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Estimation of the reproduction capacity of European eel. (Enhancing the biological basis for sustainable fisheries and aquaculture)


The ultimate goal of the project is to stop the decline of the European eel population. For this purpose we need to understand the underlying cause of the decline. In this project we will determine the reproduction capacity of silver eels from different locations and the impact of diseases on their physical fitness. Furthermore we aim to provide management tools allowing the formulation of reliable decisions for eel ecosystems and eel fisheries management. For this we will estimate the capacity of yellow eel to transform into the downstream migratory silver eel ('silvering'). Finally we aim to provide fundamental knowledge on the reproduction process, which is likely to be critical for the recruitment of the species. This knowledge might be used in future studies to develop a procedure for artificial reproduction.

Specific Objectives
1) The capacity of the silver eel to swim to the spawning grounds will be studied. To that end they need to have an impressive endurance, and the capacity to navigate at 50-200 atm water pressure. Current knowledge suggests that pressure is an important factor because its disturbing effects on biophysical and biochemical processes (10, 39). Previous experiments have shown that the first hours under pressure constitute a critical period during which the mortality could be high (40). This mortality is related to the fish's fitness. However, pressure has also been suggested as stimulus for maturation (10). The relation between swimming fitness and infection will be determined as well as the relation between pressure tolerance and infection.
2) Fundamental knowledge will be developed that can be used to estimate the silvering capacity. So far, little is known about morphological and physiological changes coupled to the transition from yellow to silver eel stage. Basic knowledge on silvering is especially required since the ability for eels to undergo sexual maturation depends on how advanced they are in the silvering process. Particularly, the succession of events and changes in hormonal patterns must be investigated in order to understand the factors that trigger the metamorphosis. Analysis of the various morphological and physiological parameters will lead to the establishment of a silvering index. This will allow for formulation of reliable decisions for eel ecosystems and eel fisheries management
3) Fundamental knowledge on the maturation process will be developed. Silver eels are still in a prepubertal stage, the gonad development being heavily depressed which is likely related to the 6000 km they have to swim before reaching the spawning sites. The role of hormonal and metabolic factors in the regulation of silvering and sexual maturation processes will be investigated. This may result in development of selection criteria for stimulated maturation, and of new procedures for inducing sexual maturation either by long-term swimming/pressure, or by hormonal treatments.

Call for proposal

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University of Leiden
Kaiserstraat 63
2300 RA Leiden

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EU contribution
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Participants (7)