“The TOPPFORSK grant has been crucial to my career,” says Finn-Arne Weltzien. (Photo: Torkil Marsdal Hanssen) For four years, Finn-Arne Weltzien has been heading an international group of researchers studying the fundamental mechanisms that regulate sexual maturation in fish. The group has focused mainly on the interactions between the brain and the hormone-producing pituitary gland.

New discovery

“We have concentrated our efforts on determining what regulates the production of two important hormones related to reproduction,” says Dr Weltzien, “namely follicle-stimulating hormone (FSH) and luteinising hormone (LH). These are synthesised in the pituitary gland, and they regulate maturation of the testicles and ovaries. They are secreted in varying amounts and at different times, but little was known about this process.”

“Thanks to the use of advanced techniques, we have come closer to answering this question,” states Dr Weltzien.

The research project addresses challenges related to early sexual maturation in production fish, particularly cod, and to egg quality and irregularities in full maturation and spawning among broodstock fish.

“A number of attempts have been made to delay early sexual maturation – such as light manipulation and the production of sterile fish – but there is still no method that succeeds 100 per cent,” explains Dr Weltzien.

“We have spent a long time establishing methods that enable us to study individual cells that produce FSH or LH. These methods help us to study changes in gene expression and intracellular signalling under various conditions, so we can evaluate precisely how a given treatment will affect the production of key hormones involved in sexual maturation. Although the project is not yet completed, our results show that these two hormones are regulated differently than previously thought.”

“We have also demonstrated entirely new functions of LH,” continues Dr Weltzien. “It turns out that LH has an early-stage function in the gut, which had never been shown before. It is still too soon to understand the implications of this for early maturation, gut function or possibly reproduction. But the finding demonstrates the complexity of sexual maturation and reproduction in fish, and highlights the need for more basic knowledge in this field.”

“The basic insight we gain may make it easier to design well-functioning production regimes for farmed cod,” says Dr Weltzien. (Photo: Seafood.no)

Basic research needed

Dr Weltzien believes the basic knowledge generated by this type of research will benefit the aquaculture industry by providing a stronger platform for further development – even though in the short term, basic research may seem less relevant than industry-initiated projects.

“The studies we have carried out won’t result in a clear-cut prescription for delaying sexual maturation in cod,” says Dr Weltzien. “Before that can happen, we need to understand the underlying mechanisms in order to develop sound solutions while avoiding side effects. The basic insight we gain may make it easier to design well-functioning production regimes for feed composition and light regulation, for example.”

He hopes to obtain funding to carry on with this research, in order to test out the effects of various production regimes on FSH and LH secretion, among other things.

“We are seeking to collaborate with an aquaculture industry player,” continues Dr Weltzien. “The Norwegian School of Veterinary Science does not have the facilities to conduct the kind of large-scale study needed to develop optimal solutions.”

Commonalities between cod and ricefish

The project’s international collaboration has allowed the researchers to control and compare the Norwegian findings for cod with the Japanese ricefish medaka.

“Cod is an important production species in Norway, while medaka is a well-described species used a great deal in research. There are also a much larger number of methodological tools and possibilities for studying medaka. By comparing these two species,” concludes Dr Weltzien, “we can generate more general knowledge about puberty and reproduction in fish in general.”

Researchers are comparing cod with medaka, a small Japanese ricefish, to cultivate general knowledge about fish puberty and reproduction. (Photo: Guro K. Sandvik)