Josep Benito

Physiological responses to mercury in feral carp populations inhabiting the low Ebro River (NE Spain), a historically contaminated site

The low Ebro River course (Northeast Spain) is historically affected by mercury pollution due to a chlor-alkali plant operating at the town of Flix for more than a century. River sediments analysed during the last 10 years showed high mercury levels in the river section starting just downstream the factory and spanning some 90km, down to the river delta. The possible environmental impact was studied by a combination of field and laboratory studies. Mercury concentrations in liver, kidney and muscle of feral carp (Cyprinus carpio) sampled downstream Flix were one to two orders of magnitude higher than those from carps sampled upstream Flix. Elevated levels of mercury in these samples associated with significant increases on the concentration of reduced glutathione (GSH) in liver and on mRNA expression of two metallothionein genes, MT1 and MT2, in kidney and, partially, in scales, but not in liver. Conversely, no biochemical evidence for oxidative stress or DNA damage was found in these tissues. Non-contaminated carps subjected to intraperitoneal mercury injection resulted in a 20-fold increase of MT1 and MT2 mRNA levels in carp kidney, with minimal changes in liver levels. Our data suggests the coordinate increase of metallothionein mRNA in kidney and of GSH in liver constitutes an excellent marker of exposure to sub-toxic mercury levels in carps. This study also demonstrates that apparently healthy fish populations may exceed the mercury contamination acceptable for human consumption.

Methylmercury levels and bioaccumulation in the aquatic food web of a highly mercury-contaminated reservoir

The low Ebro River basin (NE Spain) represents a particular case of chronic and long-term mercury pollution due to the presence of an industrial waste (up to 436 μg/g of Hg) coming from a chlor-alkali plant Albeit high total mercury (THg) levels have been previously described in several aquatic species from the surveyed area, methylmercury (MeHg) values in fish individuals have never been reported. Accordingly, in order to investigate bioaccumulation patterns at different levels of the aquatic food web of such polluted area, crayfish and various fish species, were analysed for THg and MeHg content. At the hot spot, THg mean values of crayfish muscle tissue and hepatopancreas were 10 and 15 times, respectively, greater than the local background level. Higher mean THg concentrations were detected in piscivorous (THg=0.848 ± 0.476 μg/g wet weight (ww); MeHg=0.672 ± 0.364 μg/g ww) than in non-piscivorous fish (THg=0.305 ± 0.163 μg/g ww; MeHg=0.278 ± 0.239 μg/g ww). Although these results indicated that THg in fish increased significantly with increasing trophic position, the percentage of the methylated form of Hg was not strongly influenced by differences in relative trophic position. This is an important finding, since the fraction of THg as MeHg in the top fish predator was unexpectedly lower than for other species of the aquatic food chain. Moreover, mean THg concentrations in piscivorous fish exceed the maximum level recommended for human consumption. From our findings, it is clear that for this specific polluted system, speciation becomes almost mandatory when risk assessment is based on MeHg, since single measurements of THg are inadequate and could lead to an over- or under-estimation of contamination levels.

Growth and diet of European catfish (Silurus glanis) in early and late invasion stages

The ecological impact of many invasive species is usually unknown because of the absence of data before their introduction. We exemplify the usefulness of comparing early and late invasion stages to understand the ecological changes caused by invasive species, particularly concerning large species and large ecosystems, such as reservoirs, where experimental work is not easily carried out. We also report the first data on growth and diet for the European catfish (Silurus glanis) in the Iberian Peninsula and compare three populations in the Ebro River system, corresponding to the earliest introductions (> 30 years ago) with two recently introduced populations in reservoirs of the Ter River basin. The total length and age of the catfish varied significantly among populations and recent introductions consisted of smaller and younger catfish with significantly higher condition and size-specific growth rates compared to older (as well as native) populations. For example, 7+ old catfish were around 100cm in the older populations and 150 cm in the more recent ones. Diet also depended on site and catfish size. Catfish measuring less than 30 cm consumed mostly invertebrates, thereafter shifting to red swamp crayfish Procambarus clarkii (old introductions) or fish (recent introductions). A number of fish species were present in stomachs but common carp (Cyprinus carpio) and birds were only present in very large fish (> 120 cm). The median length of common carp was significantly larger in reservoirs with late-stage catfish invasion. The abundance of waterbirds, particularly anatids, was significantly lower in reservoirs where catfish were present, suggesting a direct ecological impact, or else avoidance learning by the birds. Our results suggest that in the early stages of invasion, catfish display higher condition and growth rates by profiting from relatively unexploited resources (large fish and, secondarily, water-birds), shifting to other prey (and thus reducing mean growth) in the late invasion stages.

Integrated biological and chemical analysis of organochlorine compound pollution and of its biological effects in a riverine system downstream the discharge point.

Pollution in riverine systems, along with its biological effects, may propagate downstream even at considerable distances. We analyzed the organochlorine compound (OC) pollution in a section of the low Ebro River (Northeast Spain) downstream a long-operating chlor-alkali plant. Maximal levels of OCs and of their associated dioxin-like biological activity occurred in residue samples from the plant, and persisted in river sediments some 40km downstream (Xerta site). Biological analysis at multiple organization levels in local carp (Cyprinus carpio, EROD, Cyp1A mRNA expression in the liver, hepatosomatic index, condition factor, and micronuclei index in peripheral blood) showed a similar pattern, with a maximal impact in Ascó, few kilometers downstream the plant, and a clear reduction at Xerta. This combination of chemical, molecular, cellular and physiological data allowed the precise assessment of the negative impact of the chlor-alkali plant on the quality of river sediments and on fish, and suggests that sediments may be a reservoir for toxic substances even in dynamic environments like rivers.

Prevalence and sequence comparison of Phyllodistomum folium from zebra mussel and from freshwater fish in the Ebro River

We utilised DNA analysis to detect the presence of the digenean Phyllodistomum folium in three cyprinid species, Scardinius erythrophthalmus, Cyprinus carpio and Rutilus rutilus. DNA sequencing of the region containing the genes ITS1-5.8S-ITS2 revealed 100% sequence identity between DNA from the sporocysts found in zebra mussels and DNA from adults located in the urinary system of 29 cyprinid fish. A second genetically different (variation=1.6%) sequence was observed in two samples from R. rutilus. In our opinion, the existence of a complex of species reported as P. folium is supported by recent genetic studies, including our own results. The overall prevalence of P. folium in mussels from the Ebro River was 4.67% in 2006, although during the summer months the rates frequently exceeded 10%.

Diel Cycle and Effects of Water Flow on Activity and Use of Depth by Common Carp

AbstractCommon Carp Cyprinus carpio is among the most popular and commercially important fishes globally. For this reason, it has been introduced worldwide and is invasive in many regions, with well-known ecosystems impacts. Like many other freshwater invaders it is thought not to tolerate strong flows well, but knowledge of the effects of flow on their activity, habitat use, and diel cycles are limited, despite this being crucial information for management and control. By means of ultrasonic telemetry we investigated depth use and activity of Common Carp in a small reservoir with a very low water residence time on the main stem of the Ebro River, the largest river by discharge in the Iberian Peninsula, over a 19-month period. The activity of carp and their use of depth displayed low seasonality compared with abiotic factors. However, carp exhibited diel vertical migration patterns, mostly in the warm season, shifting from deep positions near the reservoir bottom during the night (with decreased activity)...