I have this data set that contains information on the group (control or treatment) and the initial weight and final weight of the test subjects (fish). And I want to compare the effect of treatment on fish's weight gain. However, this data set is not paired; there is no identification and it's just a list of observed weight. I am planning to use mixed anova to analyse this, but mixed anova assumes the observations are paired.
Since all the fish did gain weight, is it ok for me to just pair up the data based on the observation order? Or should I assume that there are four groups (control fish weight before, control fish weight after, treatment fish weight before, and treatment fish weight after) and just run a regular anova test on the four groups.