Description and epidemiological characterization of the cyprinid fish parasite fauna in the upper and middle River Duero Basin (NW Spain)
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1
Universidad de Zaragoza, Animal Pathology, Spain
River Duero Basin, located in the mid-north plateau of the Iberian Peninsula, represents about 82% of the surface of the Castilla y León Region (Northwest Spain). In a high altitude, it presents a Continental climate. Its main riverbed, the Duero River, is the second in length (913 km) and the first in river flow, characterized by its irregularity. Its instability, intermittence and environmental stress, are all characteristics of these types of Mediterranean fluvial ecosystems (Garcia-Asenjo, 2007).
Their behaviour has determined the life cycles of the fish populations, of which Cyprinidae is the most representative family (Wieser et al. 1992). Adapted to such conditions, their life strategies are oriented to the exploitation of the ecosystem most productive seasons, and their population dynamics adjusted to the seasonal oscillations of the hydrological regime, so that the only few moments in which there’s a concentration of fish individuals, and so an increase in the population density, are the breeding season, the nursery phase, and the periods of summer drought (Granado-Lorencio, 1992; Encina et al. 2006).
With its actions, human being has modified the characteristics of this aquatic habitat, affecting directly and/or indirectly to the estate of health of these fish populations. Their parasite fauna, which act as a real control mechanism of the population size, and the details of the parasite-host system, are still pretty much unknown for these ecosystems.
The present study deals with the behaviour of the fish parasites at the displayed situation, and the impact of the anthropogenic alterations of the environment in the parasite-host relations. In order to establish the prevalence of infection of the different parasite groups identified (Bush et al. 1997), as well as the most important associations between the presence of such groups and the risk factors that could be involved, a transversal epidemiological study was performed during 3 years in 6 rivers of the Duero river basin.
For that purpose, 7 sampling stations were selected: two of them in the upper part of the basin, four in the middle part and a single sampling point in a tench fish farm. Sampling was randomized, stratified and distributed along three seasons (spring, summer and autumn) being captured by electrofishing a total of 781 fish belonging to 7 species of the family Cyprinidae (18,2% Iberian barbel, 4,5% “Bermejuela”, 11,6% Duero nase, 1,5% Iberian chub, 22,3% Iberian gudgeon, 27,3% Eurasian minnow and 14,6% tench). The fish were killed by cervical dislocation immediately prior to examination and then were checked for ecto- and endoparasites under steromicroscope. Cleaned parasites were separated, put in certain fixatives and then prepared form examinations with appropriated techniques of staining and clearing (Álvarez-Pellitero, 1988; Eiras et al. 2000; Lasee, 2001). All species of parasites found were identified according to keys proposed by Bykhovskaya-Pavlovskaya, 1964; Bauer, 1987; Lom and Diková, 1992).
Other relevant epidemiological data were also collected, such as total length and weight, sex, age, condition factor K, reproductive state, season and some physic-chemical and microbiological water quality parameters.
All data were included in a database and they were processed with WinEpi 2.0 (de Blas et al. 2006) and SPSS 15.0 for Windows.
A total of 11 parasite groups were recovered from fish along the Duero basin and distributed as follows (Table 1): 3 protozoan species, Ichthyophthirius multifiliis (47,8%), Tripartiella sp. (9,3%) and Myxobolus sp. (17,2%), 2 metazoans, Gyrodactylus sp. (9,2%) and Dactylogyrus sp. (17,4%), 2 copepode crustaceans, Ergasilus sieboldi (1,7%) and Lernaea cyprinacea (3,1%), 1 nematode, Rhabdochona sp. (1,9%), 1 cestode, Caryophyllaeus sp. (2,7%), 1 digenetic trematode, Hysteromorpha triloba (1,3%) and a glochidium mollusc, Unio sp.(1,1%) (Table 1).
Seasonality was the most outstanding risk factor, showing its effect over the presence of 8 out of the 11 parasite groups recovered, especially in the warmer seasons of the year. In the rivers, parasite diversity was much higher than in the fish farm, in which only 4 groups were isolated, but on the other hand it behaved as a risk factor in the presence of ciliated protozoa. It was also observed an influence of the river zone, with the middle stretch of the studied rivers behaving as a risk factor in the presence of 4 parasite groups. In particular, the lentic zone of the river Arlanza under the influence of a small dam, stimulated the presence of 8 groups of parasites. It was only observed a clear influence, as environmental risk factors, of three water quality parameters: temperature, dissolved oxygen and pH.
We conclude that the development, reproduction and transmission of these parasite groups are stimulated in the most stable conditions of the ecosystem (geomorphological, hydrological, physicochemical and biological), which are preferably found in the middle stretches of the rivers, or concurring with the most favourable moments of the life cycle of the cyprinids (breeding and nursery). Besides, slight changes in these “normal” conditions of the ecosystem, natural or caused by human, triggers the development of one/several phases of the parasite’s life cycles, and so it infects a fish with a higher intensity or a higher number of individuals in a fish population. And further, these environmental disturbances lead to the same stabilizing conditions in the aquatic environment and affect in the same way to the host-parasite relations.
Acknowledgements
We thanks to Consejería de Agricultura y Ganadería from the Junta de Castilla y León Government (Spain) for it financial support. Ministerio de Educación of Spain is funding a FPU/MEC doctorate fellowship for Ana Muniesa.
References
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Keywords:
Cyprinid fish,
Epidemiological characterization,
Parasite fauna,
Risk factors,
transversal epidemiological study
Conference:
AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.
Presentation Type:
Poster
Topic:
Aquatic Animal Epidemiology
Citation:
Illán
G,
Muniesa
A,
De Blas
I and
Ruiz-Zarzuela
I
(2016). Description and epidemiological characterization of the cyprinid fish parasite fauna in the upper and middle River Duero Basin (NW Spain).
Front. Vet. Sci.
Conference Abstract:
AquaEpi I - 2016.
doi: 10.3389/conf.FVETS.2016.02.00011
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Received:
23 May 2016;
Published Online:
14 Sep 2016.
*
Correspondence:
DVM. Ana Muniesa, Universidad de Zaragoza, Animal Pathology, ZARAGOZA, ZARAGOZA, 50013, Spain, animuni@unizar.es