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Author
Torrents Vives, Carla
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Abstract
Baltic cod (Gadus morhua) is a marine fish species that inhabits at the bottom sea layer of the coastal Baltic Sea. The stock and physical condition of this species has suffered a decreasement in the past decade and many studies have been carried out to investigate the causes and consequences of this phenomenon.
It has been demonstrated that Baltic cod is experiencing a reduced growth rate and an early sexual maturation, and therefore individuals develop and reproduce at a smaller size, which successively leads to further diminishment of the fish’s growth potential. Thus, growth and reproduction are closely related physiological processes which compete with each other in terms of energy allocation and consumption. Here, the analyses of some parameters like the gonadosomatic index or the liver condition (hepatosomatic) index show that fish, in particular the female gender, make a high investment in reproduction, which influences growth due to energy being allocated to gamete development.
The fish reproductive cycle has different and well-differentiated reproductive stages and the expression of different hormones affecting growth and reproduction may vary depending on the stage. In this context, the objective of this study is to analyse the expression of genes involved in growth and reproduction and their receptors in tissue samples representing the hypothalamicpituitary-gonad-liver axis of the endocrine system. The study uses organs from female Baltic cod caught in different developmental stages to investigate whether the gene expression of fishes that are sexually immature differs from those ones that are sexually mature. Also, among the latter it is investigated, if stages in the earliest reproductive development can be distinguished from resting individuals, i.e., regenerating between reproductive seasons. This comparison among stages will make it possible to examine the endocrine regulation of growth and reproductive processes in the cod samples and explore how are these processes interact with each other.
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