绿色合成纳米银材料的制备及其对水产病原菌的抗菌效果测定

近年来随着水产养殖规模不断扩大,渔药安全问题备受重视。为积极寻找抗生素替代品,本研究采用银杏叶提取物和硝酸银反应合成纳米银材料,并通过紫外-可见光全波段扫描、透射电镜以及X射线衍射对其结构表征进行鉴定。在此基础上,以金黄色葡萄球菌、大肠杆菌,以及水产病原菌迟缓爱德华氏菌和嗜水气单胞菌为测试对象,采用杯碟法、常量肉汤稀释法以及抑菌动力学实验测定合成的纳米银抗菌效果。结果显示,在波长450 nm处有纳米银等离子共振体形成的吸收峰;透射电镜观察到纳米银颗粒平均直径小于10 nm;X射线衍射图谱验证了金属银的生成;本研究所合成的纳米银材料对4种病原菌均有良好的抗菌效果。研究表明,采用银杏叶绿色合成纳米银,不仅方便、快捷,而且成本低廉、环境友好,在水产病害防控中具有良好的前景。     

Effects of dietary zinc oxide and selenium nanoparticles on growth performance,immune responses and enzyme activity in rohu,Labeo rohita (Hamilton)

A 120‐day feeding trial was conducted to assess the effects of dietary supplementation of zinc oxide (ZnO) and selenium (Se) nanoparticles (NPs) on growth, immunological and enzymatic profiles in rohu, Labeo rohita. Fishes were fed with basal diet incorporated with laboratory‐synthesized nanoparticles, viz., zinc oxide nanoparticles—10 mg/kg and Se nanoparticles—0.3 mg/kg throughout the experimental period. At an interval of every 30 days, treated and control fishes were randomly collected and subjected to estimation of growth, non‐specific immune parameters and serum enzyme assays. It was observed that there was significant (p < 0.05) increase in growth and non‐specific immune parameters like respiratory burst, lysozyme and myeloperoxidase activities as compared to the control group (only basal diet). Serum enzymatic profiles such as lactate dehydrogenase and alkaline phosphatase activities down‐regulated (p < 0.05) in treated group compared to control group, and superoxide dismutase and acetylcholine esterase activity up‐regulated in treated group. The relative percentage survival (RPS) found to be significantly higher in treated groups (60.00 ± 8.82%) as compared to control group (45.00 ± 6.17%) while challenged with virulent bacterial strain Aeromonas hydrophila. These results indicated that dietary supplementation of zinc oxide (ZnO) and selenium (Se) nanoparticles stimulates immunity and enhances resistance to bacterial infection in L. rohita.     

Application of nanosilver-coated zeolite as water filter media for fungal disinfection of rainbow trout (Oncorhynchus mykiss) eggs

This study investigated the indirect use of silver nanoparticles (AgNPs) for reduction of fungal infections during incubation period of fertilized rainbow trout eggs. Different concentrations of nanosilver-coated zeolite (0.5, 1, and 1.5 % AgNPs) were compared with unmodified zeolite as water filter media in semi-recirculation systems. For testing the effect of AgNPs on reduction of fungal infection, fertilized eggs were transferred in incubators receiving water from filters coated with nanosilver. The eggs in each incubator were inoculated with Saprolegnia-infected trout eggs. Any dead or infected eggs and embryos were periodically removed, while the performance of the filters was assessed by calculating the survival rates from fertilization up to completion of the yolk–sac absorption stage. The results showed that the filters containing 0.5 % AgNPs increased the survival rate by 4.56 % from fertilization to the swim up stage compared to the control (p < 0.05). Also, the additional application of activated carbon (as absorbent media) along with AgNP-coated media in filters caused an increase of about 11.24 % in the survival rate for the larval stage (p < 0.05). In contrast to the control group with about 6 % fungal infection, no infections were observed during the incubation period in the incubators containing nanosilver-coated filters. Therefore, the final results confirmed that the indirect use of AgNPs in the aforementioned filters were significantly effective for preventing fungal infections in semi-recirculation systems for rainbow trout, making them a candidate for replacing the chemical fungicides currently used during egg incubation in hatchery systems.     

Effects of glutamate in low‐phosphorus diets on growth performance,antioxidant enzyme activity,immune‐related gene expression and resistance to Aeromonas hydrophila of juvenile mirror carp (Cyprinus carpio)

This study investigated the effects of glutamate (Glu) in low‐phosphorus diets on growth performance, haematological indices, antioxidant enzyme activity, immune‐related gene expression and resistance to Aeromonas hydrophila in juvenile mirror carp (Cyprinus carpio) (5.07 ± 0.02 g). Fish were fed either graded levels of Glu (0 g/kg, 5 g/kg,  10 g/kg and 20 g/kg, named G0, G0.5, G1 and G2, respectively) in a low‐phosphorus diet (15 g/kg NaH₂PO_4, 0.49), or a normal phosphorus diet ( 20 g/kg NaH₂PO_4, 0.61) without added Glu (C), for 8 weeks. At the end of the feeding trial, the fish were challenged with A. hydrophila. Compared with G0 group, 10 g/kg and 20 g/kg Glu supplementation of the low‐phosphorus diet significantly improved the final weight, WGR, SGR and PER, and decreased FCR (p < .05). Glu supplementation of the low‐phosphorus diet significantly enhanced the T‐AOC, SOD activity and GSH content in intestine (p < .05). Glu supplementation significantly reduced MDA content in foregut and midgut and increased CAT activity in midgut and hindgut (p < .05). Regarding immune‐related gene expression, Glu supplementation significantly diminished the up‐regulation of intestinal TNF‐α, IL‐1β and IL‐8 mRNA levels induced by phosphorus deficiency (p < .05). The survival rate of the G1 group was significantly higher than that of the G0 group (p < .05). In conclusion, 10 g/kg Glu supplementation in low‐phosphorus diets can improve the growth performance, enhance the activity of intestinal antioxidant enzymes and strengthen the immune function of juvenile mirror carp.     

SNP discovery and gene annotation in the surf clam Mesodesma donacium

The main objective of this research was to identify single‐nucleotide polymorphisms (SNPs) from an Expressed Sequences Tags (EST) data set generated by 454 pyrosequencing in the soft clam Mesodesma donacium. A total of 180 159 ESTs were yielded from a M. donacium cDNA library. De novo assembly was performed using stringent calling parameters, producing 10 178 contigs and 41 765 singletons. Here, a total of 2594 SNPs were discovered related to 613 consensus sequences, achieving a frequency of 1 SNPs per 260 bp. SNP variants showed that A/G, A/T and C/T were the most abundant among the identified polymorphisms. We validated a total of 12 SNPs loci by HRMA for annotated genes such as heat shock protein‐70 and the translation elongation factor 1‐alpha. The Gene Ontology analysis regarding molecular function level revealed that sequences with SNPs were mainly classified to protein and nucleotide binding, as well hydrolase activity, ion binding and oxidoreductase activity. Further, biological processes like cellular and metabolic process, biogenesis, localization and biological regulation were highly annotated. The most expressed genes were related to the mitochondrial electron transport chain, senescence‐associated protein, ubiquitin and actin. Interestingly, some relevant genes related to immune response and biomineralization showed a high abundance, such as tumor necrosis factor (TNF)‐alpha‐receptor‐like protein, serine protease inhibitor, heat shock protein, aragonite‐binding protein and ferritin. This study contributes to relevant genes associated with functional polymorphisms and gives an overview for future genetic investigations.     

Estimation of production and long‐term changes in the population of European eel Anguilla anguilla (L.) in an Irish lake

Monitoring of yellow‐phase and silver‐phase Anguilla anguilla during their continental life history is necessary for evaluation of stock recovery measures. Eel population data for an Irish lake (Lough Sheelin) were compiled for the period 1993–2014. Catch data from 2009 to 2014 provided minimum estimates of recent silver eel production ranging annually from 0.79 to 1.84 kg/ha. Long‐term changes in yellow eel abundance and silver eel size structure were assessed as part of a fishery monitoring programme. Yellow eel catch per unit effort (CPUE) in the lake (from longline surveys) was considerably higher in the 1990s (52.2–62.1 eels/100 hooks) than 2002–2008 (1.9–15.8 eels/100 hooks). Conversely, during 1993–2014, the mean size of silver eels migrating from the lake increased significantly (p < .001), from 659 mm to 838 mm. The results suggest that in the absence of direct yellow eel abundance data, interannual variation in silver eel size structure may be a useful monitoring tool for local eel stocks as part of Eel Management Plans (EMP's).     

Antioxidant‐related parameters,digestive enzyme activity and intestinal morphology in rainbow trout (Oncorhynchus mykiss) fry fed graded levels of red seaweed,Gracilaria pygmaea

This study was conducted to investigate the effects of dietary red seaweed, Gracilaria pygmaea level on growth, antioxidant‐related parameters, digestive enzyme activity and intestinal morphology of rainbow trout (Oncorhynchus mykiss) fry. Five isocaloric and isonitrogenous diets were formulated to contain four G. pygmaea levels (30 (GL‐30), 60 (GL‐60), 90 (GL‐90) and 120 g/kg (GL‐120)), and a control diet was used, without inclusion of seaweed. Results of the feeding trial indicated that final body (FBW: 2.8–3.5 g) and specific growth rate (SGR: 4.8–5.2) were significantly improved when 60 g/kg G. pygmaea was supplemented in the diets. However, there was a significant reduction (p < .05) of final body weight (FBW) and specific growth rate (SGR) in fish fed 120 g/kg G. pygmaea. Protease activity was significantly lower in fish fed GL‐120 diet when compared to GL‐30 or control (p < .05). Lipase was significantly affected by dietary seaweed regardless its level of supplementation (p < .05). The inclusion of the Gracilaria in the diet led to evident changes in the fish antioxidant status with significant reduction of superoxide dismutase, glutathione peroxidase activity and lipid peroxidation products. The histological study demonstrated that all groups of fish displayed normal morphology of anterior intestine and pyloric caeca. Villi absorptive area in the anterior intestine of treatment groups GL‐90 and GL‐120 significantly decreased (p < .05). Overall, the results obtained in this study indicate that dietary G. pygmaea supplementation up to 90 g/kg improves growth performance in rainbow trout fry without compromising antioxidant responses and digestive function.     

Effects of dietary Bacillus pumilus on growth performance,innate immunity and digestive enzymes of giant freshwater prawns (Macrobrachium rosenbergii)

The present study was conducted to investigate the effects of Bacillus pumilus on the growth performance, innate immunity and digestive enzymes of the giant freshwater prawn, Macrobrachium rosenbergii. Prawns (mean weight: 1.81 ± 0.01 g) were fed different levels of B. pumilus at doses of 0, 1 × 10⁷, 1 × 10⁸ and 1 × 10⁹ CFU/g to produce one control group and three experimental groups (G1, G2 and G3), respectively. After a 60‐day experimental feeding period, the results showed that the final weight, weight gain rate (WGR) and specific growth rate (SGR) were significantly higher in experimental groups than in the control (p < 0.05), whereas these improvements did not differ significantly (p > 0.05) among experimental groups. The improvements in phagocytic activity, respiratory burst (RBs) activity and the activity of catalase (CAT), nitric oxide synthase (NOS) and acid phosphatase (ACP) were significantly higher in G2 and G3 than in the control and G1 (p < 0.05). Further, the activity of CAT, NOS and ACP significantly increased with an increase in the dietary level of B. pumilus (p < 0.05). The activity of phenoloxidase (PO) in G3 was significantly higher than that in the control (p < 0.05). The activity of amylase was significantly higher in the groups G2 and G3 than that in the control group. G3 improved the activity of protease compared with the control (p < 0.05). In conclusion, the results of this study indicated that the potential use of B. pumilusat a dose of 1 × 10⁸ CFU/g feed could improve the growth, immunity and digestive enzymes of M. rosenbergii.     

Nano zinc vis‐à‐vis inorganic Zinc as feed additives: Effects on growth,activity of hepatic enzymes and non‐specific immunity in rohu,Labeo rohita (Hamilton) fingerlings

The effects of dietary administration of inorganic zinc (zinc sulphate, ZnSO₄) and nano zinc (zinc oxide nanoparticles, ZnO‐NP) were evaluated in rohu, Labeo rohita fingerlings. Fish were fed with a basal diet (Control) supplemented with ZnSO₄ (T1, T2 and T3) and ZnO‐NP (T4, T5 and T6) at 10, 20 and 30 mg/kg, respectively, for a duration of 45 days. The results revealed that fish fed diet containing 20 mg ZnO‐NP per kg (T5) had the highest weight gain and specific growth rate (SGR, % per day), which was significantly different (p < .05) from the other experimental diets. Significantly (p < .05), higher activities of the digestive and metabolic enzymes were recorded in the fish fed ZnO‐NP containing diets as compared to the diets containing inorganic Zn or control diet. The maximum serum glucose and protein levels were noted in fish reared on diet T5. Both SGOT and SGPT activities were significantly increased in fish fed Zn‐supplemented diets (T1 to T6), as compared to the control group. Similarly, innate immune parameters were improved with feeding Zn incorporated diets. The highest phagocytic (40.74 ± 0.65%) and respiratory burst (0.33 ± 0.001, OD 630nm) activities were recorded in the fish fed diet containing ZnO‐NPs at 20 mg/kg (T5). The maximum superoxide production and serum peroxidase activity were detected in the fish fed T5 and T6 diets. Overall, results indicated that short‐duration feeding (≤45 days) of dietary ZnO‐NP (20 mg/kg) improved growth, enzyme activity, serum biochemical parameters and immune function in rohu fingerlings.     

Citrus x aurantium essential oil as feed additive improved growth performance,survival, metabolic,and oxidative parameters of silver catfish (Rhamdia quelen)

The effects of dietary supplementation of graded level (0, 0.25, 0.5, 1.0, and 2.0 ml/kg diet) of Citrus aurantium essential oil (EOCA) on the growth, metabolic, and oxidative parameters of silver catfish (Rhamdia quelen) were investigated in a 60‐day growth trial. Fish fed with 2.0 ml EOCA per kg exhibited significantly better growth performance than those fed the control diet. Glucose, lactate, and protein levels in liver and muscle were altered significantly by dietary addition of EOCA. Hepatic lipid peroxidation levels, measured using thiobarbituric acid reactive substance and lipid hydroperoxides assays, were reduced in animals receiving the diet containing EOCA. Superoxide dismutase activity was higher, while glutathione S‐transferase activity was lower in the liver of fish receiving 0.5, 1.0, and 2.0 ml EOCA per kg of diet than in control. The nonprotein thiols content was higher in fish receiving the EOCA‐containing diet. Thus, dietary addition of EOCA improved growth, biochemical, and antioxidant parameters in silver catfish and could be useful as dietary supplement.     

Antibacterial activity of immobilized silver nanoparticles on TEPA‐Den‐SiO2 against shrimp pathogen,Vibrio sp. Persian1

In this study, we prepared silver nanoparticles immobilized onto silica sand beads as an antibacterial material against pathogenic luminous Vibrio sp. Persian1. Silica beads were modified with 3‐aminopropyltriethoxysilane (APTES), cyanuric chlorid and tetraethylene pentamine, and silver nanoparticles were generated in various concentrations (0.5, 1, and 2 mM g^?1 of silica beads) of AgNO₃ on the surface using chemical reduction. Ag/TEPA‐Den‐SiO₂ samples were characterized by TEM, FE‐SEM/EDS, FT‐IR and ICP OES and their antibacterial activity assayed by zone of inhibition and test tube tests against pathogenic Vibrio sp. The results of the zone inhibitory test revealed that all the Ag/TEPA‐Den‐SiO₂ samples had an antibacterial effect against luminous Vibrio sp. Persian1. In addition, the tube test results showed 100% killing of bacteria in 2 h contact period. Ag/TEPA‐Den‐SiO₂ samples maintained their antibacterial activity after 14‐day immersion in seawater by slow release of silver ions. These results suggest that Ag/TEPA‐Den‐SiO₂ substrates could be effective antibacterial materials for disinfection of seawater used to culture Penaeid shrimp larvae.     

Evaluation of immune response and performance of silver catfish fed functional linseed fibres in response to hypoxia stress

This study was conducted to evaluate the immunostimulating activity and growth promoting of diets supplemented with different rations of soluble and insoluble linseed fibre to Rhamdia quelen under hypoxia‐induced acute stress. For this reason, soluble and insoluble fractions of linseed fibre were concentrated separately and combined into four ratios (1:0.5; 1:1; 1:2 and 1:4), which were added to the diets of silver catfish (6.43 ± 0.12 g) and evaluated in a biological assay, along with a control diet (without addition of linseed fibre). After being fed the experimental diets for 45 days, specimens of silver catfish were submitted to hypoxia‐induced acute stress. They were kept out of water for 60 s. Immediately afterwards, blood and cutaneous mucus were collected for subsequent determination of immunological indicators and stress. After stress, the fish were weighed and measured for performance parameter calculation. The experimental design was completely randomized with five treatments and four replications. The data underwent analysis of variance and the means were compared by Tukey's test (p < .05). The fish fed diets containing the 1:2 and 1:4 soluble:insoluble fibre ratios, showed higher total protein content, globulin, plasma alkaline phosphatase activity, and performance in addition to higher mucoprotein content in the cutaneous mucus of the fish. Regardless of their ratio in the diet, linseed fibre provided higher plasma levels of total immunoglobulins and reduction in cortisol levels. The 1:1, 1:2 and 1:4 diets led to higher levels of total immunoglobulins and alkaline phosphatase activity in cutaneous mucus. The results indicate that linseed fibre has a stress‐ reduction, immunostimulant and a growth promoter effect on silver catfish. The 1:2 or 1:4 soluble: insoluble fibre ratios provided greater stimulation of the target immunological indicators and performance.     

The effect of fresh seaweed and a formulated diet supplemented with seaweed on the growth and gonad quality of the collector sea urchin,Tripneustes gratilla,under farm conditions

This gonad enhancement study investigates the effect of different fresh and formulated feeds and feeding regimes on the growth and gonad quality of wild‐collected adult sea urchin, Tripneustes gratilla, under farm conditions for over 18 weeks. In the first 12 weeks (phase 1), urchins were fed fresh Ulva rigida (U); a 50:50 mixture of fresh U. rigida and Gracilaria gracilis (UG); fresh G. gracilis (G) and a formulated diet 20U (containing 20% U. rigida), and in the final 6 weeks (phase 2) of the study, diet was changed to a formulated feed (20U diet). By the end of phase 1, urchins fed the 20U diet produced gonads (50.72 ± 5.4 g) that were significantly heavier (p < .001) than the gonads of urchins fed the fresh seaweed diets (U, UG & G). By the end of phase 2, gonad weight of urchins in treatment groups UG‐20U and G‐20U were similar to those fed the 20U‐20U diet. Gonad colour of urchins in the G‐20U treatment became significantly lighter (ANOVA, p = .029) and poorer quality, compared with urchins in the U‐20U group. This gonad enhancement study, conducted on wild‐collected adult T. gratilla, has shown that a formulated feed (20U diet) can enhance gonad growth and produce commercially acceptable gonads. This farm‐based study supports previous findings from aquarium‐based studies by our group and indicates that short‐term sea urchin gonad enhancement can be carried out under farm conditions in South Africa.     

Immunomodulation and interferon gamma gene expression in sutchi cat fish,Pangasianodon hypophthalmus: effect of dietary fucoidan rich seaweed extract (FRSE) on pre and post challenge period

A 45‐days feeding trial was conducted to study the immunomodulatory effect and interferon gamma gene expression of dietary fucoidan rich seaweed extract (FRSE) from Sargassum wightii on Pangasianodon hypophthalmus fingerlings. One hundred and eighty fingerlings were distributed into six experimental groups in triplicates. Each group was stocked with 10 fish and fed to satiation with iso‐nitrogenous (34.96 ± 0.09–35.18 ± 0.03 CP%) and iso‐caloric (368.65 ± 0.86–375.09 ± 0.26 Kcal/100 g) purified diets containing either 0% FRSE (control), 1% FRSE (TF₁), 2% FRSE (TF₂), 3% FRSE (TF₃), 3% seaweed powder (TS₃) or 6% seaweed powder (TS₆) in the feed. After feeding trial the experimental fish were challenged with Aeromonas hydrophila. Immunological parameters like respiratory burst activity, lysozyme activity, phagocytic activity and total leukocyte count (TLC) were increased with the increasing level of dietary FRSE, whereas serum Albumin/Globulin (A/G) ratio and blood glucose level exhibited decreasing trend (P < 0.05). Increased TLC, blood glucose level, respiratory burst activity, serum A/G ratio, lysozyme and phagocytic activities were recorded during the post‐challenge period. Maximum expression of interferon gamma (IFN‐γ) gene was recorded in FRSE fed groups than the control group both in pre and post challenge condition. After challenged with A. hydrophila the highest survival was observed in TF₂ and TF₃ groups whereas lowest survival was observed in the control group. Hence, dietary supplementation of FRSE at an optimum level of 2% reduced the stress and improved the immune status of P. hypophthalmus fingerlings.     

Effects of dietary levels of essential oil (EO) extract from bitter lemon (Citrus limon) fruit peels on growth,biochemical, haemato‐immunological parameters and disease resistance in Juvenile Labeo victorianus fingerlings challenged with Aeromonas hydrophila

Essential oils (EOs) are used in the food industry because of their biological activity. We evaluated the effects of administration of essential oil (EO) extracted from bitter lemon (Citrus limon) fruit peels on the growth performance, biochemical, haemato‐immunological parameters and possible disease resistance in fingerlings (4 weeks old) Labeo victorianus challenged with Aeromonas hydrophila. Fish were divided into five groups and fed diets supplemented with C. limon fruit peels EO extract at 1%, 2%, 5% and 8% [as fed basis] and treatment compared with control group fed diet without C. limon fruit peels EO extract. The experiment was executed in triplicate. Concentration of plasma cortisol, glucose, triglyceride and cholesterol decreased while that of total protein and albumin increased as dietary inclusion of the EO extract of C. limon fruit peels was increased from 2% to 5%. Meanwhile haemato‐immunological parameters including red blood cell (RBC), white blood cell (WBC) counts, haematocrit (Htc), mean cell haemoglobin (MCH), mean cell haemoglobin concentration (MCHC) and neutrophiles increased with increasing dietary inclusion from 1% to 5% inclusion of C. limon fruit peels EO extract. Serum immunoglobulins, lysozyme activity and respiratory burst increased with increasing dietary levels up to 5% inclusion of EO extract of C. limon fruit peels. We demonstrate that formulation of feeds by incorporating upto 5% the EO extract from C. limon fruit peels significantly improved biochemical, haematological and immunological response in juvenile fish resulting to lower mortality than the untreated groups and appear to be effective antibacterial against A. hydrophila.     

Potential implications of acoustic stimuli as a non‐physical barrier to silver carp and bighead carp

The effectiveness of an acoustic barrier to deter the movement of silver carp, Hypophthalmichthys molitrix (Valenciennes) and bighead carp, H. nobilis (Richardson) was evaluated. A pond (10 m × 5 m × 1.2 m) was divided in half by a concrete‐block barrier with a channel (1 m across) allowing fish access to each side. Underwater speakers were placed on each side of the barrier opening, and an outboard motor noise (broadband sound; 0.06–10 kHz) was broadcast to repel carp that approached within 1 m of the channel. Broadband sound was effective at reducing the number of successful crossings in schools of silver carp, bighead carp and a combined school. Repulsion rates were 82.5% (silver carp), 93.7% (bighead carp) and 90.5% (combined). This study demonstrates that broadband sound is effective in deterring carp and could be used as a deterrent in an integrated pest management system.     

Identification of three SNPs in smad4 gene by tetra‐primer ARMS PCR and analysis of their associations with growth traits in gynogenetic populations of Culter alburnus

Three single nucleotide polymorphisms, c.1462C > T, c.1663G > T and c.2023G > A, in smad4 gene were isolated and typed in a normal population (meio‐G0), a first‐generation gynogenetic population (meio‐G1) and a second‐generation gynogenetic population (meio‐G2) in topmouth culter (Culter alburnus) by using the tetra‐primer amplification refractory mutation system (ARMS) PCR. The homozygosity of different loci in the three populations was analysed to study the efficiency of gene purification in this fish. Correlation of the three populations to seven growth traits (body length, body weight, body thickness, body height, total length, caudal peduncle length and caudal peduncle height) was estimated. Results showed that homozygosity and homozygosity rates of three SNP loci from meio‐G0 to meio‐G2 increased obviously, and the average homozygosity of c.1462C > T and c.1663G > T loci was 0.930 and 0.880 in meio‐G2 population, which was significantly higher than that in meio‐G0 population. In the meio‐G1 and meio‐G2 populations, correlation of seven growth traits with the CC genotype was significantly higher than that with the TT and TC genotypes in the c.1462C > T locus (p < .05). These results suggested that the CC genotype in the c.1462C > T locus could be an advantage mutation that stably affects the growth of different generations of this fish. It may be used as a potential molecular marker for gene‐assisted selection to improve a range of growth traits in topmouth culter.     

Direct and indirect impacts of pumping station operation on downstream migration of critically endangered European eel

Downstream passage of European eel Anguilla anguilla (L.) in catchments with pump(s) for water level management is a major concern. Catchment‐wide acoustic telemetry revealed silver eels quickly migrated downstream through unobstructed reaches (n = 12; mean ± SD = 17.9 ± 1.9 km/day). Fourteen of 17 acoustic‐tagged eels detected at the pumping station (82.1%) retreated back upstream and ten (58.8%) passed through pumps after delays (9.5 ± 11.0 days). Multi‐beam sonar imaging across the intake screen (55‐mm gaps) revealed that peaks in migration occurred during the nights preceding the new moon but 76.7% retreated back upstream. All passive integrated transponder (PIT)‐tagged eels recaptured (n = 56) downstream of a large (2.23‐m diameter) mixed flow pump survived but 96.5% had minor injuries, reduced physical condition and/or abnormal behaviour. By contrast, 64.7% of PIT‐tagged eels recaptured (n = 17) downstream of a small (0.8‐m diameter) axial flow pump died. No acoustic‐tagged eels that passed through the small axial flow pump (n = 10) performed onward migration at sea, unlike “control” eels released downstream (n = 11). This evidence may help develop effective remediation measures, such as operational changes, to maximise escapement of catadromous eel species at pumping stations.     

The placement of Gyrodactylus salmonis (Yin & Sproston) in the molecular phylogeny of studied members of the Gyrodactylus wageneri‐group parasitizing salmonids

The molecular phylogeny of Gyrodactylus salmonis from brook charr, Salvelinus fontinalis, rainbow trout, Oncorhynchus mykiss, cutthroat trout, O. clarkii, and Atlantic salmon, Salmo salar, in Canada is presented using sequences from ITS‐rDNA and the mitochondrial COX 1 gene. Sequence variation among G. salmonis specimens from the different North American hosts was consistent with within‐species variation reported for other Gyrodactylus. Sequence data are compared to those from other members of the wageneri group parasitizing salmoniform fishes in northern Europe (G. derjavini, G. derjavinoides, G. lavareti, G. salaris, G. salvelini, G. teuchis and G. truttae) and Asia (G. brachymystacis). Sequence divergence between G. salmonis and the recently described G. salvelini on Arctic charr, Salvelinus alpinus, in Finland was consistent with within‐species levels of variation in Gyrodactylus; however, phylogenetic analyses and morphological comparisons provided evidence of their distinctiveness such that they appear to be sister species. They grouped with G. lavareti (a parasite of a coregonid) to form a clade separate from European and Asian species of the wageneri lineage known from salmonid fish. Further study of gyrodactylids from across salmonid, coregonid and thymallid fish in the northern hemisphere would shed more light on the phylogeography of these parasites and serves as an important backdrop to understanding the evolution of their emergent virulence.