Astyanax mexicanus is an emerging model organism in the field of evolutionary biology. Specifically, it is a prime candidate for numerous developmental and genetic studies including convergent/parallel evolution and metabolic adaptation. This is due to the independently evolving cave and surface morphs that remain interfertile. Unlike other common aquatic model organisms, the surface morph of the Mexican cavefish has a high rate of aggression. This study shows a potential inverse relationship between that aggression and the condition factors for certain age ranges of Astyanax mexicanus.
The length-mass relationship (LMR) and condition factor (K) were characterized for Surface Mexico cavefish (n=752) using a power function (M=aLb) and Fulton's condition factor (K=100*M/L3) respectively. When comparing Fulton's condition factor (K) of Astyanax mexicanus, we found at three to six months old the condition factor (2.2± 0.02) was significantly lower (P< 0.05) than the condition factor at two months (2.4±0.02). This difference was coupled with a spike in aggression related deaths during months three to six (n = 208).
Based on these results, a trial program has been implemented to increase the condition factor of fish post two months of age through a change in the feeding regime. With this change, we expect to see a decrease in aggression rates for fish aged from three to six months old. This is an ongoing study that will continue to be monitored during this new trial period.