Excretion of nitrogen and phosphorus by Gambusia holbrooki

Excretion experiments were performed to assess the rates of Nitrogen and Phosphorus excretion by male and female Gambusia holbrooki. The effects of feeding (fed and unfed fish) and time since feeding (0, 4, 8 and 24 hours) on the N and P excretion rates and N:P ratio excreted were also examined. Results showed that N and P excretion rates significantly increased after feeding and declined thereafter for both male and female Gambusia. The P excretion rate decreased more rapidly after feeding than did the N excretion rate, thereby increasing the excreted N: P ratio with time since feeding. Males excreted more N and P in comparison to female son mass specific basis. The high density of Gambusia holbrooki in Lake Nainital is strongly correlated with nitrogen and phosphorus concentrations in the surface water of the Lake Nainital. It was concluded that nutrients excreted by Gambusia could be an important source of nutrients (bottom up control) for the phytoplankton community of Lake Nainital.