Physiological and hormonal changes during prolonged starvation in fish

Abstract

Starvation periods are common for many animals, including fish, birds, and mammals. Many fish species exhibit extraordinary resilience to prolonged starvation, but the reasons for that and the mechanisms employed during these periods are poorly understood. This study shows that similar to mammals and birds, many fish species undergo three phases during starvation: (I) a short transient phase, (II) a long, protein conservation steady state phase with mainly fat oxidation as the primary energy source, and (III) a shift to protein mobilization as a main energy source. These starvation states and their transitions were quantified by a meta-analysis of large empirical data available in the literature, revealing that low critical levels of fat reserves trigger the transition to the third state. The critical fat level, denoted as γ (percentage of total lipid in body mass), ranges between 0.7% and 5%, depending on the species. It appears that these transitions in the energy mobilization phases are regulated by hormonal changes, including growth hormone (GH), leptin, cortisol, and ghrelin, but the exact mechanisms are still unclear and should be further investigated. Simulations in silico of starvation periods at various temperatures using a dynamic model indicated that temperature affects the length of Phase II because of changes in protein metabolism, with consequences on the ability to withstand prolonged starvation.