Simulated migration of European eel (Anguilla anguilla, Linnaeus 1758)

The European eel ( Anguilla<span class=GramE>anguilla</span> L.) is a catadromic fish species with its spawning grounds thousands of kilometers away in the ocean, possibly the<st1:place w:st="on">Sargasso Sea</st1:place>. The objective of this study was to elucidate this oceanic phase of migration for the European eel (<st1:place w:st="on">Anguilla</st1:place><span class=GramE>anguilla</span> L.) in the laboratory.<o:p></o:p></span>This thesis focuses on several aspects of the life cycle of the European eel:<o:p></o:p></span>A)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt'>Preparation to migration, B)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt'>Simulated migration,<o:p></o:p></span><p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l1 level1 lfo2; tab-stops:list 36.0pt'><![if !supportLists]><span lang=EN-US style='font-size: 12.0pt;mso-bidi-font-size:10.0pt'><span style='mso-list:Ignore'>C)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt'>Effect of environmental factors (viruses and PCB's) on the migration,<o:p></o:p></span><p class=MsoNormal style='margin-left:36.0pt;text-indent:-18.0pt;mso-list:l1 level1 lfo2; tab-stops:list 36.0pt'><![if !supportLists]><span lang=EN-US style='font-size: 12.0pt;mso-bidi-font-size:10.0pt'><span style='mso-list:Ignore'>D)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-US style='font-size:12.0pt;mso-bidi-font-size:10.0pt'>Effect of swimming on maturation.<o:p></o:p></span>In order to investigate this we simulated the migration of spawners in the laboratory by building 22 large swim tunnels of 127 liter specially developed for long term migration. Therefore the title of this thesis is: 'Simulated migration of European eel' . What matters is how much energy is required for the crossing of the Atlantic Ocean. An eel uses only 58 g fat/kg fish while a salmon uses 300 g fat/kg. The energy<span class=GramE>cost of transportation (COT) are</span>4-6 times lower for eels than for salmonids. The second aims of the investigations were to study environmental factors that may have impact on the migration capacity like viruses and pollutants (PCB's). The third aims of the investigations were to test whether endurance swimming induces sexual maturation and development of the gonads.<o:p></o:p></span>We can conclude that European eels are very efficient swimmers and that healthy well fed eels are able to reach the<st1:place w:st="on">Sargasso Sea</st1:place>leaving enough reserves for the reproduction. Endurance swimming of eels and the ability to migrate are negatively influenced by infections with viruses like EVEX. Also PCB's which are released from depleted lipid stores after migration may interfere with energy use and metabolism.<o:p></o:p></span>So, although we have found several habitat factors that may interfere with fitness and endurance swimming such as viruses and toxicants (PCBs) which could be a contributing factor to declining eel populations we found two positive results which in future studies may be of importance for reproduction of eels under artificial conditions. <strong>a)</strong> First, we found strong evidence that swimming triggers silvering and early maturation, <strong>b)</strong> Second, we observed for the first time in hormone treated eels that group spawning was collective and simultaneous