Morphological development and body shape change of Sterlet (Acipenser ruthenus) using geometric morphometric technique during early development

This research was conducted to study the morphological development and body shape changes of the Sterlet (Acipenser ruthenus) using geometric morphometric technique during early development from hatching up to 50 days post-hatch (dph). A total of 190 specimens were collected from different early developmental stages. The left side of specimens was photographed to extract body shape data. Then 8 homologous landmark-points were defined and digitized on 2D pictures using tpsDig2 software. Landmark data after Generalized Procrustes Analysis (GPA), analyzed using Relative Warp. The results showed that change of body shape in the Sterlet during early development includes the increased length of head and tail up to 6 dph at first phase and the decreased relative growth of the depth and length of head, development of the trunk region and upward bending of tail at next stages. The cluster analysis based on body shape changes of specimens to identify age and size groups revealed that larval stages of this species can be divided into three stages including (1) 1-6 dph comprising development of the head,  caudal region, opening mouth, gill slits, the taste and olfactory buds, (2) 7-23 dph consisting of  increased relative growth of the trunk region, complete formation of the gills and fins and starting exogenous feeding and (3) juvenile stage (from 24-50 dph) including formation of a miniaturized specimen similar to that of adults. Based on the finding, the body shape changes of this species during early development is due to adjusting its vital priority.