Transgenerational epigenetic inheritance of hypoxia tolerance in Zebrafish: a morphological and physiological approach

The epigenetic transfer of phenotypes from parental generations (P0) to subsequent generations provides important insights into biological processes including development, disease susceptibility, and evolutionary adaptations. We studied the transgenerational epigenetic inheritance of hypoxia tolerance in backcrossed NHGRI-1 zebrafish from a P0 to three subsequent generations (F1 to F3). We hypothesized that the hypoxia-tolerant phenotype in the P0 would ‘wash out’ across generations. To test our hypothesis, the P0 was exposed to control oxygen conditions (PO 2 ~21 kPa), moderate hypoxia (PO 2 ~12 kPa), or severe hypoxia (PO 2 ~9 kPa) for three weeks. After exposure, fish were bred and the offspring (F1) was raised in normoxia to adulthood to produce the F2, and then the F3 under the same protocol. The offspring of each generation was tested for morphological changes (body mass, fork length), hypoxia tolerance (as time to loss of equilibrium; TLoE), oxygen consumption (ṀO 2 ), and cardiac function (heart rate, stroke volume, cardiac output) at 7 days post-fertilization. Juveniles from each generation (8 weeks) were tested for changes in mass, length, TLoE, and ṀO 2 , and adult fish (16 weeks) were also tested for condition factor. Hypoxia tolerance was significantly higher (2- to 3-fold) in adult females compared to males from all generations. TLoE gradually decreased (from ~5.5 min to ~2 min) in subsequent generations of moderate and severe hypoxia-exposed P0s. Interestingly, significant differences were more evident in larval fish compared to the subsequent juveniles and adults. Offspring from P0 exposed to either level of hypoxia were smaller in both mass (~650 mg) and length (~32 mm) in the F1 and F2, but by the F3 values were returning to those of the controls (~90 mg and ~40 mm), especially in the moderate-hypoxia offspring. Cardiac output as the final product of cardiac function was elevated in larval fish from the F1 and F2 in the moderate-hypoxia offspring (~55 nL/min), but values were closer to the controls in the F3 (~30 nL/min). In the severe-hypoxia offspring, cardiac output was still higher in F3 fish compared to controls (~38 vs ~30 nL/min), but lower than in previous generations. Collectively, these data suggest the hypothesized ‘wash out’ of morphological and physiological traits related to hypoxia-induced phenotypes across generations. This wash out was dependent on oxygen level with a PO 2 of ~9 kPa leading to more pronounced long-term changes in developmental trajectories compared to a PO 2 of ~12 kPa. Importantly, we also demonstrated how morphological and physiological responses to hypoxia differ significantly between sexes across multiple generations. Future studies will continue to investigate the epigenetic inheritance effect of hypoxia tolerance and associated molecular mechanisms. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.