Another Round Of Kicking Around Data

This week we've started a new round of analyzing data about telescope shiners and their gill flukes. There's always a large number of ways to look at data, and we've tried several lines of inquiry. One obvious result we found is that female telescope shiners from Hurricane Creek in 2007 were carrying more eggs with larger size. This is hardly groundbreaking, but analyzing the peak reproductive months April through July with a regression of standard length vs. total eggs, the F statistic always gave a statistically significant result. We also did the same statistical analysis for any significant relationship between number of gill flukes and total eggs. These tests were all negative. But there are positive relationships between both standard length and fish body mass vs. gill fluke number. Simply put, longer, heavier female fish tend to have more gill flukes and certainly produce more eggs.

BUT - Andrew has set up tests comparing fish with below average and above average numbers of gill flukes as to the individual fish's percentage of average GSI for the month of capture. For both pooled males and females, and only females, there's a statistically significant (using t-tests) difference between the groups, with less infected fish have relatively higher average GSI. So gill fluke infection is linked to gonadal size and condition, but not to total oocyte count.

Correlation isn't causation, of course, and individual fish are probably affected by other parasite infections such as liver trematodes which we didn't examine. Even so I think we're on to something with Dactylogyrus gill flukes having a negative effect on a host's reproductive capability. The fun part would be to look for a similar effect on scarlet shiners, of which we have almost a good collection. Maybe this semester.