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We analyzed the expression of genes involved in the hypothalamic-pituitary-thyroid axis (HPT-axis) in the longfin yellowtail Seriola rivoliana early larva, including temperature effects (22, 26 and 28 °C) and days of development (day one, day two, and day six after hatching). We aimed to determine if egg and larval incubation at different temperatures could disrupt this critical endocrine axis, which, in an aquaculture context, it could provoke mortality during early metamorphosis. There was a significant interaction between temperature and developmental timing on the relative expression of thyrotropin releasing hormone (trh). Larvae at 22 °C was the longest and increased more trh expression than larvae at higher temperatures. Interestingly, thyrotropin stimulating hormone (tsh) was highly expressed after hatching. Subsequently, it was downregulated at any temperature at least until day four, suggesting a temporal inhibition of the HPT axis. Therefore, we suggest that tsh-binding (tshr) to follicles should have occurred from hatching, creating a further "cascade effect" of upregulation of larval thyroglobulin (tg) from day two in a temperature-dependent manner. Consequently, new thyroid hormones should have been produced after yolk sac absorption. The above may indicate a narrow window of larval survival, where the larval transition from endogenous to exogenous feeding would depend on the correct timing to synthesize tg. Temperature significantly affected the expressions of deiodinase 1 (dio1-downregulated) and deiodinase 2 (dio2-upregulated) after hatching. The expressions of thyroid receptors alpha (trα) and beta (trβ) remained constant after hatching without significant effects of temperature and days of development. Then, the differential expression on day six showed that all HPT-axis transcripts increased their expressions as larvae developed, which suggested a functional HPT. Finally, there was no evidence that any temperature would disrupt the endocrine's larval axis, which indicated that the longfin yellowtail has a wide temperature adaption. Nevertheless, based on tg upregulation, we suggest that larvae should be maintained around 25-26 °C after hatching for a better chance of survival and development., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The longfin yellowtail Seriola rivoliana is an emerging species for aquaculture diversification worldwide and production relies on fertilized eggs from captive broodstock. Temperature is the main factor that influences the developmental process and success during fish ontogeny. However, the effects of temperature on the utilization of the main biochemical reserves and bioenergetics are scarcely investigated in fish, whereas protein, lipid and carbohydrate metabolism have critical roles in maintaining cellular energy homeostasis. In this context, we aimed to evaluate metabolic fuels (protein, lipids, triacylglicerides, carbohydrates), adenylic nucleotides and derivates (ATP, ADP, AMP, IMP), and the adenylate energy charge (AEC) during embryogenesis and in hatched larvae in S. rivoliana at different temperatures. For this purpose, fertilized eggs were incubated at six constant (20, 22, 24, 26, 28 and 30 °C) and two oscillating (21⇄29 °C) temperatures. Biochemical analyses were made at blastula, optic vesicles, neurula, prehatch and hatch periods. Results indicated that the developmental period had a major influence on the biochemical composition at any temperature regime tested during the incubation. Protein content decreased only at hatching mainly due to the loss of the chorion, total lipids tended to increase at the neurula period and variations in carbohydrates depended on the particular spawn analyzed. Triacylglicerides were a critical egg fuel during hatching. The high AEC during embryogenesis and even in hatched larvae suggested an optimal energy balance regulation. The lack of critical biochemical changes from different temperature regimes during embryo development confirmed that this species exhibits a high adaptive capacity in response to constant and fluctuating temperatures. However, the timing of hatching was the most critical period of development, where biochemical components and energy utilization significantly changed. The oscillating temperatures tested may have physiological advantages without detrimental energetic effects that will require further research on larval quality after hatching., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

We investigated a time-course larval transcriptional analysis (RNA-seq) in the longfin yellowtail Seriola rivoliana, from hatching to day four at 22 °C, without providing zooplankton as food. Larval starvation is a critical physiological stage that must be prevented to ensure survival. However, the transcriptional mechanisms to endure starvation have not been investigated in marine fish. Differential gene expression showed newly day-specific transcriptome events during larval development. On day 1 (yolk sac absorption), the predominant upregulated developmental processes were larval growth, muscle and vision development, cytoskeletal structure, protein synthesis, protein and fat digestion-absorption, and hormone biosynthesis, whereas the cell cycle was suppressed. On day 2 (yolk sac exhaustion), a new stage of energy regeneration (ATP) was supplied by the oil drop reserve, whereas protein digestion-absorption and growth were suppressed. On day 3 (mouth opening and starvation), stress signals and nutrition deprivation upregulated the p53 signal and triggered autophagy and the AMP-activated protein kinase (AMPK) pathways as an alternative catabolic pathway to enduring starvation, and the circadian rhythm was established. On day 4 (starving and weakened larvae condition), autophagy supported subsequent protein synthesis, activated the immune system, and promoted estrogen signaling and skeleton renovation. However, larvae suppressed muscle development, vision and carbohydrate, and fat digestion-absorption and became lethargic, evidencing limited physiological support by autophagy to maintain survival without exogenous nutrition in this species., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Social factors and aromatase gene expression in the leopard grouper Mycteroperca rosacea was studied when captive fish were separated by sex during the reproductive (April-June) and post-reproductive (July-September) seasons. Monosex females, monosex males, and mixed-sex, held in social sextet units were analyzed for sex steroids throughout confinement. At the end of the experiment, the gonad-sex was defined by histology, and gonad and brain aromatase gene expressions were quantified. Only males held in the monosex social units changed sex. Histology showed one male remained unchanged, six were found in a transitional sexual stage, in which two had intersex-predominantly-testes, and four had a more defined intersex ovo-testes pattern, and 11 were immature de novo females (neofemales). Neofemales and most intersex fish did not survive. In spring, 11-ketosterone showed a specific male profile, which suggests that male-to-female sex change was not triggered during the reproductive season. The low steroid levels in summer made it impossible to associate the sex change to a gonad hormonal shift; in September, gonad aromatase gene expression was not significantly different among groups. However, brain aromatase expression in intersex fish was significantly higher than monosex females, mixed-sex females, and neofemale groups. These results suggest that in the absence of female hormonal compounds, and at a time when male gonad steroidogenesis was diminished, the brain mediated male-to-male social-behavioral interactions, including stress, by increasing aromatization, resulting in derived intersex-male, which triggered more aromatization, followed by a sex change., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Reproduction in yellowtail snapper Lutjanus argentiventris took place after compressing the seasonally changing day length into a 3 month period applied during two consecutive winters, with the longest and shortest days in December and February, respectively. During the first winter, there was no clear peak of days of spawning and the production of viable eggs was similar from the longest and throughout the decreasing day lengths until reproduction ceased. The level of plasma vitellogenin rose abruptly to a maximum concentration during the increasing day length and then decreased dramatically before the longest day length. During the second winter, a clear peak in the number of days of spawning and the highest production of viable eggs occurred around the longest day length. These results showed that it is feasible to synchronize day length between winter-induced and natural summer and autumn reproduction to produce eggs and larvae during the year., (© 2010 The Authors. Journal of Fish Biology © 2010 The Fisheries Society of the British Isles.)

The peripheral blood cells and differential blood profile of captive female and male leopard grouper Mycteroperca rosacea are described for aquacultural purposes. Basophilic, polychromatic, and orthochromic erythroblasts were observed as immature erythrocytes that develop into mature erythrocytes. Young erythrocytes were not evident, and bi-lobed erythrocytes were extremely scarce. Types of leukocytes included lymphocytes; three types of granulocytes (basophiles, eosinophiles, and neutrophiles); monocytes; and a specialized amoeboid-like macrophage in the blood, which has not been previously described in fish-blood literature. Thrombocytes were commonly observed. There was significantly higher erythropoiesis in males. Granulocytes and lymphocytes of females were significantly higher than males, whereas monocytes and thrombocytes were not.

Oreochromis karongae, one of the "chambo" tilapia species from Lake Malawi, has a karyotype of 2n = 38, making it one of the few species investigated to differ from the typical tilapia karyotype (2n = 44). The O. karongae karyotype consists of one large subtelocentric pair of chromosomes, four medium-sized pairs (three subtelocentric and one submetacentric) and 14 small pairs. The five largest pairs could be distinguished from each other on the basis of size, morphology and a series of fluorescence in situ hybridisation (FISH) probes. The largest pair is easily distinguished on the basis of size and a chromosome 1 (linkage group 3) bacterial artificial chromosome (BAC) FISH probe from Oreochromis niloticus. BAC clones from O. niloticus chromosome 2 (linkage group 7) hybridised to one of the medium-sized subtelocentric chromosome pairs (no. 5) of O. karongae, distinguishing the ancestral medium-sized pair from the three other medium-sized chromosome pairs (nos. 2, 3 and 4) that appear to have resulted from fusions. SATA repetitive DNA hybridised to the centromeres of all 19 chromosome pairs and also revealed the locations of the relic centromeres in the three fused pairs. Telomeric (TTAGGG)(n) repeats were identified in the telomeres of all chromosomes, and an interstitial telomeric site (ITS) was identified in three chromosomal pairs (no. 2, 3 and 4). Additionally, two ITS sites were identified in the largest chromosome pair (pair 1), confirming the origin of this chromosome from three ancestral chromosomes. SATA and ITS sites allowed the orientation of the fusions in pairs 2, 3 and 4, which all appear to have been in different orientations (q-q, p-q and p-p, respectively). One of these fusions (O. karongae chromosome pair no. 2) involves a small chromosome (equivalent to linkage group 1), which in O. niloticus carries the main sex-determining gene. 4',6-Diamidino-2-phenyloindole staining of the synaptonemal complex in male O. karongae revealed the presumptive positions of the kinetochores, which correspond well to the centromeric positions observed in the mitotic karyotype.

Total synaptonemal complex (SC) lengths were estimated from Oreochromis aureus Steindachner (which has a WZ/ZZ sex determination system), O. mossambicus Peters and O. niloticus L. (both of which have XX/XY sex determination systems). The total SC length in oocytes was greater than that in spermatocytes in all three species (194 +/- 30 microm and 134 +/- 13 microm, 187 +/- 22 microm and 127 +/- 17 microm, 193 +/- 37 microm and 144 +/- 19 microm, respectively). These sex-specific differences did not appear to be influenced by the type of sex determination system (the female/male total SC length ratio was 1.45 in O. aureus, 1.47 in O. mossambicus and 1.34 in O. niloticus) and do not correlate with the lack of any overall sex-specific length differences in the current Oreochromis linkage map. Although based on data from relatively few species, there appears to be no consistent relationship between sex-specific SC lengths and linkage map lengths in fish. Neomale (hormonally masculinized genetic female) O. aureus and O. mossambicus had total SC lengths of 138 +/- 13 microm and 146 +/- 13 microm respectively, more similar to normal males than to normal females. These findings agree with data from other vertebrate species that suggest that phenotypic sex, rather than genotype, determines traits such as total SC length, chiasmata position and recombination pattern, at least for the autosomes.

Bivalent 1 of the synaptonemal complex (SC) in XY male Oreochromis niloticus shows an unpaired terminal region in early pachytene. This appears to be related to recombination suppression around a sex determination locus. To allow more detailed analysis of this, and unpaired regions in the karyotype of other Oreochromis species, we developed techniques for FISH on SC preparations, combined with DAPI staining. DAPI staining identified presumptive centromeres in SC bivalents, which appeared to correspond to the positions observed in the mitotic karyotype (the kinetochores could be identified only sporadically in silver-stained EM SC images). Furthermore, two BAC clones containing Dmo (dmrt4) and OniY227 markers that hybridize to known positions in chromosome pair 1 in mitotic spreads (near the centromere, Flpter 0.25, and the putative sex-determination locus, Flpter 0.57, respectively) were used as FISH probes on SCs to verify that the presumptive centromere identified by DAPI staining was located in the expected position. Visualization of both the centromere and FISH signals on bivalent 1 allowed the unpaired region to be positioned at Flpter 0.80 to 1.00, demonstrating that the unpaired region is located in the distal part of the long arm(s). Finally, differences between mitotic and meiotic measurements are discussed.

A concerted experimental (mass-selective, double-resonance laser spectroscopic technique) and theoretical (correlated quantum chemistry calculation) study of hydrogen-bonded clusters of 1-cyanonaphthalene (CNN) with water has been carried out to probe geometrical structures of the conformational isomers. The structures of the two low-energy conformers of CNN-H2O and CNN-(H2O)2, calculated at the MP2/cc-pVDZ level of theory, are consistent with the mass-selective infrared-ultraviolet double-resonance spectra and the partially resolved rotational band contours of the S1 <-- S0 origin bands. The facile loss of a neutral water molecule from the cluster ion of CNN-(H2O)2, relative to that of CNN-H2O, is in accord with the proposed structures of the clusters.

Mass-selected resonant two-photon ionization and infrared-ultraviolet double-resonance spectroscopies are combined with correlated (second Moller-Plesset perturbation) quantum chemistry calculation to probe electronic spectra and ground-state geometries of the jet-cooled dimer and higher clusters of 1-cyanonaphthalene. The results indicate that the dimer and trimer have stacked geometries, consistent with the highly efficient, rapid excimer formation that follows photoexcitation of the ground-state clusters.

In the Nile tilapia, Oreochromis niloticus, sex determination is primarily genetic, with XX females and XY males. While the X and Y chromosomes (the largest pair) cannot be distinguished in mitotic chromosome spreads, analysis of comparative hybridization of X and Y chromosome derived probes (produced, by microdissection and DOP-PCR, from XX and YY genotypes, respectively) to different genotypes (XX, XY and YY) has demonstrated that sequence differences exist between the sex chromosomes. Here we report the characterization of these probes, showing that a significant proportion of the amplified sequences represent various transposable elements. We further demonstrate that concentrations of a number of these individual elements are found on the sex chromosomes and that the distribution of two such elements differs between the X and Y chromosomes. These findings are discussed in relation to sex chromosome differentiation in O. niloticus and to the changes expected during the early stages of sex chromosome evolution., (Copyright 2003 S. Karger AG, Basel)

The karyotype of Oreochromis species is considered to be highly conserved, with a diploid chromosome complement of 2n = 44. Here we show, by analysis of mitotic and meiotic chromosomes, that the karyotype of O. karongae, one of the Lake Malawi 'chambo' species, is 2n = 38. This difference in chromosome number does not prevent the production of inter-specific hybrids between O. niloticus (2n = 44) and O. karongae (2n = 38). Analysis of the meiotic chromosomes of the O. niloticus x O. karongae hybrids indicates that three separate chromosome fusion events have occurred in O. karongae. Comparison of the O. karongae and O. niloticus karyotypes suggests that these consist of one Robertsonian fusion and two fusions of a more complex nature.

Differentiated sex chromosome pairs in diverse species display certain common characteristics, normally comprising one largely heterochromatic genetically inactive chromosome and one euchromatic genetically active chromosome (e.g. the mammalian Y and X respectively). It is widely accepted that dimorphic sex chromosomes evolved from homologous pairs of autosomes. Although the exact mechanisms through which the pair diverged are not fully understood, an initial suppression of recombination in the sex-determining region is required by all of the major theories. Here we address the question of the mechanism by which this initial suppression of recombination occurs. Our model postulates that the stochastic, de novo accumulation of heterochromatin in the sex determining region can delay pairing of the sex chromosomes in meiosis, resulting in a decrease in recombination. Data to support this model is presented from the cichlid fish, Oreochromis niloticus. Although such a decrease would in most circumstances be evolutionarily disadvantageous, if the region concerned included the major sex determining gene and other gene(s) with sex-specific functions, then this would be selectively advantageous and could trigger the process(es) which, ultimately, lead to the differentiation of the sex chromosomes., (Copyright 2002 S. Karger AG, Basel)

Sex determination in the blue tilapia, Oreochromis aureus, is primarily a ZW female-ZZ male system. Here, by analysis of the pachytene meiotic chromosomes of O. aureus, we demonstrate the presence of two distinct regions of restricted pairing present only in heterogametic fish. The first, a subterminal region of the largest bivalent is located near to the region of unpairing found in the closely related species O. niloticus, while the second is in a small bivalent, most of which was unpaired. These results suggest that O. aureus has two separate pairs of sex chromosomes.