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Digestive tract parasites in rhynchoteuthion 

 squid paralarvae, particularly in 

 ///ex argentinus (Cephalopoda: 

 Ommastrephidae) 



Erica A. G. Vidal 



Manuel Haimovici 



Departamento de Oceanografia 



Universidade do Rio Grande (FURG) 



C- P, 474 Rio Grande RS 96 201-900, Brazil 



E-mail address (for E A G Vidal) eavidalauimbedu 



Present address (for E. A G. Vidal): National Resource Center for Cephalopods 



Marine Biomedical Institute 

 University of Texas Medical Branch 

 301 University Blvd., Galveston, Texas 77555-1163 



Cephalopods play an important role 

 in the transfer of parasites through 

 the food web. They are second and 

 third intermediate hosts for larval 

 stages of digeneans, cestodes, and 

 nematodes. The final hosts are usu- 

 ally fishes, sea birds, and marine 

 mammals (Hochberg, 1990). Nev- 

 ertheless, the interactions of cepha- 

 lopods and their parasites are still 

 poorly understood, and almost 

 nothing is know about parasitism 

 in cephalopod paralarvae and early 

 juveniles (Vecchione, 1987). Infor- 

 mation on parasitism in the early 

 stages of cephalopod life cycles can 

 provide a better understanding of 

 host-parasite relationships as well 

 as the environment and conditions 

 in which infection first occurs. 



Ommastrephid paralarvae are 

 among the smallest cephalopods at 

 hatching and are termed "rhyncho- 

 teuthion" because their tentacles are 

 fused into a proboscis-like structure. 

 Three distinct morphological types 

 of rhynchoteuthion paralarvae 

 (types "A," "B," and "C") are found 

 commonly off southern Brazil 

 (Haimovici et al., 1995). "Type C" 

 is Illex argentinus (Castellanos, 

 1960) and "type A" probably is 

 Ommastrephes bartramii (Lesueur, 

 1821). Illex ctrgentinuf: is distrib- 



uted in the southwestern Atlantic 

 Ocean from 22" to 54°S (Roper et 

 al., 1984), and it currently supports 

 the largest squid fishery in the 

 world. This species is an important 

 link in the trophic relations of the 

 pelagic ecosystem of this region and 

 constitutes a major element of the 

 diet of several commercial fishes, 

 such as Thunnus obesus, Merluccius 

 hi/bbsi, Xiphias gladiiis, and Poly- 

 prion americanus (Santos, 1992; 

 Ivanovic and Brunetti, 1994). 



The digestive tract contents of 

 Illex argentinus and the other rhyn- 

 choteuthion types were examined 

 by Vidal and Haimovici (1998). 

 During examination of the diges- 

 tive tracts, observations on parasit- 

 ism were made. In this note we re- 

 port the parasites (protistans and 

 metazoans) found in the digestive 

 tract of rhynchoteuthion paralarvae, 

 mainly Illex argentinus. 



Material and methods 



Ommastrephid paralarvae were col- 

 lected in four surveys carried out be- 

 tween Cape of Santa Marta Grande 

 (28"30'S)and Chui (34 20'S), Brazil, 

 during the spring of 1987, summer 

 of 1990, autumn of 1991. and win- 



ter of 1988. Paired bongo nets, with 

 60-cm mouth diameter and 0.33- 

 mm mesh were used in oblique tows 

 between the surface and depths of 

 approximately 300 m. This gear 

 was towed at a speed of 2 kn and 

 deployed for 5-15 min. Afterwards, 

 paralarvae were fixed and pre- 

 served in formalin. 



Digestive tracts were examined 

 from paralarvae of 72 I. argentinus 

 ( 1.0-8.0 mm of mantle length (ML)), 

 12 "type A" ( 1.0-5.8 mm ML) and 4 

 "type B" (2.0-4.0 mm ML). Para- 

 larvae were stained with alcian 

 blue and then cleared with trypsin, 

 following the method of Vecchione 

 (1991). This method makes the 

 paralarvae semitransparent and 

 the parasites in the gut easier to 

 see. The stomach, caecum, and in- 

 testine of all paralarvae were ex- 

 amined for parasites with a light 

 microscope at a magnification of 

 400x. The esophagus was not exam- 

 ined. Five /. argentinus juveniles 

 (16.0-38.0 mm ML) and 14 para- 

 larvae (1.6-9.7 mm ML) of/, argen- 

 tinus with no previous clearing and 

 staining treatment were also exam- 

 ined. The prevalence and the mean 

 intensity of infestation (.number of 

 a particular parasite per infected 

 individuals) were calculated ac- 

 cording to Margolis et al. ( 1982). 



Results 



Parasites were not found in the 14 

 untreated paralarvae. The opaque 

 walls of the internal organs made 

 the visualization of parasites diffi- 

 cult. A single copepod parasite was 

 found in one of the five untreated 

 juveniles. 



Four types of parasites were ob- 

 sei-ved in paralarvae and juvenile 

 /. argentinus: coccidians (Apicom- 

 plexa; Sporozoea: Eucoccidiida), 

 didymozoid-metacercariae ( Platy- 

 helminthes: Trematoda: Digenea), 



Manuscript accepted 19 May 1998. 

 Fi.sli. Bull. 97:402-405 (1999). 



