ABSTRACT
This study investigated growth, condition and development of American eels Anguilla rostrata that were introduced into a European river to estimate their competitive potential in a non-native habitat. Results demonstrate that A. rostrata develops normally in European waters and successfully competes with the native European eel Anguilla anguilla. In addition, A. rostrata appears to be more susceptible to the Asian swimbladder nematode Anguillicola crassus than A. anguilla and could support the further propagation of this parasite. Detected differences in fat content and gonad mass between Anguilla species are assumed to reflect species-specific adaptations to spawning migration distances. This study indicates that A. rostrata is a potential competitor for the native fauna in European fresh waters and suggests strict import regulations to prevent additional pressure on A. anguilla and a potential further deterioration of its stock situation.
Subject(s)
Anguilla/physiology , Introduced Species , Adaptation, Physiological , Air Sacs/parasitology , Anguilla/growth & development , Anguilla/parasitology , Animals , Dracunculoidea , Europe , FemaleABSTRACT
Individual migration behaviour during the juvenile and adult life phase of the anadromous twaite shad Alosa fallax in the Elbe estuary was examined using otolith Sr:Ca and Ba:Ca profiles. Between hatching and the end of the first year of life, juveniles showed two migration patterns. Pattern one exhibited a single downstream migration from fresh water to the sea with no return into fresh water. In contrast, pattern two showed a first migration into the sea, then a return into fresh water and, finally, a second downstream migration into marine water. This first report of migration plasticity for A. fallax points to different exposure times to estuarine threats depending on the migration strategy. In adults, high Sr:Ca and low Ba:Ca in the majority of individuals confirmed prior reports of a primarily marine habitat use. Patterns reflecting spawning migrations were rarely observed on otoliths, possibly due to the short duration of visits to fresh water.
Subject(s)
Animal Migration , Barium/analysis , Calcium/analysis , Fishes/physiology , Otolithic Membrane/chemistry , Strontium/analysis , Animals , Barium/chemistry , Behavior, Animal , Calcium/chemistry , Estuaries , Fresh Water , Life Cycle Stages/physiology , Population Dynamics , Seawater , Strontium/chemistry , Time FactorsABSTRACT
To investigate the extent to which European silver eels Anguilla anguilla, originating from stocking programmes in the Baltic Sea tributaries, effectively contribute to the spawning stock, two hundred and seventy-four formerly stocked A. anguilla. emigrating from the Schwentine River near Kiel, Germany, were tagged with T-Bar anchor tags. A total of 29 Anguilla spp. were recaptured (c. 11%) up to 14 months after release. Stocking history of recaptured A. anguilla. was confirmed by otolith microchemistry. Recapture locations were concentrated around the outlet of the Baltic Sea (Danish Belt Sea) with 62% of all recaptures reported here or in the Kattegat. Recaptured Anguilla spp. showed a reduction in both L(T) and mass (mean ± s.d. = -1.5 ± 0.9 cm and -125.3 ± 50.1 g) while average total fat content remained in the order of values previously reported as high enough to provide energy resources to allow successful completion of the spawning migration (mean ± s.d. = 28.4 ± 4.4%). The documented mean rate of travel (0.8 km day(-1)), however, indicated a delay in the target-oriented migration that might be interpreted as a delayed initial migration phase of orientation towards the exit of the Baltic Sea.
Subject(s)
Anguilla/physiology , Animal Migration/physiology , Adipose Tissue/metabolism , Animals , Body Constitution , Body Size , Fisheries , Germany , Oceans and Seas , Otolithic Membrane/chemistry , RiversABSTRACT
European eel (Anguilla anguilla) elvers were intraperitoneally injected with different doses of 3,3',4,4'-tetrachlorobiyphenyl (PCB77) to examine and characterize the inductive effect of coplanar PCBs on CYP1A1 gene expression in liver and gills by using a semi-quantitative RT-PCR analysis. The influence of PCB77 injection on transcription activity of the housekeeping gene glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) was tested to determine its suitability as a reference gene for further quantitative gene expression analyses. Our results clearly indicate a significant dose-dependent increase in CYP1A1 gene expression in the gills of European eel, while in liver tissues a significant elevation in CYP1A1 gene expression was only detectable at highest contamination rates, indicating the potential of CYP1A1 differential gene expression analysis in gills as a biomarker for PCB contamination in eels. PCB77 contamination did not affect GAPDH transcription in gills but, at highest doses, resulted in a significant elevation in liver, speaking against GAPDH as a reference housekeeping gene after PCB exposure.
