 

 mens collected in late 1990 and 

 early 1991. The objectives of this 

 report are to identify the cestode, 

 and to describe alterations in intes- 

 tinal morphology and percent dry 

 weight of the gonadal tissues ("go- 

 nadal index") of A. gibbus, which 

 coincided with infection by this 

 cestode. 



Materials and methods 



Calico scallops were collected by 

 personnel of the North Carolina Di- 

 vision of Marine Fisheries or by 

 commercial fishermen at 1-3 mo in- 

 tervals from January 1990 to Feb- 

 ruary 1991. Collection sites were lo- 

 cated 10-20 km offshore (33-35° 

 lat., 76-77° long.) from Cape Look- 

 out, North Carolina at depths of 30- 

 40 m. The scallops were placed on 



ice, transported to the lab, and the 

 tissue processed within 24 h. 



Gonads were removed and fixed 

 in a seawater Bouin's solution for 

 12-24 h. After dehydration in a 

 graded ethanol series, the gonads 

 were embedded in paraffin and sec- 

 tioned at 7|.im. Tissues were stained 

 with either hematoxylin and eosin 

 Y or Mallory's trichrome stain 

 (Humason 1962). 



Dry weights of tissues were de- 

 termined by separating gonads, ad- 

 ductor muscle, and the remaining 

 tissues, and drying each tissue to 

 constant weight in an oven at 60° C 

 ( -48 h ). Dry weight of the gonad was 

 expressed as a percentage of the 

 total dry weight to obtain the go- 

 nadal index. An analysis of variance 

 (ANOVA) was used to test for dif- 

 ferences in the gonadal indices of 

 scallops from parasitized and non- 

 parasitized groups in the same 

 stages of gametogenesis. 



Results 



Encysted parasites, identified by Dr. 

 Thomas C. Cheng (Medical Univ. 

 South Carolina, Charleston) as the 

 plerocercoid stage of the cestode 

 Echeneibothrium sp., were found 

 within the connective tissue of the 

 gonads in calico scallops collected 

 only during November 1990 and 

 February 1991 (Fig. 1). Levels of 



Manuscript accepted 6 October 1992. 

 Fishery Bulletin, U.S. 91:179-181 (1993). 





* 



!tf tCr fekl& AY 





mm 





Figure 1 



Longitudinal section of Echeneibothrium (Ec) in the gonad of Argopecten gibbus. Nu- 

 merous macrophagous hemocytes (M) surround the connective tissue capsule (CT) 

 and nearby tissue. OV = ovarian acini containing developing eggs. Mallory's trichrome 

 stain. 



79 



