Intrinsic capacity evolution during aging in mouse and fish: Longitudinal perspectives from a narrative review

Intrinsic capacity (IC) is a crucial determinant of healthy aging, operationalized through five essential functional domains -- locomotion, cognition, vitality, psychological, and sensory capacities. Integrating geroscience principles with IC assessment in preclinical models with accelerated aging profiles can support bidirectional translation. This narrative review aimed to summarize measurement approaches for each IC domain and to show how IC evolves longitudinally in mouse and fish models. A literature search in PubMed, Embase and Web of Science databases yielded twenty-seven studies in the mouse models and five studies in the fish models. Studies suggested that locomotor capacity, measured via voluntary activity and rotarod, showed initial impairment in middle age followed by progressive decline, especially in female mice. In contrast, impairments in locomotor activity in killifish emerged predominantly in the last third of life. For sensory function, behavioral and electrophysiological metrics revealed hearing loss and reduced visual acuity as early as midlife in mice. Vitality declines in mice, assessed by grip strength, tended to occur during old age. Regarding cognitive capacity, working memory measured by T maze may be more sensitive to early deficits in mice, and homebase formation could capture cognitive decline in fish. Lastly, psychological capacity, as reflected by exploratory behavior, showed age-related changes in old mice. In conclusion, the findings of this review provide a basis for elaborating IC changes in mouse and fish models, facilitating mechanistic studies and enhancing the translational value of preclinical models on IC.