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Institute of Marine Research, Austevoll Research Station, N-5392 Storebø, Norway ¹ Institute of Marine Research,, N-5817 Bergen, Norway ² Department of Biosciences,, Teikyo University of Science and Technology, Uenohara, Japan ³ Laboratory of Reproductive Biology,, National Institute for Basic Biology, 444-8585 Okazaki, Japan

(Correspondence should be addressed to C Mittelholzer who is now at University of Basel, Klingelbergstrasse 60, CH-4056 Basel, Switzerland; Email: christian.mittelholzer{at}unibas.ch)

^* D Consten is now at St Elisabeth Hospital, PO Box 90151, 5000 LC Tilburg, The Netherlands

In order to better quantify the molecular mechanisms regulating final oocyte maturation and spawning, complete coding sequences with partially or fully untranslated regions for the steroidogenic enzymes, cytochrome P450 aromatase and 20ß-hydroxysteroid dehydrogenase, were cloned from ovaries of Atlantic cod (Gadus morhua). The nucleotide and amino acid sequences showed high homologies with the corresponding sequences of other fish species, and conserved features important for functionality were identified in both predicted proteins. The sequences of the corresponding genomic loci were also determined, allowing the design of mRNA-specific quantitative PCR assays. As a reference gene for the real-time RT-PCR assays, eukaryotic elongation factor 1 was chosen, and the mRNA as well as the genomic sequence was determined. In addition, a real-time quantitative PCR assay for the 18S rRNA was adapted to be used in cod. Analysis of immature and maturing female cod from July to January respectively showed that the enzyme genes showed the expected quantitative changes associated with physiological regulation. However, mRNA for eukaryotic elongation factor 1, and to a lesser extent even 18S rRNA, showed variable expression in these samples as well. To find accurate standards for real-time PCR in such a dynamic organ as the cod ovary is not an easy task, and several possible solutions are discussed.