Effects of total fish oil replacement to vegetable oils at two dietary lipid levels on the growth, body composition, haemato-immunological and serum biochemical parameters in caspian brown trout (Salmo trutta caspius Kessler, 1877) Abdolmohammad Abedian Kenari 1 , Mansour Tor¢ Mozanzadeh 1 & Reza Pourgholam 2 1 Fisheries Department, Faculty of Natural Resources and Marine Sciences,Tarbiat Modares University, Noor, Mazandaran, Iran 2 Mazandaran Fisheries Research Center, Caspian Sea Research Institute in Ecology, Sari, Iran Correspondence: A A Kenari, Fisheries Department, Faculty of Natural Resources and Marine science,Tarbiat Modares University, PO Box 64414-356, Noor, Mazandaran, Iran. E-mails: aabedian@modares.ac.ir, aabedian@yahoo.co.uk Abstract This research aimed to evaluate the e¡ects of two dietary fat levels [low fat (LF) (10%), high fat (HF) (20%)] and sources [¢sh oil (FO), vegetable oil (VO)] on the growth and some physiological parameters of Caspian brown trout ¢ngerlings for 60 days. Tuna oil or blends of canola and soybean oils (85:15) were added to diets to design four feeds namely LFFO, HFFO, LFVO and HFVO according to the fat levels and sources. The ¢sh fed the LFFO diet had lower weight gain than the other ¢sh ( Po0.05). The total n-6 fatty acids increased in ¢sh fed diets with the blends of VO, while the total n-3 fatty acids decreased in these ¢sh ( Po0.05). Serum lysozyme activity was higher in ¢sh fed the HFVO diet than the other ¢sh ( Po0.05). Serum glucose, total cholesterol, triglycer- ide and very low-density lipoprotein were lower in ¢sh fed LFFO than the other ¢sh ( Po0.05). The pre- sent study demonstrates that in terms of ¢sh growth, VOs can be used as an alternate source of dietary fat, whereas ¢sh health and nutritional value are im- proved with the LFFO diet. According to these results, a partial substitution of FO by VO in high-level fat diets is suggested for long-term feeding of Caspian brown trout. Keywords: Salmo trutta caspius , dietary lipid, growth performance, fatty acid pro¢le, haematolo- gical and immunological parameters Introduction The Caspian brown trout, Salmo trutta caspius Kess- ler, 1877, is one of the nine subspecies of brown trout Salmo trutta in the world (Quillet, Faure, Che- vassus, Kreig, Harache, Arzel, Metailler & Boeuf 1992). It attains the greatest size, weight and growth rate of all brown trout and lives in the Cas- pian Sea (Sedgwick1995). Populations occur mostly in the southwest part of the sea, in Iranian waters (Kiabi, Abdoli & Naderi 1999), where they are heav- ily ¢shed. Over the past 20 years, natural popula- tions of this species in Caspian Sea have decreased conspicuously due to river pollution, unauthorized ¢shing and destruction of natural spawning sites. Consequently, the species has been arti¢cially pro- pagated in Iran (Dr Bahonar Governmental salmo- nid farm). After almost 2 years of growth, ¢sh were released into the Caspian Sea water to increase the stocks. More recently, due to ¢llet quality, the Cas- pian brown trout has attracted interest for cage cul- ture and £ow-through systems in Iran (Sarvi, Niksirat, Mojazi Amiri, Mirtorabi, Ra¢ee & Bakh- tiyari 2006). Little is known about the nutritional needs of this species with regard to essential fatty acids (EFAs), the capacity to synthesize highly unsaturated fatty acids from C18 precursors and the e¡ects of dietary fat levels and sources on its health and nutritional value. Fish oil (FO) is the main source of dietary lipid used for this species. Aquaculture Research, 2011, 42 , 1131^1144 doi: 10.1111/j.1365-2109.2010.02701.x r 2010 Blackwell Publishing Ltd 1131