The European eel (Anguilla anguilla, Linnaeus), its lifecycle, evolution and reproduction: a literature review

The European eel (Anguilla anguilla Linnaeus 1758) is a species typical for waters of Western Europe. Thanks to early expeditions on the Atlantic Ocean by the Danish biologist Johannes Schmidt who found small (<10mm) leptocephali larvae in the Sargasso Sea about 100 years ago, we have now a strong indication where the spawning site for this species is located. The American eel (Anguilla rostrata, LeSueur) also spawns in the Sargasso Sea. The spawning time and location of both species have been supported and refined in recent analyses of the available historical data. Subsequent ichthyoplankton surveys conducted by McCleave (USA) and Tesch (Germany) in the 1980s indicated an increase in the number of leptocephali <10 mm , confirming and refining the Sargasso Sea theory of Johannes Schmidt. Distinctions between the European and American eel are based on morphological characteristics (number of vertebrae) as well as molecular markers (allozymes, mitochondrial DNA and anonymous genomic-DNA. Although recognised as two distinct species, it remains unclear which mechanisms play a role in species separation during larval drift, and what orientation mechanism eels use during migration in the open sea. The current status of knowledge on these issues will be presented. The hypothesis that all European eel migrate to the Sargasso Sea for reproduction and comprise a single randomly mating population, the so called panmixia theory, was until recently broadly accepted. However, based on field observations, morphological parameters and molecular studies there are some indications that Schmidt's claim of complete homogeneity of the European eel population and a unique spawning location may be an overstatement. Recent molecular work on European eel indicated a genetic mosaic consisting of several isolated groups, leading to a rejection of the panmixia theory. Nevertheless, the latest extensive genetic survey indicated that the geographical component of genetic structure lacked temporal stability, emphasising the need for temporal replication in the study of highly vagile marine species. Induced spawning of hormone treated eels in the aquarium was collective and simultaneous. In this work for the first time group spawning behaviour has ever been observed and recorded in eels. Studies in swim-tunnels indicate that eels can swim four to six times more efficiently than non-anguilliform fish such as trout. After a laboratory swim trial of eels over 5,500 km, the body composition did not change and fat, protein and carbohydrate were used in the same proportion. This study demonstrated for the first time that European eel are physiologically able of reaching the Sargasso Sea without feeding. Based on catches of newly hatched larvae, temperature preference tests and telemetry tracking of mature hormone treated animals, it can be hypothesised that spawning in the Sargasso Sea is collective and simultaneous, while presumably taking place in the upper 200 m of the ocean. Successful satellite tracking of longfin female eels in New Zealand has been performed to monitor migration pathways. Implementation of this new technology is possible in this species because it is three times larger than the European eel. In the future, miniaturisation of tagging technology may allow European eels to be tracked in time by satellite. The most interesting potential contribution of telemetry tracking of silver eels is additional knowledge about migration routes, rates, and depths. In combination with catches of larvae in the Sargasso Sea, it may elucidate the precise spawning locations of different eel species or groups. Only then, we will be able to define sustainable management issues by integrating this novel knowledge into spawners escapement and juvenile fishing quota

The comparison of lipid profiling in mouse brain and liver after starvation and a high-fat diet : A medical systems biology approach

We investigated with LC-MS techniques, measuring approximately 109 lipid compounds, in mouse brain and liver tissue after 48 hours of starvation and a High-Fat Diet if brain and liver lipid composition changed. We measured Cholesterolesters (ChE), Lysophosphatidyl-cholines (LPC), Phosphatidylcholine (PC), Sphingomyelin (SPM) and Triacylglycerols (TG's) for liver tissue while for brain tissue we had an extra lipid compound the Plasmalogens. In addition, dynamics of hepatic steatosis were determined in an in vivo mouse model with localized non-invasive Magnetic Resonance Spectroscopy (1H-MRS) techniques. In the experimental design Male C57bl6 mice (age 8-12 weeks) were exposed to three treatments: A: They were fed a chow Diet for a period of approximately 40 days (Control group); B: They were fed a High-Fat Diet, containing 0.25% cholesterol (Ch) and 24% energy from bovine lard for a period of approximately 40 days, C: Or they were exposed to 48 hours of starvation. For whole brain tissue of these mice groups the LC-MS techniques indicated that the brain was rather invulnerable to Dietary intervention. The (phospho-) lipid-composition of the brain was unchanged in the starvation group but the cholesterol-ester content was significantly increased in the high High-Fat Diet group. These observations suggest that the brain lipid composition is insensitive to starvation but can be affected by a high High-Fat Diet. In contrast, for liver tissue both 24 h starvation and the 40 day High-Fat Diet resulted in exponential hepatic fat accumulation, although their time course (measured with 1H MRS) techniques was distinctly different. Mass spectrometry (LC-MS) demonstrated for liver tissue remarkable differences in lipid profiles between treatments. 1H-MRS proved to be a reliable method for frequent, repetitive determination of hepatic fat in vivo and a noninvasive alternative to biopsy. Moreover, LC-MS and Principal Component Analysis (PCA) demonstrated that in liver tissue different lipid end products are formed as result of Dietary composition Apparently, for liver tissue starvation and a High-Fat Diet result in a process called hepatic steatosis which is regulated under both conditions via different metabolic pathways. In addition, 1H-MRS techniques demonstrated for liver that the relative amount of unsaturated bindings is significantly higher in the High-Fat Diet group (P≤0.001), which can be deducted from the relative intensities of the (CH=CH) elements and their conjugated unsaturated elements (C-CCH2C=C). We conclude, comparing brain vs. liver tissue that both tissues have a totally different metabolic response to both treatments. The brain is insensitive to starvation but can be affected by a High-Fat Diet while in liver tissue both treatments result paradoxically in a hepatic steatosis. However, for the liver, the dynamics and the lipid profiles of this process of this hepatic steatosis under starvation or a High-Fat Diet are totally different.</p