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Danish eel researchers set two world records

DENMARK - Danish eel researchers recently succeeded in beating the world record by keeping larvae of the European eel alive for five days. The research team is also the first to repeatedly achieve mass hatchings of this species in the laboratory, reports the Danish Institute for Fisheries Research.

Danish eel researchers set two world records - DENMARK - Danish eel researchers recently succeeded in beating the world record by keeping larvae of the European eel alive for five days. The research team is also the first to repeatedly achieve mass hatchings of this species in the laboratory, reports the Danish Institute for Fisheries Research.

This represents a breakthrough as it has proven extremely difficult to achieve hatching of the European eel in captivity. In the long run, the aim of this project is to make it possible to deliver reared eel fry both to aquaculture and to help the threatened eel stock.

A project led by scientists from the Danish Institute for Fisheries Research has achieved important results in the efforts to get the European eel to reproduce in captivity. At a research laboratory at Lyksvad Eelfarm south of Kolding, Denmark, the researchers have succeeded to repeatedly hatch eel larvae, and on the 7 July, the larvae beat the world record by surviving for 5 days.

In the laboratory tanks, several pregnant eels are ready to spawn more eggs. The scientists hope, of course, that the fertilized eggs from these females will result in more batches of larvae that live even longer. Every additional day and every additional hour contribute valuable knowledge of the European eel because the early life stages of this species have never been found in the wild.

The development from fertilization of eggs to hatching of larvae only takes 48 hours in the laboratory. The newly hatched larvae can move, but quite unusually in comparison to fish larvae in general, their hearts only begin to beat after hatching. In the beginning the larvae have no mouth, but feed on the nutrition they carry from the egg in the so-called yolk sac. We know now that the mouth in the 5-day-old larvae has almost developed to be opened, and the yolk sac is nearly used up. Thus, the next great challenge will be to find suitable feed for the larvae and getting them to eat.

A straight success

The shape of the larvae lends an indication of their well-being. Malnutrition results in crooked larvae, which die soon after. Thus, to assess the growth of the larvae, the scientists often use straight, i.e. non-crooked, larvae as a benchmark for success. The present success is a result of, among other things, an improvement of the hormone therapy applied to the breeding fish to stimulate them to develop and spawn eggs. As another measure, the breeding fish are fed special feed with the purpose of bringing them in the best possible condition before the artificial maturation process starts and they stop eating. This results in eggs, and thus also larvae, of a higher quality. As larvae do not feed in the beginning, the quantity and quality of the feed they carry from the egg is of great importance.

A long time in the making

The previous record of 3.5 days was achieved by Russian scientists in the mid 1980s, when they succeeded in hatching many larvae from a single female, a so-called mass hatching. Since then, several research groups in Europe have attempted in vain to produce larvae of the European eel. Only in 2002-2003, a preliminary Danish study succeeded again to hatch a few larvae, which lead to the present project.

The present project is led by the Danish Institute for Fisheries Research (DIFRES) in close collaboration with the Danish aquaculture industry and receives support from the FIFG programme under the Danish Ministry of Food, Agriculture and Fisheries. The project group have expertise within many fields and include scientists from DIFRES, The Royal Veterinary and Agricultural University, Billund Aquakultur Service, The Danish Association of Eel Producers and Dana Feed.

Live aid to eel stocks in aquaculture and in nature

The recent results give renewed hope that European eel sometime in the future can be produced to both the aquaculture industry as well as stocking, which hopefully will ease the pressure on the European eel in nature.

The European eel is a particularly endangered fish species. Through many years, the eel stock has been drastically reduced, and the International Council for the Exploration of the Sea (ICES) several years ago declared the eel outside safe biological limits. The EU Commission is currently working on a framework programme to develop national action programmes for reducing fisheries on eel at all life stages.

Mr. Jacob Bregnballe, president of the Danish Aquaculture Organisation says: The Danish eel researchers are producing very exciting results these days. I am happy that this research project has continued to produce results. The day is approaching when we are able to breed elvers for aquaculture and, hopefully, also give a helping hand to the European eel through restocking in nature.

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