Identification of larval stages of fish in southeastern coastal waters of the Caspian Sea- Golestan Province

This study was carried out to develop a practical guide to identify species of fish larvae in the coastal waters of the Caspian Sea-Golestan Province. A total of 18 sample sites in the Caspian Sea and 6 sampling sites in the Gorgan Bay were sampled monthly from March to September 2015. The findings showed most of the fish larvae belonged to the postflexion and transitional stages. Some morphological and meristic characteristics of fish larvae were measured. Fish larvae were represented by 5 genera including: Atherina caspia (Eichwald, 1838), Rutilus caspicus (Jakowlew 1870), Rutilus kutum (Kamensky, 1901), Cyprinus carpio (Linnaeus, 1758), Chelon saliens (Risso, 1810), Chelon aurata (Risso, 1810) and Gambusia holbrooki (Girard, 1859). The results showed C. carpio, R. caspicus, and R. kutum were separated based on the pigment patterns on their body. While R. caspicus and R. kutum were discerned by the number of pre-anal myomers. Chelon sp. could be differentiated by a different pigment pattern, as well as some morphometric characters including eye diameter, body depth, and head length. Additionally, identifying characteristics for A. caspia and G. holbrooki are described. The results of this study revealed that in contrast to the current perception, the analysis of the morphometric variations of Chelon sp., Rutilus sp., and C. carpio fry could be used for their identification.