A genetic analysis of egg,alevin and fry mortality in salmon (Salmo salar), sea trout (Salmo trutta) and rainbow trout (Salmo gairdneri)

Heritability of mortality in eggs, alevins and fry were estimated using data from salmon, sea trout and rainbow trout. The highest value (average for all species and both estimation methods) based on the sire component was obtained for the eyed egg stage, h² = 0.08, followed by the alevin stage, h² = 0.05, while estimates for fry mortality did not differ significantly from zero.The maternal effect was rather large for uneyed eggs and eyed eggs, while it was low for alevin mortality. Maternal effects were also found to have a significant influence on the mortality of salmon fry. It was, however, not possible to separate maternal effects from tank effects.     

Distribution of lipid droplets is an indicator for egg quality in brown trout, Salmo trutta fario

In the eggs of the brown trout, Salmo trutta fario, lipid droplets are clearly visible beneath the oolemma on the surface of the protein yolk. When examining the distribution of lipid vesicles in egg batches of different quality, four categories of lipid vesicle distribution could be distinguished: In the first category, the lipid droplets were evenly distributed throughout the egg. These egg batches had a high quality (percentage of eggs developing to eyed stage embryos: 96.2 ± 5.2). Some lipid droplets had the tendency to coalesce in one pole of the egg in the second category. This coalescing of lipid droplets was accompanied with a reduction in egg quality to about 50% of the first category (% of eyed stage embryos: 40.6 ± 15.2). In the last two categories, the lipid droplets were mostly coalesced in one or two poles of the egg and the egg quality was very low (% of eyed stage embryos: 3.3 ± 2.9 and zero, respectively). In conclusion, examination of lipid droplets distribution, in brown trout, can distinguish between high and low quality eggs in an easy and reliable way.     

First results on a relation between ovarian fluid and egg proteins of Salmo trutta and egg quality

By use of sodium dodecyl sulfate polyacrylamide gel electrophoresis, ovarian fluid proteins and main proteins of unfertilized eggs were qualitatively and quantitatively investigated in the brown trout, Salmo trutta, to see whether some of them were correlated with the rate of embryos reaching the eyed embryo stage. In the ovarian fluid, 12 types of proteins in the range of 39–166 kDa were detected whereby three proteins were lipoproteins and two were glycoproteins. Ovarian fluid proteins with a molecular weight of 85, 68, 62 and 39 kDa were negatively correlated with the percentage of eyed stage embryos. The statistical significance of the relations was low in simple and multiple regression models (R²≤0.534) indicating that the relations were influenced and superposed by other factors. Therefore, ovarian fluid proteins give only poor information about maturity and quality of eggs. In the eggs, nine major types of proteins in the range of 95–15 kDa were identified. The 95 kDa protein was a lipoprotein, the 85 and the 62 kDa protein were glycoproteins, and the 15 kDa protein was a phosphoprotein. The 95, 85, 77 and 39 kDa protein were positively correlated with embryo survival to the eyed embryo stage. The explanatory effect of the multiple regression model was very high (R²=0.961) indicating that distinct egg proteins are closely related with egg quality.     

Efficacy of clove oil and ethanol against Saprolegnia sp. and usability as antifungal agents during incubation of rainbow trout Oncorhynchus mykiss (Walbaum) eggs

Inhibitory concentrations of clove oil and ethanol against growth of Saprolegnia sp. hyphae were screened by a modification of the hemp (Cannabis sativa L.) seed MicroPlate (HeMP) method and their usability as antifungal agents during incubation of rainbow trout Oncorhynchus mykiss eggs was tested. In vitro experiment showed that in continuous static exposure, clove oil at 100 mg L^?1 significantly inhibited the growth of Saprolegnia, whereas in bath exposures, clove oil at 500 mg L^?1 had no significant effect at any exposure time tested (15, 60 and 240 min), but clove oil at 10 000 mg L^?1 significantly inhibited growth at all exposure times. Clove oil and ethanol treatments had no visible effects on the onset or spread of the fungus during incubation of rainbow trout eggs. Clove oil at 1000 mg L^?1 resulted in 95–100% mortality before the eyed stage was reached. Sublethal concentrations of clove oil and ethanol had no effects on the development rate of the embryo or growth and yolk utilization efficiency after hatching. This study suggests that clove oil and ethanol may not be options in controlling aquatic fungi infestations during incubation of rainbow trout eggs.     

Studies on cryopreservation of eggs from rainbow trout (Salmo gairdneri) and coho salmon (Oncorhynchus kisutch)

The effect of pre-freezing treatments as well as freezing of inseminated, not water-activated eggs from rainbow trout Salmo gairdneri, and coho salmon, Oncorhynchus kisutch, was investigated in relation to survival and further development.Effects above freezing temperatures included: the temperature at insemination, viability of inseminated and unactivated eggs after storage, suitability of an incubation medium and the tolerance of eggs to various levels of the cryoprotectant dimethylsulfoxide (DMSO). Freezing experiments included: investigating the action of DMSO (0, 1, 2 mole) and the tolerance of coho eggs to temperatures between ?4.6 to ?30°C. Insemination temperatures between 0.5°C and 9.8°C (coho eggs) as well as incubation in an artifical medium (1-0°C) for 80 min (rainbow trout eggs) and 170 min (coho eggs) did not influence subsequent fertility. Storage of inseminated and unactivated rainbow trout eggs for 135 min and beyond reduced egg fertility. DMSO at 2 and 4 mole was detrimental to coho eggs (1-0°C). One mole DMSO had no (coho) or reduced (rainbow trout) influence on egg fertility when it was added gradually.In the presence of 1 mole DMSO most eggs remained unfrozen (67–89%) when kept for 10 min in frozen artificial medium (?4.6%) and 27–32% subsequently reached the eyed stage (control = 100). Further cooling (0.3°C/min) to ?10°C was still tolerated (62% unfrozen, 22% eyed eggs) but not to ?20°C (6% unfrozen, no development) and ?30°C (no survival). Use of 2 mole DMSO did not improve the results.     

Developmental rates,structural asymmetry,and metabolic fingerprints of steelhead trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) eggs incubated at two temperatures

Temperature stress on developing steelhead (Oncorhynchus mykiss) was evaluated using asymmetry of skeletal characters, fish condition factor, and metabolic fingerprints. Eggs from three female hatchery steelhead were fertilized by a single male. The eggs from each female were divided into two groups and incubated at either 8°C or 18°C. Mortality, growth, and condition factor were measured at stage 6 (32 cells), stage 20 (eyed), and stage 21 (caudal flexing). In addition, ¹H-nuclear magnetic resonance (NMR) spectroscopy was used to establish metabolic fingerprints of developing eggs at the three stages. After hatching, all alevins were moved to tanks at 18°C and allowed to develop to 60 days post-emergence (DPE), at which point they were examined for structural asymmetry. Eggs incubated at 18°C experienced higher mortality, with all eggs from one hen dying at the higher temperature. Eggs incubated at the higher temperature that did survive hatched as larger larval fish than eggs incubated at the lower temperature. Fish incubated at the higher temperature exhibited greater structural asymmetry than fish incubated at the lower temperature. A principle components (PC) analysis of the metabolic fingerprints indicated that PC1 and PC2 accounted for 60% of the variance in the metabolites. Separation along PC1 corresponded to differences in developmental stage, and separation along PC2 corresponded to differences in hen. Eggs incubated at 18°C lagged behind eggs incubated at 8°C along PC1, indicating a potential problem with embryo staging. PC1 scores were highly correlated with the accumulated thermal units during development, indicating that scores along PC1 were a robust measure of developmental stage.     

Cryopreservation of sperm of common carp, Cyprinus carpio L.

Milt of common carp, Cyprinus carpio L. was cryopreserved in pellet form with the use of 12 extenders. Most efficient were: BE2 original extender (containing 85 mM NaCl, 50 mM KCl, 3 mm CaCl₂, 1 mm MgCl₂ with 10% dimethyl-acetamide (DMA) and 10% addition of hen's egg yolk) and Kurokura et al.'s extender with 15% DMA and 10% yolk (about 73% and 69% of eyed eggs, about 61% and 52% of swim-up larvae, respectively). Within the most effective treatments, survival from the eyed-egg stage to the swim-up stage was similar to that observed in the control group. Survival from the eyed-egg stage to the swim-up stage (percentage of eyed eggs was considered as 100%) was highly significantly and positively correlated with the actual rate of swim-up larvae.     

Impact of origin and condition of host fish (Salmo trutta) on parasitic larvae of Margaritifera margaritifera

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Survival and development of Atlantic salmon eggs and fry at three different temperatures

Groups of Atlantic salmon (Salmo salar) eggs were incubated at 12, 10 and 8° C. At 12° C mortality was high and fry averaged little more than half the weight of those hatched at 10 or 8° C. Development of alevins to the ‘swim-up’ stage was also abnormal at 12° C. The results suggest that 10° C is optimal for incubating Atlantic salmon eggs. For the period between hatching and swim-up, the most favourable temperature varies according to the temperature used during incubation. Mortality rate during the first 6 weeks of feeding was correlated with mortality during earlier development. Total numbers of day-degrees required by the eggs and fry to reach the eyed, hatching, and swim-up stages of development were significantly less at 12° C than at 10 or 8° C. However, total day-degrees required to reach an average weight of 0.5 or 0.6 g were almost the same regardless of temperature during hatching.     

Hatch rate of channel catfish Ictalurus punctatus (Rafinesque 1818) eggs treated with 100 mg L−1 copper sulphate pentahydrate

Catfish hatcheries use copper sulphate pentahydrate (CuSO₄·5H₂O) as an economical control for saprolegniasis on eggs. This study determines hatch rate of channel catfish, Ictalurus punctatus (Rafinesque 1818), eggs in hatching troughs containing 23.8 °C flow‐through well water when treated with 100 mg L^?1 CuSO₄·5H₂O (10 times the proposed therapeutic dose). Eggs were treated daily until the embryos reached the eyed stage. Fry survival in the control and 100 mg L^?1 CuSO₄·5H₂O treatments was significantly different (15% and 71% respectively). This study demonstrates that there is a considerable margin of safety in using CuSO₄·5H₂O as a catfish egg treatment to control saprolegniasis.     

Commercial Bacillus probiotic supplementation of rainbow trout (Oncorhynchys mykiss) and brown trout (Salmo trutta): growth,immune responses and intestinal morphology

Probiotic administration is associated with the enhancement of host resistance to environmental and nutritional stressors, improving survival and growth rates. This study was carried out to evaluate the effects of dietary supplementation of Bacillus subtilis and Bacillus cereus toyoi on growth performance, innate immune responses and gut morphology of two trout species feeding a commercial diet high in soybean meal. A commercial probiotic (4.2 × 10⁹ CFU g^?1 of additive) was supplemented to the experimental diets at 0% (control), 0.03% (P₁; 6 × 10³ CFU g^?1 of diet) or 0.06% (P₂; 1.5 × 10⁶ CFU g^?1 of diet) and fed to brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) for 9 and 20 weeks respectively. Rainbow trout showed significantly better growth performance than brown trout, regardless of the dietary treatment. No effect of dietary probiotic supplementation was detected on growth performance, body composition or innate immune parameters (plasma lysozyme, alternative complement and peroxidase activities). In both species, after 9 weeks, intestinal lamina propria and submucosa were widened, with increased presence of inflammatory cells, significantly higher in groups fed probiotics. This inflammatory process, with villi and enterocytes noticeably damaged compared with the control group, was more pronounced in brown trout. Under the current trial conditions, the B. subtilis + B. cereus toyoi had no positive impact in either trout species, on the contrary a harmful effect was observed.     

Dose-Confirmation of Copper Sulfate for Treating Fungus on Channel Catfish,Ictalurus punctatus,Eggs at a Commercial Hatchery

This study at a commercial hatchery was required by the U.S. Food and Drug Administration to provide independent substantiation of the results of previous laboratory dose-confirmation studies on the use of copper sulfate (CuSO₄) to control fungus (Saprolegnia spp.) on the eggs of channel catfish, Ictalurus punctatus. The study compared an untreated control group of eggs to eggs treated with 10 mg/L CuSO₄ in a flow-through system; mean water temperature was 23.5°C. Eggs were treated once daily until the embryos reached the eyed stage (5 treatments). Hatching was complete by day 11, and fry were counted to determine the percentage of survival in each treatment. Fungus was identified by polymerase chain reaction (PCR) as Saprolegnia spp. The mean survival in the control treatments was 4% and 40% in the CuSO₄ treatments; the latter survival was significantly higher, but still lower than normal. This study confirms that 10 mg/L CuSO₄ is an effective treatment to control fungus on catfish eggs when used daily until the eggs are eyed. However, continued treatment of eggs until hatching occurs may be warranted based on fungal growth rates observed after treatments were discontinued.     

The Irish sea trout enhancement programme: a review of the broodstock and ova production programmes

The Irish sea trout, Salmo trutta L., broodstock programme was instigated in response to the collapse of sea trout stocks in the west coast of Ireland in 1989 and 1990. Wild sea trout kelts and post-smolts were successfully reconditioned and used as broodstock to produce eyed ova for distribution to affected fisheries. From 1991 to 1999, a total of 8.2 million green ova from four separate stocks were produced. The number of females stripped increased from 34 in 1991 to a peak of 1435 in 1997. Green ova survival to the eyed ova stage ranged from 65 to 96%. The eyed ova produced were distributed to 23 affected fisheries along the west coast. The average cost per eyed ova decreased from €2.02 at the start of the programme to €0.04 at the end. The growth rates recorded for broodstock held in captivity were comparable with those recorded for wild sea trout. Relationships between fish size, egg size and number of eggs produced were examined for each stock and for each stock in each year. Significant positive relationships were found between fish size and egg number and fish size and egg size, with the exception of the first year in which fish were stripped, when a negative correlation between fish size and egg size was found.     

Electrophoretic evaluation of a supplemental stocking programme for brown trout, Salmo trutta L.

Abstract. Over a 15-year period hatchery brown trout, Salmo trutta L., have been added 10 Lower Lough Erne, Northern Ireland to supplement declining native populations. Introductions have mainly comprised eyed ova and fingerlings, stocked into a number of rivers in the Erne drainage. Utilizing a natural genetic tag an electrophoretic assessment of the stocking programme was undertaken. The percentage hatchery genetic contribution in trout populations varied widely from river to river (19%-91%). Lough-caught brown trout (3+ and older) showed a substantial (21·5%) hatchery genetic component. Introgression of native-and hatchery stocks was evident. The resultant deleterious genetic consequences for the conservation of the unique Lough Erne brown trout gene pool arc discussed and alternative management strategies are proposed.     

Computer-controlled freezing of rainbow trout Oncorhynchus mykiss (Walbaum) spermatozoa for routine programmes

The effects of extender composition and freezing rate on cryopreservation efficiency of refrigerated spermatozoa of rainbow trout Oncorhynchus mykiss (Walbaum) were evaluated in order to test the suitability of a computer-controlled ultrafreezer to cryopreserve milt samples obtained in field conditions and stored for several hours. A very highly significant first-order interaction between freezing rate and the type of extender was found. Six of the eight experimental variants did not differ significantly, resulting, after fertilization of eggs with cryopreserved sperm, in a range of 62.3–74.8% of eyed embryos. This procedure was effective for samples stored at 1 °C for 2 days.     

Seawater tolerance in Atlantic salmon, Salmo salar L., brown trout, Salmo trutta L., and S. salar?×?S. trutta hybrids smolt

High levels of hybridization between Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) have been reported in the Gyrodactylus salaris infected Rivers Vefsna and Driva in Norway. The survival and behaviour during the sea phase of such hybrids is unknown. The reported work documents ionoregulatory status after 24 h seawater challenge tests (24hSW) and gill Na⁺/K⁺-ATPase (NKA) activity of migrating wild smolts of Atlantic salmon, brown trout and hybrids at two sampling dates during the 2006 smolt run in River Driva. Salmon, trout and hybrids contributed to 27, 52 and 21% of the catches, respectively. The large contribution of hybrids suggests both a high hybridization rate and a high survival rate from fry to smolt. Both salmon and hybrids had a well-developed seawater tolerance at the time of downstream migration, revealed by small ionoregulatory effects and no or low mortality rates during the 24hSW tests. The trout were not fully adapted to seawater, and high mortality rates were observed (71 and 92%) during the 24hSW tests. The NKA activity was not significantly different between salmon and hybrids. Most of the hybrids were physiologically capable of direct entry to full strength seawater. The incomplete seawater tolerance in trout compared to salmon corresponds well with differences in life-history patterns between these two species. The life history strategy of the hybrids during the sea phase is not known, and further investigations on the marine behaviour and survival is needed to evaluate the role of hybrids in the risk of spreading G. salaris to nearby river systems.     

Induced spawning in bream, Abramis brama (L.), using carp and bream pituitary extract and hCG

Induced spawning in bream, Abramis brama (L), was studied using acetone-dried common carp pituitary (CP) and bream pituitary (BP) with or without the addition of human chorionic gonadotrophin (hCG). The total dose administered to fish was of 5.0 mg kg^?1 BP or 4.0 mg kg^?1 CP with or without 2000-2200 IU hCG kg^?1 for females and 2.5 mg kg^?1 BP or 2.0 mg kg^?1 CP with or without 1000–1100 IU HCG kg^?1 for males. In all male treated groups 100% of spermiation was observed: in females the most effective method was a triple injection with hCG and carp pituitary, resulting in 79% of females ovulated (over 68% of eyed eggs). Biological quality of eggs, expressed as a percentage of eyed eggs, was negatively correlated with time elapsing between resolving (final) injection and ovulation. Spawning success, expressed as a value of S_e (spawning effectiveness coefficient), was higher in fish treated with triple injection.     

Reproductive performance of cultured brown trout (Salmo trutta L.) in Chile

Data on reproductive traits in a cultured population of brown trout (Salmo trutta L.) in southern Chile were collected over three consecutive reproductive seasons: 1999, 2000 and 2001, corresponding to the first (at 3 years), second and third spawnings in females. Data were collected from individual females (n=238, 273 and 169 respectively). The reproductive season lasted mainly from June to August. The peak (July) tended to increase with each season (55.46%, 62.27% and 80.81% of total spawning fish respectively). Female body weight (470.8±102.5, 735.0±150 and 1263.9±263.4 g), total fecundity (1182±344, 1904±595 and 2744±605) and egg diameter (4.64±0.11, 4.67±0.27 and 5.24±0.12 mm) increased significantly (P<0.01) over successive reproductive seasons, particularly between the second and third spawnings. Relative fecundity, on the other hand, decreased significantly with each season (3577±471, 2591±900 and 2181±360). Following analysis of the variables over the three seasons, the correlation pattern of female body weight with total fecundity (r=0.91, n=458; P<0.001) and relative fecundity (r=?034, n=451; P<0.001) proved similar to that described in other salmonid females. Fertilization rate and survival to the eyed egg stage were also positively correlated (r=0.73, n=453; P<0.001). The systematically high values obtained for these latter variables over the seasons evaluated (consistently above 90%) are clearly greater than those we registered in other species of salmonids bred in Chile under similar conditions and suggest highly efficient biological variables that determine the gamete fertilization of this species. The brown trout is, therefore, an interesting potential aquaculture resource in Chile.     

Effects of ascorbic acid enrichment by immersion of rainbow trout (Oncorhynchus mykiss, Walbaum 1792) eggs and embryos

This study was conducted to examine the effects of different forms and concentrations of ascorbic acid (vitamin C), and different enrichment times (24 and 48 h post ovulation) on egg, embryo and alevin ascorbate concentrations and survival of rainbow trout (enrichment was at the ova stage). In experiments 1 and 2, fertilized eggs were immersed in water containing ascorbate at 0 (control), 100, 1000 mg L^?1 l ‐ascorbic acid (AA) and 2000 mg L^?1 l ‐ascorbyl monophosphate (AP). In experiment 3, 0 (control), 500 and 1000 mg L^?1 AA neutralized (N) with NaOH, 1000 mg L^?1 AA non‐neutralized (NN), 1000 and 2000 mg L^?1 AP immersions were used. The mean total ascorbic acid (TAA) and dehydroascorbic acid (DHA) concentrations were measured before fertilization, at 3 and 24 h after fertilization, at the eyed stage, and in hatched alevins. We observed significant differences in TAA concentration at different immersion levels at 3 and 24 h after fertilization. Survival decreased significantly depending on the level of vitamin C, pH of the solutions and immersion time. We suggest that when broodstock rainbow trout do not have enough vitamin C in their ovaries, immersion of eggs in 1000 mg L^?1 of neutralized AA may be useful.     

Effects of storage duration and storage media on initial and post-eyeing mortality of stored ova of rainbow trout Oncorhynchus mykiss

The effects of storage duration and storage media on the viability of unfertilized eggs of rainbow trout from fertilization to hatching stage was studied. The unfertilized eggs were stored in coelomic fluid and Cortland artificial media buffered with Tris–HCl (C₄H₁₁NO₃–HCl) and Hepes (C₈H₁₈N₂O₄S) at 2–3 °C. These eggs were fertilized after 0 (i.e. control eggs fertilized prior to storage), 2 and 9 days post-stripping using fresh, pooled sperm obtained from 4 to 5 males. According to the results of present study, after 2 days of storage, no significant (p > 0.05) change in survival to eyeing and hatching of eggs stored in coelomic fluid (85.5 ± 4.8%, 80.2 ± 6.3%) and Cortland medium buffered with Hepes (73.3 ± 4.1%,68.1 ± 4%) was observed in comparison to the control (82.6 ± 8%,78.7 ± 7.8%). However, eyeing and hatching survival rates of eggs stored for the same period in Cortland medium buffered with Tris–HCl (44.5 ± 7%,34.2 ± 8.2%) decreased significantly (p < 0.05) in comparison with the control. Also, eggs stored for 2 days in Cortland medium buffered with Tris–HCl (25 ± 6.7%) had significantly (p < 0.05) greater eyed egg mortality compared to the control (4.7 ± 0.6%), while no significant (p > 0.05) differences were observed between eyed egg mortality rates of eggs stored in coelomic fluid (6.7 ± 2.1%) and Cortland medium buffered with Hepes (7.3 ± 0.9%) compared to control. After 9 days of storage, the eggs that were stored in coelomic fluid showed no significant (p > 0.05) differences in eyeing (77.5 ± 7.2%) and hatching (67 ± 8.1%) rates in comparison with control, while both Cortland storage media exhibited significant (p < 0.05) loss in eyeing (44.4 ± 11.5%, 24.7 ± 13.8% for Hepes and Tris–HCl, respectively), and hatching (24.5 ± 5.9%, 19.2 ± 14.4% for Hepes and Tris–HCl, respectively) in comparison with control. Furthermore, eyed egg mortality increased significantly (p < 0.05) in coelomic fluid (14 ± 2.9%), media buffered with Hepes (43 ± 6.2%) and Tris–HCl (49.3 ± 26.9%) compared to control. Based on this study, unfertilized eggs of rainbow trout can be successfully stored in coelomic fluid for 9 days at (2–3 °C) without significant loss of fertility. However, storage within a similar period in artificial media showed lower fertilization rates and higher eyed egg mortality compared to coelomic fluid.