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.
•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.
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. 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 (less than or equal to 20 microm 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. 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.
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.
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.
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.
•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.
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.
Striped bass, Morone saxatilis, is an anadromous fish native to the North American Atlantic Coast and is well recognized as one of the most important and highly regarded recreational fisheries in the ...United States. Decades of research have been conducted on striped bass and its hybrid (striped bass × white bass Morone chrysops) and culture methods have been established, particularly for the hybrid striped bass, the fourth largest finfish aquaculture industry in the United States (US $50 million). Domesticated striped bass have been developed since the 1990s and broodstock are available from the government for commercial fry production using novel hormone‐free methods along with traditional hormone‐induced tank and strip spawning. No commercial‐scale intensive larval rearing technologies have been developed at present and current fingerling production is conducted in fertilized freshwater ponds. Larval diets have not been successfully used as first feeds; however, they have been used for weaning from live feeds prior to metamorphosis. Striped bass can be grown out in marine (32 ppt) or freshwater (<5 ppt); however, they require high hardness (200+ ppm) and some salinity (8–10 ppt) to offset handling stress. Juveniles must be 1–10 g/fish prior to stocking into marine water. Commercially available fingerling, growout, and broodstock feeds are available from several vendors. Striped bass may reach 1.36 kg/fish in recirculating aquaculture by 18 months and as much as 2.27 kg/fish by 24 months. Farm gate value of striped bass has not been determined, although seasonally available wild‐harvested striped bass are valued at about US $6.50 to US $10.14 per kg and cultured hybrid striped bass are valued at about US $8.45 to US $9.25 per kg whole; the farm gate value for cultured striped bass may be as much as US $10.00 or more per kg depending on demand and market. The ideal market size is between 1.36 and 2.72 kg/fish, which is considerably larger than the traditional 0.68 to 0.90 kg/fish for the hybrid striped bass market.
Abstract
Objective
Investigate Striped Bass
Morone saxatilis
growth in different photothermal environments and generate an interest in strain‐specific broodstock development for marine net‐pen ...culture.
Methods
In this effort, Striped Bass strains from Atlantic (Delaware, Virginia, and Maryland) and Gulf Coast (Florida and Texas) states were cultured in recirculating aquaculture systems, simulating a full‐production cycle to early market size in each respective region's photothermal environment. The Atlantic and Gulf strains were initially maintained in recirculating aquaculture systems “nurseries” until 400 and 160 days postspawn, respectively, when offshore conditions (temperature) were conducive for stocking juvenile fish. Individuals from all strains were implanted with PIT tags and stocked (“common garden design”) into a pair of identical recirculating systems (three 5000‐L tanks/system). One system received 48 Atlantic fish/tank (16 fish/strain; Delaware, Virginia, and Maryland), and the second system received 48 Gulf fish/tank (24 fish/strain; Florida and Texas). Salinity was maintained at 30‰, and photothermal regimes corresponded with ambient ocean conditions at selected locations off the mid‐Atlantic and Gulf coasts. Studies were conducted for up to 2 years, and production parameters (feed conversion, absolute growth rate, survival) were compared.
Result
The final weights of ungraded fish in both simulated locations averaged approximately 900 g by 600 days postspawn and early market size (~1.3 kg) by 800 days postspawn.
Conclusion
Growth rates differed by strain in both nursery and grow‐out phases, but the results indicate high potential for production of Striped Bass in U.S. coastal waters.
Impact statement
This study demonstrates performance of pure Striped Bass strains in different environmental conditions. It continues building upon existing information and supports development of a U.S. aquaculture industry for the species.
To evaluate the pond culture potential of purebred Striped Bass Morone saxatilis, the thermal stress tolerance and associated feeding behavior of Atlantic coast (Delaware River; DE) and Gulf of ...Mexico (Florida; FL) strains (~1.0–1.6 kg) were evaluated. In the first experiment, critical thermal maxima (CTmax) temperatures were determined by gradually increasing the water temperature of individual fish that were housed in 311‐L insulated containers (0.3°C/min) and determining when the fish experienced loss of equilibrium (n = 6/strain). The results indicated that the fish from the FL strain had a higher CTmax value (36.7 ± 0.32°C) than did those from the DE strain (35.7 ± 0.57°C). In the second experiment, feeding behavior and feed consumption were evaluated during simulated summer temperature fluctuations by increasing the water temperature from 26°C to 34°C by 2°C every 2 d (n = 30 fish/strain). Feed consumption decreased inversely with temperature in both strains until a mortality event occurred at 34°C. The results suggest that there are physiological adaptations to elevated temperatures among Striped Bass strains and they may be suitable for pond culture if feeding is restricted at high temperatures (>30°C).
River herring (Alewives;
Alosa pseudoharengus
and Blueback Herring;
Alosa aestivalis
) populations have undergone dramatic declines in recent years. Although the exact causes for these population ...declines are unclear, evidence suggests that factors such as habitat loss and dam construction may prevent upstream migration to spawning grounds, resulting in river herring spawning below the head of tide. As below the head of tide spawning may prematurely expose river herring embryos and larvae to saline environments, a series of experiments were conducted to determine the effect of elevated salinity on embryonic and larval survival. Embryos of both species were acutely exposed to salinities of 2, 5, 10, 15, 20, 25, and 30 g/L as well as to simulated tidal salinity fluctuations, and survival was assessed. Larvae (1–8 days post hatch; DPH) were acutely transferred to 2.5–30 g/L water, and survival was assessed after 24 h. Larvae (0–12 DPH) were also gradually acclimated to salinities ranging from 2.5–30 g/L, and survival assessed 24 h post exposure. Embryonic alewife survival was high (>97%) at salinities ≤10 g/L while blueback herring embryos displayed a wide salinity tolerance throughout the range. Embryos of both species exhibited high survival in tidal salinity exposures. Survival of acutely-transferred alewife and blueback herring larvae decreased with increasing salinity (>20 g/L). Both species were tolerant of high salinity conditions by 15 DPH. These experiments demonstrate that survival of river herring embryos and larvae may be possible in tidally-influenced areas, depending on the developmental stage and rate of salinity exposure.
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