Eyed Eggs Research Articles

English

To evaluate the effects of water hardness on survival to hatch of eyed rainbow trout Oncorhynchus mykiss eggs during iodophor disinfection, hard (300 mg/L CaCl2) and soft water (20 mg/L CaCl2) solutions were used in combination with iodophor treatments of 0, 100, 200, 400, 800, and 1600 mg/L. Water hardness did not significantly influence egg survival-to-hatch. In addition, there was no significant interaction between water hardness and iodine concentration on egg survival. However, significant differences in egg survival due to iodine concentration were observed. Egg survival significantly decreased at 800 mg/L, with near complete mortality occurring at 1,600 mg/L. Rainbow trout eyed egg disinfection using iodine concentrations of 800 mg/L or greater are not recommended, regardless of water hardness (calcium) concentrations. Keywords: Eyed eggs, iodophor, disinfection, rainbow trout, water hardness, mortality.

Population differences in Chinook salmon (Oncorhynchus tshawytscha) DNA methylation: Genetic drift and environmental factors.

Local adaptation and phenotypic differences among populations have been reported in many species, though most studies focus on either neutral or adaptive genetic differentiation. With the discovery of DNA methylation, questions have arisen about its contribution to individual variation in and among natural populations. Previous studies have identified differences in methylation among populations of organisms, although most to date have been in plants and model animal species. Here we obtained eyed eggs from eight populations of Chinook salmon (Oncorhynchus tshawytscha) and assayed DNA methylation at 23 genes involved in development, immune function, stress response, and metabolism using a gene‐targeted PCR‐based assay for next‐generation sequencing. Evidence for population differences in methylation was found at eight out of 23 gene loci after controlling for developmental timing in each individual. However, we found no correlation between freshwater environmental parameters and methylation variation among populations at those eight genes. A weak correlation was identified between pairwise DNA methylation dissimilarity among populations and pairwise F ST based on 15 microsatellite loci, indicating weak effects of genetic drift or geographic distance on methylation. The weak correlation was primarily driven by two genes, GTIIBS and Nkef. However, single‐gene Mantel tests comparing methylation and pairwise F ST were not significant after Bonferroni correction. Thus, population differences in DNA methylation are more likely related to unmeasured oceanic environmental conditions, local adaptation, and/or genetic drift. DNA methylation is an additional mechanism that contributes to among population variation, with potential influences on organism phenotype, adaptive potential, and population resilience.

Interactions between Rainbow Trout Eyed Eggs and Flavobacterium spp. Using a Bath Challenge Model: Preliminary Evaluation of Bacteriophages as Pathogen Control Agents.

The microbial community surrounding fish eyed eggs can harbor pathogenic bacteria. In this study we focused on rainbow trout (Oncorhynchus mykiss) eyed eggs and the potential of bacteriophages against the pathogenic bacteria Flavobacterium psychrophilum and F. columnare. An infection bath method was first established, and the effects of singular phages on fish eggs was assessed (survival of eyed eggs, interaction of phages with eyed eggs). Subsequently, bacteria-challenged eyed eggs were exposed to phages to evaluate their effects in controlling the bacterial population. Culture-based methods were used to enumerate the number of bacteria and/or phages associated with eyed eggs and in the surrounding environment. The results of the study showed that, with our infection model, it was possible to re-isolate F. psychrophilum associated with eyed eggs after the infection procedure, without affecting the survival of the eggs in the short term. However, this was not possible for F. columnare, as this bacterium grows at higher temperatures than the ones recommended for incubation of rainbow trout eyed eggs. Bacteriophages do not appear to negatively affect the survival of rainbow trout eyed eggs and they do not seem to strongly adhere to the surface of eyed eggs either. Finally, the results demonstrated a strong potential for short term (24 h) phage control of F. psychrophilum. However, further studies are needed to explore if phage control can be maintained for a longer period and to further elucidate the mechanisms of interactions between Flavobacteria and their phages in association with fish eggs.

ПРИМЕНЕНИЕ НОВОГО МЕТОДА ИСКУССТВЕННОЙ ИНКУБАЦИИ ИКРИНОК СЕВАНСКОЙ ФОРЕЛИ (SALMO ISCHCHAN, KESSLER) В ЕСТЕСТВЕННЫХ УСЛОВИЯХ ПРИТОКОВ ОЗ. СЕВАН (АРМЕНИЯ)

Endemic fish species of Armenian ichthyofauna – the Sevan trout (Salmo ischchan, Kessler, 1877) is registered in the Red Book of Animals of the Republic of Armenia as critically endangered (corresponds to IUCN category: CR A2cd). Its natural reproduction hardly occurs as a result of numerous problems related to the use and management of water and bio-resources in the drainage basin of Lake Sevan. The Lichq River is formerly known as a spawning river for two ecological races of Sevan trout, but because of different factors there are no more wild populations of Sevan trout spawning. The aim of the study was checking the efficiency of two methods of egg incubation in the Lichq River for restoration of Gegarkuni population. The experiments were carried out with newly fertilized and eyed eggs of Gegarkuni in the same periods and in the same areas to avoid the unforeseen effects of environmental factors on assessment. The results showed that the mortality rate of green eggs in the natural conditions is quite high before reaching eyed egg stage (65-68%), while the mortality rate of eyed eggs planted in the natural conditions is only 9-17%. This means that the effectiveness of planting eyed eggs is higher for the artificial restoration of Gegarkuni stocks in the nature.

Chilled storage of unfertilized and fertilized rainbow trout (Oncorhynchus mykiss) eggs in sealed polyethylene bags at different temperatures

Three experiments were conducted to study the effect of chilling temperature on unfertilized and fertilized rainbow trout eggs sealed in polyethylene (PE) bags. Experiment 1 showed that after 18days of storage at 2°C fertilization capacity of eggs was undiminished. At 7°C, unimpaired fertilization capacity was maintained for 12days and at 10°C for 6days. This leads to the conclusion that for storage up to approximately 1week an ordinary household refrigerator will suffice; for more extended storage periods lower temperatures are advised. If PE bags filled with unfertilized eggs were submerged in water during chilling, similar results were obtained, though at a slightly lower level. The second experiment showed that fluctuations in chilling temperature between 2°C and 10°C were tolerated by unfertilized eggs as long as sufficient adaptation time was granted. One or two temperature changes within a 12day period had no impact on fertilization capacity, whereas repeated changes at 2day intervals caused a reduction in fertilization capacity. The attempt to apply the method of chilled storage of unfertilized rainbow trout eggs in PE bags to fertilized eggs (Experiment 3) indicated that early eyed eggs (14days incubation at 10°C) may be stored at 2°C for 10days without loss in hatching rate. Reasonable hatching rates may be achieved at 7°C for about one week and at 10°C for about 4days. Storage of fertilized eggs of a more advanced stage of development (21days incubation at 10°C) calls for low temperature (2°C) and storage periods of no >4days.

In vitro storage of unfertilized eggs of the Eurasian perch and its effect on egg viability rates and the occurrence of larval malformations

Ova ageing is the most important factor affecting fish egg quality after ovulation. Long-term storage of fish ova, using cryopreservation and vitrification techniques, has been unsuccessful to date. Instead, short-term in vitro ova storage has been used successfully and optimized in some cultured fish species. In vitro ova storage can drastically improve mass production of larvae and juveniles in the hatcheries by providing the possibility of the synchronous artificial fertilization for different females. To study how long unfertilized eggs of Eurasian perch (Perca fluviatilis L.) can retain their fertilizing ability after stripping, eggs were stored at temperatures of 4°C, 8°C and 12°C for 72 h post-stripping (HPS). The stored eggs of four female perch were separately fertilized at 0 h (i.e. control eggs fertilized before storage) and at 6-hour intervals during the experimental period of 72 h. The embryos reaching the eyed-egg and hatched-larvae stages, eyed-egg mortality and larval malformation rates were recorded as indices of egg quality. The results indicated that the maximum eyed eggs and hatched larvae (86% and 63%, respectively) were observed for eggs fertilized immediately after stripping, whereas the storage of the eggs at 4°C for 48 HPS decreased the eyed-egg and hatched-larvae rates to 46% and 17%, respectively. The use of a higher storage temperature resulted in a more rapid decrease in egg viability: eyed-egg and hatched-larvae rates of 23% and 9%, respectively, were obtained after 48 HPS storage at 8°C and 2% and 1% for eggs stored at 12°C. Eyed-egg mortality and larval malformation rates were not significantly affected by post-stripping ova ageing for at least up to 36 h. Thereafter, both values increased significantly and were measured to be the highest in the most aged ova. The present study demonstrated that stripped Eurasian perch eggs can be stored for at least 12 h at 4°C to 12°C without a significant reduction in their quality.

Effect of riverbed conditions on survival of planted eyed eggs in chum salmon Oncorhynchus keta

Wild stocks of chum salmon Oncorhynchus keta are supplemented by hatchery fry enhancement programs in northern Honshu, Japan. To maintain these programs, there is a need to reduce expenses and labor. Eyed egg planting is more cost effective than hatchery production of fry. Therefore, we evaluated the effect of environmental conditions on survival of chum salmon eyed eggs planted using Whitlock–Vibert boxes. We measured the percent cumulative weight of fine sediments, Fredle index (FI) as a measure of permeability, vertical hydraulic gradient, water depth (WD), and flow velocity at planting locations. Egg-to-fry survival averaged 92.7% (range: 57.2–100%) in 2013 (N = 19) and 71.5% (range: 6.4–100%) in 2014 (N = 23). Survival was significantly positively correlated with FI and flow velocity, negatively associated with percent cumulative weight of fine sediments and WD. Vertical hydraulic gradient had no effect on survival. Our results suggest that a higher FI (i.e., low amount of fine material and larger particle size), higher flow velocity, and shallower WD reduce the mortality of planted chum salmon eyed eggs. This is likely a result of increased permeability in the substrate and restriction of fine sediment intrusion into the incubation zone.

サケ科魚類の細菌性腎臓病

The first outbreak of bacterial kidney disease (BKD) of salmonids occurred in the autumn of 1973 in Hokkaido, Japan. Subsequently, outbreaks of BKD were confirmed in Hokkaido and main land of Japan. Most of the cases were caused by imported eyed eggs of coho salmon Oncorhynchus kisutch. In this review, pathogenicity of the causative agent R. salmoninarum (Rs), culture methods of Rs, serological and Rs specific gene detection methods for diagnoses, disease signs of infected fish, and distribution of BKD in Japan are described. Also, preventive measures of vertical transmission and control methods of BKD are introduced.

The battle of the eyed egg: Critical junctures and the control of genes in Norwegian salmon farming

Abstract In the pioneering period (1970s) of Norwegian salmon and trout aquaculture, the biological knowledge underlying this industry evolved in an institutional world of open science. Universities developed novel breeding techniques, and small grow out mom-and-pop farms implemented them. Eyed eggs were generic and standardized products, and traded at the lowest possible cost. As an eyed egg, the fry and in particular the eyes are visible through the membrane. The interplay between the regimes of open science and proprietary science has changed significantly in salmon aquaculture over the last two decades. One aspect of this change is that husbandry breeding has become more industrialized and subsequently more controlled by large, specialized and capital intensive breeding corporations. This paper explores this development from the perspectives of process-oriented institutional theory. We identify critical junctures in the coevolution of the breeding and grow-out sectors, and analyze how these junctures structure and change the direction of industrial and economic development. Ultimately, the generic, standardized and undervalued eyed eggs were subject to revaluation by the novel dominant international actors in the Atlantic salmon industry. We primarily draw data from interviews with core actors and informants at relevant universities, breeding companies and governmental agencies, as well as from white papers and other secondary material.

Evaluation of Glutaraldehyde, Chloramine-T, Bronopol, Incimaxx Aquatic® and Hydrogen Peroxide as Biocides against Flavobacterium psychrophilum for Sanitization of Rainbow Trout Eyed Eggs

The effective conditions of glutaraldehyde, chloramine-T, bronopol, Incimaxx Aquatic® and hydrogen peroxide as some biocides commonly used by the aquaculture industry were investigated against F. psychrophilum in sanitization of rainbow trout eyed eggs. Bacteriostatic tests as well as bactericidal tests using ethidium monoazide bromide PCR assays were conducted in vitro on Flavobacterium psychrophilum while impacts of chemical treatments were studied in vivo on 240 [°C × days] rainbow trout eyed eggs. A 20-min contact time with bronopol (up to 2,000 ppm), chloramine-T (up to 1,200 ppm), glutaraldehyde (up to 1,500 ppm), hydrogen peroxide (up to 1,500 ppm) or with Incimaxx Aquatic® (up to 185 ppm, eq. peracetic acid) was effective against F. psychrophilum and did not affect the eyed eggs/fry viability. Collectively, the data obtained here clearly demonstrate that concentrations and duration of treatments commonly used to sanitize eyed eggs are widely overestimated in their effectiveness against F. psychrophilum. The new treatment conditions with the five studied biocides are bactericidal for F. psychrophilum and safe for rainbow trout eyed eggs. In this work, we developed an experimental approach to test some chemicals against fish pathogens to assist fish farmers in the effective and safe disinfection of eyed eggs.

Evaluation of the Antifungal Activity of Zataria multiflora, Geranium herbarium, and Eucalyptus camaldolensis Essential Oils on Saprolegnia parasitica–Infected Rainbow Trout (Oncorhynchus mykiss) Eggs

The purpose of the present study was to evaluate and assess the capability of Zataria multiflora, Geranium herbarium, and Eucalyptus camaldolensis essential oils in treating Saprolegnia parasitica-infected rainbow (Oncorhynchus mykiss) trout eggs. A total of 150 infected eggs were collected and plated on glucose-pepton agar at 24°C for 2 weeks. The antifungal assay of essential oils against S. parasitica was determined by a macrodilution broth technique. The eggs were treated with essential oils at concentrations of 1, 5, 10, 25, 50, and 100 ppm daily with three repetitions until the eyed eggs stage. Of 150 eggs examined, S. parasitica (54.3%), Saprolegnia spp. (45%), and Fusarium solani (0.7%) were isolated. The minimum inhibitory concentrations of Z. multiflora, E. camaldolensis, and G. herbarium essential oils against S. parasitica were 0.9, 2.3, and 4.8 ppm, respectively. Zataria multiflora and E. camaldolensis at concentrations of 25, 50, and 100 ppm, and G. herbarium at concentration of 100 ppm had significant differences in comparison with negative control (p<0.05). The results revealed that malachite green, followed by Z. multiflora, E. camaldolensis, and G. herbarium treated eggs had remained the most number of final eyed eggs after treatment. The highest final larvae rates belonged to malachite green, E. camaldolensis, Z. multiflora, and G. herbarium, respectively. The most hatching rates were recorded with malachite green (22%), and then Z. multiflora (11%), E. camaldolensis (7%), G. herbarium (3%), and negative control (1%). Zataria multiflora and E. camaldolensis were more effective than G. herbarium for the treatment of S. parasitica-infected rainbow trout eggs in aquaculture environment.

Low Likelihood of Intra-Ovum Infection with Flavobacterium psychrophilum in Cultured Salmonids in Japan

We evaluated the occurrence of intra-ovum infection with Flavobacterium psychrophilum, the causative agent of bacterial cold-water disease (BCWD) and rainbow trout fry syndrome (RTFS), in the eggs of six salmonid species in Japan. Flavobacterium psychrophilum was isolated from four eggs in one of 13 lots of eyed eggs (999 eggs) imported from the United States. In contrast, the bacterium was not isolated from 28 lots (1,680 eggs) or 61 lots (3,693 eggs) of domestically produced unfertilized or eyed eggs, respectively. Our results indicate there is a low likelihood of intra-ovum infection in cultured salmonids in Japan.

Petri Dish Incubation of Eyed Eggs from Rainbow Trout and Splake

AbstractFour experiments were conducted from 2004 to 2006 to evaluate different protocols for incubating eyed eggs of salmonids in petri dishes. In the first two experiments, which used eyed eggs from Erwin strain rainbow trout Oncorhynchus mykiss or splake (lake trout Salvelinus namaycush ×brook trout S. fontinalis), dishes were loaded at either 10 or 20 eggs/dish and incubated at 10°C. Water changes occurred every 3 or 7 d until complete hatch; for each species, one group of dishes received no water change. Survival to hatch was not affected by the number of eggs per dish or the frequency of water changes in either species. However, in experiments 1 and 2, hatch was significantly earlier in the dishes containing 20 eggs than in dishes containing 10 eggs. In the last two experiments, 15 eyed eggs from Shasta or McConaughy strain rainbow trout were incubated at either 10°C or 12°C; the water was changed every 3 d or not at all. Shasta strain eggs exhibited no significant difference in survival or time to hatch between any of the treatments. For McConaughy strain eyed eggs, survival to hatch was significantly greater at 10°C than at 12°C, but water change treatment did not affect survival. No significant differences in time (d) to complete hatch were observed between temperature treatments or between water change regimes. To successfully mimic vertical‐flow incubation of eyed salmonid eggs in petri dishes, we recommend a density of no more than 15 eggs/dish; no water change is needed at a temperature of 10°C. Daily removal of dead eggs and hatched fry is also required.

Evaluation of Formalin and Hydrogen Peroxide Treatment Regimes on Rainbow Trout Eyed Eggs

AbstractThis study examined the use of antifungal chemicals at nonstandard treatment concentrations or treatment intervals during the incubation of eyed eggs of rainbow trout Oncorhynchus mykiss until hatch in vertically stacked incubation trays. Daily chemical treatments of 500, 1,000, and 1,667 mg of commercial formalin (containing 37% formaldehyde)/L for 15 min and a nonchemical, dead‐egg‐removal control were included in three trials. The second and third trials added a true control (no antifungal measures) and the third trial also incorporated a treatment of formalin at 1,667 mg/L for 15 min every other day. In these three trials, formalin at 1,000 or 1,667 mg/L daily or 1,667 mg/L every other day significantly improved egg survival to hatch relative to the other treatments and completely controlled fungal growth. A fourth trial evaluated treatments of formalin at 750 mg/L for 15 min daily or every other day, hydrogen peroxide at 500 mg/L for 15 min daily or every other day, and control groups for both treatments. Egg survival to hatch was significantly different among the treatments; the daily 750‐mg/L formalin treatment produced the greatest number of hatched fry, followed by the treatment with 750 mg/L formalin every other day, the dead‐egg‐removal control, and daily hydrogen peroxide treatment. Survival in the every‐other‐day hydrogen peroxide treatment and the true control could only be estimated because of extreme fungal growth, and was substantially less than the other treatments. Only daily 750 mg/L formalin treatments and dead egg removal completely controlled fungal growth. To adequately control fungus and maximize egg survival, either daily 15‐min treatments of formalin at concentrations of at least 750 mg/L or every‐other‐day treatments of formalin at 1,667 mg/L are recommended.

In vitro storage of unfertilized ova of endangered Caspian brown trout ( Salmo trutta caspius) in artificial media

In order to study the effects of storage media and time of storage on the viability of unfertilized eggs of endangered Caspian brown trout ( Salmo trutta caspius), the ova of this fish was stored in coelomic fluid and Cortland artificial media at 2–3 °C for 120 h. In this research, Cortland artificial medium was buffered with 20 mM of three different buffers: Hepes (C 8H 18N 2O 4S), Tris–HCl (C 4H 11NO 3–HCl) and sodium salt Hepes (C 8H 17N 2O 4SNa). The pH of these media were adjusted according to natural pH of coelomic fluid. The eggs that stored in these media fertilized at times 0 h (eggs fertilized prior to storage), 48, 72 and 120 h of post-stripping, using fresh and pooled sperm obtained from four to six males. According to the results of present study, time of storage showed a significant ( p < 0.05) main effect on eyeing, hatching and eyed eggs mortality rates. Eyeing and hatching rates significantly ( p < 0.05) decreased from 97.4 ± 2.1% and 95.1 ± 4.4% at time 0 (eggs fertilized prior to storage) to 77.9 ± 3% and 65.5 ± 5% after 120 h of storage. Within a similar period of time, eyed eggs mortality significantly ( p < 0.05) increased from 2.4 ± 2.4% to 17.2 ± 3.9%. No significant ( p > 0.05) main effect was found among media buffered with Tris–HCl (82.8 ± 3.2%, 73.4 ± 5.4%, 12.1 ± 4.5%), Hepes (88.2 ± 3.4%, 80.7 ± 5.5%, 9.3 ± 3.4%), sodium salt Hepes (77.8 ± 3.8%, 69.3 ± 5.7%, 12.2 ± 3.9%) and coelomic fluid (84.8 ± 3.8%, 77.7 ± 5.1%, 8.9 ± 2.7%) for eyeing, hatching and eyed eggs mortality rates. There was a negative correlation ( r = −0.895, p < 0.001) between eyed eggs mortality and hatching rates. In conclusion, unfertilized eggs of endangered Caspian brown trout can be successfully stored for 48 h without significant loss of fertility. But, storage for 120 h results in the falling of hatching rate. In addition, no significant difference was found between viability rates of ova stored in coelomic fluid and artificial media, 120 h post-storage. It reveals that artificial media could be substituted for coelomic fluid as storage medium at least for 120 h in Caspian brown trout.

Genetic analysis of female reproduction traits of farmed coho salmon (Oncorhyncus kisutch)

Based on 8 years of data on 891 daughters from 190 sires and 398 dams, females produced an average (standard deviation) of 4251 (957) green eggs with a total weight of about 680 (191) g; the females produced 3226 (1255) eyed eggs, average egg weight was 180 (27) mg, and the average day of spawning was 137.5 (9.8) days measured from December 31. Average body weight was 3247 (879) g at harvest, 3702 (876) g at spawning and 3022 (730) g post-spawning. Estimated heritability of weight of green eggs spawned was 0.39, while that for number of green eggs was 0.42, that for heritability for average egg weight (egg size) and number of eyed eggs were slightly lower at 0.32 and 0.33, respectively, while the estimate for spawn day was low (0.24). Number of green eggs was highly, and positively, correlated with weight of eggs spawned (0.79), number of eyed eggs (0.82) and number of eyed eggs with weight of eggs spawned (0.53) and spawn day (0.52). The genetic correlations between number of eggs and average egg weight were negative (−0.63 for green eggs and −0.44 for eyed eggs). None of the estimated genetic correlations between spawn day and the four measures of fish size differed from zero, suggesting genetic independence of spawning date and body size, within spawning season; however, this may have been due to the inclusion of only early spawning females in the study. Estimates of genetic correlations between the various measures of fish size were all positive and ranged from 0.60 to 0.70 for spawning weight and spawning length, spawning length and post-spawning weight and harvest weight and post-spawning length of females. Spawning weight was highly correlated with weight of eggs spawned (0.69) and moderately related genetically to number of green eggs (0.34) and average weight of ova (0.37). Estimates of genetic correlation between spawning weight and number of eyed eggs did not differ from zero. The corresponding phenotypic correlations all were low or near zero. Harvest weight and post-spawning weight were not correlated with number of green or eyed eggs, but were associated with egg weight and weight of eggs spawned; both genetic correlations were 0.46 for harvest weight, while the correlations with post-spawning weight were 0.37 for egg weight and 0.56 for weight of eggs spawned. The results indicate that the coho population under study contains a high level of additive genetic variation for all traits related to female reproduction and estimates of genetic correlations suggest that correlated changes that may accompany selection for larger body size at market will be favourable in most instances.

Use of Formalin during Incubation of Rainbow Trout Eyed Eggs

Abstract The influence of daily formalin treatments on eyed egg and fry mortality was evaluated during the incubation of eyed eggs of Cleghorn strain rainbow trout Oncorhynchus mykiss in vertical-flow incubators. The study was initiated in 1995 and replicated yearly through 1998. In 1997 and 1998, significant (P < 0.05) increases in survival were observed in trays of eggs treated with formalin at 1,667 mg/L for 15 min daily from egg eye-up until just before hatch compared with incubation trays where dead eggs were manually removed for control of Saprolegnia sp. In 1996, 1997, and 1998, significant mortality reductions were observed prehatch when using formalin. A significant improvement in survival from hatch to fry swim-up occurred only in 1998. No significant differences in survival occurred during any life stage in 1995. Yearly differences in formalin influences are attributed to changes in the age of broodfish, spawning frequency, and sample sizes. Both formalin treatments and hand picking of dead egg...

Effects of Varying Voltage and Pulse Pattern during Electrical Immobilization of Adult Chum Salmon on Egg Survival to the Eyed Egg Stage

Abstract Electrical shock is becoming widely used to immobilize adult salmon before gamete removal. Working with immobilized fish reduces repetitive motion injuries among workers and decreases staff requirements, but survival rates of eggs obtained from adults immobilized by electrical currents have varied. Eleven DC wave forms and voltage combinations were used to immobilize adult chum salmon Oncorhynchus keta, and survival rates of eggs taken from shocked fish were compared with survival rates from fish immobilized with carbon dioxide. Egg survival rates increased as voltage and pulse pattern intensity decreased. Similar egg survival rates were recorded for those obtained from the carbon dioxide controls (98%) and those obtained at the lower voltage and pulse patterns (96-98%), thus validating the use of electrical immobilization on adult chum salmon before gamete removal.

Rehabilitation efforts for Atlantic Salmon in the Meuse basin area : Synthesis 1983-1998

In the 1950s, Atlantic salmon had become extinct in the river Meuse basin, mainly owing to the construction of navigation weirs. In 1987 started a rehabilitation program of Atlantic salmon in Belgium. Stockings are being performed in six tributaries of the river Meuse, using eyed eggs, parr and pre-smolts obtained from foreign eggs reared in a hatchery of the `Service de la Peche'. By the end of 1998, 896033 young salmon have been released in the wild, especially in the river Ourthe basin. In most of the cases, the evaluation of stocking operations indicates good adaptation of parr in the tributaries where they are stocked, with autumnal 0+ parr densities up to 20–30 ind 100 m-2. However, fish mortality may occur when smolts pass through the turbines of the hydropower stations in the river Meuse (5% per power plant), and most of the fish passes located downstream of Namur are not suitable for anadromous fish migration. The paper reports the results of stocking experiments, the evaluation of mortality rates in turbines and the advancement of programmes aiming at the restoration of downstream and upstream migration (construction of fish migration facilities).

Effects of pH, Aluminum, and Calcium on Survival and Growth of Eggs and Fry of Brook Trout (Salvelinus fontinalis)

Freshly fertilized eggs, eyed eggs, yolk-sac fry, and swim-up fry of brook trout (Salvelinus fontinalis) were exposed to a matrix of 84 combinations of pH (4.0–6.5), aluminum (0–1000 μg/L), and calcium (0.5–8.0 mg/L) in 21–91-d experiments. The response to pH, aluminum, and calcium exposure was dependent on life stage. Sensitivity to acid toxicity generally decreased with age (freshly fertilized eggs&gt;eyed eggs&gt;yolk-sac fry = swim-up fry). Survival or hatching of freshly fertilized and eyed eggs decreased at pH 5.2 and below, whereas survival of yolk-sac and swim-up fry was reduced at pH 4.4–4.0. Sensitivity to aluminum toxicity generally increased with age (freshly fertilized eggs = eyed eggs&lt;yolk-sac fry&lt;swim-up fry). At low pH, survival of freshly fertilized and eyed eggs increased with exposure to increasing aluminum concentrations, in contrast, elevated aluminum [Formula: see text] was often toxic to fry. Increasing calcium was beneficial to all life stages, although the magnitude of this benefit depended on life stage and on the specific pH and aluminum concentration. Survival after previous exposure to toxic combinations of pH, aluminum, and calcium generally improved during a post-exposure recovery period at pH 6.5. However, increased mortality in many exposure combinations did not begin until this recovery period.