Eyed-egg Stage Research Articles

Thermal stressors during embryo incubation have limited ontogenic carryover effects in brook trout

Winter climate is changing rapidly in northern latitudes, and these temperature events have effects on salmonid thermal biology. Stressors during winter egg incubation could reduce hatching success and physiological performance of fall-spawning fishes. Here we quantified the potential for ontogenic carryover effects from embryonic thermal stress in multiple wild and hatchery-origin populations of brook trout (Salvelinus fontinalis), a temperate ectotherm native to northeastern North America. Fertilized eggs from four populations were incubated over the winter in the laboratory in four differing thermal regimes: ambient stream-fed water, chronic warming (+2 °C), ambient with a mid-winter cold-shock, and short-term warming late during embryogenesis (to stimulate an early spring). We examined body size and upper thermal tolerance at the embryonic, fry (10 weeks post-hatch and 27–30 weeks post-hatch) and gravid adult (age 2+) life stages (overall N = 1482). In a separate experiment, we exposed developing embryos to acute seven-day heat stress events immediately following fertilization and at the eyed-egg stage, and then assessed upper thermal tolerance (CTmax) 37 weeks post-hatch. In all cases, fish were raised in common garden conditions after hatch (i.e., same temperatures). Our thermal treatments during incubation had effects that varied by life stage, with incubation temperature and life stage both affecting body size and thermal tolerance. Embryos incubated in warmer treatment groups had higher thermal tolerance; there was no effect of the mid-winter melt event on embryo CTmax. Ten weeks after hatch, fry from the ambient and cold-shock treatment groups had higher and less variable thermal tolerance than did the warmer treatment groups. At 27–30 post-hatch and beyond, differences in thermal tolerance among treatment groups were negligible. Collectively, our study suggests that brook trout only exhibit short-term carryover effects from thermal stressors during embryo incubation, with no lasting effects on phenotype beyond the first few months after hatch.

Ovarian lavage / artificial insemination method as an alternative approach for controlled reproduction of the northern pike (Esox lucius)

This study aimed to compare the effectiveness of the ovarian lavage / artificial insemination method with the traditional hormonal administration and fertilization methods over the artificial reproduction of the northern pike (Esox lucius). For this purpose, groups of five females were treated as follows: intraperitoneal injection of saline (C1); ovarian lavage with saline (C2); intraperitoneal injection of carp pituitary extract (CPE, T1); ovarian lavage with CPE (T2); intraperitoneal injection of CPE and ovarian lavage with semen after 72 h (T3); ovarian lavage with CPE and ovarian lavage with semen after 72 h (T4). According to the results, no fish ovulated in the control groups (C1 and C2). There were no significant differences (n.s.) among experimental treatments (P > 0.05, n.s.) in the reproductive parameters, such as latency time, ovulation rate, stripped egg amount, and pseudo-gonadosomatic index. The lowest fertilization rate (54.8%) was observed in the T4 treatment and significantly differed from the T1 and T2 treatments (P < 0.05). Moreover, the highest survival at swim-up stage was measured in the T4 treatment with a significant difference compared to the T1 group (P < 0.05). The survival at the eyed-egg stage, hatching rate, and malformations were similar (P > 0.05, n.s.) in all applied strategies. The results demonstrated that the ovarian lavage / artificial insemination method could be applied to control northern pike reproduction, like the traditional fertilization method. Consequently, this novel technique can be suggested as an alternative strategy to facilitate the hatchery operations in the controlled reproduction of this species.

Influence of Salinity on the Survival Rate of Fertilized Chum Salmon (Oncorhynchus keta) Eggs

Chum salmon (Oncorhynchus keta) exhibit a remarkable ability to adapt to changes in salinity during their life cycle. However, the fertilized egg stages are sensitive to salinity, affecting ontogeny and hatching. This study investigated the effect of salinity (0, 1, 3, and 5 PSU) on the survival of two developmental stages (&lt;1 day after fertilization and &lt;1 day after the eyed-egg stage) of fertilized eggs. Based on the experimental results, we assessed the spawning ground environment using the in situ salinity data of the Namdae River from 1997 to 2002, where the largest number of salmon in Korea migrate to spawn. Survival of the &lt;1-day-old fertilized eggs decreased sharply at 3 PSU or more, and all eggs died at 5 PSU. Hatching of the eyed-egg stage occurred under all environmental conditions. After 2010, the salinity of the layer of water in contact with the sediment in the lower reaches of the river increased (&gt;6.9 PSU) with the frequency of high waves. Overall, the function of the lower river in spawning and hatching is weakening. This study enhances our understanding of the effects of climate change, including increased wave activity, on salmon spawning grounds.

Spawning manipulation, broodfish diet feeding and egg production in farmed Atlantic salmon

Atlantic salmon aquaculture relies on continuous supply of high quality eggs. Broodfish nutrition and manipulation of ovulation time (photoperiod and temperature) are key factors. The optimum feeding period with broodfish diet has not been investigated before. The present study examined how feeding period with broodfish diet (9 vs. 17 months) interacted with manipulation of ovulation time (early (Nov), normal (Dec), late (Feb)) on broodstock egg production capacity and egg quality in two-sea-winter female Atlantic salmon (∼12 kg). All groups were fed until June 2021 when they were transferred to tanks and starved until ovulation.There were no measurable main or interaction effects of feeding period. Manipulation of ovulation gave several significant effects compared to normal ovulating females:1.Early ovulating females had higher viscerosomatic index, smaller eggs with higher swelling rate (early 1.36, normal 1.27, late 1.23), and lower egg quality shown as reduced survival from fertilization to the eyed egg stage (mortality: early 11%, normal 5%, late 14%).2.Late ovulating females: (i) were emaciated as shown by low condition factor calculated on gutted weight, and hepatosomatic and viscera indexes; (ii) had larger gonads caused by larger eggs; (iii) had reduced egg quality measured as elevated mortality from fertilization to first-feeding (eyed egg – first feeding: early 11%, normal 8%, late 23%).3.All groups spawned a similar number of eggs per female.The current results show that the feeding period with broodstock diet may be set to 9 months. This would make Atlantic salmon egg production more economical and environmentally sustainable. The results also show that manipulation of ovulation time reduce egg quality but not fecundity. Further research should investigate feeding periods with broodstock diet shorter than 9 months and determine the threshold for jeopardized fish welfare with respect to starvation time for manipulated late ovulating females.

Maternal and genetic effects on embryonic survival from fertilization to swim up stage and reproductive success in a farmed rainbow trout line

Reproductive success and offspring survival until sexual maturity are essential traits both for fish fitness and aquaculture development. Variation in offspring’s survival among family results in unbalanced parental contributions to the next generation and may explain the loss of genetic diversity observed in some farmed populations. Therefore, we studied the variance in parental contributions to a progeny cohort, as well as the biological factors impacting offspring early survival in rainbow trout. The data consisted of 945 individual survival observations from fertilization to the juvenile stage from 135 full-sib families of the INRAE experimental synthetic line. Survival was assessed at eyed-egg stage, hatching, and 3 weeks after first feeding. We used a full-factorial mating design to partition phenotypic variance in early survival traits into maternal and additive genetic effects under threshold GBLUP models considering the inclusion of genomic information for 32,725 SNP. Average offspring survival proportions were 91.0% at the eyed-egg stage, 87.2% at hatching, and 84.4% three weeks after first feeding. Significant unbalanced dam contributions were observed at the eyed-egg and hatching stages. Low heritability was estimated for early survival traits (h²=0.20 ± 0.12 and 0.13 ± 0.09 for survival from egg-eyed stage and, respectively, hatching and first feeding), revealing that additive genetic variance was not significantly different from zero, while maternal effects explained a larger part (c²=0.37 ± 0.16 and 0.15 ± 0.07, respectively) of the phenotypic variances. There was no evidence of inbreeding depression on survival in our study. Phenotypically, offspring early survival was positively correlated with dam fecundity, while it was negatively correlated with dam post-spawning weight. Negative, but not significant association was observed between early survival and dam’s average egg weight. If a study of genetic correlations confirms these phenotypic trends, promoting high fecund females should help the breeders to increase offspring early survival and to maintain genetic diversity in breeding programs.

Reproduction parameters of hatchery reared grayling (Thymallus thymallus) females

European grayling (Thymallus thymallus) is an endangered salmonid fish species and its populations have decreased considerably in European waters in recent decades. One of the conservation measures applied to grayling is stocking with hatchery-reared fish. To advance the knowledge of grayling reproduction in the hatchery, husbandry data were systematically collected in the period from 2006 to 2015 during grayling spawning seasons and analyzed to quantify grayling female reproductive parameters such as fecundity, egg size, and embryo survival to the eyed egg stage. Data was collected for first time spawners (3 years old) and repeat spawners reared in the hatchery. Statistically significant differences were found for the number of eggs between first time spawners, producing on average 3600 eggs, and repeat spawners, producing on average 8000 eggs. Absolute fecundity was positively correlated to grayling female total length and weight for both first time and repeat spawners. However, relative fecundity did not correlate with these parameters. A positive correlation was observed between female total length and mean egg weight for repeat spawners, while the correlation was negative for first time spawners. Heavier eggs tended to have a higher rate of survival until the eyed egg stage, though the correlation was stronger for first time spawners than for repeat spawners. Due to the higher reproductive success of repeat spawners, it could be concluded that larger and older grayling females should be included in hatchery reproduction.

Reproductive characteristics of the giant gurami sago strain ( Osphronemus goramy Lacepède, 1801): basic knowledge for a future hatchery development strategy.

Background: The giant gourami sago strain ( Osphronemus goramy Lacepède) has been approved in 2018 as a candidate for freshwater aquaculture in Indonesia. However, information on the species' reproduction is minimal. This study analyzed the reproductive characteristics of the gourami sago strain broodfish to provide basic knowledge for a future hatchery development strategy. Methods: A total of 10 female and 10 male mature gourami sago strain broodfish were measured for body weight and length, and were evaluated for their reproductive characteristics. Breeding fish were spawned naturally in a 2×1×0.6 m concrete pond with a male-female sex ratio of 1:1. Egg weight and diameter were measured in 25 eggs per female using, respectively, ACIS AD- 600i scales with 0.01 g accuracy, and a microscope (Labo model L-711) using Canon Digital Camera Software 3 . Semen was collected using plastic syringes in 3 mL aliquots, then placed in an insulated ice-cooled container, and analyzed within two hours of collection. Results: Average weights of female and male broodfish before spawning were 2180±159.78 g and 3060±134.99 g, respectively. The relative fecundity and egg diameter were 1029±36 eggs kg -1 and 2.42±0.05 mm, respectively. The hatching rate and embryo survival to an eyed-egg stage were respectively 76.40±2.27% and 94.76±0.42%. Sperm characteristics showed that volume was 0.60±0.12 ml kg -1 and percentage of motile sperm was 70.04±2.27%. Female broodfish weight after spawning was strongly correlated with the weight before spawned ( r2 = 0.999) and absolute fecundity was also strongly correlated with female broodfish weight before spawning ( r2= 0.921). Sperm concentration was moderately correlated with sperm motility ( r2 = 0.556) and duration of sperm motility ( r2 = 0.502). Conclusions: The gourami sago strain broodfish has suitable reproductive characteristics for the development of hatcheries. Successful natural spawning should be followed by larval weaning and feeding technology to increase growth and survival.

Reproductive characteristics of the giant gurami sago strain ( Osphronemus goramy Lacepède, 1801): basic knowledge for a future hatchery development strategy

Background: The giant gourami sago strain ( Osphronemus goramy Lacepède) has been approved in 2018 as a candidate for freshwater aquaculture in Indonesia. However, information on the species’ reproduction is minimal. This study analyzed the reproductive characteristics of the gourami sago strain broodfish to provide basic knowledge for a future hatchery development strategy. Methods: A total of 10 female and 10 male mature gourami sago strain broodfish were measured for body weight and length, and were evaluated for their reproductive characteristics. Breeding fish were spawned naturally in a 2×1×0.6 m concrete pond with a male-female sex ratio of 1:1. Egg weight and diameter were measured in 25 eggs per female using, respectively, ACIS AD- 600i scales with 0.01 g accuracy, and a microscope (Labo model L-711) using Canon Digital Camera Software 3 . Semen was collected using plastic syringes in 3 mL aliquots, then placed in an insulated ice-cooled container, and analyzed within two hours of collection. Results: Average weights of female and male broodfish before spawning were 2180±159.78 g and 3060±134.99 g, respectively. The relative fecundity and egg diameter were 1029±36 eggs kg -1 and 2.42±0.05 mm, respectively. The hatching rate and embryo survival to an eyed-egg stage were respectively 76.40±2.27% and 94.76±0.42%. Sperm characteristics showed that volume was 0.60±0.12 ml kg -1 and percentage of motile sperm was 70.04±2.27%. Female broodfish weight after spawning was strongly correlated with the weight before spawned ( r 2 = 0.999) and absolute fecundity was also strongly correlated with female broodfish weight before spawning ( r 2= 0.921). Sperm concentration was moderately correlated with sperm motility ( r 2 = 0.556) and duration of sperm motility ( r 2 = 0.502). Conclusions: The gourami sago strain broodfish has suitable reproductive characteristics for the development of hatcheries. Successful natural spawning should be followed by larval weaning and feeding technology to increase growth and survival.

Artificial reproduction of Caspian roach, Rutilus caspicus following stimulating ovulation with Ovaprim, Ovopel, and their combinations under controlled conditions

The aim of this study was to evaluate the efficiency of different hormonal agents and their combinations for spawning induction of females Caspian roach, Rutilus caspicus. Five groups of fish were injected intraperitoneally as follows: two injections of Ovaprim (T1), two injections of Ovopel (T2), a priming dose of Ovopel with a resolving dose of Ovaprim (T3), a priming dose of Ovaprim with a resolving dose of Ovopel (T4), and two injections of sterile 0.9% NaCl solution as a control group. The results showed that no fish ovulated in the control group. In hormone-treated groups, no differences were observed in ovulation success (P > 0.05). The shortest latency time and highest working and relative fecundities were observed in fish stimulated with two injections of Ovaprim (T1 group). The mean values of fertilization success in treated fish were in the range of 87.9–93.1% and the highest values were observed in T3 and T1 groups (P < 0.05). The best results in terms of ovulation index (92.1%), hatching rate (93.7%), and survival up to the eyed egg stage (89.4%) were achieved after administering two injections of Ovaprim (T1 group). There were no significant differences in the incubation time and embryos survival rates up to absorbing the yolk sac among different groups (P > 0.05). Overall, the best results of controlled reproduction of Caspian roach were obtained after using two injections of Ovaprim. Consequently, the Ovaprim is more suitable for restocking and aquaculture purposes of endangered populations of Caspian roach.

The effects of temperature and salinity of hatchery water on early development of chum salmon (Oncorhynchus keta)

Chum salmon Oncorhynchus keta is the most abundant and industrially important salmonid in Japan, of which Japanese hatcheries release about 1.8 × 109 fry annually. However, recent global warming and earthquake-induced crustal movement might have changed hatchery water environments. To sustainably maintain and operate hatcheries in Japan, we report the effects of rearing water temperature and salinity on the early development of chum salmon derived from the Chitose River. Effects are evaluated in terms of eyed-egg (Eer), hatching (Htr), and survival (Sur) rates, alevin body size, and the quality of the egg envelope. Fertilized eggs were reared in groundwater (GW) at different temperatures (4, 7, 10, 13, 16 °C). Alevin reared at 4 °C were larger but had less yolk, while those reared at 16 °C were smaller but hatched precociously. A significant decrease in Htr and Sur was observed in the 4 °C treatment, which we regard to be because of the small amount of residual egg yolk at the time of hatching. Eggs were also fertilized in GW or different concentrations of brackish groundwater (BGW 0.5, 1.0, 2.1, 4.1, 8.3 psu), and continuously reared under the same salinity conditions at fertilization. Those BGW treatments at 1.0 and 2.1 psu had much lower Htr values than those reared in GW and salinities of 0.5 psu, despite their having a comparable Eer. Mortality in BGW treatments of 1.0 and 2.1 psu occurred during hatching, because of precocious hatching. No change in egg membrane proteins occurred after fertilization in 4.1 and 8.3 psu treatments, and embryos did not develop to an eyed-egg stage. These results suggest that constant temperatures of 4 and 16 °C, and salinities exceeding 1.0 psu during fertilization can prevent or interfere with the normal early development of chum salmon eggs and larvae in the Chitose River. To avoid the adverse effects of salination, fertilization with GW and hardening of the egg envelope effectively increase Sur dramatically, even after transfer to BGW.

Reproductive characteristics of the giant gurami sago strain (Osphronemus goramy Lacepède, 1801): basic knowledge for a future hatchery development strategy

Background: The giant gourami sago strain ( Osphronemus goramy Lacepède) has been approved in 2018 as a candidate for freshwater aquaculture in Indonesia. However, information on the species' reproduction is minimal. This study analyzed the reproductive characteristics of the gourami sago strain broodfish to provide basic knowledge for a future hatchery development strategy. Methods: A total of 10 female and 10 male mature gourami sago strain broodfish were measured for body weight and length, and were evaluated for their reproductive characteristics. Breeding fish were spawned naturally in a 2×1×0.6 m concrete pond with a male-female sex ratio of 1:1. Egg weight and diameter were measured in 25 eggs per female using, respectively, ACIS AD- 600i scales with 0.01 g accuracy, and a microscope (Labo model L-711) using Canon Digital Camera Software 3 . Semen was collected using plastic syringes in 3 mL aliquots, then placed in an insulated ice-cooled container, and analyzed within two hours of collection. Results: Average weights of female and male broodfish before spawning were 2180±159.78 g and 3060±134.99 g, respectively. The relative fecundity and egg diameter were 1029±36 eggs kg -1 and 2.42±0.05 mm, respectively. The hatching rate and embryo survival to an eyed-egg stage were respectively 76.40±2.27% and 94.76±0.42%. Sperm characteristics showed that volume was 0.60±0.12 ml kg -1 and percentage of motile sperm was 70.04±2.27%. Female broodfish weight after spawning was strongly correlated with the weight before spawned ( r 2 = 0.999) and absolute fecundity was also strongly correlated with female broodfish weight before spawning ( r 2= 0.921). Sperm concentration was moderately correlated with sperm motility ( r 2 = 0.556) and duration of sperm motility ( r 2 = 0.502). Conclusions: The gourami sago strain broodfish has suitable reproductive characteristics for the development of hatcheries. Successful natural spawning should be followed by larval weaning and feeding technology to increase growth and survival.

배합사료와 생사료 공급이 쏘가리(Siniperca scherzeri) 암컷의 발안율과 부화율에 미치는 영향

This study was carried out to investigate the effect of artificial diet and live food on eyed egg stage rate and hatchability of eggs of broodstock mandarin fish (Siniperca scherzeri) for 10 months. Two groups (five fish per group) of fish with mean body weight of 892±65.7g (Mean±SD) were fed either artificial diet (commercial Japanese eel diet) or live food (crucian carp and common carp juveniles), respectively. Fish were cultured in running water culture system in which water temperature was kept at 3.9±0.4°C to 23.5±1.7°C. Averaged eyed egg stage rate (74.5±4.7%) and hatchability (68.6±1.1%) of eggs for broodstock mandarin fish fed artificial diet were significantly higher (P<0.05) than those of fish fed live food (eyed egg stage rate; 57.3±4.4%, hatchability; 51.8±3.3%).

NOFSal-MP10: A single hypervariable STR 12-plex for accurate verification of triploidy in Atlantic salmon (Salmo salar L.)

An increasing interest in production of sterile fish in aquaculture requires rapid, accurate and efficient testing for certification of triploid eggs prior to sale. Further, validation of triploidy can be beneficial, and even required, for accrediting methods of triploid production. A PCR-genotyping approach using a single megaplex of 12 hypervariable STR markers shows accurate and highly repeatable results enabling verification of ploidy in a single test. The NOFSal-MP10 panel contains 12 STR markers mapped to 9 chromosomes with an average of 21.4 alleles per marker for a combined total of 257 alleles based on genotyped samples to-date. The hypervariable nature of these 12 STRs leads to a large probability for three uniquely sized alleles to be observed at each marker, thus providing a rapid confirmation of ploidy based on the count of allele fragments per marker. Further, as a PCR amplification step is involved, this method is robust to DNA quality and quantity, making it suitable for very early determination of ploidy, as early as the eyed-egg stage. Repeat genotyping of positive control diploid Atlantic salmon over two different capillary electrophoretic instruments in different laboratories and with multiple laboratory personnel proves the panel's robustness to scoring errors with an overall allelic error rate of 0.3% and a false-positive triploid assignment rate of zero. Genotyping of DNA from 1238 eggs and larvae from 18 independent triploid production batches over three years confirmed triploidy in 98% of samples based on a semi-strict criterion of three unique alleles at one or more loci, and 95% based on a strict criterion of three unique alleles at two or more loci.

Wild Salmo trutta labrax from the Bıçkı Stream in the Marmara Region: Gamete Quality and First Reproduction Under Aquaculture Conditions

In this study, the quality and reproductive success of wild Black Sea Trout (Salmo trutta labrax) were investigated. In total 32 wild trout (27.3±13.6 g and 13.9±2.3 cm) from the Bıçkı Stream in Kocaeli Province in the Marmara Region were kept in circular fiberglass outdoor flow-through tanks (1.5m ø) at the mean water temperature of 11.8±4.5 °C. In November 2016, when the water temperature was 8.4 °C, the first spawning of wild trout occurred. Sperm volume (ml), Motility (%) and VCL (µm/ sec) values were determined to be 7.5±2.5, 70.42±0.83 and 70.35±3.98, respectively. The weight (g), total fecundity and egg diameter (mm) values of female fish were listed to be 513.75±78, 1.171±171, and 3.84±0.02, respectively. In the experiment, 5.859 wild Black sea trout eggs were fertilized. The eyed-egg stage occurred 24 days (288 day-degree) post fertilization and the survival rate from fertilization to the eyed-stage was 28%. Wild Black Sea trout larvae from P1 (Paternal Generation) hatched 48 days after fertilization with the hatching rate of 7%.

Effects of magnetic fields related to submarine power cables on the behaviour of larval rainbow trout (

The aim of this study was to determine the effects of artificial magnetic fields on the behaviour of rainbow trout (Oncorhynchus mykiss) larvae. Individuals (from the eyed egg stage) were exposed to a static magnetic field (SMF) of 10 mT or a low-frequency alternating (electromagnetic) field (EMF) of 1 mT, whereas larvae in the control treatment were reared under a natural geomagnetic field (GMF). After 40 days exposure, larvae were tested for 46 h for their attraction to or avoidance of magnetic fields. None of the groups of larvae avoided either the static or alternating field. By contrast, a mean of 54–60% of individuals was recorded in magnetic fields. Moreover, larvae exposed to SMF or EMF were more attracted to their respective magnetic field than individuals reared under a natural GMF. In addition, no stress response (i.e. a change in the oxygen consumption rate) was recorded for O. mykiss larvae exposed to magnetic fields. These results suggest, for the first time, that early life stages of rainbow trout can detect and are attracted to artificial magnetic fields of a magnitude recorded in the vicinity of submarine cables, with no visible signs of stress (i.e. increased oxygen consumption).

Gonadal steroid fluctuations and reproduction results of European grayling (Thymallus thymallus L.) from broodstock farmed in a recirculation aquaculture system

The initial experiment of this study was conducted to determine whether sex steroid concentrations varied before, during and after the reproductive season of European grayling (Thymallus thymallus L.) farmed broodstock confined in a recirculation aquaculture system (RAS). The results indicated that the plasma sex steroid (testosterone - T, progesterone - P4 and estradiol - E2) concentrations varied (P < 0.05) during these reproductive periods. There were greater concentrations of T, P4 and E2 before and during the grayling reproductive season indicating there are important functions of these steroid hormones associated with gonadal maturation, gamete production and reproductive behavior during the spawning period. In the second experiment of this study, the effectiveness of European grayling controlled reproduction treatment regimens was analyzed and there were 34.69 % and 68.18 % having ovulations in the 2 and 3-year-old broodfish, respectively. Of the embryos developing to the eyed-egg stage, there were 3.70 % and 6.87 % derived from eggs of 2- and 3-year-old grayling females, respectively. Proportions of embryos developing from the eyed-egg stage to hatching were 38.1 % and 52.1 % from eggs of 2- and 3-year-old grayling females, respectively, when there was culturing in a RAS. The results indicate that with grayling broodfish there is greater efficacy in induction of reproduction when there is imposing of the controlled reproduction treatment regimen on 3- rather than 2-year-old broodfish.

The effects of constant and cyclical hypoxia on the survival, growth and metabolic physiology of incubating Atlantic salmon (Salmo salar)

Salmonids reared in aquaculture incubation systems are susceptible to periods of cyclical or fluctuating hypoxia caused by embryo crowding, water flow rates and management protocols. Hypoxia during early development can reduce salmon growth, development and survival, and delay hatching, potentially impacting future performance and survival in subsequent phases of life. However, salmon embryos can also limit the effects of hypoxia by metabolic depression, premature hatching or physiological modifications to improve oxygen delivery. Here, we investigated the effects of constant and cyclical hypoxia on the growth, development, hatching, survival, oxygen uptake rate (ṀO2) and hypoxia tolerance (O2crit) of Atlantic salmon (Salmo salar) from fertilisation, through hatching, until 113 days post-fertilisation (DPF). We incubated salmon in either normoxia (100% dissolved oxygen [DO; as percent air saturation]), moderate hypoxia (~63% DO), severe hypoxia (~27% DO) or cyclical hypoxia (~100–25% DO daily). At the eyed-egg stage routine oxygen uptake (ṀO2rout) was reduced by ~20% in salmon from the cyclical and moderate hypoxia treatments, although reduced ṀO2rout was not associated with a reduction in O2crit. Moderate hypoxia did not affect growth, development, survival or hatching. However, at 113 DPF cyclical hypoxia-incubated salmon were ~12% smaller and developmentally delayed by ~5 days compared to normoxia-incubated salmon as a result of reduced growth and development prior to the eyed-egg stage (~39 DPF). Survival was unaffected by moderate or cyclical hypoxia, but hatching was delayed by ~2–3 days in cyclical hypoxia incubated salmon. Severe hypoxia produced deformed embryos, greatly decreased growth and development and resulted in 99.3% mortality by 113 DPF. This study demonstrates that Atlantic salmon have a considerable capacity to survive daily bouts of extreme hypoxia, however, the consequent reductions in growth, development and hatching may still have implications in aquaculture systems.

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.

Are magnetic and electromagnetic fields of anthropogenic origin potential threats to early life stages of fish?

The number of underwater cables transferring electric current in sea and freshwater environments is constantly increasing. As a result, the risk of negative effects of magnetic fields generated in the vicinity of those cables on fish eggs and larvae is also growing. This is especially the case for species that settle on the bottom for certain periods of time during early development. To study those effects, eggs and larvae of rainbow trout, Oncorhynchus mykiss, were subjected under experimental conditions to a static magnetic field (MF) of 10 m T and a 50 Hz electromagnetic field (EMF) of 1 m T for a period of 36 days (i.e., from eyed egg stage to approximately 26 days post hatching, dph). Neither MF nor EMF had significant effect on embryonic or larval mortality, hatching time, larval growth, or the time of larvae swim-up from the bottom. However, both MF and EMF enhanced the yolk-sac absorption rate. Although it was not related directly to magnetic field effect, it was also shown that larvae with absorbed yolk-sacs by the time of swim-up were less efficient in taking advantage of available food at first feeding (i.e., obtained smaller weight at age). That indicates the importance of processes affecting yolk-sac absorption rate.

Sperm quality analysis of normal season (NG) and out-season by photoperiod manipulation (PG) of male rainbow trout broodstock (Oncorhynchus mykiss)

Sperm quality parameters in rainbow trout (Oncorhynchus mykiss) were investigated during normal season spawning (November-January) and out-season spawning (July-August) treated with artificial photoperiod manipulation. Normal spawning males (n = 15) were kept in an open concrete pond under natural condition. Out-season spawning males (n = 15) were treated with artificial LED light (50lm/m2) in a closed concrete pond. In these two experimental groups, five fish were used in each of three spawning periods. The mean weight and body length of males (2 + years, n = 30) were 1213.43 ± 39.43g and 45.08 ± 0.62cm, respectively. Sperms were collected from July to August 2016 in the out-season spawning or photoperiod-manipulated group (PG) (water temperature 14.21 ± 0.31°C) and from December 2016 to January 2017, in the normal season spawning group (NG) (water temperature 8.81 ± 1.03°C). Volume of sperm, osmolality of seminal plasma, density of sperm, percentage of motile spermatozoa (MOT), curvilinear velocity (VCL), and duration of motility were measured for each male. Seminal plasma osmolality, density of sperm, and the motility of duration were 358.47 ± 37.24 and 308.87 ± 44.09, 4.37 ± 2.10 and 9.8 ± 1.56, and 8.8 ± 2.42 and 24.6 ± 6.76 in PG and NG, respectively. Fertilization rate was 37.79 ± 9.37% and 94.51 ± 1.33% in PG and NG, respectively. Sperm quality parameters showed significant differences in most of the cases (p < 0.05) and fertilization rate at eyed egg stage (150-160 degree-days) was significantly higher in normal season spawning group than the photoperiod-manipulated group (p < 0.05). Though the rate of fertilization was low in out-season, it was able to get enough gametes in summer using only artificial light having no changes in other parameters.