The Effects of Chronic Nitrite Exposure on Tissue Morphology and Physiology in Xiphophorus couchianus




Hughes, Hannah

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The increase of agriculture production to sustain growing populations is associated to an increase of fertilize-derived nitrogenous compounds in aquatic ecosystems. One of these nitrogenous derivatives, nitrite, has been known to cause physiological and morphological damage in aquatic species in acute, short term, exposures. However, it is unknown how chronic exposure to contemporary water nitrite concentrations can affect fish physiology. Moreover, there is a lack of current knowledge on how nitrite effects maternal health and, consequently, embryo health and development. Therefore, we used the live-bearing fish species Xiphophorus couchianus as a model organism to better understand the effects of chronic nitrite exposure on tissue physiology, morphology and oxidative stress in live-bearing female fish. We hypothesized that chronic nitrite exposure would lead to elevated levels of accumulated nitrite in tissues, altered morphology of tissues, and affect oxidative stress (relating to maternal immunity). Our primary objective was to characterize the effects of exposure to sublethal and common environmental nitrite concentrations on morphology and physiology in pregnant X. couchianus. To test our hypotheses, three exposures were conducted: one acute nitrite exposure (to determine chronic concentrations) and two chronic exposures. Our acute exposure lasted for a period of 48 hours and fish were exposed to two nitrite concentrations (0 mM and 0.44 mM). Our first chronic exposure lasted for 28 days, and fish were exposed to two nitrite concentrations (0 mM and 0.3 mM). Our second exposure exposed fish to contemporary environmental (or sub sublethal) and sublethal concentrations of nitrite for 28 days (0 mM, 0.05 mM, and 0.5 mM). Preliminary results from the acute exposure showed impairment of typical olfactory functioning and morphology. The results from the first chronic exposure (0 and 0.3 mM) showed accumulation of nitrite in tissues and changes to reproductive organs and behavior. Results from the second chronic exposure (0, 0.05, and 0.5 mM) showed significant accumulation of nitrite in tissues, altered morphology of various tissues, and changes in oxidative stress parameters in response to chronic exposure to sublethal nitrite concentrations. Our results showed chronic exposure to sublethal nitrite concentrations causes significant accumulation of nitrite in tissues, alters morphology of tissues, and induces oxidative stress in X. couchianus mothers. We found that gestating mothers undergo structural and functional changes from chronic nitrite exposure. Specifically, that mothers accumulated nitrite in tissues and faced morphological and physiological changes that threatened their health, and potentially, the health of their young. We were unable, however, to draw solid conclusions on how maternal nitrite exposure directly affects embryo health and development due to sample size constraints.



nitrite, Xiphophorus, morphology, physiology, live-bearing


Hughes, H. (2023). The effects of chronic nitrite exposure on tissue morphology and physiology in Xiphophorus couchianus (Unpublished thesis). Texas State University, San Marcos, Texas.


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