Student Research Projects

Nutrient Excretion in Sexually Dimorphic Fish

Student Lisa Murray ‘14
Faculty Mentor(s)
Department Biology
Course Biology 489: Research Methods in the Natural Sciences


Previous research on nutrient cycling by fishes has examined factors such as mass, temperature, and diet, which can have important effects on nutrient excretion. However, no previous study has examined the effect of sex on nutrient excretion, even though sex can have large impacts on fish size and reproductive investment. This study was undertaken to determine whether the sex of a fish impacts the excretion of nitrogen and phosphorus in Betta splendens and Poecilia reticulata. It was hypothesized that nutrient excretion would be significantly impacted by both mass and sex. We conducted direct nutrient excretion measures by examining changes in N and P concentrations over a 4-hour period. We detected no significant differences in excretion rates of males and in females for B. splendens or P. reticulata. Ammonia nitrogen excretion was significantly higher in the fed fish treatment of B. splendens, compared to the unfed treatment. In both species, we detected no significant effect of mass, likely because we restricted our measures to adult fish of similar size. Our results indicate that sex is likely not important to nutrient cycling rates. Feeding history can have an important impact on excretion rates, especially for nitrogen.