Low water pH is an ionoregulatory challenge to freshwater teleosts. Larval zebrafish (Danio rerio) exposed to pH 4 water experience increased loss of Na⁺ and respond with increases in ionocyte abundance and whole-body concentrations of cortisol. Because cortisol plays a role in regulating early development, particularly of the stress axis, the present study asked whether the increase in cortisol in embryos exposed to pH 4 water causes dysregulation of the stress axis in later life. Baseline whole-body cortisol levels measured at 4, 6, and 15 days post-fertilization (dpf) did not differ between pH 4-exposed and control fish. At 6 dpf, pH 4-exposed fish had higher concentrations of cortisol compared to control fish following a stressor, but no difference was detected at 15 dpf. In addition, transcript abundances for key genes of the stress axis did not differ between control and pH 4-exposed fish. Based on these results, exposure to pH 4 water in early life does not influence the stress axis or cortisol responses later in life.
Increases in ionocyte abundance in response to low pH have the potential to alter gill morphology, thereby impairing gas transfer, a trade-off known as the osmorespiratory compromise. The present study tested the hypothesis that zebrafish reared in pH 4 water have reduced gas transfer capacity in accordance with the osmorespiratory compromise. Indicators of gas transfer and ionoregulation were measured at 6, 15, 30 and 90 dpf. Across all ages examined, fish reared in pH 4 water had significantly higher whole-body concentrations of Na⁺, higher ionocyte abundances and thicker gills than control fish. These differences were accompanied by higher ventilation frequencies and higher critical PO₂ (Pcrit) values. Additionally, adult fish raised in low pH had a significantly higher rate of oxygen consumption compared to control fish. These results support the hypothesis that development in water of low pH impairs gas transfer, as predicted by the osmorespiratory compromise.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/42087 |
| Date | 05 May 2021 |
| Creators | Tigert, Liam |
| Contributors | Gilmour, Kathleen |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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