Identification of ovarian gene expression patterns during vitellogenesis in Atlantic cod (\u3ci\u3eGadus morhua\u3c/i\u3e)

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

Effects of Partial Replacement of Fish Meal Protein by Microalgae on Growth, Feed Intake, and Body Composition of Atlantic Cod

A feeding trial was conducted with juvenile Atlantic cod Gadus morhua (initial mean weight, 40.7 g) in which a combination of dried Nannochloropsis sp. and Isochrysis sp. replaced fish meal protein in isonitrogenous, isocaloric diets. Three experimental diets (55% protein, 16.5% fat; calculated gross energy = 5,328 kcal/kg) were formulated to replace 0, 15, or 30% of dietary fish meal protein. At the conclusion of the 84-d study, no differences in survival, feed conversion ratios, viscerosomatic indices, and n-3 and n-6 fatty acids in the muscle were found among the treatment groups. Feed intake and growth, which were proportional to the level of algal incorporation, were significantly reduced in the algae-fed fish and were probably due to palatability problems. Feed intake improved in the fish fed the diet with 15% fish meal protein replacement as the study progressed, but hepatosomatic indices indicate that those fed the diet with 30% replacement were approaching starvation

Characterizing ovarian gene expression during oocyte growth in Atlantic cod (Gadus morhua)

Vertebrate oocytes undergo dramatic changes during development as they accumulate many RNA transcripts, glycoproteins, and yolk proteins, necessary to ensure proper fertilization and embryogenesis. Oogenesis in teleosts often requires several years for completion, but very little is known about the early developmental stages. Recently, two-stage gene expression comparisons were made during oocyte growth in coho salmon (Oncorhynchus kisutch) and Atlantic cod (Gadus morhua), but more broad-scale, comprehensive assessments have not been conducted. The objectives of the present study were to characterize the gene expression patterns throughout oocyte growth in cod and compare them to changes previously identified in coho salmon. A quantitative PCR survey was conducted using 50 genes at six ovarian stages, ranging from the onset of primary growth (oocyte differentiation) to late vitellogenesis. Most expression patterns could be grouped into three major clusters, consisting of oocyte-derived (cluster 1) and likely follicle cell (clusters 2 and 3) genes. Oocyte genes were elevated during primary growth, while many follicle cell transcripts were abundant during oocyte differentiation and vitellogenesis. Few expression changes identified in coho salmon were evident in cod, which is likely due to differences in reproductive strategies. These results demonstrate that dynamic changes in gene expression occur during oocyte growth in teleost fish

Induced sex change in black sea bass

Experiments were conducted to identify factors involved in sex change in the protogynous black sea bass Centropristis striata. Black sea bass maintained in the ratio of 8 females (F):0 males (M) for 9 months reversed sex while those kept at the ratios of 6F:2M or 4F:4M did not. Female black sea bass implanted with 1.0 mg 11-ketotestosterone (11-KT) or 10 mg fadrozole (FAD) changed sex and began spermiating while those implanted with 0.1 mg 11-KT or 1.0 mg FAD underwent incomplete sex reversal. One fish implanted with 1.0 mg FAD initiated sex change but was not spermiating at the end of the study. One fish in the control group, the largest fish in the study, initiated sex change. These results suggest that the presence of males may restrict sex reversal in black sea bass and that high 17 beta-oestradiol:11-KT is required for maintaining ovarian function. (c) 2006 The Authors Journal compilation (c) 2006 The Fisheries Society of the British Isles

Effect of acclimation temperature on the acute stress response in juvenile Atlantic cod, Gadus morhua L., and haddock, Melanogrammus aeglefinus L.

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 degrees C respectively. Both species responded to the stressor with increases in plasma cortisol at all temperatures tested. At 14 degrees C cortisol levels peaked within 1 h post-stressor, and returned to pre-stressor levels within 24 h. In contrast, at 4 degrees 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 degrees 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 degrees C. The results show that cod and haddock acclimated to different temperatures respond to common, acute stressors in a manner similar to other teleosts

The effects of photoperiod manipulation on the reproduction of black sea bass, Centropristis striata

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. © 2003 Elsevier Science B.V. All rights reserved

Sex differentiation of summer flounder (Paralichthys dentates L.) raised at practical hatchery temperatures

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

Brain aromatase (cyp19a1b) and gonadotropin releasing hormone (gnrh2 and gnrh3) expression during reproductive development and sex change in black sea bass (Centropristis striata)

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

Surface Disinfection and Removal of Adhesiveness from Rainbow Smelt Eggs

The survival of rainbow smelt Osmerus mordax embryos was evaluated after treating fertilized eggs with tannic acid (150, 300, 600, or 1,200 mg/L) in suspension for 10 min to remove adhesiveness or treating them with calcium hypochlorite (25, 50, 75, or 100 mg/L), polyvinylpyrrolidone iodine (PVP-I; 25, 50, 75, or 100 mg/L), or hydrogen peroxide (H(2)O(2); 500, 1,000, 1,500, or 2,000 mu L/L) for 15 min to achieve surface disinfection. Nonlethal concentrations of egg disinfectants were also evaluated for their germicidal effects by culturing disinfected eggs in sterile Bacto Tryptic Soy Broth. The hatching success of the eggs treated with tannic acid (at all concentrations) was not different from that of the controls. Disinfecting eggs with H(2)O(2) (all doses) and low doses of calcium hypochlorite (25-75 mg/L) or PVP-I (25 mg/L) did not reduce embryo survival, but exposure to calcium hypochlorite and PVP-I at higher concentrations (100 mg/L and 50, 75, or 100 mg/L, respectively) was lethal. In the first disinfection trial both H(2)O(2) and PVP-I (25 mg/L) prevented bacterial growth, but only H(2)O(2) at 2,000 mu L/L did so in the second trial