College of Science and Health Theses and Dissertations

Date of Award

Summer 8-20-2023

Degree Type


Degree Name

Master of Science (MS)



First Advisor

Jason Bystriansky, PhD

Second Advisor

Caleb McMahan, PhD

Third Advisor

Windsor Aguirre, PhD


The swordtail, Xiphophorus hellerii, is a freshwater fish species native to Mexico and Central America and is commonly used in the tropical aquarium trade. Swordtails have been shown to have limited survival in 6 ‰ salinity (Nanda et al., 2016), suggesting they may have a greater salinity tolerance than previously expected. Using a gradual acclimation method, we examined the salinity tolerance and swim performance of this species. Freshwater-reared female swordtails were housed in 29-gallon aquaria. A control group was held in freshwater throughout the experiment. For the experimental group, the salinity was increased by 2 ‰ every week until 30 ‰. Critical swimming speed (Ucrit) was determined repeatedly for each individual fish (every second week) for both control and salinity acclimated (at 0, 4, 8, 12, 16, and 28 ‰) fish to assess the impact of increased salinity on swimming performance. The critical swimming speed was stable throughout the study for the control group. An initial increase in swim performance was seen at 4 ‰ salinity from the beginning of the experiment but then decreased to control levels by 8 ‰ and was not different from control rates for the remainder of the experiment. Gill Na+/K-—ATPase (NKA) activity was measured at the end of the experiment. There was a 64% increase in NKA activity for the experimental group over the control. Based on these results, swordtails can tolerate much higher salinity than originally thought, with minimal impact on their swimming performance and are able to increase their NKA activity to adapt to the higher salinity environment.

SLP Collection


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Biology Commons