Sex steroids in the seminal fluid and milt quality indices in the endangered Caspian brown trout,Salmo trutta caspius

In this study, the relationships between the seminal fluid sex steroids sperm quality parameters (i.e. sperm motility and sperm production were investigated in the endangered Caspian brown trout. According to results, the variation of sex steroid concentrations was comparatively high. The seminal fluid levels of 17α‐Hydroxyprogesterone (OHP) had positive correlation with percentage and duration of sperm motility. Similar correlation was found between the seminal fluid concentration of testosterone (T) and estradiol‐17β (E2) with sperm concentration. As well as, there was no significant correlation between progesterone (P) with sperm quality indices. The significant correlation of some steroids i.e. OHP, T and E2 and sperm quality parameters of Caspian brown trout confirms the key role of these steroids in acquisition of the potential of motility during final stage of the maturation.     

Sperm density, seminal plasma composition and their physiological relationship in the endangered Caspian brown trout (Salmo trutta caspius)

Sperm density, mineral and organic composition of the seminal plasma and their physiological relationship were investigated in the Caspian brown trout (Salmo trutta caspius). To establish a rapid and accurate method for assessment of sperm density, three different techniques were used: sperm counting, spectrophotometry (at 480 nm) and determination of the spermatocrit. The seminal plasma contained 159.26±8.84 mM sodium (Na), 33.72±2.01 mM potassium (K), 133.04±5.96 mM chlorine (Cl), 1.68±0.2 mM calcium (Ca) and 0.988±0.13 mM magnesium (Mg). The following organic components were found: total protein 0.75±0.14 mg 100 mL⁻¹, cholesterol 2.86±0.58 mg L⁻¹ and glucose 3.81±1.04 mM L⁻¹. The mean sperm density was estimated to be 3.3 × 10⁹ spermatozoa mL⁻¹. The spermatocrit (%) ranged from 25 to 52 in sperm samples. Highly significant linear relationships were found between sperm density and spermatocrit (R²=0.703, P<0.001) and sperm density and optical density (R²=0.909, P<0.001), indicating that optical density can be used as a quick and accurate method of estimating sperm density. Significant relationships were also found between sperm density and Ca, Mg and total protein of seminal plasma. A significant correlation was also observed between the Ca and Mg concentrations (R²=0.774, P<0.01). The following correlations were observed between mineral and organic components: total protein and Ca (R²=0.462, P<0.05), total protein and Mg (R²=0.518, P<0.05) and glucose and Cl (R²=0.374, P<0.05). These parameters should be considered when developing procedures for either artificial fertilization or for cryopreservation of sperm.     

Dietary nucleotide supplements influence the growth,haemato‐immunological parameters and stress responses in endangered Caspian brown trout (Salmo trutta caspius Kessler, 1877)

A feeding trial was conducted to evaluate the effects of Optimûn, a commercial nucleotide (NT) product, on the growth, haemato‐immunological and serum biochemical parameters and stress responses of Caspian brown trout fingerlings (average initial weight of 12.26 g). A basal diet was supplemented with levels of 0 (control), 1.5, 2.5, 3.5 and 5 g NT kg^?1 to formulate five experimental diets. After 8 weeks of feeding trial, fish fed diet with 2.5 g NT kg^?1 had the highest final weight compared with other treatments. The fish fed diets with 2.5 g NT kg^?1 had higher blood protein, albumin, albumin/globulin ratio, red blood cells, white blood cells and lymphocyte content and lower alkaline phosphatase. The lysozyme activity in serum was found to be significantly (P < 0.05) greater in fish fed diet with 2.5 g NT kg^?1. Concerning both stressors (confinement and salinity stress), fish fed diet with 2.5 g NT kg^?1 had lower plasma cortisol and glucose levels. Thus, administration of 2.5 g kg^?1 of the Optimûn dietary nucleotide formula is recommended to promote growth and immunity as well as to enhance stress responses of Caspian brown trout.     

Gonadotropin releasing hormone‐analogue (GnRHa) treatment improves the milt production and sperm motility of endangered Caspian brown trout,Salmo trutta caspius,over the course of a spawning season

To determine the effect of gonadotropin releasing hormone‐analogue (GnRHa) treatment on the milt quality of endangered Caspian brown trout, Salmo trutta caspius, the sperm motility (percentage and duration of motility), sperm production (sperm density, spermatocrit and milt volume) and milt pH were measured for GnRHa‐treated (the treatment group) and untreated groups (the control group) during the spawning season. For untreated brooders, the values of the motility per cent, sperm density and spermatocrit decreased continuously during the spawning season while the milt volume, duration of motility and milt pH showed only a significant decrease at the end of the season. For GnRHa‐treated males, these parameters increased 14 days after GnRHa treatment (first milt collection) and then decreased continuously towards the end of the season. In addition, the values of milt and sperm density yielded per treated male were higher than that in the untreated group, although these were not statistically different. In any case, the total sum of yielded milt from the treatment group over the spawning season was higher than that in the untreated group. In this experiment, significant positive correlations were found between milt parameters as follows: sperm motility vs. milt pH; sperm density vs. spermatocrit; milt volume vs. spermatocrit; and milt volume vs. sperm density. The results show that the treatment of Caspian brown trout by GnRHa can improve the milt quality in terms of sperm motility and sperm production during a spawning season.     

Changes in Sperm Production,Sperm Motility,and Composition of Seminal Fluid in Caspian Brown Trout,Salmo trutta caspius,Over the Course of a Spawning Season

This study was carried out to evaluate milt quality in male Caspian brown trout (Salmo trutta caspius) over the course of the winter spawning season. Milt samples were collected biweekly during December and January. Chemical composition of seminal fluid, sperm production (milt volume, sperm density, spermatocrit,) and sperm motility characteristics (percentage and duration of motility) were measured. Milt volume, sperm density, osmolality, seminal minerals (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^?), and total protein gradually decreased over the spawning season. Glucose and triglyceride content of milt did not show significant changes over the spawning season. Milt pH and the percentage and duration of motility were comparatively stable, declining only at the end of the season. Significant positive correlations were found between sperm density and seminal minerals, total protein and spermatocrit; percentage of motile spermatozoa and seminal minerals, total protein; and duration of motility and K⁺, Cl^?, total protein, and pH. Results show that season has a significant influence on milt quality in male Caspian brown trout, with the best milt being available at the beginning of spawning season.     

Dietary soybean phosphatidylcholine affects growth performance and lipolytic enzyme activity in Caspian brown trout (Salmo trutta Caspius) alevin

The effects of supplemental dietary phosphatidylcholine (PtCho) on the growth performance, survival and digestive enzyme activity of Caspian brown trout (Salmo trutta caspius Kessler 1877) alevins were investigated in this study. Alevin (initial weight 0.8 ± 0.12 g) was fed for 5 weeks with an isoproteic‐ and isolipidic‐formulated diet with increased levels of PtCho from 0 to 60 g kg^?1 dry matter and decreasing levels of soybean oil. The increase in dietary PtCho up to 4% led to an increase in alevin final weight, suggesting that moderate PtCho levels are needed during this stage of Caspian brown trout. Survival was not affected by the dietary PtCho level. Phosphatidylcholine incorporation into the diet caused higher phospholipase A2‐specific activity. Phosphatidylcholine did not show a beneficial effect on the specific activity of amylase and protease. Lipase‐specific activity was significantly higher in the PtCho groups compared with the control group. The hepatosomatic index (HSI) was significantly influenced by the dietary PtCho level. The results of the present study indicated that the dietary supplementation of PtCho in the diet of Caspian brown trout alevin improved growth and lipolytic enzyme activity.     

Effect of spirulina Spirulina platensis as a complementary ingredient to reduce dietary fish meal on the growth performance,whole‐body composition,fatty acid and amino acid profiles,and pigmentation of Caspian brown trout (Salmo trutta caspius) juveniles

Spirulina has been highlighted as a valuable complementary ingredient in aquafeeds due to its high protein and vitamin content, in addition to other nutritional benefits. To evaluate the effect of dietary spirulina inclusion in fish meal sparing (FMS) on juvenile Caspian brown trout as a slow‐growth fish, a complete randomized experimental design was developed with five treatments: 0% (control), 2% FMS (13.2 g/kg spirulina in diet), 4% FMS (26.4 g/kg spirulina in diet), 6% FMS (39.6 g/kg spirulina in diet) and 8% FMS (52.8 g/kg spirulina in diet). Six hundred juveniles (11.0 ± 1.0 g) were assigned to 15 experimental tanks. Although this fish is sensitive to diet composition, fish fed the 6% FMS and 8% FMS diets had a significantly higher weight gain rate (239.51% and 231.27%) and specific growth rate (1.74% bw per day and 1.71% bw per day) compared with those fed the control diet. Furthermore, 6% FMS and 8% FMS treatments had statistically higher protein efficiency (0.76 and 0.78), lipid efficiency (1.89 and 1.94) and statistically lower feed conversion ratio (2.47 and 2.41) compared with other treatments, respectively (p < 0.05). In terms of whole‐body composition, the higher amount of protein and lower content of lipid were observed in fish fed the 8% FMS diets as compared to control. Although no significant differences in ash and moisture content were observed, the highest protein deposition (157.3 g/kg) and the lowest lipid content (77 g/kg) in whole body were reported in fish fed 8% FMS diet. Based on the fillet fatty acid outcome, fish fed the 8% FMS diet had significantly higher saturated fatty acids (SFAs), C20:3n‐6, C18:3n‐3, polyunsaturated fatty acids (PUFAs) and total n‐3 fatty acids as compared to those fed the control diet (p < 0.05). Accordingly, increasing dietary spirulina content significantly enhanced the amount of these fatty acids in fish fillet. As regards of whole‐body amino acid profile, arginine and lysine in fish fed 6% FMS and 8% FMS diets were higher and lower than in those fed the control diet, respectively (p < 0.05). Fillet and skin colour parameters, such as luminosity, redness and yellowness, significantly increased with spirulina supplementation with the 8% FMS treatment displaying higher values than the control. In summary, according to our results, 8% FMS (52.8 g/kg spirulina in diet) treatment improved juvenile Caspian brown trout growth, carcass composition and pigmentation.     

The role of temperature in the prey capture probability of drift‐feeding juvenile brown trout (Salmo trutta)

Abstract – Cold water temperatures are widely supposed to reduce the food intake of stream salmonids. Although cold temperatures have been documented to reduce swimming ability, digestion and gastric evacuation rates, little is known about how temperature influences the ability of fish to capture prey. We examined the effects of water temperature on the prey capture probability of drift‐feeding juvenile brown trout (Salmo trutta) in a laboratory stream. Temperatures ranged between 5.7 °C and 14 °C. We found significant effects of water temperature on prey capture probability and capture manoeuvre time. The mean capture probability dropped from 96% at 14 °C to 53% at 5.7 °C. At 8 °C and higher temperatures, foraging performances did not differ much among treatments. We suggest that reduced swimming ability could be one of the most important mechanisms for the observed pattern of reduced prey capture probability at cold water temperatures, but prey detection limitations and predator avoidance may play a role. Our results will be of use for bioenergetics‐based drift‐foraging models, which to date have not incorporated a temperature‐dependent prey capture function.     

Functional response and size‐dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.)

Gustafsson P, Bergman E, Greenberg LA. Functional response and size‐dependent foraging on aquatic and terrestrial prey by brown trout (Salmo trutta L.).Ecology of Freshwater Fish 2010: 19: 170–177. © 2010 John Wiley & Sons A/S Abstract – Terrestrial invertebrate subsidies are believed to be important energy sources for drift‐feeding salmonids. Despite this, size‐specific use of and efficiency in procuring this resource have not been studied to any great extent. Therefore, we measured the functional responses of three size classes of wild brown trout Salmo trutta (0+, 1+ and ≥2+) when fed either benthic‐ (Gammarus sp.) or surface‐drifting prey (Musca domestica) in laboratory experiments. To test for size‐specific prey preferences, both benthic and surface prey were presented simultaneously by presenting the fish with a constant density of benthic prey and a variable density of surface prey. The results showed that the functional response of 0+ trout differed significantly from the larger size classes, with 0+ fish having the lowest capture rates. Capture rates did not differ significantly between prey types. In experiments when both prey items were presented simultaneously, capture rate differed significantly between size classes, with larger trout having higher capture rates than smaller trout. However, capture rates within each size class did not change with prey density or prey composition. The two‐prey experiments also showed that 1+ trout ate significantly more surface‐drifting prey than 0+ trout. In contrast, there was no difference between 0+ and ≥2+ trout. Analyses of the vertical position of the fish in the water column corroborated size‐specific foraging results: larger trout remained in the upper part of the water column between attacks on surface prey more often than smaller trout, which tended to seek refuge at the bottom between attacks. These size‐specific differences in foraging and vertical position suggest that larger trout may be able to use surface‐drifting prey to a greater extent than smaller conspecifics.     

Benefits of repeated stocking with adult,hatchery‐reared brown trout,Salmo trutta,to recreational fisheries?

Abstract  Recaptures of adult, hatchery-reared, brown trout, Salmo trutta L., and fishing time from anglers were used to evaluate the benefits of stocking programmes with repeated releases of adult brown trout. The recapture rate varied between 17% and 29%. The time between stocking and capture (referred to as residence time) varied between 1 and 160 days (median 3–49 days). Between 67% and 84% of trout caught in the river were recently released fish. Fishing effort increased after stocking, thereby increasing the impact of angling on wild stocks. Stocking with adult brown trout decreases the impact of angling on wild trout only if the time spent fishing by all anglers is kept stable. Furthermore, because of the short residence time of stocked trout, long-term impacts through competition for space and food, or genetic impact through introgression, are limited.     

Spectrophotometric determination of sperm concentration and short‐term cold‐storage of sperm in Atlantic croaker Micropogonias undulatus L. broodstock

The objective of this study was to optimize the methodology for spectrophotometric determination of sperm concentration in Atlantic croaker Micropogonias undulatus L. milt and to estimate its potential for short‐term cold‐storage. The spectrophotometric determination of sperm concentration was evaluated using milt samples from six males serially diluted in Hank's balanced salt solution at 200 mOsm kg^?1 (HBSS). The predictive power of regression models between sperm concentration and absorbance was determined from 200 to 500 nm and found to be highest within the visible spectrum despite a peak of milt absorbance at 288 nm. Absorbance reading at 400 nm was selected for further analysis to maximize the absorbance of the sample hence the sensitivity of the method while minimizing the impact of potential sample contamination with blood. The standard‐curve of correlation between sperm absorbance at 400 nm and concentration was validated and held an accuracy ranging between ?7.40% and +4.56% across males. Total sperm motility duration and the proportion of motile spermatozoa were significantly higher in milt samples diluted 1:3 in HBSS than in the undiluted control during up to 30 h of cold‐storage.The methodologies investigated in this study can be applied to optimize sperm usage and achieve predictable artificial fertilization protocols in Atlantic croaker.     

Use of first‐order tributaries by brown trout (Salmo trutta) as nursery habitat in a cold water stream network

Many investigators have examined the importance of suitable in‐stream habitat and flow regime to salmonid fishes. However, there is much less known about the use of small (<5 l·s^?1 discharge) first‐order streams within a larger stream network by salmonids. The purpose of this study was to evaluate the use of small headwater streams by juvenile brown trout Salmo trutta in the Emmons Creek stream network in Wisconsin, USA, and to determine whether abundance was related to habitat variables in these streams. Fishes in eight spring‐fed first‐order streams were sampled during a 7‐month period using a backpack electroshocker and measured for total length. Habitat variables assessed included stream discharge, water velocity, sediment composition and the abundance of cover items (woody debris and macrophytes). Densities of YOY trout ranged from 0 to 1 per m² over the course of the study and differed among first‐order streams. Stepwise multiple regression revealed discharge to be negatively associated with trout density in spring but not in summer. All other habitat variables were not significantly related to trout density. Our results demonstrate the viability of small first‐order streams as nursery habitat for brown trout and support the inclusion of headwater streams in conservation and stream restoration efforts.     

LHRHa‐induced ovulation of the endangered‐Caspian brown trout (Salmo trutta caspius) and its effect on egg quality and two sex steroids: testosterone and 17α‐hydroxyprogestrone

To induce synchronized ovulation, migrating wild Caspian brown trout (Salmo trutta caspius) females were treated with two interperitoneal injections of Des‐Gly¹⁰, d ‐Ala⁶ LHRH (LHRHa), given 3 days apart. Two injections of 100 μg kg^?1 body weight of this hormone effectively induced ovulation. Within 27 days from the second injection, all fish injected with 100 μg kg^?1 LHRHa had ovulated compared with 54.5% of the controls. The mean time to ovulation was reduced significantly (P<0.05) from 31.67±4.84 days in control fish and 28.83±7.31 days in sham‐treated fish to 16.36±1.61 days in fish injected with 100 μg kg^?1 LHRHa. The fertilization rate in 50 and 100 μg kg^?1 LHRHa‐injected fish was significantly lower than that in the control fish (P<0.05). In fish injected with 50 and 100 μg kg^?1 LHRHa, significant (P<0.05) changes in testosterone (T) and 17α‐hydroxyprogestrone (OHP) levels were observed. After the second LHRHa injection, the fish injected with 100 μg kg^?1 showed the highest serum levels of testosterone and OHP. These results demonstrate that the use of LHRHa can effectively reduce the mean time to ovulation and induce synchronized ovulation in Caspian brown trout.     

Combination effects of dietary EPA and DHA plus alpha‐tocopherol: effects on performance and physiological status of Caspian brown trout (Salmo trutta caspius) fry

The effects of dietary n‐3 highly unsaturated fatty acids [eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA)] with α‐tocopherol on growth, non‐specific immune response and oxidative status were investigated in Caspian brown trout, Salmo trutta caspius, fry. Six experimental diets containing three different dietary levels of n‐3 HUFAs (low: 1 + 0.5% of total fatty acids, DHA+ EPA, medium: 2 + 1%, DHA + EPA, high: 4 + 2%, DHA + EPA) with two different levels of α‐tocopherol (low: 300 and high: 1000 mg kg^?1 diet) were prepared and named: LL, LH, ML, MH, HL and HH (HUFA/α‐tocopherol) groups, respectively. Diets were fed to triplicate groups of 60 fry with an initial weight of 600 ± 25 mg for 10 weeks. Results showed that increase in dietary DHA and EPA up to high level improved fry growth in terms of the body weight and specific growth rate, particularly when dietary α‐tocopherol levels were high, suggesting a higher antioxidant protection value when these fatty acids are high. At all dietary n‐3 HUFA levels, increase in α‐tocopherol from low to high level enhanced the alternative complement (ACH50) activity. Fry fed diets medium and high n‐3 HUFA displaying significantly higher lysozyme activity (P < 0.05). Moreover, fish fed medium or high levels of n‐3 HUFA had significantly lower prostaglandin E2 (PGE2) than those fed low n‐3 HUFA (P < 0.05). Significant differences in antioxidant enzymes (catalase, glutathione peroxidase, glutathione S‐transferase, glutathione reductase and superoxide dismutase) activity were also observed between groups, with higher activity in high levels of n‐3 HUFA (P < 0.05). Results of this study suggest that the effect of dietary n‐3 HUFA on examined non‐specific immunity parameters are not uniform; however, these impacts are closely related to the α‐tocopherol supplement and their interaction. In conclusion, increased dietary levels of n‐3 HUFA and α‐tocopherol would enhance growth performance and welfare of this species.     

Changes in the density and growth of brown trout (Salmo trutta) after intensive removal of sympatric Arctic charr (Salvelinus alpinus) in the sub‐Arctic lake Møkkelandsvatn,Norway

This study tests the basic hypothesis that the removal of charr, Salvelinus alpinus (L.), would cause an increase in both the growth and density of a sympatric trout population, Salmo trutta L. The charr population was characterised by slow‐growing individuals, with a high proportion of mature fish, that is typical for so‐called overpopulated populations. A total of 31,000 charr was removed from the lake in the period 1990–1992, and the density of younger trout (1+, 2+), but not older trout (3+, 4+), increased. The growth of older trout (3+, 4+) increased, but the evidence for similar growth increases of younger trout (1+, 2+) was limited. From 1989 to 1990, the proportion of trout increased from 30 to only 40% of the total catch, but from 1991 to 1994, it was significantly higher (60–80%) than that of charr. Total trout biomass increased to a maximum in 1992 and then decreased so that the biomass of 1994 was nearly similar to that of 1989, that is before the start of the charr removal. Back‐calculated lengths of trout from otoliths showed that 2+ and 3+ trout caught in the pelagic were growing consistently faster over previous years than those caught in the littoral, while this was not the case for the 4+ fish. Therefore, the hypothesis was partially supported; the growth rate of trout increased (age groups 1+ to 4+), while the density of juvenile trout (1+, 2+), but not the older trout (3+, 4+), increased after the removal of charr.     

Piscine reovirus (PRV) in wild Atlantic salmon,Salmo salar L., and sea‐trout,Salmo trutta L., in Norway

This is the first comprehensive study on the occurrence and distribution of piscine reovirus (PRV) in Atlantic salmon, Salmo salar L., caught in Norwegian rivers. PRV is a newly discovered reovirus associated with heart and skeletal muscle inflammation (HSMI), a serious and commercially important disease affecting farmed Atlantic salmon in Norway. A cross‐sectional survey based on real‐time RT‐PCR screening of head kidney samples from wild, cultivated and escaped farmed Atlantic salmon caught from 2007 to 2009 in Norwegian rivers has been conducted. In addition, anadromous trout (sea‐trout), Salmo trutta L., caught from 2007 to 2010, and anadromous Arctic char, Salvelinus alpinus (L.), caught from 2007 to 2009, were tested. PRV was detected in Atlantic salmon from all counties included in the study and in 31 of 36 examined rivers. PRV was also detected in sea‐trout but not in anadromous Arctic char. In this study, the mean proportion of PRV positives was 13.4% in wild Atlantic salmon, 24.0% in salmon released for stock enhancement purposes and 55.2% in escaped farmed salmon. Histopathological examination of hearts from 21 PRV‐positive wild and one cultivated salmon (Ct values ranging from 17.0 to 39.8) revealed no HSMI‐related lesions. Thus, it seems that PRV is widespread in Atlantic salmon returning to Norwegian rivers, and that the virus can be present in high titres without causing lesions traditionally associated with HSMI.     

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)

This research aimed to evaluate the effects of two dietary fat levels [low fat (LF) (10%), high fat (HF) (20%)] and sources [fish oil (FO), vegetable oil (VO)] on the growth and some physiological parameters of Caspian brown trout fingerlings 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 fish fed the LFFO diet had lower weight gain than the other fish (P<0.05). The total n‐6 fatty acids increased in fish fed diets with the blends of VO, while the total n‐3 fatty acids decreased in these fish (P<0.05). Serum lysozyme activity was higher in fish fed the HFVO diet than the other fish (P<0.05). Serum glucose, total cholesterol, triglyceride and very low‐density lipoprotein were lower in fish fed LFFO than the other fish (P<0.05). The present study demonstrates that in terms of fish growth, VOs can be used as an alternate source of dietary fat, whereas fish health and nutritional value are improved 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.     

Fatty acid,fat‐soluble vitamin and sterol contents in testis and semen,testis‐somatic index and spermatologic values of broodstock rainbow trout (Oncorhynchus mykiss) fed with different levels of omega‐3 fatty acids under regular stripping conditions

In this study, the testis and semen fatty acid, fat‐soluble vitamin and sterol levels, testis‐somatic index and spermatological values were investigated in the broodstock rainbow trout fed with the different levels of omega‐3 polyunsaturated fatty acid (PUFA) under the regular stripping conditions. For this purpose, a control and three test diets were prepared. The control, D1, D2 and D3 diets were contained the omega‐3 PUFA at 3.14%, 7.84%, 13.63% and 20.54% as a percentage of the total fatty acids respectively. The fish in the experimental groups were fed with these diets for 60 days. The testis‐somatic index (3.81–4.50), semen volume (9.30–18.5 ml) and pH (8.05–8.99), initial sperm motility (68.1%–93.7%), duration of 50% sperm motility (141.3–258.9 s), total duration of sperm motility (268.7–489.6 s) and sperm density (9.95–17.5 cells × 10⁹ ml^?1) values of the fish fed the control diet were significantly decrease (p < 0.05) depending on decline of the omega‐3 PUFA, fat‐soluble vitamin and sterol contents in the testis and semen. The omega‐3 PUFA (3.40%–14.76% and 3.96%–16.31%), vitamin A (33.9–61.2 ml/mg and 9.12–26.7 ml/mg), D₂ (0.10–0.19 ml/mg and 0.04–0.10 ml/mg), D₃ (0.75–1.30 ml/mg and 0.06–0.24 ml/mg), alpha‐tocopherol (30.1–60.4 ml/mg and 8.93–25.3 ml/mg), K₁ (0.30–0.94 ml/mg and 0.03–0.08 ml/mg) and K₂ (2.0–3.19 ml/mg and 0.25–0.34 ml/mg) vitamins, cholesterol (1,201–1,588 ml/mg and 330–596 ml/mg), ergosterol (3.12–6.40 ml/mg and 2.10–4.08 ml/mg), stigmasterol (5.57–10.4 ml/mg and 10.2–12.6 ml/mg) and beta‐sitosterol (0.20–0.60 ml/mg and 0.14–0.41 ml/mg) contents in the testis and semen of the fish were significantly affected (p < 0.05) by the dietary omega‐3 PUFA supplementation. The highest values for these parameters were provided from the fish fed the D2 and D3 diets (p > 0.05), followed by the fish fed the D1 diet (p < 0.05). These results showed that the dietary omega‐3 PUFA at 13.63% of the total fatty acids could increase the omega‐3 PUFA, fat‐soluble vitamin and sterol contents in the testis and semen, the testis‐somatic index and spermatologic values of the broodstock rainbow trout under the regular stripping conditions.