The production of rainbow trout (Oncorhynchus mykiss) is developing and it is most cultured finfish species in Turkey. It was first introduced in Turkey in the mid 1970s from Italy. In the following years, culture studies of native trout strains, mainly Black Sea trout; Salmo trutta labrax and Abant Lake trout, Salmo trutta abanticus started in late 1990. Market size trout production was performed in two main categories, inland areas (mainly concrete ponds by flow through fresh water and cages) and in sea (offshore cages). Total trout production was 61.173 tons in 2007.

Turkey has rich inland water sources, about 200 natural lakes, about 750 artificial lakes or ponds, about 193 reservoirs, 33 rivers and streams of 177,714 km length and 8333 km of coastal strips. Some lagoons covering of 70,000 ha in Aegean and Mediterranean coastal strips are very suitable for aquaculture. The main fish species cultured in Turkey are carp (Cyprinus carpio), rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar), gilthead sea bream (Sparus aurata), European sea bass (Dicentrarchus labrax), bluefin tuna (Thunnus thynnus), Blackl sea turbot (Pselta maxima), Mediterranean mussel (Mytilus galloprovincialis) and shrimp (Penaeidae spp). Aquaculture production of Turkey has grown steadily over the years from 5,782 t in 1990 to 63,000 t in 1999 and to 79,031 t in 2000. There are 1309 farms in inland water producing approximately 32,466 t of fresh water fish species and 352 farms at sea producing 40,119 t of sea fish species, mainly Gilthead sea bream and European sea bass.

The South-Esatern Anatolia Project (GAP) is a multi-sector and integrated regional development project in Turkey. The project area covers 9 administrative provinces - Adiyaman, Batman, Diyarbakir, Gaziantep, Kilis, Mardin, Siirt, Sanliurfa, and Simak - in the basins of the Euphrates and Tigris. The GAP planned in the 1970s consists of projects for irrigation and hydraulic energy production on the Euphrates and Tigris rivers. The development program encompasses such sectors as irrigation, hydraulic energy, agriculture, fish farming, rural and urban infrastructure, forestry, education, and health. This project envisages the construction of 22 dams and 19 hydraulic power plants and irrigation of 1.7 million hectares of land. The total cost of the project is estimated as US $ 32 billion. The construction of several dams will cause an increase in total capacity of more than 600 000 tons of fish in the region. Aquaculture will be an important source of income for the people and the economy of the country, a sum of US $ 1.8 billion of income will be obtained each year.

Morphological parameters and their changes common for artificially reared one year old sea trout were examined from January to May the year 2013 to determine whether these parameters indicated the smoltification in one year old sea trout and whether these fish achieved smolts stage. Fish were reared in flow-through and recirculation systems in hatcheries based on three different rivers (Brasla, Daugava, Venta basin). Sea trout were examined in the Latvia University of Agriculture, Faculty of Veterinary Medicine, Institute of Food and Environmental Hygiene and in the Institute of Food Safety, Animal Health and Environment BIOR, Laboratory of Aquaculture and Fish Pathology. To appreciate fish growth stage condition index, hepatosomatic index, spleen index was calculated and silvering level was evaluated. The fish condition index decreased in all hatcheries and flow-through and recirculation rearing systems from January to April and increased in May. Spleen index was the most stable parameter and did not change a lot showing that fish did not have migratory stress in April and May. Silvering level increased from January to April but suddenly the increase became slower in May without reaching the top level. These results made us to consider that one year old sea trout parrs released in May 2013 probably did not become smolts before release and they had to stay in river for one additional year until reaching pronounced smolt stage.

Dressing percentage and gonadosomatic index (GSI) of large (2-3 kg) rainbow trout (Oncorhynchus mykiss), produced in Estonian fish farms were estimated. The dressing percentage and GSI did not depend on fish size, but there was a strong negative correlation (r = - 081, p0.001) between themselves. During maturation the flesh color decreased significantly. The male trout had the palest color (13 color card units), the color of fillets of females decreased with maturation from 15 to 14. The immaturate females had the brightest color (17 color card units) and the highest slaughter yield (mean dressing percentage 87%, mean fillet yield 68%). Due to deterioration of quality (smaller slaughter yield and pale color) the maturation of trout causes profit loss for fish farmers and thus, rearing of late maturing all-female strains is recommended.