Background: Fish meat is outlined with high nutritional value having essential amino acids, unsaturated fatty acids, mineral and vitamins. In this short report, we compared the meat quality of rainbow TROUT (Oncorhynchus mykiss) and BROWN TROUT (Salmo trutta fario) farmed in Bulgaria. Methods: Ten fishes from each species were purchased from a fish farm and their morphological parameters were determined. The technological properties of meat were analyzed such as water holding capacity and cooking loss as well as chemical composition such as water content, protein, fat, dry matter, and ash. Results were processed by STATISTICA 6. 0 software. Results: Higher values were significantly determined in BROWN TROUT for standard body length (p<0. 05), body height (p<0. 001), and body width (p<0. 01); while differences in total body length were not relevant (p>0. 05). Water holding capacity of rainbow TROUT meat (9. 49± 3. 86%) was considerably better (p<0. 001) than that of BROWN TROUT meat (15. 85± 1. 11%). Cooking loss in rainbow TROUT (31. 78± 6. 17%) was lower (p<0. 001) than that of BROWN TROUT meat (44. 48± 4. 20%). Protein, fat, and dry matter contents were higher in BROWN TROUT (p<0. 001). No statistically significant differences were found out with respect to ash content (p>0. 05). Conclusion: Meat of rainbow TROUT cultivated in Bulgarian farm exhibited better technological properties than that of cultivated BROWN TROUT; however, nutritional value of BROWN TROUT meat was superior.

Due to the decline in the population of Caspian salmon (Salmo caspius) in the southern part of the Caspian Sea, the age and growth of this fish were studied in the Dohazar River in Tonekabon to improve conservation programs. In December 2018, 63 fish samples were collected using an electroshocker. Among these, 21 females and 42 males were captured, resulting in a sex ratio of 2:1, with a significant difference between the sexes (p<0.05). The length range of males and females was 7.5–18.5 cm and 6.5–21.5 cm, respectively, while their weight ranges were 3.99–65.5 g for males and 2.51–95.42 g for females. Age determination was conducted using scales. The age range of the population was from +1 to +5, with females distributed across 5 age groups and males across 4 age groups. The highest age frequency in all cases was in the 1+ and 2+year age groups. The von Bertalanffy growth equations for males and females were calculated as Lt = 230.462{1-exp(-0.327(t-(-0.240)))} and Lt = 300{1-exp(-0.213(t-(-0.139)))} respectively. The mean Monro index for the total sample was 2.26, with 2.23 for males and 2.28 for females. The study results show a significant decrease in the growth parameters of the species across all age groups. Both the growth coefficient and the asymptotic length of the species have decreased compared to previous years.

The length-weight relationship, age, growth parameters, sex ratio, mortality and exploitation rate of Salmo trutta fario were determined in Lar dam. The sex ratio (male: female) was 1: 1.84 which differed significantly from the expected 1: 1. The length-weight regression was W=0.028L2.706 (females) and W=0.0341L2624 (males) indicating a negative allometric growth for both sexes. Growth parameters were estimated as L¥=45.0 cm, K=0.27 yr-1, t0=-0.23 yr. The instantaneous coefficients of natural, total and fishing mortality were estimated as 0.40 yr-1, 0.75 yr-1 and 0.35 yr-1. The results showed that S. trutta fario is moderately a rapidly-growing species in Lar dam. The exploitation rate was 0.47. Therefore, the population appeared to be in good condition in 2004.

Chlorpyrifos (CPF) is used intensively as an insecticide. There is a high risk of interference with the aquatic environment due to unconscious use and has a negative effects especially fish. In this study, the responses of rainbow TROUT (Oncorhynchus mykiss) and BROWN TROUT (Salmo trutta fario) exposed to the same pollutants have been evaluated and compared in terms of target organs. Fish were exposed to different concentrations of CPF (0. 25, 0. 5, and 1 μ g L-1) through 21 days. After the process oxidative stress [superoxide dismutase (SOD), catalase (CAT glucose-6-phosphate dehydrogenase (G6PD), glutathione reductase (GR), glutathione-S-transferase (GST), glutathione peroxidase (GPx)], acetylcholinesterase (AChE) and malondialdehyde (MDA) have been measured in gill, kidney and liver tissues. CPF exposure led to a significant changes in the enzyme activities and decreased AChE in all tissues (p<0. 05). All antioxidant enzyme activities and MDA levels showed tissue-specific alterations (p<0. 05). These results put forward a close relationship between AChE inhibition and chlorpyrifos concentrations. In addition to, CPF concentrations caused oxidative stress and inhibition in all enzyme activities of two different TROUT species’ gill, liver and kidney tissues.

Khorma River is one of the main branches of Shalmanrood River in mountain areas of Langarood. One of the main fish species of this river is BROWN TROUT (Salmo trutta morpha fario). Diet of 66 BROWN TROUT has been studied since autumn 2003 till summer 2004. According to the obtained result average total length is 17.55 cm and average weight is 72.02 gr, average Index of fullness is 189.95, average Relative length gut 0.46, average growth coefficient (Fulton’s condition factor) 1639.67, average Vacuity index 15.5%. BROWN TROUT in Khorma River was fed 23 foods. He was includes which are: Heptagenia, plecoptera, Baetis, Lipunera, Odonata, Simolium, Ecdyonurus, Hydropsica, Ephemera, Shell, Frog, Pelenomus, Rhyacophila, Lipuonerose, Epuorus, Spider, Fly, Snail, Ant, Grasshopper, Caenis, Spirlin (Alburnoides bipunctatus) and other organs. Between them Hydropsica (68.18%), Plecoptera (68.16%), Baetis (57.58%) had the heighest percentage of frequency and Ant, Grasshopper, Snail and Frog (from each with .51% of abundance) had the lowest frequency percentage.

To determine the digestive capacity of larvae in Caspian BROWN TROUT and Rainbow TROUT, activity of digestive enzymes including pepsin, trypsin, chymotrypsin, a-amylase, lipase and alkaline phosphatase in 2/3  and complete yolk-sac absorption stages were assessed. Results showed enzyme activity was significantly higher in Rainbow TROUT than in Caspian BROWN TROUT at 2/3 yolk-sac absorbtion stage (P<0.05). Enzyme activity was increased in Caspian BROWN TROUT at complete yolk-sac absorption. The enzymes pepsin, trypsin, a-amylase, lipase and alkaline phosphatase were higher in Caspian BROWN TROUT than in Rainbow TROUT but of these only a-amylase was significantly different between the two (P<005). Chymotrypsin was lower in Caspian BROWN TROUT than in Rainbow TROUT but not significantly (P>0.05). At the start of feeding, activity of pepsin, trypsin, chymotrypsin and alkaline phosphatase were higher in Rainbow TROUT than in Caspian BROWN TROUT but the difference was not significant for pepsin (P>0.05) whereas trypsin, chymotrypsin and alkaline phosphatase were significant different between the two (P<0.05). A-amylase was lower in Rainbow TROUT than in Caspian BROWN TROUT but not significantly (P>0.05). Lipase was similar in both fish. Higher enzyme activity in Rainbow TROUT than in Caspian BROWN TROUT at 2/3  yolk-sac absorption shows the high ability for digesting food in rainbow at this stage. Also, low enzyme activity in Caspian BROWN TROUT at this stage is believed to be one of the reasons for low food intake and digestion at this stage.

In recent decades, BROWN TROUT populations have been declining due to river regulation and its impact on river morphology along Lar River downstream of Lar Dam located near Tehran. Currently, due to water scarcity in the country, intensity of water regulation impacts on aquatic population of streams and specific ecologic values in tributaries of Lar River, it is necessary to present a habitat assessment model to predict ecologic response of the river to natural and man-induced changes by which can be applied to strategic management of the river. Hence, in this research, an analytically applied approach is adopted to assess BROWN TROUT population by creating relation among hydrologic, hydraulic, morphologic and ecologic processes. After field work and required measurements, Shields function was applied to derive dimensionless shear stress for minimum environmental flow, bankfull discharge and critical discharge for initiation of sediment transport for Lar, Dalichai and Sefid-Ab rivers. Then, dimensionless shear stress for initiation of the bed sediments was used to investigate effects of discharge variation on frequency and distribution of aquatic life in response to morphologic changes. It was found that when water discharge is in the range of discharge corresponding to environmental flow threshold and critical discharge for sediment motion, it is identified functional discharge for bed occupation while water discharge greater than critical discharge for sediment motion is also considered functional discharge for bed preparation. Results obtained from this research, suggest that water discharge, cross-sectional geometry and bed material size could be effective on ecologic functions and life cycle of BROWN TROUT fish and inappropriate river regulation may lead to gradual elimination of that from river ecosystem.

This research has been conducted in Tonekabon River in 1996. 190 fish samples were take from diferent age groups of 0+, 1+, 2, 3+, 4+. Results indicated that the most highest and lowest abondant were %63, %5.7 in Dohezar and intersection of Dohezar and Cehezar respectively. Maximum body length and weight were 175mm and 84.5g in Dohezar respectively. Minimum body length and weight were 27mm and 0.39 g in Cehezar, respectively. Highest abundant belonged to 2 years age group with 112.3mm average length. Sex ratio was 1:1.4 (female to male). Condition factor of male and female were almost equal (1.268 and 1.257 respectively). Highest feeding intensity was in spring and the lowest was in autumn. Main preys were Simulium, Plecoptera and Ephemeroptera. Growth was positive alometric. Absolute fecundity ranged between 168-379 with an average of 268 eggs.