Antibiotics,Penicillin and Sreptomycin improve semen quality indices of endangered Caspian brown trout,Salmo trutta caspius (Kessler, 1870) during in vitro short‐term storage

In this study, we examined the effects of 500 IU mL^?1 penicillin + 500 μg mL^?1 streptomycin sulphate on semen quality indices of endangered caspian brown during 12 days short‐term storage at 4°C. Twenty‐four millilitre semen samples with good quality were considered for the experiment. The semen samples were then stored in the presence and absence of 500 IU mL^?1 penicillin + 500 μg mL^?1 streptomycin sulphate. The semen quality parameters including percentage and duration of sperm motility were measured 0, 3, 6, 9 and 12 days after storage. In the antibiotic receiving group, the values of percentage and duration of sperm motility reduced 3 and 6 days after storage respectively and reduced to lowest levels at day 12. In the antibiotic‐free group, the duration and percentage of sperm motility decreased significantly after 3 days of storage and reached to lowest values at day 12. Also, percentage and duration of sperm motility in each storage time were significantly higher in the antibiotic receiving group than in the antibiotic‐free group. The overall values of percentage and duration of sperm motility for all storage periods were higher in the antibiotic receiving group than in the antibiotic‐free group. In conclusion, our results demonstrated that 500 IU mL^?1 penicillin + 500 μg mL^?1 streptomycin sulphate improves the viability of caspian brown trout during short‐term storage.     

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.     

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.     

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.     

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.     

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.     

Karyological analysis of endangered Caspian salmon, Salmo trutta caspius (Kessler, 1877)

The karyotype and chromosomal characteristics of endangered Caspian salmon, Salmo trutta caspius, in the southern part of the Caspian Sea were investigated. From the total of 60 mitotic metaphases achieved from 15 individuals, 15, 9 and 36 metaphases were with the mode <76, 76 and 80 representing 25%, 15% and 60% of metaphases respectively. So, the most common pattern of chromosome number was 80 (36 metaphases, 60%) and the number of diploid chromosomes was thus confirmed as (2n=80) of this subspecies. The karyotype consists of seven metacentric, five submetacentric and 28 telocentric pairs. The karyological parameters of the Caspian salmon, the centromic index, arm ratio, relative length and length variation range of chromosomes, were 0–0.5, 1–∞, 0.011–0.045 and 0.507–2.028 μm respectively. The total length of chromosomes in haploid series was 44.776 μm and fundamental number of chromosome arms was 104. This study may provide the first knowledge on chromosome analysis in Caspian salmon and add basic information useful for its chromosomal manipulations.     

Commercial Bacillus probiotic supplementation of rainbow trout (Oncorhynchys mykiss) and brown trout (Salmo trutta): growth,immune responses and intestinal morphology

Probiotic administration is associated with the enhancement of host resistance to environmental and nutritional stressors, improving survival and growth rates. This study was carried out to evaluate the effects of dietary supplementation of Bacillus subtilis and Bacillus cereus toyoi on growth performance, innate immune responses and gut morphology of two trout species feeding a commercial diet high in soybean meal. A commercial probiotic (4.2 × 10⁹ CFU g^?1 of additive) was supplemented to the experimental diets at 0% (control), 0.03% (P₁; 6 × 10³ CFU g^?1 of diet) or 0.06% (P₂; 1.5 × 10⁶ CFU g^?1 of diet) and fed to brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) for 9 and 20 weeks respectively. Rainbow trout showed significantly better growth performance than brown trout, regardless of the dietary treatment. No effect of dietary probiotic supplementation was detected on growth performance, body composition or innate immune parameters (plasma lysozyme, alternative complement and peroxidase activities). In both species, after 9 weeks, intestinal lamina propria and submucosa were widened, with increased presence of inflammatory cells, significantly higher in groups fed probiotics. This inflammatory process, with villi and enterocytes noticeably damaged compared with the control group, was more pronounced in brown trout. Under the current trial conditions, the B. subtilis + B. cereus toyoi had no positive impact in either trout species, on the contrary a harmful effect was observed.     

Are growth and recapture of hatchery‐reared and resident brown trout (Salmo trutta L.) density dependent after stocking?

Abstract –  The population density of brown trout ( Salmo trutta ) in a small natural system was manipulated in six equal-length stream sections by stocking hatchery-reared 1+ brown trout (unstocked, tripled and quintupled) over two consecutive years. The results showed that hatchery-reared trout grew more slowly and were more mobile than resident trout, and that their growth was inversely density dependent. In contrast, growth of the resident trout was density independent. The recapture of 1+ resident and hatchery-reared trout was inversely density dependent. This is most likely a consequence of increased competition. However, after a single winter the population density returned to its base level prior stocking and older resident trout showed no density-dependent recapture. Thus, the advantage of stocking, here higher biomass, may have the detrimental effect of decreasing resident stocks of the same size class during summer.     

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.     

Response of resident brown trout, Salmo trutta L., and rainbow trout, Oncorhynchus mykiss (Walbaum), to the stocking of hatchery-reared brown trout

Two strains of hatchery-reared adult brown trout, Salmo trutta L., [208–334 mm total length (TL); n =  591] were individually marked and released into a limestone stream. The estimated survival after one month (86%; n =  508) was comparable to that for resident brown trout and rainbow trout, Oncorhynchus mykiss (Walbaum), (89%; n =  771), but declined to 14% ( n =  83) after 8 months compared with 52% ( n =  451) for resident trout. The movement of resident trout out of stocked stretches was higher (14%) than from control sites (5%), but the population size in both individual sites and the overall study area were unaffected. The growth of resident brown trout was unaffected by stocking, but rainbow trout showed lower growth rates in stocked versus unstocked stretches both one and 8 months after stocking ( P <  0.002).     

Survival and growth of hatchery and wild brown trout (Salmo trutta) parr in three Austrian headwater streams

Brown trout populations of three headwater streams in the Northern Limestone Alps of Austria were supplemented by three‐month‐old hatchery‐reared parr from a wild and locally adapted strain and a nonresident domesticated hatchery strain. Growth and survival were monitored with three surveys over a period of 16 months after stocking. Fish descending from the wild reared origin strain demonstrated higher survival rates than the hatchery strain. Differences in growth were found among the investigated streams but not among the investigated strains. The differing temperature regimes of the streams were considered as the primary factor causing those disparities. We conclude that stocking measures had little or no additive effect on successful natural reproduction, as the resident wild brown trout performed significantly better than the stocked fish.     

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.     

Effects of Sangrovit‐supplemented diet on growth performance,blood biochemical parameters,survival and stress resistance to salinity in the Caspian roach (Rutilus rutilus) fry

This study was carried out to show the effects of Sangrovit on growth, blood biochemical parameters, survival and resistance to salinity stress in the Caspian roach. Fish (1.24 ± 0.13 g) were divided into four groups fed diets containing Sangrovit at different levels: 0 (control), 0.05, 0.1 and 0.15% for 45 days. The results showed that there was a significant increase in final weight, weight gain and specific growth rate in those fish fed 0.15% Sangrovit diets compared with the control (P < 0.05). Food conversion rate of fish fed 0.05% Sangrovit diet was significantly (P < 0.05) lower than the control group. Condition factor was not significantly affected by Sangrovit dosage (P > 0.05). The blood glucose and cholesterol levels were significantly lower in treated groups compared with the control (P < 0.05). The highest total protein was obtained in the 0.15% group and it was significantly higher than in all other groups (P < 0.05). Challenges were carried out after 45 days of feeding, to determine the effect of Sangrovit on resistance to salinity stress. Blood samples were obtained four times after challenge (day 1, 3, 5 and 7) for evaluate haematocrit levels. On the first day, haematocrit increased significantly in all groups compared to day 5 and 7 (P < 0.05). The haematocrit levels decreased gradually in all groups from the third day. Before and after stress, no differences were observed for survival rate among the experimental diets (P > 0.05). These results indicate that the inclusion of 0.15% Sangrovit in the diet of the Caspian roach enhances feed efficiency, fish growth and blood biochemical parameters.     

Effect of habitat type on growth and diet of brown trout, Salmo trutta L., in stream enclosures

The effect of habitat on the growth and diet of brown trout, Salmo trutta L., stocked at the same densities in nine stream enclosures, comprising three habitat types of different quality, were tested. The habitats, which were created based on microhabitat preference data, were a shallow water habitat lacking cobbles (habitat 1), a deeper, mixed cobble-bottomed (128-384 mm diameter) habitat (habitat 2) and a large cobble-bottomed (256-384 mm) habitat of intermediate depth (habitat 3). Brown trout were found to have greater increases in total biomass in habitats 2 and 3 than in habitat 1. The pattern for length did not follow that of biomass as trout had greater increases in total length in habitat 2 than in the other two habitats. Biomass of food in trout diets reflected habitat-specific fish biomass changes, with a greater total biomass of prey as well a greater biomass of the leech, Erpobdella, in habitats 2 and 3 than in habitat 1. There were no habitat-specific differences in the biomass of benthic or drifting invertebrates in the enclosures, with the exception of a tendency for an effect of habitat on the biomass of Erpobdella. Although there may have been habitat-specific differences in food resources that were not detected, it is believed that the higher biomass growth in habitats 2 and 3 may have reflected differences in cover afforded by the deeper water and coarser substrates and/or improved foraging opportunities facilitated by the larger volumes of water in the deeper habitats in which the trout could search for prey.     

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.     

Exploring the relative influence of biotic interactions and environmental conditions on the abundance and distribution of exotic brown trout (Salmo trutta) in a high mountain stream

Abstract – In the Logan River, UT, USA, exotic brown trout demonstrate a strong allopatric distribution and occur at high densities at low‐elevation sites and in tributaries, and in low densities at native trout dominated, high‐elevation sites. Summer temperatures and discharge do not appear limiting for growth; adult growth rates were high overall and were greatest when fish were held experimentally at high elevation where they do not occur naturally. Brown trout are superior competitors; competition for space or food was stronger with their own con‐specifics than with other species. Evidence of density dependence was not observed at the juvenile life stage; no consistent relationships were detected between brown trout density and age‐1 condition or lagged, age‐0 weight (g). In contrast, adult brown trout demonstrated density‐dependent effects on condition and growth when reared experimentally. Field estimates of adult growth rates (g·day^?1), although variable, declined subtly with increasing density, and annual survival was significantly greater in the mainstem sites (mean = 52%) relative to a high‐density tributary site (mean = 22%). Annual predicted age‐0 brown trout growth potential was four‐times greater at the lowermost site, compared with the highest elevation site, although fish lost weight over winter months at all sites. While adult density dependence may influence population abundance at some sites, extreme spring–winter conditions may ultimately limit the upper elevational extent of brown trout in this system. With changing climatic conditions and the potential for habitat degradation in the future, these results have important implications for native fish conservation.