Study on diet composition of Caspian sand goby, Neogobius fluviatilis pallasi, (Berg, 1916), in South of Caspian Sea (Noor Beach)

Caspian Sea sand goby, Neogobius fluviatilis pallasi (Berg, 1916), due to lack of commercial exploitation and richness of their population, have an important role in food chain of Caspian Sea.This study carried out during July 2004 to June 2005 and documents their diet in shallow coastal waters of Noor at southern part of Caspian Sea. In this regard, diet regim of 240 specimens were analyzed. According to results of present study, the relative length of gut was 0.576 ± 0.099, Vacuity Index for all of specimens was 39.58, so this subspecies classified in relatively gluttonous group. While matured males show increased value of this index during reproduction season, so they can be categorised as medium feeders group. In April, May and June Gastrosomatic Indices were higher than other months. Also study on composition of digestive system, shows that Caspian sand goby was fed on nine different kind of food with Preferences following food: 1- Amphipods from order Amphipoda, 2 - fish larvae, 3- Barnacels from family Balanidae, 4 - Shrimps from family Plaemonidae, 5 - Bivalves from family Mytilidae, 6 - Round crabs from family Xanthidae, 7 - Bivalves from family Cardidae, 8 - Fish eggs, 9- Wormes from order Oligochaeta. In the basis of food prefrence indices, non of mentioned organism were considered as main food item during the study period. It seems that Caspian sand goby diet has been changed during different seasons,according to adaptation with environmental changes.