Investigation on food preference in Salmo trutta fario in Hevigh, Shafarud,Tonekabon and Lar Rivers

Salmo trutta fario is a vulnerable fish from Salmonid family in Iran and it exists in upstream areas of most Iranian rivers at southern Caspian Sea basin such as Hevigh, Shafarud, Tonekabon and Lar Rivers. The fish, samples were caught with electro-shocker, Cast-net and hook lines from winter to autumn 2010 and the aim was more information on the fish, feeding habit and its changes in different stations, seasons, fish body sizes and two sexes. Body weight was measured in studied fish specimens 1.87-893.9 (71.40±89.80)g, total length 46-462 (161.00±64.94)mm and age was 0+ - 7+ years old (3-aged specimens were dominant), too. The average index of intensity of food was measured, 344.16±327.07, gastero-somatic index 7.17±5.58 and relative length of gut 0.89±0.10 and Kruskal-Wallis test showed significant statistical differences among rivers in these indexes and in fish, weight and length. The coefficient of gut vacuity was 0 (Zero), too. The fish has fed on 56 animal families belong to 20 orders in studied area consist of Gastropoda, Bivalvia, Hirudinea, Opistopora (Oligochaet vorms), Amphipoda, Isopoda, Coleoptera, Diptera, Ephemeroptera, Hemiptera, Hymenoptera, Lepidoptera, Megaloptera, Odonata, Orthoptera, Plecoptera, Trichoptera, Hydracarina, Myriapoda and Salmoniformes, that Dipteran, Coleopteran and Trichopteran insects with 12, 7 and 6 families are diversified, respectively in the alimentary tract of the fish. Current study showed little changes in food preference in different stations, seasons, fish ages and its sexuality, that Chironomidae, Simuliidae and Baetidae families were as preferred foods in all rivers, Heptagenidae in 3 rivers, Tipulidae in Shafarud river, too. Baetidae family was as preferred food in all seasons, Chironomidae in 3 seasons, Simuliidae and Hydropsychidae in 2 seasons and Tipulidae in one season, too. Chironomidae and Baetidae families were as preferred foods in all age-groups and Heptagenidae and Simuliidae in two age-groups, too. It was not observed any difference between males and females in food preference. In general, it can be said that the fish is a benthos-feeder and a euryphagous fish in studied Rivers.