Objective The European eel shows a sex dimorphism in growth. Females grow larger and thereby reach a better marketable size compared to males. In eel farm the majority of the stock develops into males. From all environmental factors possibly involved in the induction of sex, water temperature may be crucial. It has been considered of great economic importance if sexual differentiation of eel could be controlled in such a way that all female hatchery populations can be obtained. Objectives of the present research proposal: Is sexual differentiation in the European eel a consequence of interaction between environment (temperature) and the genotype? Can sexual differentiation in eel be manipulated in an acceptable way in order to obtain predominantly female hatchery populations ? Purpose: Manipulation of sexual differentiation into female direction by means of a temperature treatment during early development in order to improve eel farm economics. Hormonal treatment has to be rejected as a method for large scale manipulation of sexual differentiation, since this will not easily be accepted by the public, and thus will cause more harm than profit to the fish farming industry. This proposal has mainly applied aspects, in addition to fundamental research objectives. This combination will result in a better understanding of the mechanism underlying the process of sexual differentiation in fish. Experimental approach: The effect of temperature will be investigated in three different glass eel populations originating respectively from Southern, Middle and Northern Europe. All groups will be raised at three temperatures: 18, 21 and 25 C. In order to determine the period of gonadal differentiation and the effect of temperature, at regular time intervals samples will be taken from the experimental stocks for histological examination of the gonads. The genetic sex of all animal will be screened with the H-Y antigen test. Also sex specific DNA will be screened by DNA-hybridization techniques to investigate genetic sex. Several fish DNA-probes are available and will be checked for applicability in the near future. Yellow and silver eel (+2-3 years), originating from the six experimental groups, will be screened, to examine whether the sex ratio remains the same or can still change after the differentiation period has been passed. If the preliminary programme is successful, a long term programme will be focussed on the following subjects : During the period of sexual differentiation samples of gonadal tissue will be screened for sex steroid synthesising capacity. This capacity will be characterized in two ways: enzymecytochemically and by means of in vitro conversion of radioactive labelled steroid hormone precursors. Both techniques are operated by research groups taking part in this project. Attention will be given to the development of the gonadotropin (GTH) secretion in the pituitary, as well as the gonadotropin releasing hormone (GnRH) and dopaminergic neurosecretory systems in the hypothalamus in relation to different temperature regimes. Sex reversed fish will be investigated for their growth performance. Studies on growth not only will include a screening of the growth rates, but also the influence of growth factors. Fields of science agricultural sciencesagriculture, forestry, and fisheriesfisheriesnatural sciencesbiological sciencesgeneticsDNAsocial scienceseconomics and businesseconomicsengineering and technologymaterials engineering Programme(s) FP2-FAR - Community research and coordination programmes (EEC) in the fisheries sector, 1988-1992 Topic(s) Data not available Call for proposal Data not available Funding Scheme Data not available Coordinator Universiteit Wageningen/Landbouw EU contribution No data Address Postbus 338 6700 AH Wageningen Netherlands See on map Total cost No data Participants (2) Sort alphabetically Sort by EU Contribution Expand all Collapse all UNIV LEUVEN (KUL)-ZOOL INST-LAB ECOLOGIE AQUACULTURE Belgium EU contribution No data Address Leuven See on map Total cost No data UNIV UTRECHT-DEPT EXPERIMENTAL ZOOLOGY Netherlands EU contribution No data Address Utrecht See on map Total cost No data
