Atlantic cod is a prime species for Norwegian aquaculture, with tremendous potential in food security, new job creation and economic growth. Within the last few years, an increasing number of farmers are interested in cod aquaculture but critical knowledge gaps in its biology (including reproduction) threaten its success. Wild cod become sexually mature from 3 years onwards, whereas their farmed counterparts reach puberty within the first 2 years of age, just before attaining the market size of 2 to 4 Kg. Puberty initiates a shift of energy reserves towards the maturation of the gonads (eggs and sperm), which has a negative effect on growth, fillet quality and post-spawning mortality. This limits the profitability of the industry and has been partly responsible for the collapse of cod farming in the past. Moreover, precocious maturation has a negative impact on the environment, since sexually mature farmed cod can reproduce in sea cages and release fertilized eggs in the sea. As the farms are located within fjords along the Norwegian coastline, “gene pollution” is unavoidable and represents a major threat for wild fish stocks. Our goal is to understand the biological mechanisms responsible for the early initiation of puberty in farmed Atlantic cod and identify key markers that control it. To achieve this, we will screen specific cells in two main glands responsible for light sensing (pineal) and hormonal regulation (pituitary) using state-of-the-art genetic, epigenetic and transcriptomic approaches. In the long term, the biological markers that we will discover may be used to select fish for delayed puberty, thus minimizing gene pollution, preventing mortalities and losses in body mass and fillet quality.
Aquaculture is one of the most important and international industries in Norway, however, major challenges such as climate change, food security, market and resource fluctuations threaten its future. The diversification of cultured species in aquaculture is one of the most promising solutions to these challenges. Atlantic cod is a prime species with proven economic potential. Its successful domestication is a strategic resource of food security, however, several aspects of its biology are still unknown including the early onset of puberty under farmed conditions. Although the onset of puberty in cod is largely controlled with photoperiod manipulation, in large-scale production of the species in sea cages the application of light-stimulation is limited, thus puberty is controlled to some extent. This phenomenon has a major impact both on the environment and the wild cod populations that share habitats with farms (reproduction of farmed animals in sea cages) and on the growth, fillet quality and post-spawning mortalities of the farmed animals due to the shift of energy reserves towards gonadal development.
Because puberty is largely affected by external stimuli, we hypothesize that epigenetic mechanisms are largely responsible for the control of this mechanism. We will perform a photoperiod manipulation experiment, and investigate cell-specific epigenetic signals and gene expression from the pineal and pituitary gland of fish under normal (12L:12D) and continuous (24L:0D) light. We will focus on cell populations such as the gonadotropes that are responsible for the secretion of puberty-promoting hormones. To capture the bigger picture, we will profile the Pituitary-Liver-Gonad axis for tissue-specific DNA methylation and gene expression changes and combine it with interdisciplinary methods such as the biochemical analysis of the liver. Validation of these markers will be performed in multiple cod families and the interspecies applicability will be tested in sea bass.