Genetic characterization of Portuguese brown trout (Salmo trutta L.) and comparison with other European populations

Abstract– Allozyme and other protein loci were examined to study the genetic structure of Portuguese brown trout ( Salmo trutta ) populations. A total of 247 individuals from three tributaries of the Lima hydrological basin and a hatchery, all located in northern Portugal, were analyzed. Four of 22 protein coding loci were found to be polymorphic: CK-A1^*, GPI-A2^*, MPI-2^* and TF^*. A new allelc at the latter locus was found in Atlantic populations. The data obtained for Portuguese brown trout were compared with published data for 14 European populations and three hatchery stocks. Six polymorphic loci (CK-A1^*, GPI-A2^*, GPI-B2^*, LDH-C^*, ME^* and MPI-2^*) were used in a cluster analysis. This showed the similarity of Portuguese natural populations and northern Iberian populations and that Portuguese hatchery fish have an autochthonous origin, distinct from that of other Atlantic hatchery stocks.     

Piscine orthoreovirus‐3 is prevalent in wild seatrout (Salmo trutta L.) in Norway

In 2017, a PCR‐based survey for Piscine orthoreovirus‐3 (PRV‐3) was conducted in wild anadromous and non‐anadromous salmonids in Norway. In seatrout (anadromous Salmo trutta L.), the virus was present in 16.6% of the fish and in 15 of 21 investigated rivers. Four of 221 (1.8%) Atlantic salmon (Salmo salar L.) from three of 15 rivers were also PCR‐positive, with Ct‐values indicating low amounts of viral RNA. All anadromous Arctic char (Salvelinus alpinus L.) were PCR‐negative. Neither non‐anadromous trout (brown trout) nor landlocked salmon were PRV‐3 positive. Altogether, these findings suggest that in Norway PRV‐3 is more prevalent in the marine environment. In contrast, PRV‐3 is present in areas with intensive inland farming in continental Europe. PRV‐3 genome sequences from Norwegian seatrout grouped together with sequences from rainbow trout (Oncorhynchus mykiss Walbaum) in Norway and Coho salmon (Oncorhynchus kisutch Walbaum) in Chile. At present, the origin of the virus remains unknown. Nevertheless, the study highlights the value of safeguarding native fish by upholding natural and artificial barriers that hinder introduction and spread, on a local or national scale, of alien fish species and their pathogens. Accordingly, further investigations of freshwater reservoirs and interactions with farmed salmonids are warranted.     

Genetic effects of introduced hatchery stocks on indigenous brown trout (Salmo trutta L.) populations in Spain

Abstract– To assess the levels of gene introgression from cultured to wild brown trout populations, four officially stocked locations and four nonstocked locations were sampled for one to three consecutive years and compared to the hatchery strain used for stocking. Allozyme analysis for 25 loci included those previously described as providing allelic markers distinguishing hatchery stocks and native populations. Different levels of hybridization and introgression with hatchery índividuals were detected in stocked drainages as well as in protected locations. These findings indicate that new policies for stocking and monitoring hatchery fish are needed if gene pools of wild Spanish brown trout populations are to be preserved.     

The effects of ration size on migration by hatchery‐raised Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)

Abstract – The possibility to increase the proportion of migrating hatchery‐reared smolts by reducing their food ration was studied. Lake‐migrating, hatchery‐reared salmon (Salmo salar) and trout (Salmo trutta) smolts were either fed normal rations, based on recommendations from the fish‐farming industry, or reduced (15–20%) rations. They were released into the River Klarälven, western Sweden, and followed as they swam downstream to Lake Vänern, a distance of around 25 km. For both Atlantic salmon and brown trout, smolts fed a reduced ration migrated faster than fish fed a normal ration. Furthermore, a higher proportion of salmon smolts fed reduced rations migrated to the lake than fish fed normal rations in 2007 but not in 2006. This difference between years corresponded to greater treatment differences in size and smolt status in 2007 than in 2006. For trout, the proportion of migrating individuals and smolt development did not differ with ration size. Trout migrants fed a normal ration had a higher standard metabolic rate (SMR) than nonmigrants, whereas there was no difference in SMR between migrating and nonmigrating salmon. These results show that it is possible to use a reduced food ration to increase the migration speed of both Atlantic salmon and brown trout and to increase the proportion of migrating Atlantic salmon.     

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.     

养殖和野生亚东鲑机体成分比较分析

亚东鲑(Salmo trutta fario)是鲑属鱼类在青藏高原仅有的鱼类种群,是亚东地区全国农产品地理标志产品。本研究对西藏亚东地区野生和养殖亚东鲑的常规营养成分及各组织氨基酸和脂肪酸组成进行分析,旨在比较野生和养殖亚东鲑营养成分的异同,为养殖亚东鲑的品质评价和饲料配方的完善提供参考信息。实验采集亚东河中野生亚东鲑和亚东渔业产业园中使用配合饲料养殖的亚东鲑各10尾用于相关成分分析,每尾为一个独立样本。结果显示,野生组肥满度显著低于养殖组,而全鱼水分和灰分显著高于养殖组。全鱼粗蛋白、粗脂肪以及肝脏常规成分在野生组和养殖组间无显著差异。野生组肌肉粗脂肪显著低于养殖组,而水分含量显著高于养殖组。野生组全鱼必需氨基酸总量显著高于养殖组,且野生组肌肉中苏氨酸、缬氨酸、苯丙氨酸、赖氨酸和甘氨酸含量显著高于养殖组。野生组全鱼、肌肉和肝脏中饱和脂肪酸、n-3多不饱和脂肪酸(n-3 PUFA)总量、EPA、C20:4n-6以及肌肉中DHA含量高于养殖组,而全鱼和组织中单不饱和脂肪酸和n-6 PUFA总量低于养殖组。综上所述,目前养殖亚东鲑和野生亚东鲑在机体成分上存在较大差异。由于养殖鱼类体成分很大程度上反映了饲料组成,因此,亚东鲑养殖中饲料营养组成可能有待进一步优化。     

Incidence of hybridization between Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., in Ireland

The substantial growth of the farmed salmon industry in Europe since the 1970s has highlighted concerns regarding the genetic impact of escaped farmed salmon on wild salmonid stocks. High incidences of salmon × trout hybrids have been recorded in rivers situated near intensive salmon farming in Norway and Scotland, which may be indicative of a breakdown in reproductive isolation between salmon, Salmo salar L., and brown trout, Salmo trutta L. In the present study, salmonid fry and 0+ parr were collected from rivers in western Ireland. Allozyme and minisatellite DNA analysis were carried out on fry to determine the frequency of F1 hybrids from 10 rivers located within 38 km of salmon farms and three rivers at least 80 km from salmon farms. A total of 49 hybrids were recorded from 4135 salmonid fry (frequency = 1.2%). Mitochondrial DNA analysis showed that all hybrids arose from Atlantic salmon female × brown trout male crosses. Hybrid parr were recorded from one of the low-risk rivers (1.0%), but were present in seven out of the 10 catchments located within 38 km of salmon farms, with frequencies ranging from 0.7% to 3.1%. The results of the present survey, which represents the first extensive record of the levels of salmon-trout hybridization in Ireland, are discussed in relation to the continued growth of salmon farming in this country.     

An investigation on the gamete quality of Black Sea trout (Salmo trutta labrax) broodstock fed with mealworm (Tenebrio molitor)

In this study, the effect of combined feeding Black Sea trout (Salmo trutta labrax) broodstock with commercial feed and mealworm larvae (Tenebrio molitor) for 50 days before the breeding period in order to evaluate the gamete quality. While the control group was fed with commercial feed, mealworm larvae were given as an additional protein source 2 days a week and 3 days a week to the experimental groups formed from female and male individuals. In addition to the growth parameters, the number of eggs (number/individual) and the egg diameter (mm), sperm volume (ml), density of spermatozoa (×10⁹ cell/ml), total motility (%), progressive motility (%) and average curvilinear velocity (VCL, µm/sec) values were determined. At the end of the study, the highest live weight gain was found as 46.2 g in the control group of male. The egg diameters were 4.3 ± 1.8 mm and 4.5 ± 1.4 mm in the worm treatment groups fed twice and three times with mealworm respectively. As a result, it was determined that feeding fish with mealworm larvae as an addition to the commercial diet in female individuals did not affect the amount of eggs (p > .05), but the egg diameters were significantly smaller in the control group than the mealworm groups (p < .05). In spermatological characteristics, only the amount of sperm was different between the groups (p < .05); all other parameters were found to be similar to each other with no statistical differences (p > .05).     

Recovery of Hafnia alvei from diseased brown trout,Salmo trutta L., and healthy noble crayfish,Astacus astacus (L.), in Bulgaria

Hafnia alvei was isolated in Bulgaria from healthy noble crayfish, Astacus astacus (L.), and then from farmed diseased brown trout, Salmo trutta L., with signs of haemorrhagic septicaemia. The isolates were identified initially with conventional phenotyping and commercial Merlin Micronaut and API 20E rapid identification systems, followed by sequencing of the 16S rRNA gene. Hafnia alvei Bt1, Bt2 and Aa4 were of low virulence to rainbow trout and brown trout, although cytotoxicity was demonstrated by Bt1 and Bt2, but not by Aa4.     

Effect of iodophor disinfection of non‐hardened Salmo trutta eggs on their bacterial and fungus load

This study investigated the efficiency of iodophor disinfection (135 ppm active iodine for 15–30 min) of non‐hardened Salmo trutta eggs against different groups of bacteria and against fungus. Egg samples were taken from non‐disinfected and from disinfected eggs, microorganisms were cultured on specific nutrient media and their mass was measured by turbidimetric methods. Bacteria and fungus mass of non‐hardened eggs could be reduced but not eliminated by iodophor disinfection with 135 ppm active iodine for 15 min. The extent of reduction was 47–65% (Experiment 1). The efficiency of disinfection increased with disinfection time as the reduction in bacteria and fungus mass was 40–55% after 15 min and 58–74% after 30 min (Experiment 2). Disinfection efficiency of iodophor solution diluted in water (reduction 49–57%) and of iodophor solution diluted in sodium chloride solution iso‐osmolar to the oocytes (reduction 52–61%) was similar (Experiment 3). The reduction in bacteria and fungus mass was persistent as it was 39–72% lower in embryos deriving from disinfected eggs than in embryos deriving from non‐disinfected ones (Experiment 4). In conclusion, the tested disinfection method is inadequate to eliminate pathogens completely but it could positively influence immune defence of eggs and embryos.     

Characteristics and rehabilitation of the spawning habitats of the sea trout, Salmo trutta, in Gotland (Sweden)

Characteristics of the natural spawning habitat of sea trout, Salmo trutta L., were studied in Själsöån, a small stream of Gotland, Sweden, from 1992 to 1999. Each year, trout spawned on 17 ± 7 different areas (156 places ha^?1). Most of the spawning grounds were used every year. Overcutting was evident for at least 60% of the spawning grounds. Fish spawned on a gravel of 19 ± 7 mm in diameter. From 1978 to 1992, 242 artificial spawning grounds were constructed by the Gotland Sport Fishermen Association in four Gotland streams. A sediment trap was dug upstream to the spawning grounds. The artificial spawning ground comprised of a downstream V‐shape stream deflector of large stones with a log weir at the narrowest point of the deflector. Upstream of the dam, 15–60 mm diameter gravel was deposited to constitute the spawning ground substratum. To keep the installation efficient, maintenance is needed every year before the spawning season.     

Lack of trophic polymorphism despite substantial genetic differentiation in sympatric brown trout (Salmo trutta) populations

Sympatric populations occur in many freshwater fish species; such populations are typically detected through morphological distinctions that are often coupled to food niche and genetic separations. In salmonids, trophic and genetically separate sympatric populations have been reported in landlocked Arctic char, whitefish and brown trout. In Arctic char and brown trout rare cases of sympatric, genetically distinct populations have been detected based on genetic data alone, with no apparent morphological differences, that is “cryptic” structuring. It remains unknown whether such cryptic, sympatric structuring can be coupled to food niche separation. Here, we perform an extensive screening for trophic divergence of two genetically divergent, seemingly cryptic, sympatric brown trout populations documented to remain in stable sympatry over several decades in two interconnected, tiny mountain lakes in a nature reserve in central Sweden. We investigate body shape, body length, gill raker metrics, breeding status and diet (stomach content analysis and stable isotopes) in these populations. We find small significant differences for body shape, body size and breeding status, and no evidence of food niche separation between these two populations. In contrast, fish in the two lakes differed in body shape, diet, and nitrogen and carbon isotope signatures despite no genetic difference between lakes. These genetically divergent populations apparently coexist using the same food resources and showing the same adaptive plasticity to the local food niches of the two separate lakes. Such observations have not been reported previously but may be more common than recognised as genetic screenings are necessary to detect the structures.     

Artificial reconditioning of wild sea trout, Salmo trutta L., as an enhancement option: initial results on growth and spawning success

Abstract  Following a sea trout stock collapse in 1989 and 1990, wild sea trout kelts were successfully reconditioned in brackish water using semi-moist pellets and a commercial broodstock diet. The on-growing of wild sea trout smolts was not so successful. Natural mortality was 12.9%, and 36.1% of the fish failed to adapt to the artificial diets: 82% of these were smolts. Instantaneous growth was highest from June to August (0.74%), with an overall rate for April to September of 0.51%. At the end of the first year. 36 females and 26 males matured; 34 females, with a mean fork length of 33.2 cm, were stripped yielding 22860 ova at a mean rate of 682 ova per female or 1586 ova kg^-1 body weight. The survival of green ova to eyed ova was 90–98%, and survival from green ova to hatched alevin was 95%.     

Genetic characterization of naturalized populations of brown trout Salmo trutta L. in southern Chile using allozyme and microsatellite markers

This study describes the genetic structure of five naturalized populations of brown trout in southern Chile using allozyme and microsatellite markers to establish levels of intra‐ and interpopulation genetic variability and divergence. Fourteen enzymatic systems were used comprising 20 loci and three microsatellite loci specific to brown trout. The genetic variability values (allozymes, P=20–35%, average=27%, H_O=0.118–0.160, average=0.141; microsatellites, P=33.3–100%, average=66.66%, H_O=0.202–0.274, average=0.229) are similar to values described in other naturalized populations of brown trout present in Chile, but higher than those observed in European populations of this species. Values of total genetic diversity (H_T) (allozymes=0.1216 and microsatellites=0.3504) and relative genetic divergence (G_ST) (allozymes=9.5% and microsatellites=15%) were also similar to the results obtained in previous studies of Chilean populations of brown trout. These values, when compared with those obtained in Europe, proved to be similar for H_T but lower for G_ST. The low interpopulational genetic differentiation was in accordance with the small genetic distance observed between the populations analysed (D Nei=0.004–0.025). On the other hand, the high frequency of one of the two alternative alleles of the phylogeographic marker locus LDH‐5* in the populations analysed (LDH‐5*90>0.84) would indicate a European origin, in particular Atlantic as opposed to Mediterranean, for the brown trout introduced into Chile. The high levels of genetic variability suggest a mixed origin for the naturalized brown trout in Chile, which could have originated either before or during the introduction process. Nevertheless, the low level of genetic differentiation between populations could reflect the short lapse of time in evolutionary terms, during which populations introduced into Chile have been exposed to different evolutionary forces, and which has not been sufficiently long to produce greater genetic differentiation between populations.     

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.     

Biotic and abiotic regulation of a low‐density stream‐dwelling brown trout (Salmo trutta L.) population: effects on juvenile survival and growth

The effects of biotic (density‐dependent) and environmental (flow and temperature) factors on the apparent survival, mean length and size variation of a low‐density brown trout population in the juvenile stage, that is, from their first summer (0+) to the end of the second year (1+), were determined. Apparent survival was negatively related to the age class density during the three periods (first summer, first winter and second summer). A significant interaction between the mean flow and 0+ density highlighted a gradient towards strong density dependence acting on fish loss (i.e., mortality or migration) with decreasing summer flow. Conversely, no density dependence was reported at higher mean flows. The mean length was determined by density‐dependent and density‐independent (temperature and flow) factors throughout the study period. The negative relationship between fish length and intracohort density was highly significant during the three periods. The yearling (1+) density was negatively related to 0+ fish length measured after the first summer, suggesting intercohort effects. A positive effect of temperature on fish length was observed. Mean length after the summer seasons (0+ and 1+ fish) was also positively related to mean flow. Fish size variation around the mean measured with the coefficient of variation (CV) increased with increasing 0+ densities, both at the end of the first summer and the first winter. Results suggested that density‐dependent and density‐independent factors acted jointly on apparent survival and growth with a predominance of biotic processes. We discussed the potential implications of density‐dependent regulations on growth and survival for population resilience after catastrophic events.     

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.     

First results on a relation between ovarian fluid and egg proteins of Salmo trutta and egg quality

By use of sodium dodecyl sulfate polyacrylamide gel electrophoresis, ovarian fluid proteins and main proteins of unfertilized eggs were qualitatively and quantitatively investigated in the brown trout, Salmo trutta, to see whether some of them were correlated with the rate of embryos reaching the eyed embryo stage. In the ovarian fluid, 12 types of proteins in the range of 39–166 kDa were detected whereby three proteins were lipoproteins and two were glycoproteins. Ovarian fluid proteins with a molecular weight of 85, 68, 62 and 39 kDa were negatively correlated with the percentage of eyed stage embryos. The statistical significance of the relations was low in simple and multiple regression models (R²≤0.534) indicating that the relations were influenced and superposed by other factors. Therefore, ovarian fluid proteins give only poor information about maturity and quality of eggs. In the eggs, nine major types of proteins in the range of 95–15 kDa were identified. The 95 kDa protein was a lipoprotein, the 85 and the 62 kDa protein were glycoproteins, and the 15 kDa protein was a phosphoprotein. The 95, 85, 77 and 39 kDa protein were positively correlated with embryo survival to the eyed embryo stage. The explanatory effect of the multiple regression model was very high (R²=0.961) indicating that distinct egg proteins are closely related with egg quality.     

Effects of dietary protein at two lipid levels on growth,gonadal development,body composition and liver metabolic enzymes of brown trout (Salmo trutta fario) broodstock

This study was conducted to estimate the effects of dietary protein and lipid levels on the growth, body composition, gonadal development and activity of liver metabolic enzymes of the brown trout Salmo trutta fario broodstock. Ten diets were formulated containing five different protein levels (360, 390, 420, 450 and 480 g/kg) and two different lipid levels (90 and 180 g/kg). The experiment was a completely randomized 5 × 2 factorial design. The fish with an initial body weight of 462.53 ± 45.40 g were cultured in a spring water flow‐through system for 77 days. The growth performance was affected by dietary protein and lipid levels. Increase in the dietary protein and lipid resulted in increase in the body lipid and protein contents. The male gonadosomatic index decreased in the groups treated with relatively high levels of protein (390–480 g/kg). The activities of the hepatic amino acid‐catabolizing enzymes—alanine aminotransferase and aspartate aminotransferase—increased significantly with the increase in the dietary protein level. The activities of the lipogenic enzymes (fatty acid synthetase and glucose‐6‐phosphate dehydrogenase) and gluconeogenic enzyme (fructose‐1,6‐bisphosphatase) increased with the increase in the dietary protein level. Further, an increase in the activities of glycolytic enzyme in liver with an increase in the dietary lipid was observed. The variation in some intermediary metabolizing enzymes due to dietary components supports the high‐metabolic adaptability of this species to dietary protein and lipid levels. A diet with 450 g/kg protein and 90 g/kg lipid with 24.56 mg/kJ protein/energy ratio maximizes the growth, feed efficiency and gonadal development.