The effect of short-term starvation on ovarian development and egg viability in rainbow trout (Salmo gairdneri)

Adult female rainbow trout (Salmo gairdneri) were fed a commercial trout production diet until approximately 40 days prior to spawning at which time the fish were divided in two groups. One group continued to be fed while the other group was starved until spawning. Egg size, egg number, ovary weight, and egg proximate composition were examined periodically starting 5 months before spawning. Muscle tissues of the fish were sampled at spawning to measure somatic depletion of proximate consituents in the two groups. Egg hatchability was determined by incubating test lots from each spawning female. No significant differences (P > 0.05) were found in egg hatchability between the fed and starved groups. Changes in proximate composition were observed in the eggs during the months prior to spawning, but no differences were detected between the eggs of the starved and the fed groups. Short-term starvation did not significantly alter the proximate composition of muscle tissue of the spawned female trout.     

A genetics analysis of the performance of three rainbow trout broodstocks

The reproductive performance of three domesticated rainbow trout broodstocks spawning at 2 years of age was analysed using data collected over a period of 5 years. Data were collected for post-spawning body weight, volume of eggs spawned, egg size, egg number and fertility to the eyed egg stage. There were significant differences among the stocks attributable to both genetic and environmental causes. In addition, there were marked differences between year-classes, isolated from each other due to 2-year spawning. The differences appeared to be genetic in origin and demonstrated the effect of sampling the original parents.Heritabilities estimated from full-sib comparisons indicated male weight was more influenced by environmental stress at spawning than was female weight. Heritability estimates for egg volume, egg size and egg number ranged from 0.05 to 0.76 for individual stocks, but when averaged for the three stocks the range was from 0.32 to 0.52. Egg size was found to have the lowest heritability of the three traits. The heritability of fertility was found to be low and was the lowest for the stock with the poorest fertility.Genetic and phenotype correlations among the traits were also estimated. The relationship between body weight and egg volume and size were both positive as was that between egg volume and egg size. It was determined that egg volume was the principal determinant of egg number and that the relationship of number to size could be negative. The latter evidence was obtained by artificially adjusting the egg production traits to a constant female body size. The result suggested that females that produce larger numbers of eggs are likely to produce smaller eggs unless the change is associated with a marked increase in body weight. It is recommended that selection for egg size be included in all selection programs and that egg number be ignored in any selection program designed to increase body size.     

Individual variation in progeny size and quality in rainbow trout, Oncorhynchus mykiss (Walbaum)

Early life history traits of fish are very variable as a result of both genetic and environmental factors. In this study, we examine individual variation in early life history traits in progeny of seven females crossed with one male rainbow trout, Oncorhynchus mykiss (Walbaum). Individual eggs were followed from fertilization through hatching until death of the larvae by starvation. Larvae and yolksac size (size was shown to be a good indicator of energy content) increased with increasing egg size, but there were still differences between families after variation in egg size was accounted for. Incubation time was not correlated with egg size, and did not differ between families. The progeny from the different families utilized the available energy differently, as both longevity and growth-rate without food was independent of yolk-sac size, but strongly dependent on family. The observed between-family differences in early life history traits in rainbow trout were mainly caused by genetically based effects; egg size and thus probably egg quality, which differed strongly bet ween females, could not adequately explain these differences.     

Testing hypotheses about fecundity, body size and maternal condition in fishes

Recent research suggests that maternal condition positively influences the number of eggs spawned in fishes. These studies commonly choose a priori to use body length rather than weight as an explanatory variable of offspring production, even though weight is usually the better predictor of fecundity. We are concerned that consistent exclusion of body weight as a predictor of egg production inflates the variance in fecundity attributable to maternal condition. By analysing data on three populations of Atlantic cod (Gadus morhua, Gadidae) and 10 populations of brook trout (Salvelinus fontinalis, Salmonidae), we illustrate the need for a statistically defensible method of model selection to distinguish the effects of maternal condition on egg production from the effects of body size alone. Forward stepwise regression and null model analyses reveal how length‐based regressions can significantly over‐estimate correlations between condition and fecundity, leading us to conclude that the effect of condition on egg productivity may not be as ubiquitous or as biologically important as previously thought. Our work underscores the need for greater statistical clarity in analyses of the effects of maternal condition on reproductive productivity in fishes.     

Indicators of reproductive performance in rainbow trout Oncorhynchus mykiss (Walbaum) selected for high and low responsiveness to stress

A number of indicators of reproductive performance were assessed in rainbow trout divergently selected on the basis of their plasma cortisol response to a standardized stressor. For both male and female rainbow trout Oncorhynchus mykiss (Walbaum), body weight was significantly related to stress responsiveness. High‐responding (HR) females were significantly heavier than low‐responding (LR) females overall, and HR males were significantly heavier than LR males overall. There was no significant difference in the specific growth rate (SGR) of HR and LR female fish during the experimental period, whereas in contrast the mean SGR of HR males was significantly greater than that of LR males. The divergent confinement‐induced levels of blood cortisol in HR and LR groups were stable for more than 1 year after selection. There was no significant difference in the extent to which confinement stress reduced blood oestradiol‐17β levels in HR and LR females, despite a large difference in relative blood cortisol levels. The onset and rate of ovulation was similar within the HR and LR groups. Differences in fecundity, relative fecundity and egg volume and weight were wholly attributable to the different mean body weights of the HR and LR fish. There was no difference between the sperm counts of HR and LR males. There was significantly higher mortality among eggs derived from HR parents overall between fertilization and hatch, but maximum mean mortality did not exceed 12%. Mean time to eyeing in the HR groups was 224 degree days, and in the LR groups was 244 degree days. Hatching commenced at 344 and 347 degree days in the HR and LR groups, respectively, and was complete within 412 and 416 degree days respectively. Overall, selection for stress responsiveness was associated with no significant benefits or costs in reproductive performance.     

Larger eggs in resident brown trout living in sympatry with anadromous brown trout

Abstract– Freshwater resident brown trout ( Salmo trutta L.) in the stream Jorlandaan (southwestern Sweden) had larger eggs (range of actual mean egg wet weights, 65.9–108.5 mg) than both sympatric migratory trout (76.8–84.2 mg) and trout from five other Swedish streams with allopatric resident (23.7–80.1 mg) or migratory populations (44.5–121.9 mg), after accounting for differences in body size. In Jörlandaån, some resident females even had a larger absolute mean egg weight than any of the migratory females found in the stream. Resident trout had low absolute fecundity, and our data suggest that resident females in Jörlandån produce large eggs at the expense of their fecundity. The extremely large relative egg size in resident Jörlandaån females suggests that the production of large offspring enhances fitness, possibly through increased fry survival.     

Fecundity, egg size and early hatchery survival for wild Atlantic salmon, from the River Bush

Abstract  A total of 118 wild Atlantic salmon, Salmo salar L., females were stripped at the River Bush Salmon Station. The total number of eggs (fecundity) and egg diameters were compared for three age groups of adults. Adult length explained the majority of the variation in fecundity whilst freshwater age explained the majority of the variation in egg diameter. Parallel regression analysis for the total number of eggs on fish length relation for 3 years (2000–2002) showed significant temporal variation among years. Larger eggs from 2.1+ adults produced longer and heavier swim-up fry than smaller eggs from 1.1+ adults. There was also the suggestion that the survival of eggs from 1.1+ adults was lower than eggs from 2.1+ adults to the swim-up stage.     

Egg quality in rainbow trout: The relation between egg viability,selected aspects of egg composition,and time of stripping

Batches of eggs (1 batch/female) from 17 rainbow trout in their first spawning season were stripped and reared separately, and the percentage which hatched and the percentage which reached the stage of first feeding were determined. The fertilised egg batches were analysed for egg wet weight, egg dry weight, chorion weight and levels in the eggs of free, bound and total lipid, precipitable protein, protein phosphorus, lipid phosphorus, calcium and iron. All determinations were made on single eggs, and six eggs from each batch were analysed for each variable. Results were expressed in absolute terms (as weight of component per egg) and as percentage of egg dry weight. Highly significant variations in all these aspects of egg composition were shown to occur between parent females. However, there was no significant correlation between the percentage of the original number of eggs which hatched and any one aspect of egg composition, except for a weak positive correlation (P<0.05) with the percentage of protein phosphorus in the eggs. Similarly, there was no significant correlation between the percentage of the original number of eggs which reached first feeding and any one aspect of egg composition except for weak positive correlations (P<0.05) with egg wet weight and with both the absolute level and the percentage of protein phosphorus in the egg. There was significant positive correlation (P<0.05) between the percentage of hatched eggs (alevins) surviving to first feeding and each of the following: egg wet weight, egg dry weight and absolute levels in the egg of bound lipid, precipitable protein and protein phosphorus. Egg batches with higher hatching percentage (>50%) differed significantly from those with zero hatching percentage in having (in absolute terms) higher egg weight, chorion weight, protein phosphorus (all P<0.001), egg dry weight, bound lipid and precipitable protein (all P<0.01) and (percentages) higher chorion weight (P<0.05) and protein phosphorus (P<0.001), and lower free and total lipid (both P<0.01) and iron (P<0.05). In a separate experiment to investigate the effects of allowing the eggs to be retained by the female within the abdominal cavity for increasing periods of time after ovulation, eggs were obtained from three females on three or four successive occasions 2–11 days apart. Although the above aspects of egg composition remained almost constant when the eggs were held in the female for up to 18 days after ovulation, the hatching percentage declined sharply within this period, in two females falling from over 90% to near zero. These results together indicate that the time of stripping of the eggs in relation to the date of ovulation is a much more significant determinant of egg quality than any of the chemical and physical aspects of egg composition which were investigated.     

Use of minimally invasive surgical technique for egg removal from the beluga,Huso huso

Reuse of sturgeon broodfish for propagation could provide an opportunity to ease fishing pressure on the wild stocks of these valued species. A minimally invasive surgical technique (MIST) for the removal of ovulated eggs from the beluga, Huso huso, was tested on broodfish caught from the wild to determine whether it affected fecundity or hatching rates when compared with the traditional stripping method that involves killing the fish and removing the eggs. In comparison with the traditional procedures, MIST is rapid: it can be performed in between 8 and 15 min per fish. Morphological parameters of female beluga, germinal vesicle position, weight of obtained eggs, fertilization rate, and percentage hatching during incubation were not significantly different between the MIST and the traditional procedure. The fish remained healthy 4 weeks after surgery. The final results of this study showed that the MIST approach is efficient, practical, and less stressful to beluga broodfish during artificial propagation than other reported egg collection procedures.     

Cryopreservation of rainbow trout spermatozoa: The influence of sperm quality,egg quality and extender composition on post-thaw fertility

The presence of 5% to 20% hen's egg yolk in a sucrose-based extender significantly improved post-thaw fertility of cryopreserved rainbow trout (Salmo gairdneri) spermatozoa compared to when the extender without hen's egg yolk was used. However, the degree of increased cryoprotection associated with hen's egg yolk was affected by the quality of the milt. Considerable variation was detected in the performance of various batches of trout eggs used to test post-thaw fertility and the composition of the extender was shown to affect fertilizations differentially with some of the eggs. Despite this variation, the extender containing 10% hen's egg yolk consistently gave high post-thaw fertility in samples of cryopreserved milt (67.3±3.0% S.E.M.) in thirty replicated trials. As such, the method described is reliable for cryopreserving rainbow trout milt and fertilizing small quantities of eggs.     

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.     

Efficacy of formalin, hydrogen peroxide, and sodium chloride on fungal-infected rainbow trout eggs

Antifungal agents are essential for the maintenance of healthy stocks of fish and their eggs in intensive aquaculture operations. In the USA, formalin is the only fungicide approved for use in fish culture. However, hydrogen peroxide and sodium chloride have been granted low regulatory priority drug status by the United States Food and Drug Administration (FDA) and their use is allowed. We evaluated the efficacy of these fungicides for controlling fungal infections on rainbow trout eggs. A pilot study was conducted to determine the minimum water flow rate required to administer test chemicals accurately in Heath incubators. A minimum water flow rate of 7.6 1 min⁻¹ was necessary to maintain treatment concentrations during flow-through chemical exposures. The antifungal activity of formalin, hydrogen peroxide, and sodium chloride was evaluated by treating uninfected and 10% fungal-infected (Saprolegnia parasitica) rainbow trout eggs (Oncorhynchus mykiss) for 15 min every other day until hatch. There were no significant differences among treatments in percent hatch or final infection for uninfected eggs receiving prophylactic chemical treatments. Eggs of the negative control group (uninfected and untreated) had a mean hatch exceeding 86%. All chemical treatments conducted on the infected egg groups controlled the spread of fungus and improved hatching success compared with the positive control groups (infected and untreated). Formalin treatments of 1000 and 1500 μl l⁻¹ and hydrogen peroxide treatments of 500 and 1000 μl l⁻¹ were the most effective. Sodium chloride treatments of 30 000 mg l⁻¹ improved fry hatch, but the compound was less effective at inhibiting fungal growths compared with hydrogen peroxide and formalin treatments.     

Variation in semen production of farmed Atlantic salmon and rainbow trout

The variation in semen production among farmed Atlantic salmon (Salmo salar) and rainbow trout (Salmo gairdneri) has been studied. Both species were stripped at weekly intervals, the Atlantic salmon four times and the rainbow trout three times.The individual variation in volume of semen was very high, particularly in rainbow trout. The total volume of semen obtained was 137 ml (20 ml/kg body weight) in Atlantic salmon and 23 ml (5 ml/kg body weight) in rainbow trout. The intraclass correlation for volume of semen was estimated at 0.73 in Atlantic salmon and at 0.59 in rainbow trout. The correlations between volume of semen and body size (weight and length) were all positive. They were all significant and medium in Atlantic salmon whereas in rainbow trout they were all low and significant only for volume of semen at first stripping.The number of males needed to supply the Norwegian fish farming industry with semen is discussed. It is concluded that the possibility of disseminating genetic improvement throughout the whole population of farmed Atlantic salmon and rainbow trout by transport of semen from selected males is considerable.     

Reproductive development, GnRHa-induced spawning and egg quality of wild meagre (Argyrosomus regius) acclimatised to captivity

The objective of the study was to acclimatise wild-caught meagre (Argyrosomus regius) to captivity to produce viable eggs for aquaculture production. Twelve meagre (3 males and 9 females, mean weight?=?20?±?7?kg) were caught and transported to a land-based facility on 26 October 2006. During, March to June 2007, all three males were spermiating and five of the nine females were in vitellogenesis with mean maximum oocyte diameter ≥550?μm. No spontaneous spawning was observed. Two hormone treatments, either a single injection of gonadotropin-releasing hormone agonist (GnRHa, 20?μg?kg(-1) for females and 10?μg?kg(-1) for males) or a slow-release implant loaded with the same GnRHa (50?μg?kg(-1) for females and 25?μg?kg(-1) for males), were used to induce spawning on three different dates on 26 March 2007, 4 May 2007 and 18 April 2008. From each spawning event, the following parameters were determined: fecundity, number of floating eggs, egg size, fertilisation and hatching success, unfed larval survival, and proximal composition and fatty acid profile of the eggs. In 2007, two females that were injected on 26 March and 4 May spawned a total of 5 times producing 9,019,300 floating eggs and a relative fecundity of 198,200 eggs?kg(-1) and two different females that were implanted on the same dates spawned 14 times producing 12,430,000 floating eggs and a relative fecundity of 276,200 eggs?kg(-1). In 2008, a pair that was implanted spawned five times producing a total of 10,211,900 floating eggs and a relative fecundity of 527,380 eggs?kg(-1). The latency period was 48-72?h. Parameters were compared between hormone treatments, date of hormone induction and parents determined by microsatellites. Percentage hatch and egg size were 70?±?0.3% and 0.99?±?0.02?mm, respectively, for GnRHa-implanted fish and were significantly higher (P?相似文献   

The bacterial flora of rainbow trout, Salmo gairdneri Richardson, and brown trout, Salmo trutta L., eggs and its relationship to developmental success

Abstract. The bacterial flora of rainbow, Salmo gairdneri Richardson, and brown trout, Salmo trutta L., eggs was studied during incubation. Few bacteria were considered to exist internally, although Pseudomonas species and Aeromonas hydrophila were isolated. During incubation, large numbers of bacteria approaching 500 colony forming units/mm² accumulated around egg surfaces. Both rainbow and brown trout eggs placed in a through-flow system were colonized mainly by Pseudomonas sp. and A. hydrophila , whilst rainbow trout eggs in a separate recycling system were dominated by a Cytophaga species. Glass beads were also incubated (as an inert surface) and found to support significantly lower numbers of bacteria. Egg mortalities were recorded daily and found to differ significantly between both fish species and water conditions. Statistical analysis indicated a potentially significant correlation between hatching success and numbers of surface bacteria.     

Life‐history variation in a species complex of nonmigratory galaxiids

Life‐history theory predicts that the optimal strategy in the trade‐off between egg size and number varies in relation to resource availability and environmental disturbance. We assessed interspecific differences in egg size, fecundity and other life‐history traits in a species complex of stream‐resident galaxiid fish, which are distributed across a range of contrasting habitat types on the South Island, New Zealand. Oocyte size, fecundity and reproductive effort were measured from gravid females collected immediately before spawning. Proxy measures of stream productivity, flow variability and predation pressure were extracted from modelled data sets. A suite of different egg sizes were identified across species within the Galaxias vulgaris complex, with mean oocyte volume differing by up to 133% between species. The species with the smallest eggs showed mean size‐relative fecundities 246% higher than the species with the largest eggs. A significant negative relationship was found between species’ mean egg size and size‐relative fecundity, suggesting a trade‐off between these traits. Species with larger eggs had larger maternal body size, lower reproductive effort and delayed maturity compared to ‘small‐egg’ species. Consistent with the predictions of life‐history theory, species with larger eggs, lower size‐relative fecundity, lower reproductive effort and delayed maturity were associated with low productivity, stable streams, whereas species exhibiting the opposite set of traits occurred in relatively productive but disturbed systems.     

Effects of unilateral ovariectomy on recruitment and growth of follicles in the rainbow trout,Oncorhynchus mykiss

Virgin female rainbow trout, Oncorhynchus mykiss, were unilaterally ovariectomised at various stages of ovarian development to investigate the effect of the removal of one ovary on subsequent recruitment and growth of follicles in the remaining ovary. The right ovary was removed from groups of 12–15 fish, 12, 7 and 4 months before they were due to ovulate, and the gonadosomatic index and follicle number and size determined just prior to ovulation. There were no differences in fecundity or follicle size in fish unilaterally ovariectomised at 12 and 7 months prior to ovulation compared to the controls. However, in the females unilaterally ovariectomised 4 months prior to ovulation, the remaining ovary either had the normal number of follicles for a single ovary but of a significantly larger size than follicles in the controls, or alternatively had almost 70% more than the normal number of vitellogenic follicles but comprising two distinctly different size populations. Differences in plasma oestradiol-17β concentrations at the final sample were seen only in females unilaterally ovariectomised 4 months prior to ovulation, where the levels were significantly lower than both the sham operated and control fish (p < 0.05). These data show that in the rainbow trout, complete compensatory ovarian hypertrophy following unilateral ovariectomy can occur throughout a major part of ovarian development, but that follicle recruitment is limited to stages up to (and therefore fecundity is determined by) mid-vitellogenesis.     

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.     

Evaluation of egg quality in broodstock cobia Rachycentron canadum L.

Twenty egg batches spawned naturally from 17 different females over two spawning seasons were used to evaluate the egg quality of cobia Rachycentron canadum. A reduction in egg size was observed towards the end of the spawning season for both years. The proportion of floating eggs demonstrated a positive linear relationship with both yolk‐sac larval survival (r²=0.91, P<0.05) and batch larval production (r²=0.80, P<0.01). Viable egg batches (i.e. fertilization success >50%) were of higher batch fecundity, had larger eggs and a higher proportion of floating eggs than non‐viable batches (i.e. 0% fertilization success). Also, biochemical analyses revealed that these viable eggs had significantly higher protein and amino acid contents. A multiple regression model based on the proportion of floating eggs, batch fecundity and fertilization success provided the most accurate predictions of batch larval production (r²=0.95, P<0.001). Similarly, using the egg content of arginine/glycine and methionine significantly increased the correlation coefficient in the multiple regression model predicting larval deformity (r²=0.92, P=0.002). This study reveals that accurate determination of egg quality in cobia can be improved using a combination of several variables rather than a single variable.     

Growth and fillet quality attributes of five genetic strains of rainbow trout (Oncorhynchus mykiss) reared in a partial water reuse system and harvested at different sizes

Genetics and harvest size influence fish growth performance and product quality attributes, making selection of fish strain and harvest size critical for optimizing quality. Definition of performance and quality outcomes in a recirculating aquaculture system (RAS) environment may guide selection of fish stocks best suited for RAS farmers to meet production and product quality goals. Accordingly, five genetic lines of rainbow trout, Oncorhynchus mykiss were reared to 3 kg in a partial water reuse system and sampled at common harvest sizes (0.5, 1, 2 and 3 kg) to compare growth performance and product quality attributes. Fish weight affected fish processing yields and cook yields. Genetic line affected fish weight. When correcting for fish size, differences in fillet yields due to genetic line were present. Both fish weight and genetic line affected different organ indices, fillet colour scores and mortality. Muscle composition and texture were similar at each harvest, but changed with increasing fish size over time. Differences in growth performance and product quality traits due to genetic line identify variation in available fish stocks, and balancing change to these traits due to fish size can guide producer selection of fish stocks and optimal harvest size to meet individual production goals.