mausMasse = { {25.0, 25.4, 25.7, 30.2, 35.1, 37.7}, {21.2, 21.9,
22.4, 25.1, 28.2, 29.8}, {21.3, 21.2, 21.9, 24.1, 26.1, 28.1},
{22.5, 23.2, 23.7, 26.1, 32.3, 34.6}, {24.4, 24.1, 24.9, 27.3,
31.5, 34.7}}; 
bild = ListPlot3D[mausMasse, AxesLabel -> {"Tag","Maus","Masse"},
                  ImageSize->{400,300}];