Search

Anguillid eels were once considered to be the classic example of catadromy. However, alternative life cycles have been reported, including skipping the freshwater phase and habitat shifting between fresh, brackish, and saltwater throughout the growth phase. There is a lack of knowledge regarding these alternate life strategies, for example, the proportion of individuals in the population that adopt them compared to classic catadromy. We provide a description of these alternate life cycle strategies in temperate anguillids, their possible drivers, and the methods available to investigate them. These methods (lethal and non-lethal), include otolith microchemistry, fatty acid and stable isotope analyses, parasite identification, blood transcriptomics, and electronic tags. We argue that since the current management framework for the European eel and other temperate eels is based mainly on the freshwater component of the population, it ignores eels growing in saline waters. Many of the factors that are thought to be responsible for the precipitous decline of the eel population are more prevalent in freshwater systems. Therefore, the contribution of saline eels may be more important than currently estimated. The habitat-shifting ability of eels may be all the more crucial for the persistence and recovery of those species that are endangered. [ABSTRACT FROM AUTHOR]

Worldwide, populations of catadromous eels are in decline. Knowledge on downstream migration patterns is needed to mitigate damage caused by hydroelectric stations. Silver eel migration and its relation with environmental factors were investigated using data from a fishery located in the lower reaches of a large catchment (110 000 m2). Migration days, indicative of different proportions (50%, 75% and 95%) of the annual run of eels (i.e. represented by the annual catch), were predicted using discriminant analyses. Efficiency of prediction was 58–95% depending on the proportion of the run targeted. The onset of migration was correlated with sunshine hours, August temperature and discharge. Julian days (i.e. photoperiod) was significantly correlated with migration days, indicating between-year similarity in the dynamics of the runs. The size of migrants varied within the migration season, reflecting differences in their initial spatial distribution. [ABSTRACT FROM AUTHOR]

The identification of five stages for female and two stages for male eelsAnguilla anguillausing multivariate analysis was carried out on a large sample of individuals collected at six different locations in France. Stages corresponded to a growth phase(stages I and II), a pre-migrant phase(III) and two migrating phases(IV and V). It is likely that an important period of growth triggered silvering through the production of growth hormone(GH) in stage III eels. In migrating eels gonad development, gonadotropin hormone(GTH-II) production and increase of eye surface were similar at all sites. Differences among locations were found in gut regression and pectoral fin length. As variability for these increased with the size of the watershed and values were highest for the most downstream locations, fin length and gut regression may indicate the time since an eel started its migration. [ABSTRACT FROM AUTHOR]

A simple approach is proposed to fit a body growth model for the European eel Anguilla anguilla to data-poor case studies. The model is a modified von Bertalanffy curve allowing for delayed sex determination and sexual dimorphism. The proposed procedure provides preliminary estimates of model parameters on the basis of average age and body length of silver eels. [ABSTRACT FROM AUTHOR]

Several dinoflagellate species in the genus Blastodinium are gut parasites of marine planktonic copepods. However, there is only limited information on the occurrence and infection frequencies of Blastodinium spp. in the field and almost no information on the functional impact on their hosts. We report upon the effects of Blastodinium sp. infection on Calanus finmarchicus from the northeastern Atlantic coast off southern Norway during April 2013 and 2014. Up to 58% of C. finmarchicus were infected near the coast, while <5% were infected several kilometers offshore. Ingestion rates of infected females were below detection limits and significantly lower than uninfected females. Blastodinium sp.-infected females showed characteristic symptoms of starvation, including lower respiration rates (implying a lower metabolic rate), production of smaller and fewer fecal pellets and significantly fewer eggs than uninfected females. A few females in this study were able to void the infection, however the extended period of starvation is likely to have longer-term repercussions on egg production rates well after the copepod clears the infection. The degree to which the infection affects C. finmarchicus recruitment depends on the extent of the spatial distribution of the infection. Monitoring of parasitic infection during routine field surveys will be required in order to clarify this. [ABSTRACT FROM PUBLISHER]

Kinematics of swimming behavior of larval Atlantic cod, aged 12 and 27 days post-hatch (dph) and cultured under three pCO conditions (control-370, medium-1800, and high-4200 μatm) from March to May 2010, were extracted from swim path recordings obtained using silhouette video photography. The swim paths were analyzed for swim duration, distance and speed, stop duration, and horizontal and vertical turn angles to determine whether elevated seawater pCO-at beyond near-future ocean acidification levels-affects the swimming kinematics of Atlantic cod larvae. There were no significant differences in most of the variables tested: the swimming kinematics of Atlantic cod larvae at 12 and 27 dph were highly resilient to extremely elevated pCO levels. Nonetheless, cod larvae cultured at the highest pCO concentration displayed vertical turn angles that were more restricted (median turn angle, 15°) than larvae in the control (19°) and medium (19°) treatments at 12 dph (but not at 27 dph). Significant reduction in the stop duration of cod larvae from the high treatment (median stop duration, 0.28 s) was also observed compared to the larvae from the control group (0.32 s) at 27 dph (but not at 12 dph). The functional and ecological significance of these subtle differences are unclear and, therefore, require further investigation in order to determine whether they are ecologically relevant or spurious. [ABSTRACT FROM AUTHOR]