Search

Methods were developed to assess whole-body immunoreactive corticosteroid concentrations (IRC) and plasma levels of cortisol in Atlantic cod subjected to several common, acute stressors. A measurable corticosteroid stress response was observed at the first sampling in whole bodies of 8-day post-hatch (dph) larvae. Two groups of juveniles (∼5 and 30 g) were subjected to a 30 s net stressor and whole-body IRC and plasma cortisol levels were determined. Post-stressor IRC in smaller fish rose approximately 14-fold, peaked at 1 h, were sustained for 3–6 h and returned to pre-stressor levels within 24 h. Post-stressor plasma cortisol levels in larger fish rose approximately 18-fold, peaked at 0.5–1 h, were sustained for 1–3 h and then returned to near pre-stressor levels after 24 h. Immunoreactive corticosteroid concentrations appeared to remain elevated longer than plasma cortisol levels suggesting that steroids other than cortisol were contributing to total immunoreactivity in homogenates. Juveniles exposed to either a grading procedure or high density transport had maximal IRC and plasma cortisol levels within 90 min which returned to pre-stressor levels within 24–72 h. A reduction in water salinity (20 g L−1) did not moderate the corticosteroid response in juveniles. The results show that Atlantic cod respond to common, acute stressors in a manner similar to other teleosts. Whole-body homogenates can be used to identify changes in IRC in response to acute stress in cod with the caveat that recovery IRC may differ from plasma cortisol concentrations. [ABSTRACT FROM AUTHOR]

Abstract: Interest in commercial production of black sea bass has increased in recent years, but reliable spawning methods remain problematic. The objective of this study was to evaluate the effects of oocyte size and luteinizing hormone releasing hormone analogue (LHRHa) dosage and delivery systems on ovulatory success for in vitro fertilization. Vitellogenic females with maximum oocyte diameters of 400–625 μm were implanted with a 95% cholesterol–5% cellulose pellet containing 50 μg of LHRHa. Fish with maximum oocyte diameters <450 μm failed to ovulate. In contrast, 90% of fish with 500 μm oocytes spawned within 36 h and 40% of this group ovulated a second time. All of the females containing oocytes >550 μm ovulated. In a second experiment, females with uniformly vitellogenic oocytes (>500 μm) and implanted with 50 μg LHRHa ovulated substantial numbers of eggs (45,000–192,000 eggs/kg body weight (BW), but fertility was consistently low (0–15%). In a third experiment, 19 of 39 females receiving implants containing 6.3–23.6 μg LHRHa/kg BW during the spawning season ovulated, but fecundity (17,000–339,000 eggs/kg) and fertilization (0–98%) were highly variable. When fish were grouped by developmental index, calculated as the number of oocytes with diameters >400 μm/total number of oocytes measured, there were no statistical differences among groups with respect to the number of spawns, fecundity or fertilization success. In a fourth experiment, 11 of 13 females with a clutch of fully vitellogenic oocytes that were injected with 20 or 100 μg/kg BW LHRHa ovulated between 1 and 2 times on consecutive days. Five of seven given an implant containing 12.5 μg LHRHa ovulated one or more times. Fish implanted with shams or injected with vehicle alone did not ovulate in any of the experiments. No differences were found in the number of spawns, fecundity or fertilization success from fish receiving different doses of injected or implanted LHRHa. Incubation of pooled eggs produced 155,000 larvae (60% hatch) and 95,000 one-gram juveniles. These results demonstrate that injected or implanted LHRHa is effective for inducing ovulation in black sea bass with maximum oocyte diameters >500 μm. [Copyright &y& Elsevier]

Haddock ( Melanogrammus aeglefinus L.) were maintained on either simulated natural (SNP) or advanced, phase-shifted photoperiods (ADV) and reproductive characteristics of female fish were measured throughout two reproductive cycles. By advancing the seasonal photoperiod 8 weeks, relative to ambient conditions, follicle development, peak levels of estradiol and initiation of spawning were all accelerated compared with fish maintained on an SNP. Profiles of steroid synthesis and follicular development were similar between the two groups but the spawning period was protracted by 40 days in the fish maintained on ADV. Ultrasound imaging proved to be an effective and non-invasive tool for accurately assessing ovarian development throughout the reproductive cycle. These results suggest that photoperiod manipulation has significant potential for extending the availability of eggs and larvae for haddock aquaculture. [ABSTRACT FROM AUTHOR]

The black sea bass, Centropristis striata, is a potential candidate for commercial aquaculture in the United States. One of the most significant constraints limiting commercial production of black sea bass is the lack of a reliable supply of eggs and larvae. A narrow window of annual spawning prevents year-round availability of juveniles for grow out. The present study reports on the use of photoperiod manipulation to alter the timing of spawning in C. striata and increase availability of larvae. Adult black sea bass were maintained under a simulated natural (SNP) or an accelerated long day (ALD) photoperiod regimen. Water temperature was adjusted from 14 to 20 °C to correspond to seasonal changes in daylength. Reproductive development was monitored by histological analysis of gonadal biopsies and plasma levels of sex steroids (estradiol-17β, testosterone and 11-ketotestosterone). Females in both regimens were induced to spawn by implantation of 25 μg luteinizing hormone-releasing hormone analogue (LHRHa) when follicle diameters exceeded 500 μm. Acceleration of the photoperiod advanced the annual cycle of circulating gonadal steroids in both sexes without altering the profile. The onset of spermiation in males was unaffected by photoperiod manipulation, but follicle growth and spawning in females were advanced approximately 2 months by exposure to the ALD regimen. Of interest, the ALD photoperiod regimen accelerated the time frame of sexual succession from female to male without reducing the mean volume of eggs produced per female. These findings suggest that photoperiod manipulation can be used to alter the timing of reproduction in black sea bass and increase the supply of eggs for commercial aquaculture. [Copyright &y& Elsevier]

The article focuses on a study related to the validation of the non-lethal radioimmunoassay (RIA) for steroid hormones from autotomized tail tissue in Plethodontid Salamanders. Topics discussed include conduction of blood sampling for steroid analysis in salamanders; higher testosterone in gravid females; and extraction of the steroid hormones and its measurement from autotomized salamander tail.

Recent growth in striped bass aquaculture has generated interest in broodstock development programs for improved growth, disease resistance and stress tolerance. This research evaluated differential stress responsiveness of captive‐bred striped bass originating from Canada, Virginia, Florida and a domestic strain, following a repeated acute stressor. Fish were communally stocked into a six tank recirculating system, and fish in three tanks were net‐chased for 1 min two days/week (stressed), and three undisturbed tanks served as controls. After 14 weeks, fish in the control and stressed treatments were chased, and blood collected from all fish in one tank per treatment at 0, 1 and 3 h post‐stressor. Growth, cortisol, glucose, haematological indices and selected hepatic gene expression were compared among strains and between treatment groups. To further compare cortisol responsiveness, a second study was conducted with lower net chasing frequency (once/month) and cortisol measured. A cortisol stress response was not detected in Canada fish in either study, but all other strains exhibited similar expression patterns. Differences in plasma parameters, growth and immunocompetence were detected, but no single measure predicted greater growth. These results indicate that strains differ in acute stress responsiveness, which may be useful in selective breeding programs. [ABSTRACT FROM AUTHOR]

Background: Understanding growth regulatory pathways is important in aquaculture, fisheries, and vertebrate physiology generally. Machine learning pattern recognition and sensitivity analysis were employed to examine metabolomic small molecule profiles and transcriptomic gene expression data generated from liver and white skeletal muscle of hybrid striped bass (white bass Morone chrysops x striped bass M. saxatilis) representative of the top and bottom 10 % by body size of a production cohort. Results: Larger fish (good-growth) had significantly greater weight, total length, hepatosomatic index, and specific growth rate compared to smaller fish (poor-growth) and also had significantly more muscle fibers of smaller diameter (≤ 20 µm diameter), indicating active hyperplasia. Differences in metabolomic pathways included enhanced energetics (glycolysis, citric acid cycle) and amino acid metabolism in good-growth fish, and enhanced stress, muscle inflammation (cortisol, eicosanoids) and dysfunctional liver cholesterol metabolism in poor-growth fish. The majority of gene transcripts identified as differentially expressed between groups were down-regulated in good-growth fish. Several molecules associated with important growth-regulatory pathways were up-regulated in muscle of fish that grew poorly: growth factors including agt and agtr2 (angiotensins), nicotinic acid (which stimulates growth hormone production), gadd45b, rgl1, zfp36, cebpb, and hmgb1; insulin-like growth factor signaling (igfbp1 and igf1); cytokine signaling (socs3, cxcr4); cell signaling (rgs13, rundc3a), and differentiation (rhou, mmp17, cd22, msi1); mitochondrial uncoupling proteins (ucp3, ucp2); and regulators of lipid metabolism (apoa1, ldlr). Growth factors pttg1, egfr, myc, notch1, and sirt1 were notably up-regulated in muscle of good-growing fish. Conclusion: A combinatorial pathway analysis using metabolomic and transcriptomic data collectively suggested promotion of cell signaling, proliferation, and differentiation in muscle of good-growth fish, whereas muscle inflammation and apoptosis was observed in poor-growth fish, along with elevated cortisol (an anti-inflammatory hormone), perhaps related to muscle wasting, hypertrophy, and inferior growth. These findings provide important biomarkers and mechanisms by which growth is regulated in fishes and other vertebrates as well. [ABSTRACT FROM AUTHOR]

Anadromous rainbow smelt (Osmerus mordax, [Mitchill 1814]) are found along the northeast Atlantic coastline of North America, with their range now limited to north of Cape Cod, Massachusetts, USA. Although their anadromous life cycles are described broadly, gaps remain regarding how adult rainbow smelt use estuaries post‐spawning, including movement behaviors, habitats used, and specific timing of emigration to coastal waters. In spring 2021, we used acoustic telemetry to characterize movements during and after the spawning season of rainbow smelt captured in tributaries to Great Bay, New Hampshire, USA, a large estuarine system near the southern edge of their range. Forty‐four adult rainbow smelt (n = 35 male, n = 9 female) were tagged with Innovasea V5 180‐kHz transmitters and an array of 22,180 kHz VR2W receivers were deployed throughout Great Bay to detect movements of tagged fish from March to October 2021. Rainbow smelt were detected 14,186 times on acoustic telemetry receivers, with 41 (93%) of the tagged individuals being detected at least once post‐tagging. Individuals were detected moving between tributaries, revealing that rainbow smelt can use multiple rivers during the spawning season (March–April). Mark‐recapture Cormack‐Jolly‐Seber models estimated 83% (95% confidence interval 66%–92%) of rainbow smelt survived to the mainstem Piscataqua River, and a minimum of 50% (22 of 44) reached the seaward‐most receivers and were presumed to have survived emigration. Most individuals that survived remained in the estuary for multiple weeks (average = 19.47 ± 1.99 standard error days), displaying extended use of estuarine environments. Downstream movements occurred more frequently during ebb tides and upstream movements with flood tides, possibly a mechanism to reduce energy expenditures. Fish emigrated from the estuary by mid‐May to the coastal Gulf of Maine. Our results underscore that rainbow smelt need access to a variety of habitats, including multiple tributaries and high‐quality estuarine habitat, to complete their life cycle. [ABSTRACT FROM AUTHOR]

The decline in anadromous rainbow smelt ( Osmerus mordax) populations may be due to anthropogenic causes including spawning habitat degradation. The purpose of this study was to assess the survival of rainbow smelt embryos incubated under sediment layers of different depths (0.00, 0.25, 1.00, and 6.00 g/45.6 cm2) and in contact with periphyton communities of different biomass. Embryo survival was also assessed when cultured on periphyton in combination with sterilized sediment or eutrophying compounds (nitrates and phosphates). Oxygen consumption was monitored from embryos cultured alone, on periphyton layers, and under a sediment layer. Survival was significantly reduced under the highest sediment treatment and attributed to low oxygen availability to the embryos. Embryonic survival was also significantly reduced when incubated on the highest periphyton biomass. Embryos under the sediment layer consumed oxygen at a significantly greater rate than the controls, and the dissolved oxygen concentration below the sediment–water interface decreased to near anoxic. These results suggest that embryonic survival could be impacted in rivers with heavy sedimentation or a high standing biomass of periphyton. [ABSTRACT FROM AUTHOR]

To examine the effects of temperature on sex differentiation in the black sea bass ( Centropristis striata L.), a protogynous hermaphrodite, juveniles (∼0.5 g) were cultured in recirculating systems at 17, 21 or 25 °C. Growth was assessed at 155, 182, 241 and 275 days post hatch and sex differentiation was determined histologically. No differences were found in the sex ratios of fish reared at different temperatures, but only 55–64% developed as females. Growth was significantly greater in males across all temperature treatments. These results suggest that black sea bass exhibit sexually dimorphic growth patterns and that female-specific sex determination can be disrupted in culture. [ABSTRACT FROM AUTHOR]

Mature black sea bass, Centropristis striata L. (200–800 g), were captured in coastal South Carolina during the spawning season and administered hormones for ovulation induction and strip spawning. During both study years, control groups of females were incorporated into the study design and administered sham injections containing physiological saline solution. In 2004, females received a single intramuscular injection of human chorionic gonadotropin (hCG) (330 IU kg−1) ( n=8) or two injections of hCG at 24-h intervals ( n=8). In 2005, females received a single injection of hCG ( n=10) or an analogue of luteinizing hormone releasing hormone (LHRHa) ( n=10). In 2004, all fish administered a single dose of hCG ovulated at least once. Six fish ovulated on two consecutive days and one fish ovulated on 3 days consecutively. In contrast, six of eight fish receiving two doses of hCG ovulated once, five ovulated on 2 days successively and three fish ovulated 3 days in succession. Of the fish that spawned, no differences were found in any reproductive parameters. In 2005, all fish administered hCG or LHRHa ovulated at least once. Three fish administered hCG ovulated twice, four fish ovulated on three consecutive days and one fish 4 days successively. All fish administered LHRHa spawned at least twice, six fish ovulated thrice and three fish ovulated 4 days, successively. A significant difference in fertility was found between hCG (75.6±11.4%) and LHRHa (55.6±27.4%). The results of this study indicate that both hCG and LHRHa are effective for ovulation induction in prespawning black sea bass. [ABSTRACT FROM AUTHOR]

Juvenile Atlantic cod ( Gadus morhua L.) and haddock ( Melanogrammus aeglefinus L.) were subjected to 30 s air exposure stressors following acclimation to 4, 10 and 14 and 4, 8 and 14°C respectively. Both species responded to the stressor with increases in plasma cortisol at all temperatures tested. At 14°C cortisol levels peaked within 1 h post-stressor, and returned to pre-stressor levels within 24 h. In contrast, at 4°C, peak cortisol levels were not attained until 6 h post-stressor in haddock and remained elevated beyond 24 h in both species. The rate of plasma glucose accumulation was greater at higher temperatures in both species and no increase was seen at 4°C. Lysozyme activity in cod, in response to the stressor, was lower than the values reported for some other species and increased slightly at 14°C. The results show that cod and haddock acclimated to different temperatures respond to common, acute stressors in a manner similar to other teleosts. [ABSTRACT FROM AUTHOR]

Four experiments were conducted to investigate the effects of feeding frequency on growth of juvenile Atlantic halibut,Hippoglossus hippoglossusL. Fish (22–75 g) fed three (3×) or five times per day (5× day−1) under constant light and temperature (13±1°C) consumed significantly more feed than fish fed 1× day−1 but by the end of the experiment only fish fed 5× day−1 were heavier and had greater specific growth rates (SGR). Under simulated winter conditions (9L:15D, 5±1°C), halibut (∼300 g) fed every other day consumed more feed, had a greater SGR and final weight compared with fish fed every third day. Feed conversion ratios were not different among treatment groups in any of the experiments. These results suggest that growth rates may be improved by feeding juvenile halibut more than 1× day−1. [ABSTRACT FROM AUTHOR]

Populations of anadromous European smelt Osmerus eperlanus (L.) are declining across its geographical range in northern Europe, but no practical culture techniques exist to develop stock enhancement programmes for this species. In this study, a culture protocol is described to rear fish from fertilised eggs to mature adults in 2 years involving the use of 'green water', live feed and artificial diets. The sequence of embryonic development for eggs incubated at 10°C/0 ppt was described and photographed. To determine the optimum conditions for larval culture, fertilised eggs were reared at a range of salinities (0–20 ppt) and temperatures (5–18°C) until first feeding. Best hatching success (ca. 97%), size at hatch (ca. 0.8 mm) and survival to first feeding (ca. 96%) of larvae were achieved under combined conditions of low salinity (0–0 ppt) and temperature (5–10°C). No larvae survived a salinity of 20 ppt. The time taken from fertilisation to hatch (FtH) and hatching duration (HD) were temperature‐dependent ranging from 42 days FtH and 10 days HD at 5ºC, to 10 days FtH and 2 days HD at 18°C irrespective of salinity. The results indicate that conservation programmes could utilise existing salmonid hatchery facilities (i.e. freshwater, ≤10°C water temperature) for stock enhancement. Since on‐growing of smelt involves the logistical and technical problems of live feed production, it is recommended that smelt enhancement programme utilise freshwater hatchery facilities to rear fish until hatching, and then stock out onto known spawning grounds in rivers allowing hatched larvae to drift into estuaries to complete the larval and juvenile phases. This approach would minimise the time spent in the hatchery post‐hatching, eliminate the need for live food production, prevent the development of predator‐naïve fish, and hence would mimic the natural life cycle of the species as closely as possible. [ABSTRACT FROM AUTHOR]

Abstract Many teleost fishes exhibit sequential hermaphroditism, where male or female gonads develop first and later undergo sex change. Model sex change species are characterized by social hierarchies and coloration changes, which enable experimental manipulations to better understand these processes. However, other species such as the protogynous black sea bass (Centropristis striata) do not exhibit these characteristics and instead receive research attention due to their importance in fisheries or aquaculture. Black sea bass social structure is unknown, which makes sex change sampling difficult, and few molecular resources are available. The purpose of the present study was to induce sex change using exemestane, an aromatase inhibitor, and assess gonadal gene expression using sex markers (amh , zpc2) and genes involved in steroidogenesis (cyp19a1a , cyp11b), estrogen signaling (esr1 , esr2b), and apoptosis or atresia (aen , casp9 , fabp11 , parg , pdcd4 , rif1). Overall, dietary exemestane treatment was effective, and most exposed females exhibited early histological signs of sex change and significantly higher rates of ovarian atresia relative to control females. Genes associated with atresia did not reflect this, however, as expression patterns in sex changing gonads were overall similar to those of ovaries, likely due to a whole ovary dilution effect of the RNA. Still, small but insignificant expression decreases during early sex change were detected for ovary-related genes (aen , casp9 , fabp11 , zpc2) and anti-apoptotic factors (parg , rif1). Exemestane treatment did not impact spermatogenesis or testicular gene expression, but testes were generally characterized by elevated steroidogenic enzyme and estrogen receptor mRNAs. Further research will be needed to understand these processes in black sea bass, using isolated ovarian follicles and multiple stages of sex change. Highlights • Exemestane induced the initiation of female-to-male sex change in black sea bass. • Exemestane-exposed females exhibited significantly greater ovarian atresia than control fish. • Males did not exhibit gonadal effects from exemestane treatment. • All testes exhibited elevated steroidogenic enzyme and estrogen receptor mRNAs. • Small decreases in apoptosis-related mRNAs were evident in sex changing gonads. [ABSTRACT FROM AUTHOR]

Abstract Sex differentiation in many lower vertebrates (e.g. reptiles, amphibians, and fishes) can be influenced by environmental factors experienced during sensitive developmental periods. Environmental stressors, acting through cortisol, masculinize some teleost fishes during development by limiting gonadal cytochrome P450 aromatase (cyp19a1a), the enzyme that irreversibly converts testosterone to 17β-estradiol. In this study, we examined the influence of cortisol, cortisol inhibitors and a repeated, acute stressor (net-chasing) on sex differentiation in black sea bass (BSB; Centropristis striata), a protogynous hermaphroditic teleost. Wild-caught, sexually-undifferentiated, BSB juveniles (~90 mm) were collected from Rhode Island waters, raised in recirculating systems and fed diets supplemented with cortisol, a cortisol receptor antagonist (mifepristone), a cortisol synthesis inhibitor (metyrapone), or net-chased twice a week for two min until gonads were differentiated (77–89 days). Long term cortisol administration partially masculinized all female fish, but repeated net-chasing did not alter sex differentiation relative to the control group. Blocking cortisol receptor binding delayed sex differentiation in some individuals, but overall led to increased masculinization compared to control fish. The proportion of treatment fish that developed as males suggests a functionally, diandric protogynous reproductive strategy in this species. We also identified a glucocorticoid response element in the gonadal aromatase (cyp19a1a) promoter, indicating a possible relationship between cortisol and cyp19a1a gene expression. Highlights • Long-term cortisol administration partially masculinized all black sea bass, but repeated acute stressors did not alter sex differentiation. • Blocking cortisol receptor binding, but not cortisol synthesis, delayed sex differentiation in some individuals. • A partial aromatase promotor sequence was identified and contained response elements associated with sex differentiation. • Although black sea bass are protogynous hermaphrodites, 2050% of the fish in all treatments differentiated directly as males. [ABSTRACT FROM AUTHOR]

Striped bass ( Morone saxatilis ) and their hybrids have been well studied and are widely cultured in freshwater ponds as food and gamefish. Recent industry expansion has generated an interest in strain-specific broodstock development for marine netpen and pond culture. In this effort, Atlantic and Gulf coast striped bass strains were cultured in recirculating aquaculture systems (RAS) at different salinities for up to two years and production and morphometric parameters (specific growth, feed conversion, fillet yield, condition factor and stripe patterns) were compared. Striped bass juveniles produced from wild-caught broodstock from rivers in Nova Scotia, Delaware, Virginia, North and South Carolina, Florida, Texas and a selected, domesticated strain were reared in triplicate fresh (0 ppt), brackish (5 ppt) and saltwater recirculating (30 ppt) systems. After one year of age, a subset of fish were implanted with passive integrated transponder (PIT) tags, combined into a larger, “common-garden”, saltwater, recirculating system and monitored over an additional year. Parental broodstock and cultured offspring were fin-clipped and genotyped to identify juvenile family origin. Final weights of fish after one and two years averaged approximately 0.5 and 2.5 kg, respectively and did not differ by water salinity. Growth rates and condition factors differed by strain, but condition factor was not correlated with fillet yield. Consistent with other studies, juvenile fish from South Carolina and Nova Scotia were found to be slow growing compared to migratory Atlantic and Gulf strains. Mixed model analyses showed that family, and family by strain interactions were significant, but accounted for less growth variance than strain alone. These results indicate that family-based selection by strain may be useful in striped bass broodstock development programs. [ABSTRACT FROM AUTHOR]

The inclusion of soybean meal and soy concentrates in finfish feeds may introduce endocrine disrupting compounds in the form of phytoestrogens. Genistein, which may dually act as an oestrogen receptor agonist/antagonist, has been shown to elicit both masculinizing and feminizing effects in several teleost species. The objective of this investigation was to examine the effects of dietary genistein administration on reproductive development, growth and survival in southern flounder (Paralichthys lethostigma). Southern flounder received one of three experimental diets which contained varying concentrations of genistein (control - 0, low dose -100 and high dose -1000 mg genistein kg -1 feed) from 84 to 153 days post hatch (DPH). Fish remained in culture until 285 DPH at which time sex ratios were determined. Growth and survival were evaluated at 153 and 285 DPH. Greater numbers of female fish resulted from the low and high dose genistein treatments (98 ± 2% and 78 ± 12% respectively), as compared to the control group (21 ± 10%). Reduced growth at 153 DPH and poor survival (28%) at 285 DPH were also observed for the high dose genistein treatment. Collectively, these results demonstrate the feminizing effects of genistein in southern flounder, but reduced growth and survival with high dietary administration. [ABSTRACT FROM AUTHOR]

Female summer flounder grow considerably faster than males, and rearing temperature has been shown to influence sex differentiation in related species. The present studies were conducted to examine sex differentiation of post-metamorphic juveniles reared at temperatures conducive for commercial production. In experiments 1 and 2, offspring produced from crosses with meiogynogenetic, sex-reversed males and normal females were raised at 14, 16 or 18°C for ≥300 days or 12°C for 30, 60 or 120 days and then transferred to a male-determining temperature (21°C). In all cases, the fish developed predominantly as phenotypic males (≥74%). In a third experiment, offspring produced from crosses with normal males and females were reared at 15, 17 and 19°C for 111, 227 and 278 days and then transferred to 21°C. Most fish (≥92.1%) developed as phenotypic males irrespective of rearing temperature or length of exposure. Several hypotheses are proposed for these findings and further research is necessary to understand the sex-determining mechanisms in this species before the economic advantages associated with sexually dimorphic growth can be realized. [ABSTRACT FROM AUTHOR]

Teleost fish exhibit diverse reproductive strategies, and some species are capable of changing sex. The influence of many endocrine factors, such as gonadal steroids and neuropeptides, has been studied in relation to sex change, but comparatively less research has focused on gene expression changes within the brain in temperate grouper species with non-haremic social structures. The purpose of the present study was to investigate gonadotropin releasing hormone (GnRH) and brain aromatase (cyp19a1b) gene expression patterns during reproductive development and sex change in protogynous (female to male) black sea bass ( Centropristis striata ). Partial cDNA fragments for cyp19a1b and eef1a (a reference gene) were identified, and included with known gnrh2 and gnrh3 sequences in real time quantitative PCR. Elevated cyp19a1b expression was evident in the olfactory bulbs, telencephalon, optic tectum, and hypothalamus/midbrain region during vitellogenic growth, which may indicate changes in the brain related to neurogenesis or sexual behavior. In contrast, gnrh2 and gnrh3 expression levels were largely similar among gonadal states, and all three genes exhibited stable expression during sex change. Although sex change in black sea bass is not associated with dramatic changes in GnRH or cyp19a1b gene expression among brain regions, these genes may mediate processes at other levels, such as within individual hypothalamic nuclei, or through changes in neuron size, that warrant further research. [ABSTRACT FROM AUTHOR]

The summer flounder, Paralichthys dentatus L., is a high-value species and considerable research has been conducted to determine practices conducive for its culture. As milt can be limited in this species, experiments were conducted to develop a practical sperm cryopreservation protocol for hatchery use. Two dilution ratios (1:2 and 1:4; sperm:extender), 2 diluents (saline and sucrose-based), 2 cryoprotectants (10% DMSO and 12% glycerol) and 3 freezing rates (−5, −10 and −15°C min−1) were evaluated using differential staining to assess post-thaw sperm survival. Seven combinations of the factors examined reduced post-thaw viability by less than 30%. The average viability of sperm from fresh, pooled flounder milt (67.2 ± 2.9%) was not different from that of thawed milt diluted 1:4 with sucrose diluent (10% DMSO) frozen at −5°C min−1 (38.4 ± 7.7%) and fertilization and hatch success were not different in trials using fresh or thawed, cryopreserved sperm. From these experiments a practical sperm cryopreservation method was developed, but further refinement of the freezing protocol is necessary to optimize results. [ABSTRACT FROM AUTHOR]

Abstract: Locally-adapted subpopulations of Atlantic cod are found in both the northwest and northeast Atlantic and exhibit differences in morphology, behavior and physiological characteristics. We conducted experiments to determine if demonstrable differences were evident in egg buoyancy and antifreeze glycoprotein production between captive populations of genetically divergent winter and spring-spawning cod from the Gulf of Maine. Fertilized eggs (<24h post-spawning) were collected from both populations on 3 dates and transferred to 3 controlled-temperature rooms (5, 10, and 12°C). Egg buoyancy was determined in triplicate samples, at each temperature, in seawater ranging from 28 to 35ppt with 0.5ppt increments. No significant differences in mean neutral buoyancy (∼1.024g/mL) were found between stocks or treatment temperatures. Antifreeze glycoprotein (AFGP) production was examined in captive-bred cod juveniles (13–24cm) from both populations held at 0°C for periods ranging from 20 to 35 days. AFGP were first produced on day 30, although no differences were found in AFGP production in either population. Our results do not support the hypothesis that physiological differences in egg buoyancy and anti-freeze protein product exist between these two cod populations. The similarity in expression of these traits may reflect the high level of nutrition that both broodstock populations received, and the common juvenile size during cold-water exposure. [Copyright &y& Elsevier]

Abstract: Identifying conservation units based on the scale of biological processes is important in fisheries management. In anadromous fish, the spatial scale of population structure results from the opposing effects of homing and dispersal and varies among species by life history and geographic location. We used genetic data to evaluate the population structure of anadromous rainbow smelt (Osmerus mordax), a species of concern in U.S. waters. A total of 2211 smelt were genotyped at 10 microsatellite loci from 18 river systems and 11 bays along the northeastern Atlantic coast, spanning the entire U.S. range of the species. Across the study area gene flow was relatively high (F ST =0.017) and genetic variation followed an isolation by distance model, consistent with dispersal occurring most frequently among nearby rivers. Bayesian clustering approaches identified 4–6 genetically distinct population clusters, which varied in their geographic extent according to coastal circulation patterns. Genetically divergent populations were identified in topographically structured bays with local hydrography favoring larval retention. Conversely, gene flow was high across long stretches of topographically indistinct coastline where circulation patterns maximize passive larval dispersal. Overall, our results suggest that larval retention patterns, driven by hydrography, influence the population structure of rainbow smelt, and homing occurs to broad coastal zones of retention. The genetic structure identified in this study can be used in conjunction with ecological data to inform management at the appropriate spatial scale. [Copyright &y& Elsevier]

Abstract: Follicular maturational competence and ovulatory competence in teleost fish refer to the ability of the ovarian follicle to undergo final oocyte maturation and ovulation, respectively, in response to gonadotropin stimulation and other external cues. Some gene products related to competence acquisition are likely synthesized during vitellogenic growth, as these follicles gain in vivo responsiveness to exogenous gonadotropin stimulation and can be induced to undergo maturation and ovulation. In Atlantic cod (Gadus morhua), gonadotropin responsiveness has been shown to be oocyte size-dependent, and only ovaries containing late-stage vitellogenic follicles can be induced to ovulate. The purpose of the present study was to compare gene expression patterns between mid (unresponsive) and late (responsive) vitellogenic ovaries to identify genes involved in gonadotropin responsiveness and the acquisition of maturational and ovulatory competencies. Representational difference analysis was conducted in two reciprocal comparisons using intact ovarian fragments and follicle wall-enriched tissues, and genes of interest were used in real time quantitative PCR to confirm differential expression. Few differences were detected in intact ovarian fragments, but type IV ice-structuring protein and gephyrin were upregulated later in development and may be involved in lipid and sulfur metabolism, respectively. Candidate gene assays for luteinizing hormone receptor and aromatase also exhibited significant upregulation during vitellogenesis. Many genes were differentially expressed in follicle wall-enriched tissues, including endocrine maturational regulators and smooth muscle genes. Overall, maturational and ovulatory competencies during vitellogenesis in Atlantic cod are associated with up- and downregulation of many genes involved in lipid metabolism, endocrine regulation, and ovulatory preparation. [Copyright &y& Elsevier]

Abstract: We put forward a combined observing and modeling strategy for evaluating effects of environmental forcing on the dynamics of spatially structured cod populations spawning in the western Gulf of Maine. Recent work indicates at least two genetically differentiated complexes in this region: a late spring spawning, coastal population centered in Ipswich Bay, and a population that spawns in winter inshore and on nearshore banks in the Gulf of Maine and off southern New England. The two populations likely differ in trophic interactions and in physiological and behavioral responses to different winter and spring environments. Coupled physical–biological modeling has advanced to the point where within-decade forecasting of environmental conditions for recruitment to each of the two populations is feasible. However, the modeling needs to be supported by hydrographic, primary production and zooplankton data collected by buoys, and by data from remote sensing and fixed station sampling. Forecasts of environmentally driven dispersal and growth of planktonic early life stages, combined with an understanding of possible population-specific predator fields, usage of coastal habitat by juveniles and adult resident and migratory patterns, can be used to develop scenarios for spatially explicit population responses to multiple forcings, including climate change, anthropogenic impacts on nearshore juvenile habitat, connectivity among populations and management interventions such as regional fisheries closures. [ABSTRACT FROM AUTHOR]

Abstract: Captive, wild-caught female Atlantic cod, Gadus morhua, from Georges Bank (n =19) were divided into three treatment groups based on body weight and diameter of the largest clutch of oocytes present. Treatments administered were an intramuscular implant of one of two gonadotropin releasing hormone analogues — (D-Ala6, Pro9-NHEt)-LHRH ethylamide (LHRHa, 150µg) and salmon gonadotropin releasing hormone analogue (sGnRHa, 150µg, OvaplantR), or a saline injection (control). Over a period of 20days, 12 of 14 implanted and one control fish ovulated. There was no significant variation between egg volumes and percent fertilization (P ≥0.4968) of implant-treated and naturally ovulating females; however, significant variation did exist for the estimated number of hatched larvae among treatments (P =0.0169). Non-spermiating captive wild-caught Atlantic cod males (n =11 Georges Bank) were divided into two treatment groups (OvaplantR and saline control) based on body weight. Large volumes of milt with high motility and spermatocrits were obtained from each of five OvaplantR-treated males starting 6days post-implant. Over a 27day period, each of six control males produced milt at least once, but in small volumes with variable motility and low spermatocrits. Milt volumes of the OvaplantR-treated males were higher than naturally spermiating males (P =0.0002), but had similar motilities and spermatocrits (P ≥0.0462). These results demonstrate the effectiveness of GnRHa implants in inducing ovulation and spermiation in Atlantic cod broodstock without adversely affecting gamete quality. [Copyright &y& Elsevier]

Abstract: Meiogynogenesis and temperature manipulation were used to produce XX male summer flounder broodstock for future production of monosex (all female) populations. Meiogynogens were produced by fertilizing eggs with UV-irradiated (70 mJ/cm2) black sea bass sperm and applying 6-minute pressure shocks (58,600 kPa), two min post-fertilization. From 4 females, 132,000 eggs were produced, of which 95.6±1.8% were viable, 51.0±13.0% fertilized, and 15.9±8.3% hatched. Following metamorphosis, meiogynogens and controls were raised under a low temperature regime (12 °C gradually increased to 20 °C), 21, and 26 °C for up to 376 days post hatch (DPH). Female sex differentiation was greater in meiogynogens (62.5%) and control fingerlings (22.6%) raised under a low temperature regime compared to those raised at the higher rearing temperatures: 0% at 21 °C, and 0 and 3.9% at 26 °C in meiogynogens and controls, respectively. These results suggest that temperature, during the critical phase preceding gonadal development, influences sex differentiation in summer flounder. [Copyright &y& Elsevier]

Lipid content, lipid class and fatty acid compositions were determined in eggs from wild and captive black sea bass, Centropristis striata L., from northern (New England) and southern (South Carolina) regions to determine the effects of diet on egg composition and fertilization success. The formulated diets fed to the northern captive (NC) fish were higher in total lipids (22%) compared with the cut fish and squid diet fed to the southern fish (SC; 3.3% lipid) and had a higher relative amount of linoleic acid (LA) and lower relative amounts of docosahexaenoic acid (DHA) and arachidonic acid (AA). These dietary differences were broadly reflected in the egg lipid composition. The LA levels were higher in all lipid classes in eggs of NC fish while AA levels were lower. The DHA was higher in the major polar lipids (PL) (phosphatidylcholine and phosphatidylethanolamine) of SC eggs compared with NC. Compared with wild fish, both captive groups produced eggs with PLs richer in LA and lower in DHA and AA. Over all fish groups, fertilization success was directly correlated with levels of DHA and AA in the PLs and was inversely correlated with LA levels. [ABSTRACT FROM AUTHOR]

Juvenile and adult black sea bass ( Centropristis striata L.) were exposed to various concentrations of four anaesthetics to determine practical dosages for handling as well as for procedures such as bleeding, ovarian biopsy or tag implantation. In experiment 1, juveniles exposed to either 2.0 mg L−1 metomidate, 15 mg L−1 clove oil, 70 mg L−1 tricaine methanesulphonate (TMS) or 200 mg L−1 2-phenoxyethanol (2-PE) reached stage II of anaesthesia in 3–5 min and could be handled for weighing and measuring. All fish had completed recovery to stage III within 6 min. In experiment 2, the established concentrations of each anaesthetic were tested on juveniles to determine their ability to prevent a reflex to a subcutaneous needle puncture. All of the fish exposed to clove oil (20 mg L−1) and 40% of the TMS-treated (70 mg L−1) fish reacted while none of the fish anaesthetized in metomidate (2.0 mg L−1) or 2-PE (200 mg L−1) responded to the needle puncture. In experiment 3, metomidate (5.0 mg L−1), clove oil (30 mg L−1) TMS (125 mg L−1) or 2-PE (300 mg L−1) were all effective for performing an ovarian biopsy or tag implantation on adults. In experiment 4, TMS (125 mg L−1) exacerbated the cortisol response to a short handling stressor during a 30 min exposure. Fish anaesthetized in 2-PE (300 mg L−1), metomidate (5.0 mg L−1) or clove oil (40 mg L−1) had increased cortisol levels associated with the handling stressor but there were no further increases during the remainder of the experimental period. The results demonstrate that these anaesthetics are effective for sedation and anaesthesia of black sea bass and that the best choice is dependant upon the procedures to be performed. [ABSTRACT FROM AUTHOR]

Black sea bassCentropristis striataL. are protogynous hermaphrodites that develop and spawn as females before changing sex to male. Since all fish eventually become males, determining the relationship between sperm production, sperm quality and seasonal changes in plasma levels of testosterone (T) and 11-ketotestosterone (11-KT) could be useful for identifying appropriate males to maintain as broodstock. Milt and blood samples were collected three times during an 8-week spawning season. Milt volume (3.5±0.76 mL kg−1), sperm density (3.2× 108± 0.31 cells mL−1), sperm production [11× 108±3.4 cells kg−1 body weight (BW)] and sperm motility (80±0.6%) were at their highest during the first sampling interval and coincided with the highest 11-KT levels (1.0± 0.11 ng mL−1). All of the sperm indices decreased to their lowest levels during the final 3 weeks of the study. Sperm viability was highly correlated (adjustedR2=0.84) with sperm motility. Sperm cryopreserved in modified Mounib's extender (MME) had the highest post-thaw motility compared with two other extenders. Post-thaw motility of sperm cryopreserved in MME was not different from fresh after 90 days of storage. There was no difference in fertilization rates between fresh (69±2.4%) and post-thaw (67±4.1%) sperm samples taken from the same male or among males. These results demonstrate that the quality of black sea bass spermatozoa is higher earlier in the spawning season and that acceptable post-thaw fertilization rates can be obtained from cryopreserved sperm. [ABSTRACT FROM AUTHOR]