Environmental and biological factors influence the relationship between a predator fish,Gambusia holbrooki,and its main prey in rice fields of the Lower Mondego River Valley (Portugal) |
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Authors: | Cabral J A Mieiro C L Marques J C |
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Institution: | (1) IMAR –- Institute of Marine Research, Faculty of Sciences and Technology, Department of Zoology, University of Coimbra, 3000 Coimbra, Portugal. |
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Abstract: | We studied the relationships between a predator fish, Gambusia holbrooki, and its main food prey, within the content of a
rice field food web. The influence of some environmental and biological factors on these trophic interactions, in combination
with existent quantitative information, allowed us to evaluate the ecological viability of using a non-ionic surfactant, Genapol
OXD-080, to control a plague caused by crayfish (Procambarus clarkii) populations in the rice fields. In the Lower Mondego
River Valley, Portugal, G. holbrooki is abundant in rice fields. It feeds mainly on copepods, cladocerans and rotifers. Surface
insects, such as aphids, collembolans, adult (imago) chironomids and other dipterans, are additional food. Large G. holbrooki
consumed greater amounts of cladocerans and adult chironomids than other smaller size groups, while small fish prefered rotifers.
Gravid females ate copepods, cladocerans, and adult chironomids and other dipterans in significantly greater amounts than
immatures, males, and non-gravid females. Non-gravid females ate collembolans in significantly greater quantities than any
other fish group. The population density of copepods, cladocerans, adult chironomids, and other dipterans, the area covered
by aquatic vegetation, and water temperature all had significant effects on the total number of prey caught by G. holbrooki.
In contrast, a negative correlation was found with rotifers, collembolans, aphids in higher densities, and of increased water
volume, dissolved oxygen and pH. G. holbrooki holds a key intermediate position in the rice field food chain, feeding in large
amounts of aquatic invertebrates and being eaten, in turn, by piscivores. With regard to the toxicity of Genapol OXD-080 on
non-target organisms, LC50 values for G. holbrooki and some of its main prey were several times lower than the concentration necessary to decrease the
activity of crayfish populations in the rice fields. Thus, Genapol OXD-080 could potentially cause greater damage to the local
populations of non-target species and should not be used without taking precautions not to contaminate other important biological
reservoirs, such as the rice field irrigation channels.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | mosquitofish Gambusia holbrooki prey selection predator-prey interactions rice fields irrigation channels physicochemical parameters biological constraints surfactant |
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