Chemical marking of European glass eels Anguilla anguilla with alizarin red S and in combination with strontium: in situ evaluation of short‐term salinity effects on survival and efficient mass‐marking

This study presents a new chemical double‐marking technique for European glass eels Anguilla anguilla by combing alizarin red S (ARS) and strontium chloride hexahydrate (Sr). Marked eels (double marked with ARS and Sr, but also single marked with ARS) were exposed in situ to brackish water (15 g l^?1 artificial sea salt) for 14 days and did not exhibit increased mortalities compared with unmarked eels. Indeed, no mortality occurred in a marked group during the experiments. Moreover, an efficient mass‐marking approach with low handling effort for both single ARS and double ARS‐Sr techniques is described and was proven to be practicable for large‐scale stocking programmes.     

Mass‐marking of farmed European eels (Anguilla anguilla (Linnaeus, 1758)) with alizarin red S

The Working Group on Eel of the International Council for the Exploration of the Sea (ICES) regularly reports that a significant amount of stocked eels in Europe was pre‐grown in aquaculture farms prior to stocking—so called “farmed eels.” The ICES advices chemical marking of stocked recruits to ensure their traceability throughout all life stages. To date, however, there was a lack of knowledge concerning the most suitable chemical substance and its application on farmed eels. The aim of this study was to fill this gap by presenting successful attempts of marking those eels with alizarin red S (ARS). An ARS concentration of 150 mg L^?1 buffered with 150 mg L^?1 Tris(hydroxymethyl)aminomethane applied as an immersion bath over 9 h was sufficient to mark a total of 3572 kg of farmed eels (6.5–8.0 g mean body weight). The marking success was 100% on otoliths and highest stocking density of up to 67.1 kg m^?3 (corresponding 54.0 kg m^?2) turned out to have no effect on mortality which was consistently below 1%.     

Mass-marking of brown trout (Salmo trutta L.) larvae by alizarin: method and evaluation of stocking

This study describes otolith marking of brown trout (Salmo trutta L.) larvae by immersion in different solutions of alizarin red S (ARS). The best results were obtained after marking with ARS at a concentration of 150 mg L^?1. To evaluate the efficiency of stocking with brown trout fry, 10 000 20‐day‐old larvae were marked in years 2002 and 2003 with ARS and released 2 weeks later into sections of a river with natural brown trout reproduction. Electro‐fishing surveys carried out 2 months after stocking in 2002 revealed that only 4.8% of all caught young‐of‐the‐year trout originated from stocking; in 2003 the percentage was 8.9%. Based on the substantial natural reproduction and the low ratio of stocked to wild trout, it was recommended to discontinue stocking.     

Quantification of alizarin red S uptake in coregonid eggs after mass-marking

An easy method to measure the uptake rate of the persistent dye alizarin red S (ARS) during marking of whitefish eggs was established and used to measure the ARS content in three different whitefish species during and at the end of the marking procedure. Those values show that only 6–10% of the ARS in the marking solution will be absorbed by the eggs (0.0061–0.0119 mg per egg). Additional analyses 6, 15 and 36 months after marking showed ARS levels below the response level (<6.9 μg kg^–1).     

Experimental evaluation of using calcein and alizarin red S for immersion marking of bighead carp Aristichthys nobilis (Richardson, 1845) to assess growth and identification of marks in otoliths,scales and fin rays

In order to evaluate the effects of immersion marking with calcein (CAL) and alizarin red S (ARS) on growth and mortality of juvenile bighead carp Aristichthys nobilis, and assess mark quality in otoliths, scales, and fin rays, CAL from 50 to 200 mg L^?1 and ARS from 150 to 300 mg L^?1 concentrations were used. With the exception of non‐lateral line scales from 50 mg L^?1 CAL treatments, immersion for 24 h produced detectable marks in sagittae, lateral line and non‐lateral line scales, and fin rays (dorsal, pectoral, ventral, anal, and caudal) at 100 days post‐marking. Detectable fluorescent marks in sagittae were readily observed at concentrations of 150–200 mg L^?1 CAL or 150–300 mg L^?1 ARS. Marks were poorly visible in all non‐lateral line scales from both CAL‐ and ARS‐treated groups. Fluorescent marks were readily detected in lateral line scales at 100–200 mg L^?1 CAL or 150–300 mg L^?1 ARS, and in fin rays at 150–200 mg L^?1 CAL or 150–300 mg L^?1 ARS. In particular, optimal marks were observed at the highest concentrations investigated in sagittae (300 mg L^?1 ARS), lateral line scales (150–200 mg L^?1 CAL or 250–300 mg L^?1 ARS), and fin rays (200 mg L^?1 CAL or 250–300 mg L^?1 ARS). However, fluorescent marks visible to the naked eye were not produced by any of the CAL or ARS treatments in sagittae, scales, or fin rays during this experiment. In addition, there was no significant difference on survival and growth of marked fish compared to controls throughout the experiment (P > 0.05).     

A long-term study of population characteristics and downstream migrations of the European eel Anguilla anguilla (L.) and the effects of a migration barrier in the Girnock Burn, north-east Scotland

Downstream migrations and population characteristics of eels Anguilla anguilla were studied between 1967–1982 and 2002–2005 using a fish trap and electrofishing in the Girnock Burn, a small oligotrophic upland sub‐catchment of the River Dee, north‐east Scotland, 70 km from the tidal limit. In limited mark‐recapture studies, 9% of eels were recaptured up to three times and 97% of all recaptures were made at the same electrofishing site. The recaptured eels had a low mean growth rate of c. 13 mm year⁻¹. Smaller eels appeared to show preferences for shallower habitats with small boulder and gravel–sand substrata. Trap catches exhibited seasonal modes in total length at 140–180 mm in late spring, and 320–340 mm in early autumn, probably relating to water temperatures and discharges. From other studies, it is inferred that the spring mode comprised sexually undifferentiated nomadic eels and the autumn mode differentiated males beginning their spawning migration. Large female eels were rare. The fish trap appears to have formed a major barrier to upstream migration since its construction in 1966. In‐stream density has decreased significantly since then from 16 to three eels 100 m⁻², biomass from 260 to 78 g 100 m⁻² and emigrants from 700 to 100 individuals year⁻¹. Emigrants have comprised c. 5% of the standing stock year⁻¹ since the 1970s. The proportion of larger differentiated eels in the Girnock Burn has, however, remained relatively constant and escapement has been c. 100–200 (probably male) eels year⁻¹ since the late 1960s. Evidence, including that from other northerly British rivers, is reviewed to assess the possible impacts of Europe‐wide declines in glass eel recruitment since the 1980s. It is recommended that the data series be maintained, plus further sex determination and ageing studies. Installation of an upstream trap to capture immigrants and studies of recolonization are proposed.     

Study on survival,growth, haematology and body composition of Cyprinus carpio under different acute and chronic salinity regimes

Pakistan’s most of the land is less productive or no productivity at all due to erosion and salinity of the soil, which can be utilized to develop fisheries. The project, “Survival, growth and body composition of Cyprinus carpio under different salinity regimes” was undertaken in two phases. In the first phase susceptibility of Cyprinus carpio at four salinity levels in triplicate within 0–10 g L⁻¹NaCl for 96 h in each aquarium was checked after one week acclamation at 0 g L⁻¹, 2 g L⁻¹ and 4 g L⁻¹ NaCl. LC₅₀ values varied from 7.67 to 10.65 g L⁻¹ after 96 h for C. carpio. Percentage mortality of the fish and important water quality parameters after every 12 h were observed for a period of 96-h. Probit analysis showed that 96-h LC₅₀ values ranged from 7.67 to 10.65 g L⁻¹. During experimental period aquaria water temperature ranged from 29.6 to 33.7 °C, pH values fluctuated between 7.8 and 9.7, Electrical conductivity values ranged from 2.40 to 20.13 dSm⁻¹ and Dissolved oxygen ranged between 2.23 and 10 mg L⁻¹. Sub-lethal salt concentration i.e. 0 g L⁻¹ to 3 g L⁻¹ NaCl upto 40 days showed that growth of C. carpio decreased with the increase of water salinity levels and ceased at 4 g L⁻¹ salinity and increase in salinity have negatively affected hematological parameters.     

High stocking density during larviculture and effect of size and diet on production of juvenile Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae)

Different stocking densities were investigated in larviculture and feeding of Lophiosilurus alexandri, as well as analyses of the effects on juveniles of two size‐classes and two different commercial formulated diets. The first experiment was two‐phased: (a) larvae stocked at densities of 60, 120, 180, 240, and 300 larvae L⁻¹ fed with Artemia nauplii and reared for 15 days; (b) in phase 2, densities of 5, 10, 15, 30, and 40 juveniles L⁻¹ were evaluated during feed training (20 days). Mean water temperature in both phases was 28°C. In the first phase of experiment 1, the different stocking densities did not affect fish growth or survival. In phase 2, growth was similar in all densities; however, survival was lower at higher densities. The increased density provided a rise in biomass and number of individuals produced in both phases. In the second experiment, two size‐classes of feed‐trained juveniles (30.22 ± 1.84 and 34.66 ± 2.41 mm) were given pellets of two different diameters (1.2 and 2.6 mm) for 20 days. The largest juveniles fed the 1.2 mm inert diet had higher final weights and lengths. Larviculture and feed training of L. alexandri can thus be performed successfully at high stocking densities of 300 larvae L⁻¹ during the first 15 days of feeding, and at densities of up to 40 juveniles L⁻¹ during the 20 days of feed training, respectively.     

Growth and Production of Yellow Eels and Glass Eels in Ponds

Two experiments (I and II) were performed in drainable ponds. Yellow eels Anguilla anguilla (L.) were stocked in early June at three biomasses: 10, 20 and 60 kg · ha⁻¹ in experiment I; and 10, 20 and 40 kg · ha⁻¹ in experiment II. The mean body weights were 27.0 and 24.2 g respectively. Glass eels were stocked only in experiment II at equal densities of 1600·ha⁻¹. In both experiments each biomass of yellow eel was combined in a factorial design with three cyprinid communities differing in biomass and in species- and size-composition. The ponds were drained in autumn. The final body weights at draining ranged from 25.9 to 63.6 g for yellow eel and from 3.9 to 8.8 g for glass eel. The final body weights of yellow eel and of glass eel decreased with increasing biomass of yellow eel. No significant relation was found between the bream Abramis brama (L.) biomass and the growth of eel. The growth rates of yellow eel and glass eel were positively correlated in experiment II. At higher biomasses of yellow eel the percentage females decreased slightly. The recapture rates of yellow eel in experiments I and II amounted to 69.4 ± 9.8 % and 92.2 ± 4.9% (mean ± sd) respectively. The lower recapture rates in experiment I were caused by the inappropriate draining technique used. The glass eels were recaptured with 75.0·5.6% efficiency. The maximum net production of yellow eel occurred at a biomass of 20–40kg·ha⁻¹ and amounted to 19 kg·ha⁻¹.     

Effects of stocking density on survival,growth and size variation of juvenile Brachymystax lenok (Pallas, 1773)

In this experiment the effects of stocking density on growth and survival of juvenile Brachymystax lenok were studied. Experimental fishes were reared at different stocking densities (5, 25, 50 and 75 fish L^?1) for 40 days at ambient temperatures (11.2–16.4°C). During the experiment, dissolved oxygen (DO) was above 5.4 mg L^?1 and other major environmental factors were controlled at the same levels in each aquarium (DO 5.4–7.2 mg L^?1, pH 6.6–7.4, and flow‐through rates 0.3–0.4 L s^?1). Mortality data in each group was recorded daily and random samples of 30 juveniles were measured and weighed every 10 days. All statistical analyses were performed by anova . The survival rate was found to be significantly affected by stocking density, but not the condition factor (CF), specific growth rate (SGR) or coefficients of variation (CV).The results demonstrate that lenok juveniles can be reared at higher stocking densities, which can increase survival under intensive conditions.     

Implication of storage conditions on luminescence response from Photobacterium phosphoreum in free and immobilized form

Bioluminescent bacteria in the form of a cell suspension for on-site hazard analysis are not suitable as in vivo luminescence in free cells fluctuates and may lead to erroneous results. Furthermore, the culture broth cannot be stored for long durations to continue sensing analytes as the luminescence ceases over time. Factors that affect luminescence response include growth dynamism, and ambient environmental conditions. The present study investigated the effect of storage conditions such as temperature (25 ± 2°C, room temperature; 4°C; and −20°C) and ambient aqueous environment (M1: sucrose, 1.02 M; M2, bioluminescent media [tryptone, 10 g L⁻¹; NaCl, 28.5 g L⁻¹; MgCl₂.7H₂O, 4.5 g L⁻¹; CaCl₂, 0.5 g L⁻¹; KCl 0.5 g L⁻¹; yeast extract, 1 g L⁻¹; H₂O, 1 L]; M3, bioluminescent media and 95% glycerol, 1:1 ratio) on the luminescence emission from the calcium alginate-immobilized Photobacterium phosphoreum (S_b) against the cells in free suspension for an extended period. The results indicated that both the parameters that were undertaken markedly affected the luminescence. In the study, S_b showed an enhanced luminescence emission than the control up to 18.5-fold and for a prolonged period which can be efficiently utilized for rapid biosensing of hazardous materials.     

In vitro culture and micropropagation of the Baetic-Moroccan endemic plant Lapiedra martinezii Lag. (Amaryllidaceae)

Lapiedra martinezii Lag. is a potential medicinal and ornamental plant facing conservation challenges. Thus, this study was focused on determining the conditions for culture initiation and propagation using in vitro techniques. The optimal sterilization procedure combined thermotherapy at 54°C for 60 min and immersion in 7% (w/v) Ca(ClO)₂ solution for 20 min. The most suitable medium to initiate bulb scales cultures was Gamborg B5 medium containing 500 mg L⁻¹ casein, 2 mg L⁻¹ adenine, 10 mg L⁻¹ glutathione and 10 g L⁻¹ sucrose. The most productive multiplication medium tested was Murashige and Skoog medium containing 30 g L⁻¹ sucrose, 4.0 mg L⁻¹ 6-benzylaminopurine, and 0.12 mg L⁻¹ 1-naphtaleneacetic acid. Most plants developed in vitro rooted spontaneously in the multiplication phase. The vast majority of the plants (89%) were successfully transferred to ex vitro conditions, and 100% survived over 1 yr of cultivation outdoors. Sucrose at a concentration of 60 g L⁻¹ was the most effective treatment to increase the biomass of bulblets. High auxin/cytokinin ratios produced the highest callus induction efficiency. The vast majority of callus developed in dark conditions, but none regenerated in the combinations of growth regulators previously tested. The plants obtained by micropropagation did not show significant differences in morphometric traits compared with the wild specimens, which supported the stability of the materials produced in vitro. This is the first report on cell cultures and micropropagation of L. martinezii, and the results can be applied to other Amaryllidaceae for industrial or conservation purposes.

     

Nitrogen biofiltration capacities and photosynthetic activity of Pyropia yezoensis Ueda (Bangiales,Rhodophyta): groundwork to validate its potential in integrated multi-trophic aquaculture (IMTA)

Porphyra spp. (currently Porphyra and Pyropia) are major sources of seafood globally. In this study, we investigated the effects of ammonium concentration, water temperature, and thallus stocking density on N-ammonium uptake rate (NUR), tissue nutrients content, N–NH₄ ⁺ filtration efficiency (NUE: nitrogen uptake efficiency %) of Pyropia yezoensis at a laboratory scale and in a mesoscale to evaluate the potential of this species as a biofilter. Additionally, photosynthetic activity was examined using Diving-PAM fluorometer to evaluate the health status. At a laboratory scale, the NUR and tissue nitrogen (N) content of P. yezoensis increased with increasing NH₄ ⁺ concentrations in the medium. The NUR at thallus stocking densities of 5 and 10 g fresh weight (FW) L^–1 were significantly higher than that at 20 g FW L^–1. Effective quantum yield (? F/F’ _m ) and tissue N content was significantly higher at all stocking densities than that at the beginning of experiment. The NUE was over 90 % at 10 and 17 °C, while all thalli cultured at 25 °C died after 5 days. In a mesoscale, the NUE at a thallus stocking density of 10.0 g FW L^–1 was significantly higher than that at a stocking density of 5.0 g FW L^–1. No differences in the NUE occurred between 10 °C and 17 °C. Photosynthetic activity (?F/F’_m and rETR_max) of P. yezoensis at optimal culture condition (10–12 °C and 10 g FW L^–1) increased over time through the experiment. This indicates that thallus was healthy during culture and chlorophyll a fluorescence can be as a monitoring tool for evaluating the physiological status of seaweeds in an integrated multi-trophic aquaculture.     

Marking the European eel with oxytetracycline, alizarin red and coded wire tags: an evaluation of methods

After 1 week, the mortality of European eel Anguilla anguilla after marking glass eels with oxytetracycline (OTC) and alizarin red (ALC), and farm eels with coded wire tags (CWTs) was 0% within all treatments. The suitability of implanting CWTs in the nose region (tag loss 94% after 1 week) and in the dorsal musculature (tag loss 4% after 1 week) was also examined.     

Optimization of β-mannanase production by Bacillus subtilis US191 using economical agricultural substrates

The Bacillus subtilis US191 strain producing highly thermostable β-mannanase was previously selected as potential probiotic candidate for application as feed supplement in poultry industry. Initially, the level of extracellular β-mannanase production by this strain was 1.48 U ml⁻¹. To improve this enzyme titer, the present study was undertaken to optimize the fermentation conditions through experimental designs and valorization of agro-industrial byproducts. Using the Plackett–Burman design, in submerged fermentation, a set of 14 culture variables was evaluated in terms of their effects on β-mannanase production. Locust bean gum (LBG), soymeal, temperature, and inoculum size were subsequently optimized by response surface methodology using Box–Behnken design. Under optimized conditions (1 g L⁻¹ LBG, 8 g L⁻¹ soymeal, temperature of 30°C and inoculum size of 10¹⁰ CFU ml⁻¹), a 2.59-fold enhancement in β-mannanase titer was achieved. Next, to decrease the enzyme production cost, the effect of partial substitution of LBG (1 g L⁻¹) by agro-industrial byproducts was investigated, and a Taguchi design was applied. This allowed the attaining of a β-mannanase production level of 8.75 U ml⁻¹ in presence of 0.25 g L⁻¹ LBG, 5 g L⁻¹ of coffee residue powder, 5 g L⁻¹ of date seeds powder, and 5 g L⁻¹ of prickly pear seeds powder as mannans sources. Overall, a 5.91-fold improvement in β-mannanase production by B. subtilis US191 was achieved.     

Glycerol increases growth,protein production and alters the fatty acids profile of Spirulina (Arthrospira) sp LEB 18

Most of the crude glycerol produced globally is generated by biodiesel production, which makes this byproduct an environmental responsibility of the biofuel industries. Among the forms of this compound in use, microalgae cultivation is a promising alternative that may generate a reduction in crude glycerol treatment costs via using it as an organic, carbon-rich substrate in culture media. In this work, the influence of different concentrations of glycerol in the culture medium, the composition of fatty acids and proteins in Spirulina sp. LEB 18 biomass and their effect on its growth were investigated. The fatty acid profile of the biomass was altered, showing a 20% increase in the unsaturated concentration and a 60% reduction in the saturated concentration in the culture supplemented with 0.05 mol L⁻¹ of glycerol compared to those in the control. The addition of the substrate stimulated an increase in its cellular concentration (3.00 g L⁻¹, 0.05 mol L⁻¹), productivity (0.72 g L⁻¹ d⁻¹, 0.05 mol L⁻¹) and its protein production (69.78% w w⁻¹, 0.05 mol L⁻¹).     

One-pot production of d-allulose from inulin by a novel identified thermostable exoinulinase from Aspergillus piperis and Dorea sp. d-allulose 3-epimerase

Inulin has been widely used as a cheap bioresource for producing many valuable products by enzymatic hydrolysis or microbial fermentation, such as high-fructose syrup and fructooligosaccharides. In this work, a one-pot two-enzyme reaction system was developed to produce d-allulose from inulin using A. piperis exoinulinase and Dorea sp. d-Allulose 3-epimerase. The exoinulinase that was identified from Aspergillus piperis CBS 112811 was cloned and intracellularly expressed in Escherichia coli. The enzyme displayed the maximal activity as 3750 U mg⁻¹ at pH 6.0 and 55 °C. For the effects of different cations, Mn²⁺ simulated the enzyme activity by 41 %. When 10 g L⁻¹ inulin was hydrolyzed by A. piperis exoinulinase, the conversion rate reached 98 % within 6 h. Furthermore, the optimum pH, temperature and the ratio of the two enzymes loaded for one-pot reaction were measured to be pH 6.0, 60 °C and 15/15 U mL⁻¹, respectively. The conversion rate of inulin to d-allulose reached 23.3 % after reaction for 4 h with 10 g L⁻¹ inulin. When adding 100 g L⁻¹ as a substrate, 21.4 g L⁻¹ d-allulose was produced using the two-enzyme system.     

Oven,Temperature-Controlled Microwave,and Shade Drying Effects on Drying Kinetics,Bioactive Compounds and Antioxidant Activity of Knotweed (Polygonum cognatum Meissn.)

In this study, the plant node was dried in an oven (40, 50 and 60 °C), shade and temperature-controlled microwave (40, 50 and 60 °C) methods. Statistically (p<0.05), the values closest to the color values of fresh grass were determined in an oven at 40 °C drying temperature. Effective diffusion values varied between 8.85×10⁻⁸–5.65×10⁻⁶ m² s⁻¹. While the activation energy was 61.28 kJ mol⁻¹ in the oven, it was calculated as 85.24 kJ mol⁻¹ in the temperature-controlled microwave. Drying data was best estimated in the Midilli-Küçük (R² 0.9998) model oven at 50 °C. The highest SMER value was calculated as 0.0098 kg kWh⁻¹ in the temperature-controlled microwave drying method. The lowest SEC value in the temperature-controlled microwave was determined as 24.03 kWh kg⁻¹. It was determined that enthalpy values varied between −2484.66/−2623.38 kJ mol⁻¹, entropy values between −162.04/−122.65 J mol⁻¹ and Gibbs free energy values between 453335.22–362581.40 kJ mol⁻¹. Drying rate values were calculated in the range of 0.0127–0.9820 g moisture g dry matter⁻¹ in the temperature-controlled microwave, 0.0003–0.0762 g dry matter⁻¹ in the oven, and 0.001–0.0058 g moisture g dry moisture matter⁻¹ in the shade. Phenolic content 6957.79 μg GAE g⁻¹ fw - 48322.27 μg GAE g⁻¹ dw, flavonoid content 3806.67 mg KE L⁻¹ fw - 22200.00 mg KE L⁻¹ dw and antioxidant capacity 43.35 μmol TE g⁻¹ fw - 323.47 μmol TE g⁻¹ dw. The highest chlorophyll values were obtained from samples dried in an oven at 40 °C. According to the findings, it is recommended to dry the knotweed (Polygonum cognatum Meissn.) plant in a temperature-controlled microwave oven at low temperatures. In this study, in terms of drying kinetics and energy parameters, a temperature-controlled microwave dryer of 60 °C is recommended, while in terms of quality characteristics, oven 40 °C and shade methods are recommended.     

Immersion mass marking of pikeperch (<Emphasis Type="Italic">Sander lucioperca</Emphasis>) larvae in oxytetracycline hydrochloride and its detection using fluorescence microscopy

Fish marking is essential to distinguish between stocked and naturally reproduced fish. This procedure is challenging, especially in early life stages. Therefore the objective of this study was to investigate the possibility of oxytetracycline hydrochloride (800 mg L^?1 solution) immersion marking on 3–5 days old pikeperch larvae, with focus on durability and readability of marks on the otolith of marked individuals. The immediate mortality after marking was low (?5%) and growth of the pikeperch was continuous during the eight week study period. The fluorescent marks were detectable during the whole study period, but after the sixth week grinding of the otoliths was necessary. With grinding otoliths the processing time and the probability of damaging the mark increased significantly. Another critical period was the necessity of sample storage in a dark place due to the marks’ instability in light, in all phases before the final mark detection. The study confirmed the suitability of oxytetracycline hydrochloride marking for use in studies focused on pikeperch juveniles’ early growth, stocking success, distribution etc.     

Annual variability in upstream migration of glass eels in a southern USA coastal watershed

We investigated the environmental factors that affected temporal variability of eel recruitment and upstream migration in a freshwater coastal river along the southeastern US. Glass eels Anguilla rostrata were collected through ichthyoplankton sampling in the lower Roanoke River, North Carolina. Monthly samples were taken from fixed stations from May 2001 through June 2003. There was no evidence of consistent seasonal migration patterns for glass eels in Roanoke River. From May through December in 2001, glass eels were captured only during August. In 2002, glass eels arrived in February and remained in ichthyoplankton samples through October, with the exception of samples from September. Peak catch occurred in March at 4.02 ± 1.2 and declined through June to 0.18 ± 0.07 (#/1,000 m³). By August, the mean density increased to 0.96 ± 0.82 and to 3.59 ± 2.77 by October. In 2003 from January through June, glass eels were captured only during February and March. Glass eels were routinely collected when river discharge rates were <150 m³ s⁻¹. River discharge rates >650 m⁻³ s⁻¹ resulted in no glass eels in our samples. Upstream migration during 2002 was not correlated with water temperature or related to lunar phase. Glass eel freshwater upstream migration was initiated when water temperatures exceeded a threshold range of 10°C to 15°C; however, glass eels continued to migrate when water temperatures approached 30°C. The overall negative effect of river discharge suggests that changes in the water release schedules of upstream hydroelectric facilities during glass eel migration could strongly influence their recruitment success.