Precocious Males Research Articles

Involvement of sex steroids and thyroid hormones in upstream and downstream behaviors in masu salmon, Oncorhynchus masou

The involvement of testosterone (T), estradiol-17β (E2), 11-ketotestosterone (11-KT), 17,20β-dihydroxy-4-pregnene-3-one (DHP), thyroxin (T4), triiodothyronine (T3), Aromatase inhibitor 1,4,6-androstatrien-3,17-dione (ATD), or the estrogen antagonist tamoxifen in the occurrence of upstream (positive rheotaxis) and downstream (negative rheotaxis) migratory behaviors were investigated in masu salmon, Oncorhynchus masou, in artificial raceways. During their upstream migratory period, two-year-old (2+) males exhibited high plasma T, 11-KT, and DHP levels while 2+ females exhibited elevated levels of T, E2, and DHP. In yearling (1+) immature parr, T induced the occurrence of upstream behavior, while ATD and tamoxifen did not decrease the stimulatory effects of T on upstream behavior. Therefore, it is suggested that not only aromatized E2, but also its precursor T can induce the upstream behavior. In 1+ precocious males, implants of E2 induced the upstream behavior, indicating that E2 may also play a role to induce upstream behavior in male masu salmon. Interestingly, implants of tamoxifen, an E2 antagonist, did not inhibit the occurrence of upstream behavior indicating that not only E2, but also other sex steroids, such as T and 11-KT are involved in inducing the upstream behavior. In these experiments, plasma T4 or T3 levels of upstream migrants tended to decrease over the period of upstream migratory period. In 1+ immature masu salmon smolts, T induced and inhibited the occurrence of upstream and downstream behavior, respectively during their natural downstream migratory period. However, no significant decrease in plasma T4 and T3 levels appeared in upstream and downstream migrants when their levels were compared with non-migrants sampled during the same periods. Based on these results, it is suggested that sex steroids, such as T and E2 commonly regulate upstream and downstream behaviors in both sexes. While plasma T4 and T3 show changes over the duration of upstream migration, their interaction with the sex steroids remains to be determined.

Testes and brain gene expression in precocious male and adult maturing Atlantic salmon (Salmo salar).

BackgroundThe male Atlantic salmon generally matures in fresh water upon returning after one or several years at sea. Some fast-growing male parr develop an alternative life strategy where they sexually mature before migrating to the oceans. These so called 'precocious' parr or 'sneakers' can successfully fertilise adult female eggs and so perpetuate their line. We have used a custom-built cDNA microarray to investigate gene expression changes occurring in the salmon gonad and brain associated with precocious maturation. The microarray has been populated with genes selected specifically for involvement in sexual maturation (precocious and adult) and in the parr-smolt transformation.ResultsImmature and mature parr collected from a hatchery-reared stock in January were significantly different in weight, length and condition factor. Changes in brain expression were small - never more than 2-fold on the microarray, and down-regulation of genes was much more pronounced than up-regulation. Significantly changing genes included isotocin, vasotocin, cathepsin D, anamorsin and apolipoprotein E. Much greater changes in expression were seen in the testes. Among those genes in the testis with the most significant changes in expression were anti-Mullerian hormone, collagen 1A, and zinc finger protein (Zic1), which were down-regulated in precocity and apolipoproteins E and C-1, lipoprotein lipase and anti-leukoproteinase precursor which were up-regulated in precocity. Expression changes of several genes were confirmed in individual fish by quantitative PCR and several genes (anti-Mullerian hormone, collagen 1A, beta-globin and guanine nucleotide binding protein (G protein) beta polypeptide 2-like 1 (GNB2L1) were also examined in adult maturing testes. Down-regulation of anti-Mullerian hormone was judged to be greater than 160-fold for precocious males and greater than 230-fold for November adult testes in comparison to July testes by this method. For anti-Mullerian hormone and guanine nucleotide binding protein beta polypeptide 2-like 1 expression changes in precocious males mirrored mature adults (November) but for collagen 1A and beta-globin the pattern was more complex.ConclusionsExpression changes in the fish brain during the process of precocious sexual maturation were small compared to those in the testes. Microarray analysis suggested down-regulation of housekeeping functions and up-regulation of a small number of specific processes. Transcriptional changes in the testes were much more pronounced with anti-Mullerian hormone playing a major role. Expression profiles for mature parr and maturing adult testes indicate subtle differences in gene expression between these two related groups.

Examining the Conflict between Smolting and Precocious Male Maturation in Spring (Stream‐Type) Chinook Salmon

AbstractPrecocious male maturation is a natural life history strategy for spring Chinook salmon Oncorhynchus tshawytscha. During spawning, precocious males employ a “sneaker” strategy to fertilize eggs in competition with full‐size anadromous adults. Hatchery rearing practices may increase the incidence of this phenotype beyond its natural levels. Previous research reported high rates (>40%) of precocious male maturation at age 2 (minijacks) in the Yakima River spring Chinook salmon supplementation program in Washington State. Minijack rates in wild populations are believed to be less than 5%. We compiled seasonal profiles for size, condition factor (K), gill Na+,K+‐ATPase activity, whole‐body lipid levels, plasma 11‐ketotestosterone (11‐KT), insulin‐like growth factor‐I (IGF‐I), and thyroxine (T4) in minijacks and immature smolts in the hatchery and during out‐migration. In the hatchery, minijacks were larger and had higher K, whole‐body lipid, plasma 11‐KT, and IGF‐I levels than smolts. Plasma T4 and gill Na+,K+‐ATPase activity increased in minijacks in spring, but the levels were slightly lower than those of smolts. Most minijacks are thought to remain resident in headwater streams throughout the summer in preparation for autumn spawning. A subset of these minijacks migrate hundreds of kilometers toward the ocean in the spring, only to reverse course later in the summer in an effort to return to their natal spawning grounds. These migrating minijacks had elevated plasma 11‐KT, IGF‐I, and T4 levels and gill Na+,K+‐ATPase activity. It is generally thought that smoltification and reproductive maturation are mutually exclusive life history events in salmonid fishes. This investigation examined the physiology of a unique phenotype in which smoltification and downstream migration appear to occur in fish that have already initiated the maturation process. These results suggest that hatchery programs with high minijack rates may produce significant numbers of fish that are maladapted for either smoltification or competing on the spawning grounds, and it is likely that they die in the freshwater environment before contributing to subsequent generations.

Oceanic, riverine, and genetic influences on spring chinook salmon migration timing

Migrating salmonids often return to their spawning habitats in overlapping timing patterns of multiple stocks (populations) collectively called a run that varies in its genetic makeup across and within years. Managers, tasked with developing harvest strategies on these runs, may have preseason estimates of total run size but little information on run timing. Without both it is difficult to assess a run's status in real time. Consequently, to avoid overharvest, managers tend to control the timing of harvest. However, this strategy may inadvertently affect the component stocks disproportionately and therefore the run's diversity. Thus, accurate estimates of run timing are needed to improve management. We developed a model that includes genetic and environmental factors to predict the mean run timing of chinook salmon (Oncorhynchus tshawytscha) at Bonneville Dam on the Columbia River, Oregon, USA. The model predicted mean runtiming (P < 0.00001, r2 = 0.78) by characterizing genetic run timing components from the arrival timing of precocious males returning one year prior to the remainder of the adults and environmental influences of oceanic and riverine flows that impede or advance the run timing. Variations in the relative abundances of the populations in the run explain 62% of the interannual variation in mean run timing while the oceanic and riverine factors combined account for 15.5%. We suggest that when genetic run timing characteristics are preserved in species with multiple maturation strategies the information can be used to improve run time predictions and maintain genetic diversity of harvested species.

Balancing the effects of rearing at low temperature during early development on sex ratios, growth and maturation in the European sea bass ( Dicentrarchus labrax). : Limitations and opportunities for the production of highly female-biased stocks

In many cultured fish species, including the European sea bass, undesirable highly male-biased sex ratios are nevertheless frequent. High temperatures (∼ 21 °C), typically used during the larval and early juvenile stages are thought to cause sex-reversal of genotypic females. Rearing at lower temperatures (< 17 °C) has been investigated as a possible solution. However, besides reducing growth, they have sometimes resulted in equivocal sex ratios across different studies. The goal of this study was to find a thermal regime that could maximize the number of females without compromising growth. Four batches were reared at 15 °C during 10 (control group), 30, 60, 90 or 120 (treated groups) days post fertilization (dpf) and then at 21 °C. The controls had excess males (average from 4 batches: 69% males, 31% females). Increasing the duration of rearing at 15 °C doubled the average number of females up to 59% (range 22–90%) and reduced the number of 1-year-old precocious males from 29% in the control to 10–20% in the treated groups. Low temperature retarded growth in groups exposed for 60 or more days; however, fish exposed for 30 days exhibited compensatory growth by 150 dpf. Females reached a marketable size (set at 400 g) during the second year, four months earlier than males. Despite initial slower growth, an increase of 10% in biomass was estimated after rearing at 15 °C for ∼ 60 days (850–900 °C-days) by the time of marketing when compared to current industry practices. Finally, we analyzed these and all available data of the effects of temperature on European sea bass sex ratios, and show that exposures to low temperature starting at fertilization do not induce but merely allow female development. In contrast, high temperatures masculinize, on average, over half of the females. The results show that insensitive fish are not males that cannot be feminized by low temperature but instead females that cannot be masculinized by high temperature. Although there is no thermal regime that per se will result in 100% females in the European sea bass, we propose rearing at 17 °C starting soon after fertilization and until 850–900 °C-days, which at that temperature occurs at ∼ 53 dpf, as the best balance between the advantages resulting from allowing female development, and the disadvantages of initial slower growth. Combined with genetic selection for high female number and low sensitivity to high temperature, this method offers an opportunity for the routine culture of highly female-biased sex ratios to benefit European sea bass aquaculture.

Plasticity in probabilistic reaction norms for maturation in a salmonid fish

The relationship between body size and the probability of maturing, often referred to as the probabilistic maturation reaction norm (PMRN), has been increasingly used to infer genetic variation in maturation schedule. Despite this trend, few studies have directly evaluated plasticity in the PMRN. A transplant experiment using white-spotted charr demonstrated that the PMRN for precocious males exhibited plasticity. A smaller threshold size at maturity occurred in charr inhabiting narrow streams where more refuges are probably available for small charr, which in turn might enhance the reproductive success of sneaker precocious males. Our findings suggested that plastic effects should clearly be included in investigations of variation in PMRNs.

Abundance and Distribution of Precociously Mature Male Spring Chinook Salmon of Hatchery and Natural Origin in the Yakima River

AbstractPrecocious maturation of artificially propagated male Chinook salmon Oncorhynchus tshawytscha has the potential to alter abundance and distribution of males in freshwater and thereby influence ecological and genetic interactions with other fish in the natural environment. Between 1999 and 2007, the Cle Elum Supplementation and Research Facility has produced and released into the upper Yakima River basin of Washington an annual average of 124,573 males that mature precociously. We investigated the abundance and distribution of precociously mature male spring Chinook salmon of hatchery and natural (wild) origin during the spawning season (4–7 months after hatchery release) in the Yakima River. We counted the number of precocious males on the spawning grounds while snorkeling during the peak of spawning and electrofished to determine abundance and distribution of precocious males away from redds. We also collected Chinook salmon to determine percent precocity and size and age distributions. The number of precocious hatchery males on redds was less than 0.05% of the total number of fish released, and they were significantly less abundant on redds than precocious wild males. Between 1999 and 2007, the mean annual abundance of precocious age‐1 hatchery males observed on the spawning grounds was 22 fish (range, 0–78). Precocious hatchery and wild males were both found throughout the spawning range during the spawning season, but significant differences in distribution between origins were detected. Precocious hatchery males were proportionately more abundant in the most downstream sampling reach and less abundant in a tributary with no hatchery facilities. In addition, most precocious hatchery males were found downstream of spawning areas during the spawning season. It appears that many precocious hatchery males migrate downstream from release and fail to migrate back to the spawning grounds, or they die within the Yakima River before spawning. Thus, precocious male Chinook salmon resulting from hatchery production in the Yakima River do not contribute favorably to harvest and may pose ecological risks to other taxa, but most of these fish have a low probability of contributing genes to future generations.

Effects of Continuous Light on the Reproductive System of European Sea Bass Gauged by Alterations of Circadian Variations during Their First Reproductive Cycle

The European sea bass is a short‐day breeder, a characteristic that is highly valued in aquaculture. A high percentage of males of this species mature precociously before reaching commercial size, resulting in economic losses for fish farmers. We investigated the effects of continuous light (LL) on the circadian variations of several reproductive hormones in males of this species in order to understand how the presumed absence of the melatonin rhythm caused by LL affects their daily profile. The study was conducted during four critical stages of the sea bass reproductive cycle: pre‐spermatogenesis (PSpg), spermatogenesis (Spg), spermiation (Spm), and post‐spermiation (PSpm). Every 3 h during a complete 24 h cycle, six fish kept under a natural photoperiod (NP), and another six fish kept under LL were anaesthetized, measured, weighed, and bled. The pituitary was removed and frozen at ‐80°C. The pituitary content of sea bream gonadotrophin‐releasing (sbGnRH) and luteinizing hormone (LH), as well as plasma content of LH, testosterone, and 11‐ketotestosterone (11‐KT) were analyzed by ELISA. The percentage of spermiating males (precocity) per group was determined by periodic abdominal massages of the animals. Our results confirm that LL treatment, maintained from the early stages of development onward, effectively reduces the percentage of precocious male sea bass. As has already been described for caged sea bass, plasma LH showed a clearly marked nocturnal rise near midnight during Spg and Spm during NP, but which was absent under LL. Pituitary sbGnRH and LH content and plasma LH concentration, under both NP and LL, increased during the second half of the reproductive cycle, while sexual steroids were higher at the beginning of the cycle. LL inhibited steroid secretion, especially testosterone secretion, during Spg. In summary, without photoperiod cue, as accomplished by continuous exposure to LL, circadian variations of reproductive hormones appeared altered, causing irregularities in the reproductive process of male sea bass. These findings may have a practical application in aquaculture, namely by applying LL treatment in an effort to reduce the presence of precocious males in a stock.

Marine survival of reared Atlantic salmon in the Baltic Sea: The effect of smolt traits and annual factors

We examined the factors underlying the deteriorating marine survival of a hatchery stock of Atlantic salmon, Salmo salar. The stock originated from the salmon population of the Neva River, which flows into the Gulf of Finland in the Baltic Sea. During 1981–2005, about 134,000 Carlin-tagged Neva salmon smolts were released in the Gulf of Finland and the Bothnian Sea. We investigated the effects of fin damage, smolt length, sexual maturity (precocious maturation), smolt year, the time (days) between tagging and release and the release date on survival. The survival of the released smolts clearly decreased towards present. In earlier years, larger smolts tended to survive better than smaller ones, but the advantage of a large smolt size decreased in the later years of the study. No significant effect of dorsal fin damage on survival was detected. On average, immature smolts survived better than precocious males, and the proportion of precocious males increased over time. However, the proportion of precocious males among the tagged fish did not explain the decreasing trend in marine survival. Release year was the most important predictor of the long-term decreasing trend in marine survival. The optimal tagging time varies: in some years smolts tagged in the autumn survived better, while in other years spring taggings were more advantageous. For most years, a late release (in May or June) was more favourable than an early one (in April). As the releases were mainly carried out quite early in the spring in the last 13 years of the study, an unfavourable timing of release may partly explain the lower marine survival recorded during this period.

Lack of a heritable reproductive defect in the offspring of male rainbow trout exposed to the environmental estrogen 17α-ethynylestradiol

Endocrine disruptors, including environmental estrogens, have been shown to induce heritable effects through both genetic and epigenetic mechanisms in mammals. Despite this information and the wealth of knowledge regarding the significant reproductive impacts endocrine disruptors impose on fishes, no studies have reported whether the observed effects are heritable. Without this information it is difficult to establish the long-term consequences for exposed populations. To determine potential consequences of long-term effects we must consider the possibility that induced reproductive defects in fishes may be heritable. Using rainbow trout ( Oncorhynchus mykiss) as a model this study aims to determine whether a specific reproductive defect observed in 17α-ethynylestradiol exposed male parents, diminished progeny survival, is heritable in the unexposed surviving F1 males. Semen was collected from anesthetized males of the F1 generation upon sexual maturation at two time-points, one year old precocious males and two years old males. In vitro fertilization was used to produce an F2 generation. F2 embryos were then analyzed for survival at 19 days post-fertilization (eye pigmentation) and the different treatment groups statistically compared to the controls. Analysis indicated that F2 offspring survival from F1 males propagated from both exposed and unexposed parents survive normally and no heritable effect was observed in males from the F1 generation for this specific reproductive defect. These results provide scope for the recovery of fish populations exposed to environmental estrogens should the contaminant be removed.

Masculinization of the European sea bass ( Dicentrarchus labrax) by treatment with an androgen or aromatase inhibitor involves different gene expression and has distinct lasting effects on maturation

The objective of this study was to contribute to our understanding of the role of sex steroids in fish sex differentiation and male maturation. Sexually undifferentiated sea bass were administered 17α-methyldihydrotestosterone (MDHT), estradiol-17β (E 2), fadrozole (Fz), cyproterone acetate (CPA) or tamoxifen (Tx). MDHT produced 100% males whereas E 2 and Tx resulted in 100% females. Fz produced 95% males while CPA did not alter sex ratios. E 2 treatment did not affect gonadal aromatase ( cyp19a) expression levels, supporting the possibility that the feminizing effect of exogenous E 2 are not directly related to cyp19a regulation. Both MDHT and Fz decreased cyp19a expression. Moreover, androgen receptor ( ar) expression levels increased during development in all but the MDHT group, suggesting that early exposure to an androgen down-regulates subsequent ar expression in males and that Fz does not interact with the androgen receptor. Together, these observations indicate that although MDHT and Fz result in a similar phenotype, the molecular pathways involved are likely different, and show that Fz masculinization is the consequence of inhibited ovarian differentiation rather than of a direct androgenic effect. Further, since CPA did not alter sex ratios when administered during the period of highest androgen sensitivity, we suggest that androgens are not required for initial testicular differentiation in the sea bass. MDHT and Fz did not alter the number of precocious males but reduced and increased, respectively, their gonadosomatic index (GSI). In addition, Fz had lasting effects on the GSI of precocious and non-precocious males, probably due to alterations of estrogen function in the testis.

Growth and maturation of Atlantic salmon ( Salmo salar) populations with different grilse proportions under natural photoperiod and superimposed nighttime light

This study determined the influence of night illumination, superimposed on the natural photoperiod, upon growth performance in two different stocks of Atlantic salmon ( Salmo salar). One stock had been selected to yield a low proportion of grilse (fish that mature after one winter in the sea) and the second a high proportion of grilse. Growth based on weight gain, gender, and sexual maturity of 250 individually tagged postsmolts in each of four pens was analyzed using five Atlantic salmon groups; mature females and males, immature females and males, and precocious males (the earliest mature males that produce sperm), identified during and at the end of culture. Both stocks under natural photoperiod generally showed that mature females and males grew faster, followed by immature females and males, and followed by precocious males. Mature males in both stocks did better than their respective mature females and growth of immature males in the high grilse stock was similar to mature males during the last two months of rearing. Precocious males had variable growth, depending on population origin. In contrast, salmon groups in stocks subjected to nighttime light did not show growth disparity, and each group grew faster when compared to the same group under natural photoperiod, except for mature females and males from the low grilse stock. Percentage of maturation in the low grilse stock was low and not significantly different between natural photoperiod (21%) and nighttime light (16%) treatments, whereas the high grilse stock reached 87% and was significantly reduced to 56%, respectively. This reduction occurred in mature females and males, except precocious males, whose proportion remained similar in both treatments.

Effects of parental and smolt traits on the marine survival of released Atlantic salmon (Salmo salar)

Crossing experiment of sea-ranched Atlantic salmon (Salmo salar) was used to study the factors behind marine survival and precocious maturity of the offspring. The compared smolt groups differed in their parental rearing history (wild or reared), and also in their parental age at maturity. The length and potential precocious maturity of the smolts at the time of release was recorded. Altogether, about 18400 externally tagged smolts, derived from different crossing groups, were released into the estuary of the River Kemijoki, in the northern Baltic Sea, in 1986 and 1988. The total tag recovery rate was 15% for both year-classes. The results showed that the rearing history of the parents had a significant influence on both the survival and the precocious maturation of the offspring. Reared parents produced on average faster growing offspring than the wild parents. Precocious maturation reduced marine survival of the offspring in the first hatchery generation, but not anymore in the second hatchery generation. The marine survival of both immature and mature smolts generally improved with increasing smolt size, but still the large precocious males (over 21 cm) had the best survival. Maternal and paternal age at maturity and their interactions had also a significant influence on the survival and precocious maturation of the progenies. The increasing maternal and paternal age at maturity had opposite effects on precocious maturation rate of the offspring. Decreasing maternal age and increasing paternal age both increased the proportion of precocious males among the offspring. The survival of the precocious male offspring of old females (3 sea-winter) and young males (1 sea-winter) surpassed all other offspring groups. The proportion of these precocious males was, however, low consisting only 2% of all offspring. Maternal sea age was more important than maternal rearing history in determining marine survival and precocious maturation of the offspring. Survival was higher and precocious maturation was less frequent for the progenies of older females compared to those of young females. The results as a whole suggest that an increased number of hatchery generations do not necessarily reduce the marine survival of sea-ranched Atlantic salmon, but hatchery rearing may generate selection, which causes significant genetic changes in life history traits, even in one hatchery generation.

Sexually mature and immature yearling male European ground squirrels: A comparison of behavioral and physiological parameters

Early puberty may increase lifetime reproductive success, but may also entail diverse costs. In male European ground squirrels ( Spermophilus citellus), age at sexual maturity varies among individuals. We compared sexually active and inactive yearling males under standardized conditions in outdoor enclosures. Non-reproductive yearling males hibernated significantly longer than mature males and emerged when the mating period had already started. Testosterone concentrations peaked in the precocious males during premating and mating, and were depressed in the non-reproductive individuals throughout the study period. Emergence body mass was similar in both groups, although sexually immature males were significantly heavier at the end of the active season. Additionally, non-reproductive yearlings grew faster than precocious individuals. Male–male aggression peaked during mating and the following 4 weeks. Intense aggressive interactions like chases and fights were mostly initiated by reproductive males and were directed towards mature competitors. Aggressive behavior in immature males was mainly expressed as spatial displacements. Non-agonistic interactions with females were only observed in sexually active males. Concentrations of fecal cortisol metabolites did not differ between the two male groups and were elevated in the second half of the active season. Leucocyte numbers were reduced during mating in mature males, whereas in immature animals, cell numbers did not change significantly. Our results indicate that early puberty in European ground squirrels involves lower growth rates, high intrasexual aggression, lower prehibernatory body mass, and probably worse immunological condition during mating.

Study of Mathematically Precocious Youth After 35 Years: Uncovering Antecedents for the Development of Math-Science Expertise.

This review provides an account of the Study of Mathematically Precocious Youth (SMPY) after 35 years of longitudinal research. Findings from recent 20-year follow-ups from three cohorts, plus 5- or 10-year findings from all five SMPY cohorts (totaling more than 5,000 participants), are presented. SMPY has devoted particular attention to uncovering personal antecedents necessary for the development of exceptional math-science careers and to developing educational interventions to facilitate learning among intellectually precocious youth. Along with mathematical gifts, high levels of spatial ability, investigative interests, and theoretical values form a particularly promising aptitude complex indicative of potential for developing scientific expertise and of sustained commitment to scientific pursuits. Special educational opportunities, however, can markedly enhance the development of talent. Moreover, extraordinary scientific accomplishments require extraordinary commitment both in and outside of school. The theory of work adjustment (TWA) is useful in conceptualizing talent identification and development and bridging interconnections among educational, counseling, and industrial psychology. The lens of TWA can clarify how some sex differences emerge in educational settings and the world of work. For example, in the SMPY cohorts, although more mathematically precocious males than females entered math-science careers, this does not necessarily imply a loss of talent because the women secured similar proportions of advanced degrees and high-level careers in areas more correspondent with the multidimensionality of their ability-preference pattern (e.g., administration, law, medicine, and the social sciences). By their mid-30s, the men and women appeared to be happy with their life choices and viewed themselves as equally successful (and objective measures support these subjective impressions). Given the ever-increasing importance of quantitative and scientific reasoning skills in modern cultures, when mathematically gifted individuals choose to pursue careers outside engineering and the physical sciences, it should be seen as a contribution to society, not a loss of talent.

Body size versus gonad maturation form in under-yearling precocious males of the sea trout (Salmo trutta m. trutta L.)

The study was aimed at analysing body size in relation to form of gonad maturation (amount of mature germ cells) in 329 under-yearling sea trout males. The fish, aged 7 months, were caught in late October-early November in 3 streams located in north-western Poland. Each stream supported fish belonging to a different sib group. Standard histological techniques and a computer image analysis programme were used to detect the class of gonad maturation and percentage of the gonad area occupied by tubules with active spermatogenesis. Gonad maturation forms were distinguished based on the latter criteria. Gonads with developing germ cells occupying less than 90% of gonad area were classified as incomplete forms of gonad maturation, others as complete maturation forms. In each sib-groups analysed, even the smallest individual were already precocious, their gonads being incompletely mature. The smallest maturing male measured 7.1 cm in length. The average size of an incompletely maturing individual was slightly smaller than that of the completely mature one but the difference lacked statistical significance (P > 0.05). The sib-group of smaller fish contained less precocious, and the gonads of the more precocious were incompletely mature, compared to the sib-group of larger fish (P < 0.001). It seems that the incomplete form of gonad maturation (defected maturation) occurs at a smaller critical fish size than the complete gonad maturation form. Incomplete maturation is more frequent smaller individuals and possibly in among slow-growing groups of fish.

The Effects of Stock and Prerelease Marine Net‐Pen Culture on Survival to Adulthood, Age at Maturity, and Fisheries Contribution for Three Stocks of Chinook Salmon in Southeast Alaska

AbstractThree stocks of juvenile stream‐type Chinook salmon Oncorhynchus tshawytscha were evaluated as part of an ocean ranching and broodstock development program at Little Port Walter, Southeast Alaska. Fish were either cultured in freshwater throughout the presmolt period or moved to marine net‐pens with an artificial freshwater lens for five periods (2–210 d); all fish were released on the same day. The fish were tagged with coded wire tags to determine the effect, if any, of stock and duration of marine net‐pen culture on precocity, fishery contribution, survival to adulthood, and size in the commercial fisheries relative to traditional freshwater culture. Recoveries of tagged fish in the fisheries and at the hatchery weir indicated significant overall effects of stock on marine survival; the Unuk stock survived better than the Chickamin and King Salmon stocks. Culture overwinter in marine net‐pens produced higher survival to adulthood in all stocks but also resulted in higher mortality during culture and a higher proportion of precocious males in one of the stocks. The effects of short‐term spring net‐pen culture on juvenile Chinook salmon also varied by stock. Unuk and Chickamin stocks cultured for short periods in marine net‐pens generally had higher survival to adulthood, similar fishery contribution, and similar precocious maturation rates as their respective freshwater controls, while the King Salmon stock experienced variable marine survival, precocity, and fishery contribution rates. For facilities with limited freshwater or a limited number of fish to release, the use of marine net‐pens for short‐term culture could help reduce densities, ease rearing space constraints, and maximize adult production. These benefits appear to have stock‐specific limitations.

Microsatellite variation reveals weak genetic structure and retention of genetic variability in threatened Chinook salmon (Oncorhynchus tshawytscha) within a Snake River watershed

Pacific salmon (Oncorhynchus spp.) have been central to the development of management concepts associated with evolutionarily significant units (ESUs), yet there are still relatively few studies of genetic diversity within threatened and endangered ESUs for salmon or other species. We analyzed genetic variation at 10 microsatellite loci to evaluate spatial population structure and genetic variability in indigenous Chinook salmon (Oncorhynchus tshawytscha) across a large wilderness basin within a Snake River ESU. Despite dramatic 20th century declines in abundance, these populations retained robust levels of genetic variability. No significant genetic bottlenecks were found, although the bottleneck metric (M ratio) was significantly correlated with average population size and variability. Weak but significant genetic structure existed among tributaries despite evidence of high levels of gene flow, with the strongest genetic differentiation mirroring the physical segregation of fish from two sub-basins. Despite the more recent colonization of one sub-basin and differences between sub-basins in the natural level of fragmentation, gene diversity and genetic differentiation were similar between sub-basins. Various factors, such as the (unknown) genetic contribution of precocial males, genetic compensation, lack of hatchery influence, and high levels of current gene flow may have contributed to the persistence of genetic variability in this system in spite of historical declines. This unique study of indigenous Chinook salmon underscores the importance of maintaining natural populations in interconnected and complex habitats to minimize losses of genetic diversity within ESUs.

Human chorionic gonadotropin induces spermatogenesis and spermiation in 1-year-old European sea bass ( Dicentrarchus labrax): Assessment of sperm quality

The aims of the present study were (a) to compare sperm quality (percentage of motile spermatozoa, motility duration, density and fertility after cryopreservation) between precocious and normally maturing male European sea bass Dicentrarchus labrax, (b) to examine the potential of human chorionic gonadotropin (hCG) to increase spermiation in precocious males and (c) to examine the potential of hCG to induce spermatogenesis and spermiation in non-precocious 1-year-old males. One hundred precocious and 100 non-precocious fish were each randomly divided in two groups each: control (precocious saline-treated and non precocious saline-treated) and treated (precocious hCG-treated and non precocious hCG-treated). Treated groups were administered weekly with 1000 IU hCG kg − 1 body weight while control groups were injected with physiological solution. Milt volume produced, sperm concentration, motility duration and fertilising ability were assessed every week in each group. The effect of the hormonal treatment on gonadal development was examined based on the gonadosomatic index and testicular histology. The results demonstrate that sperm produced by precocious fish has characteristics (mean value of motility class, mean maximum motility duration, concentration and fertility after cryopreservation) similar ( P > 0.05) to those produced by 2-year-old fish. Human chorionic gonadotropin treatment in precocious fish resulted in a significant increase ( P < 0.05) of milt volume, without affecting sperm quality. In non-precocious fish, hCG treatment resulted in greater percentage of spermiation ( P < 0.05) compared to non-precocious saline-treated group. At the end of the trial (three weeks), 29 out of 50 non-precocious hCG-treated fish were spermiating and, within these 23 produced > 200 μl per fish of milt. No differences were observed in terms of sperm concentration, motility class, motility duration and fertilizing capacity due to hCG treatment in either precocious, or non-precocious fish. In addition, analysis of the testicular histology of fish that did not spermiate after hCG treatment, shows a significant ( P < 0.05) enhancement of testicular development stages. The present study demonstrated that (a) precocious European sea bass males produce milt of comparable sperm characteristics to adult individuals, (b) treatment of non-precocious males with hCG induced spermatogenesis and spermiation and (c) treatment of precocious males with hCG enhanced milt volume without affecting other sperm characteristics, including fertilizing ability.

Comparative analysis of growth performance and sperm motility between precocious and non-precocious males in the European sea bass ( Dicentrarchus labrax, L.)

Early puberty affects a considerable amount of males in commercially farmed fish species. It results in additional annual production costs for aquaculture that need to be reduced. The present study is focused in the sea bass ( Dicentrarchus labrax L.), an important marine teleost fish in European aquaculture that exhibits 25–30% of precocious males under farming conditions. Thus, the effects of early sexual maturation on growth performance and sperm quality between the early-maturing males (1-year-old precocious fish) and their counterparts, the normal maturing fish which mature 1 year later, were compared in this species. Sea bass males were judged to be precociously mature on the basis of their capacity to release sperm after abdominal massage at 12–14-month-old, during their first annual cycle of life. Those individuals that did not release sperm were considered as normal-maturing males. Fish, with a similar size (127.67 ± 1.2 g; 21.01 ± 0.05 cm) at the beginning of the experiment, were monthly sampled from 14 to 24 months of age for comparative growth performance between both types of males. Results evidenced that precocious fish grew up to 18% less in weight and 5% less in fork length than their counterparts during their second annual cycle of life. A computerized analysis of sperm motility was carried out to estimate sperm quality and animal reproduction performance between both types of males in the sea bass. During the first annual cycle of life, significant differences were observed in sperm volume and concentration and several motility parameters (i.e., curvilinear, straight line and average path velocity and beat cross frequency) between the 1-year-old early-maturing males and adult fish that were used for comparison at this time. Nevertheless, sperm motility was comparable between the early-maturing males and the normal-maturing ones during the second annual cycle of life of the animals, suggesting similar reproductive success of both types of males around 2 years of age.