Impact of live food on survival and growth of hatchery‐reared sea trout (Salmo trutta trutta L.) parr in the wild

Survival rates and growth parameters of hatchery‐reared sea trout (Salmo trutta trutta L.) fry were determined after stocking in the wild. The larvae were hatchery‐reared for 12 weeks in two groups: fry were fed either on live zooplankton and live chironomidae larvae (LFG), or fed a pellet diet (PFG). The survival rate and specific growth rates were higher in the LFG than in the PFG group. Most effective for hatchery‐reared fish intended for stocking was the natural, live feed. The mean number of chironomid larvae found in the stomachs of fish that were initially captured in the wild was significantly higher in the LFG than in the PFG group. The live diet supplied in the rearing period had a positive impact on the foraging skills of the sea trout fry and their survival in the wild after their release on 24 April 2010.     

Differences in growth between offspring of anadromous and freshwater brown trout Salmo trutta

In this study, individual growth of juvenile offspring of anadromous and freshwater resident brown trout Salmo trutta and crosses between the two from the River Imsa, Norway, was estimated. The juveniles were incubated until hatching at two temperatures (±S.D. ), either 4.4 ± 1.5°C or 7.1 ± 0.6°C. Growth rate was estimated for 22 days in August–September when the fish on average were c. 8 g in wet mass, and the estimates were standardized to 1 g fish dry mass. Offspring of anadromous S. trutta grew better at both 15 and 18°C than offspring of freshwater resident S. trutta or offspring of crosses between the two S. trutta types. This difference appears not to result from a maternal effect because anadromous S. trutta grew better than the hybrids with anadromous mothers. Instead, this appears to be an inherited difference between the anadromous and the freshwater resident fish lending support to the hypothesis that anadromous and freshwater resident S. trutta in this river differ in genetic expression. Egg incubation temperature of S. trutta appeared not to influence the later growth as reported earlier from the studies of Atlantic salmon Salmo salar.     

In situ management options to improve crucian carp (Carassius carassius,L.) and brown trout (Salmo trutta,L.) population status in Central Europe: A case study from the Czech Republic

The crucian carp (Carassius carassius, L.) and the brown trout (Salmo trutta, L.) are vanishing from freshwater ecosystems of central Europe. To conserve both species, tailor‐made conservation management of habitats and populations of both species was implemented and tested in the Czech Republic (central Europe). This management was adjusted to reflect the ecological needs of both species. This study aimed to describe the results of a tested in situ management and to analyze the population growth of brown trout and crucian carp under ideal conditions. An experiment was performed at 14 small gravel pit lakes. Seven of them were adjusted to fit the crucian carp habitat requirements while the other seven were treated as a control group. The same experiment was done on 14 smaller streams and with brown trout. The occurrence and growth of crucian carp and brown trout were surveyed over 2 years. A significantly faster growth of both crucian carp and brown trout was observed on the adjusted lakes and streams in comparison to the control group ones. Trout and carp prospered on small streams and gravel pit lakes (respectively) that were free of angling, fish stocking, pollution, piscivorous predators, and competition with hybridizing species like Prussian carp (Carassius auratus, L.) or hatchery‐reared brown trout.     

Effects of wastewater on fish health: an integrated approach to biomarker responses in brown trout (Salmo trutta L.)

The impact of wastewater effluent from a sewage treatment works (STW) on the health of brown trout held in cages and wild brown trout in a river was investigated. Biochemical, histological, and organismal responses as well as parasite abundances were monitored and then analyzed using multivariate analyses. Stress responses in trout induced by the water quality of the river upstream of the STW were enhanced by the discharge of the STW. For caged fish, the serum chemistry values alkaline phosphatase, blood urea nitrogen, and creatinine, as well as histological indices of gills and liver, were most effective at distinguishing among fish held in river water, a mixture of river water and wastewater, and tap water. For wild fish, total protein, histological liver alterations and abundance of two parasites (sessile peritrichia, Sphaerospora sp.) were the most indicative parameters for discriminating the health of fish between sites upstream and downstream of the STW. Considering the relationships between the measured parameters concurrently, the multivariate discriminant analysis is an effective method to evaluate which combination of parameters provide the best discrimination between the treatment groups. In contrast to the calculation of group differences based on individual responses, the integrated responses of parameters representing different biological levels lead to a more comprehensive assessment of organismal health and a more accurate distinction in differences between treatment groups.     

Recapture rate and growth of hatchery‐reared brown trout (Salmo trutta v. fario,L.) in Blanice River and the effect of stocking on wild brown trout and grayling (Thymallus thymallus,L.)

Hatchery‐reared adult brown trout, Salmo trutta v. fario L., [215–335 mm standard length (L_S), n = 82] were individually tagged and released into three sections of the Blanice River in May 2007. Wild populations of brown trout and grayling, Thymallus thymallus, L., in these sections and three non‐stocked control sections were also tagged. The recapture rate of hatchery‐reared adult brown trout after 6 months (18%, n = 15) was comparable to that of wild adult brown trout in stocked (15%, n = 14) and control (14%, n = 11) sections. The recapture rates of wild brown trout and grayling after 6 months were higher in control sections than in stocked sections, but the differences were not significant. The movement of recaptured large juvenile wild brown trout from stocked sections was significantly higher (36%) than from control sections (9%). Wild brown trout growth and grayling growth were unaffected by stocking with adult hatchery‐reared brown trout.     

Genetic differences between wild and hatchery‐bred brown trout (Salmo trutta L.) in single nucleotide polymorphisms linked to selective traits

To study effects from natural selection acting on brown trout in a natural stream habitat compared with a hatchery environment, 3,781 single nucleotide polymorphism (SNP) markers were analyzed in three closely related groups of brown trout (Salmo trutta L.). Autumn (W/0+, n = 48) and consecutive spring (W/1+, n = 47) samples of brown trout individuals belonging to the same cohort and stream were retrieved using electrofishing. A third group (H/1+, n = 48) comprised hatchery‐reared individuals, bred from a mixture of wild parents of the strain of the two former groups and from a neighboring stream. Pairwise analysis of F_ST outliers and analysis under a hierarchical model by means of ARLEQUIN software detected 421 (10.8%) candidates of selection, before multitest correction. BAYESCAN software detected 10 candidate loci, all of which were included among the ARLEQUIN candidate loci. Body length was significantly different across genotypes at 10 candidate loci in the W/0+, at 34 candidate loci in the W/1+ and at 21 candidate loci in the H/1+ group. The W/1+ sample was tested for genotype‐specific body length at all loci, and significant differences were found in 10.6% of all loci, and of these, 14.2% had higher frequency of the largest genotype in the W/1+ sample than in W/0+. The corresponding proportion among the candidate loci of W/1+ was 22.7% with genotype‐specific body length, and 88.2% of these had increased frequency of the largest genotype from W/0+ to W/1+, indicating a linkage between these loci and traits affecting growth and survival under this stream's environmental conditions. Bayesian structuring of all loci, and of the noncandidate loci suggested two (K = 2), alternatively four clusters (K = 4). This differed from the candidate SNPs, which suggested only two clusters. In both cases, the hatchery fish dominated one cluster, and body length of W/1+ fish was positively correlated with membership of one cluster both from the K = 2 and the K = 4 structure. Our analysis demonstrates profound genetic differentiation that can be linked to differential selection on a fitness‐related trait (individual growth) in brown trout living under natural vs. hatchery conditions. Candidate SNP loci linked to genes affecting individual growth were identified and provide important inputs into future mapping of the genetic basis of brown trout body size selection.     

Net ground speed of downstream migrating radio-tagged Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) smolts in relation to environmental factors

The downstream migration of Atlantic salmon (Salmo salarL.) and sea trout smolt (S. trutta L.) was investigated using radio telemetry in the spring of 1999 and 2000. Forty wild sea trout smolts, 20 F1 sea trout smolts, 20 hatchery salmon smolts and 20 salmon smolts from river stockings were radio tagged and released in the Danish River Lilleaa. The downstream migration of the different groups of fish was monitored by manual tracking and by three automatic listening stations. The downstream migration of radio tagged smolts of both species occurred concurrently with their untagged counterparts. The diel migration pattern of the radio tagged smolts was predominantly nocturnal in both species. Wild sea trout smolt migrated significantly faster than both the F1 trout and the introduced salmon. There was no correlation between net ground speed, gill Na⁺,K⁺-ATPase activity or fish length in any of the different groups. The migration speed of wild sea trout smolts was positively correlated with water discharge in both years. In F1 sea trout smolts, migration speed was positively correlated with temperature in 1999. The migration speed of salmon smolts did not correlate to any of the investigated parameters.     

Gill chloride cell surface-area is greater in freshwater-adapted adult sea trout (Salmo trutta, L.) than those adapted to sea water

An increase in the apical surface-area exposed to the environment in sea trout ( Salmo trutta , L.) branchial chloride cells, examined by scanning electron microscopy after adaptation to fresh water, indicates that salt-uptake may be dependent upon apical membrane morphology.     

Transforming growth factor‐β signalling in tumour resistance to the anti‐PD‐(L)1 therapy: Updated

Low frequency of durable responses in patients treated with immune checkpoint inhibitors (ICIs) demands for taking complementary strategies in order to boost immune responses against cancer. Transforming growth factor‐β (TGF‐β) is a multi‐tasking cytokine that is frequently expressed in tumours and acts as a critical promoter of tumour hallmarks. TGF‐β promotes an immunosuppressive tumour microenvironment (TME) and defines a bypass mechanism to the ICI therapy. A number of cells within the stroma of tumour are influenced from TGF‐β activity. There is also evidence of a relation between TGF‐β with programmed death‐ligand 1 (PD‐L1) expression within TME, and it influences the efficacy of anti‐programmed death‐1 receptor (PD‐1) or anti‐PD‐L1 therapy. Combination of TGF‐β inhibitors with anti‐PD(L)1 has come to the promising outcomes, and clinical trials are under way in order to use agents with bifunctional capacity and fusion proteins for bonding TGF‐β traps with anti‐PD‐L1 antibodies aiming at reinvigorating immune responses and promoting persistent responses against advanced stage cancers, especially tumours with immunologically cold ecosystem.     

A comparison of the effect of long-term starvation on responses to low-temperature stress by juvenile rainbow (Oncorhynchus mykiss) and brown (Salmo trutta) trout reveal different responses in the two species

Biometric parameters and oxidative stress indicators were measured in liver and muscle samples from rainbow trout and brown trout juveniles exposed to a 45-day starvation period at low water temperature. As a general tendency, hepatic antioxidant enzyme activities in both species increased with fasting to eliminate the harmful effects of reactive oxygen species (ROS). However, the metabolic response to food deprivation in the muscle of each species was different. Lipid peroxidation levels in both species increased with starvation. We concluded that (1) low water temperature enhances ROS production in salmonids because of increased polyunsaturated fatty acid content in the cell membrane; (2) starvation significantly impaired the growth parameters of brown trout, yet the reverse was found for rainbow trout; and (3) despite this negative interaction, brown trout juveniles can physiologically tolerate oxidative stress caused by starvation and can therefore be cultivated under stressful conditions even in their early life stages.     

Diet overlap among non‐native trout species and native cutthroat Trout (Oncorhynchus clarkii) in two U.S. ecoregions

The invasion of freshwater ecosystems by non‐native species can constitute a significant threat to native species and ecosystem health. Non‐native trouts have long been stocked in areas where native trouts occur and have negatively impacted native trouts through predation, competition, and hybridization. This study encompassed two seasons of sampling efforts across two ecoregions of the western United States: The Great Basin in summer 2016 and the Yellowstone River Basin in summer 2017. We found significant dietary overlaps among native and non‐native trouts within the Great Basin and Yellowstone River Basin ecoregions. Three orders of invertebrates (Ephemeroptera, Trichoptera, and Diptera) composed the majority of stomach contents and were responsible for driving the observed patterns. Great Basin trout had higher body conditions (k), and non‐native Great Basin trout had higher gut fullness values than Yellowstone River Basin trout, indicating a possible limitation of food in the Yellowstone River Basin. Native fishes were the least abundant and had the lowest body condition in each ecoregion. These findings may indicate a negative impact on native trouts by non‐native trouts. We recommend additional monitoring of native and non‐native trout diets, regular invertebrate surveys to identify the availability of diet items, and reconsidering stocking efforts that can result in overlap of non‐native fishes with native cutthroat trout.     

Evolution of a hybrid zone of two willow species (Salix L.) in the European Alps analyzed by RAD‐seq and morphometrics

Natural hybridization of plants can result in many outcomes with several evolutionary consequences, such as hybrid speciation and introgression. Natural hybrid zones can arise in mountain systems as a result of fluctuating climate during the exchange of glacial and interglacial periods, where species retract and expand their territories, resulting in secondary contacts. Willows are a large genus of woody plants with an immense capability of interspecific crossing. In this study, the sympatric area of two diploid sister species, S. foetida and S. waldsteiniana in the eastern European Alps, was investigated to study the genomic structure of populations within and outside their contact zone and to analyze congruence of morphological phenotypes with genetic data. Eleven populations of the two species were sampled across the Alps and examined using phylogenetic network and population genetic structure analyses of RAD Seq data and morphometric analyses of leaves. The results showed that a homoploid hybrid zone between the two species was established within their sympatric area. Patterns of genetic admixture in homoploid hybrids indicated introgression with asymmetric backcrossing to not only one of the parental species but also one hybrid population forming a separate lineage. The lack of F1 hybrids indicated a long‐term persistence of the hybrid populations. Insignificant isolation by distance suggests that gene flow can act over large geographical scales. Morphometric characteristics of hybrids supported the molecular data and clearly separated populations of the parental species, but showed intermediacy in the hybrid zone populations with a bias toward S. waldsteiniana. The homoploid hybrid zone might have been established via secondary contact hybridization, and its establishment was fostered by the low genetic divergence of parental species and a lack of strong intrinsic crossing barriers. Incomplete ecological separation and the ability of long‐distance dispersal of willows could have contributed to the spatial expansion of the hybrid zone.     

Lint‐O cooperates with L(3)mbt in target gene suppression to maintain homeostasis in fly ovary and brain

Loss‐of‐function mutations in Drosophila lethal(3)malignant brain tumor [l(3)mbt] cause ectopic expression of germline genes and brain tumors. Loss of L(3)mbt function in ovarian somatic cells (OSCs) aberrantly activates germ‐specific piRNA amplification and leads to infertility. However, the underlying mechanism remains unclear. Here, ChIP‐seq for L(3)mbt in cultured OSCs and RNA‐seq before and after L(3)mbt depletion shows that L(3)mbt genomic binding is not necessarily linked to gene regulation and that L(3)mbt controls piRNA pathway genes in multiple ways. Lack of known L(3)mbt co‐repressors, such as Lint‐1, has little effect on the levels of piRNA amplifiers. Identification of L(3)mbt interactors in OSCs and subsequent analysis reveals CG2662 as a novel co‐regulator of L(3)mbt, termed “L(3)mbt interactor in OSCs” (Lint‐O). Most of the L(3)mbt‐bound piRNA amplifier genes are also bound by Lint‐O in a similar fashion. Loss of Lint‐O impacts the levels of piRNA amplifiers, similar to the lack of L(3)mbt. The lint‐O‐deficient flies exhibit female sterility and tumorous brains. Thus, L(3)mbt and its novel co‐suppressor Lint‐O cooperate in suppressing target genes to maintain homeostasis in the ovary and brain.