and abundance of the parasites, and their spatial concentration in the spiral valve. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Raja undulata; Northwest Spain; Spiral valve; Helminth parasites; Seasonal trends; Infracommuni- ties
1. Introduction
Ž .
The undulate ray Raja undulata Lacepede, 1802 Chondrichthyes: Rajidae is a
`
bottom-dwelling elasmobranch that occurs on continental shelves to depths of up to 200 Ž
. m, most frequently on soft sandy bottoms Stehmann and Burkel, 1989 . It is distributed
¨
Ž .
along the eastern edge of the Atlantic, from Mauritania West Africa in the south to southern Ireland and southwest England in the north, and is also present along the
western Mediterranean coast of North Africa. It is a carnivore, feeding on a wide variety of benthic vertebrates and invertebrates. It reproduces between March and September,
Ž by laying 90 = 50 mm egg capsules. These hatch about 91 days later about 116 days
. Ž .
after copulation Pinto de la Rosa, 1998 . The high urea concentrations in tissues and
Ž body fluids of elasmobranches gives rise to a highly specialized parasite fauna Wil-
. liams, 1964; Williams et al., 1970; Cislo and Caira, 1993 .
In European waters Raja species are not generally targeted by commercial fisheries Ž
. Anonymous, 1995 . In Spain, however, and particularly in the Galicia region, ray is
widely consumed, and is an important target for the coastal fishing fleet. For example, in Ž
. the Rıa of Arousa one of the most productive coastal fishing areas in Spain , rays are
´
Ž .
the third most important fish by capture volume 80 tons in 1996 , and the fourth most Ž
. Ž .
important economically about US175,000 in the same year Iglesias Prol, 1998 . They
have also been studied by local fish farms as possible future cultivable species. There have been few previous complete studies of the parasites of rays. In the present
study, we determined the helminth parasites of R. undulata from the Rıa of Muros
´
Ž .
Galicia, Northwest Spain , and investigated possible relationships with environmental factors.
2. Material and methods
A total of 75 specimens of undulate ray, captured between February 1992 and Ž
X X
X X
December 1993 on the Misela Bank in the Rıa of Muros 42 846.5 –42848 N; 9854 –9857
´
. W were examined. All the fish were caught by trawling or in funnel traps, then
transferred to the laboratory in aerated seawater, and maintained alive until dissection Ž
. Ž
. 0–4 days . They were killed by an overdose of anesthetic MS222 Sigma . Immediately
Ž .
after death, the fish were measured total body length to the last 0.5 cm and weighed to the last 0.1 g. A body-surface mucus sample was obtained by scraping in search for
protozoa. The viscera and gills were then removed and examined with a stereomicro- Ž
. scope. Spiral intestine was examined as described by Williams 1964 and Williams et
Ž .
al. 1970 . The body surface, nasal cavities and body cavity were also examined.
Ž .
All parasites found only helminths in our case were collected and cleaned in 9‰ ClNa solution, then extended and fixed in Berland’s fluid, preserved in 70 alcohol,
´
Ž .
processed by standard methods see Alvarez et al., 1994, 1995a,b for examination by light microscopy or scanning electron microscopy.
Parasite ecology terms such as prevalence, intensity, mean intensity and mean Ž
. Ž
. abundance are used in accordance with Margolis et al. 1982 and Bush et al. 1997 .
Three measures of diversity were used as follows. Ž .
l Species richness S was estimated directly as the number of species observed in Ž
. the sample Magurran, 1988 .
Ž
X
. Ž
X
. l The Shannon–Wiener diversity index H
and the evenness index of Pielou J Ž
. were calculated using base-two logarithms Pielou, 1966, 1975; Magurran, 1988 .
Ž .
l Dominance was evaluated by the Berger–Parker index Magurran, 1988 . Parasite community composition was compared between size classes using two
Ž .
equations: The qualitative Jaccard similarity index Magurran, 1988 and the quantitative Ž
. Ž .
percentage overlap similarity index PS Brower et al., 1990 .
Ž Aggregation of each parasite species was quantified with the dispersion index D.I.;
. Ž
. Anderson and Gordon, 1982 . Significance of the values was checked by Ping’s 1995
test.
3. Results
