Léopold Ghinter, Christophe Lebigre, Karine Salin
National
ISblue
Start Date
14/09/2026
End Date
14/09/2026
Coastal nursery areas are essential habitats for the development of young fish, but they are also highly variable. Temperature, salinity, oxygen levels and even tidal conditions can change rapidly over the course of a single day. To understand what this variability actually means for a fish, the RESPI project focused on a common ‘currency’ for all its biological functions: energy.
Using the European sea bass (Dicentrarchus labrax) as a model species, RESPI has developed approaches to study the metabolism of wild juveniles at several levels, ranging from the whole animal’s oxygen consumption to the functioning of its mitochondria, which are responsible for the bulk of ATP production. This ambition was already at the heart of the project: to develop physiological indicators applicable to the study and management of fish species directly within their nursery habitats.
One of the project’s initial innovations was to take respirometry out of the laboratory. Autonomous systems sourced from Canada (in collaboration with David Deslauriers and Frédérick Bélanger of ISMER-UQAR) made it possible to monitor the metabolism of juveniles directly in their natural environment, whilst recording the environmental variations to which they were exposed. Ongoing analyses show that their energy expenditure does not depend solely on any single environmental condition in isolation: it appears to be closely linked to environmental dynamics, imposing a physiological cost on the fish associated with maintaining their functions in a constantly changing environment.
RESPI has also investigated what happens at the very heart of the cells. In wild juveniles caught in the Ria du Conquet, mitochondrial performance in the heart and liver was measured in the same individuals at temperatures ranging from 12 to 32 °C, enabling the reconstruction of various thermal performance curves.
These experiments reveal that a mitochondrion that continues to consume oxygen does not necessarily produce more energy. In the heart, ATP production peaks at around 28 °C, then decreases whilst mitochondrial respiration remains high. Conversely, in the liver, ATP production continues to increase across the entire range of temperatures studied. This difference shows that the response to temperature depends heavily on the biological function under study and the organ in question.
Furthermore, not all fish are the same. The juveniles studied exhibit significant individual differences in their mitochondrial respiratory capacity, whilst their coupling efficiency and certain characteristics of their thermal curves appear to be much more conserved.
Taken together, these results show that the quality of a habitat cannot be summarised by its average conditions alone, nor can a fish’s performance be determined by a single metabolic measure. It depends both on the variability of the environment, the energy expenditure required to cope with it, and the organisms’ ability to efficiently convert this expenditure into usable energy.
By bringing together cellular physiology, whole-animal metabolism and the natural environment, RESPI is thus contributing to the development of new indicators that enable a better understanding of the true cost of life in a hatchery — and paves the way directly for the NURSFISH project.
Laboratory Members
Contributors
Christophe Lebigre (Ifremer-DECOD)
Pierre Blier (UQAR, Québec-CANADA)
David Deslauriers (UQAR-ISMER, Québec, CANADA)
Damien Roussel (LEHNA, Lyon, FRANCE)
