The effect of salinity on the body shape of platyfish Xiphophorus maculatus (Teleostei: Poeciliidae) during early stages of development using geometric morphometric method

This study was aimed to investigate the effect of salinity on phenotypic plasticity of Platy fish (Xiphophorus maculatus) during early stages of development. For this purpose, 60 platy fish fry (30 specimens in each treatment) were raised in different environments, including fresh water (0 ppt) and salt water (12 ppt), for 30 days in laboratory conditions. After the end of this period, the left side of the fish samples was photographed with a digital camera and 16 landmarks were placed on the two-dimensional images using Tpsdig2 software. After removing size and direction effects using Generalized Procrustes Analysis, landmark data were analyzed using Principal Component Analysis, Discriminant Function Analysis, Hotelling's T test and Cluster Analysis (CA). The results showed that there is a significant difference between the body shape of platy fish among the studied treatments (P<0.001). The fry that were reared in the treatment with a salinity level of 12 ppt had a shallower head and gills with a longer snout. Also, these fish had a shorter caudal peduncle with less depth compared to fresh water treatment. The results showed that with the change of environmental conditions from fresh water to salt water, the upper position of the mouth in platy fish tends to the lower position. In addition, body depth and length were lower in fish exposed to a salinity level of 12 ppt compared to the freshwater treatment. The present study showed that water salinity plays a significant role in the early life stages of platy fish.