Dear Jakub,

You can define as many landmarks (and maybe also semilandmarks for outlines) as you consider reasonable to represent shape. There is no "best selection", but I suggest you make sure that all points have a homologous biological underpinning. For instance, I wonder how you exactly defined points 2 and 13?

Secondly, flexible organisms such as fish come with certain problems, since even small deviations in the way they are oriented may bias the distances between the points. I suggest you make sure that all specimens are equally aligned.

Good luck with your study!

Best regards, Thomas

Dear Thomas thanks for your suggestion. In case of LM placing i used information from the available literary sources. LM 2 represent the highes point on the fish eye and LM 13 the outermost point from the LM 1.

Do you have some technical solution for best alignation of specimens?

Thanks again.

Dear Jakub,

You ask for advise on "best selection on landmarks". However, you do not tell us what your goals are by taking measurements of specimens. Depending on your goals, you select possible landmarks concerning the body shape of the specimens under study. In "common" fish terminology we call the distance between LM1 y LM13 as standard length (SL). I am no sure, like Thomas, about LM2 that according to your answer, would represent the highest point of the fish eye, but what is the importance of the highest point in comparison to the lowest point or the anterior margin of the eye for example? Thus, I suggest that first you clarify what you are looking for concerning the shape of your fishes before you continue further.

It makes a difference whether the fishes are fresh or the fishes are fixed in ethanol or other fixative for certain period of time. It is difficult to have all specimens in a straight position depending in the way that they were fixed. Thus, I suggest that before you start taking measurements you study the quality of your specimens and practice with a few ones, especially those with bent bodies (because of the way they were fixed).

With my best wishes.

Dear Gloria,

Thank you for your practical and exhaustive response again.

Meanwhile, i evaluated our measurments with the R statistical model. And there is the higest variability in measuring of LMs 2 and 13. Thats mean that there is not a clear physiological base for this points. But the SL could be partially explained by the LMs 11 and 12.

Dear Jakub,

This book can help you.

Thanks Aleks!