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Accurate identification of Seriola dumerili (SD) offers crucial technical support for aquaculture practices and behavioral research of this species. However, the task of discerning S. dumerili from complex underwater settings, fluctuating light conditions, and schools of fish presents a challenge. This paper proposes an intelligent recognition model based on the YOLOv8 network called SD-YOLOv8. By adding a small object detection layer and head, our model has a positive impact on the recognition capabilities for both close and distant instances of S. dumerili, significantly improving them. We construct a convenient S. dumerili dataset and introduce the deformable convolution network v2 (DCNv2) to enhance the information extraction process. Additionally, we employ the bottleneck attention module (BAM) and redesign the spatial pyramid pooling fusion (SPPF) for multidimensional feature extraction and fusion. The Inner-MPDIoU bounding box regression function adjusts the scale factor and evaluates geometric ratios to improve box positioning accuracy. The experimental results show that our SD-YOLOv8 model achieves higher accuracy and average precision, increasing from 89.2% to 93.2% and from 92.2% to 95.7%, respectively. Overall, our model enhances detection accuracy, providing a reliable foundation for the accurate detection of fishes. [ABSTRACT FROM AUTHOR]

Copyright of Food & Fermentation Industries is the property of Food & Fermentation Industries and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Feeding habits and trophic level of juvenile greater amberjack, Seriola dumerili were studied using 170 specimens collected by set net fishery and lure fishing in the southern waters of Korea during July, August, September, October, and November 2022. The size of juvenile greater amberjack ranged from 17.5 to 49.9 cm in fork length. Juvenile greater amberjack was piscivorous predator that feed primarily on fish. We calculated the trophic level as 4.06 ± 0.80 for juvenile greater amberjack. Fishes were the main prey items for all size groups. Juvenile greater amberjack also showed size-related dietary shift from Japanese anchovy to jack mackerel. As the fork length of juvenile greater amberjack increase, the mean weight of prey per stomach tended to increased, while the mean number of preys per stomach was not significantly different. Fishes were the main prey items for summer and autumn. The main fish prey during summer and autumn was Japanese anchovy, but in the autumn, the Japanese anchovy portion decreased, and the jack mackerel portion increased. PERMANOVA analysis was used to examine seasonal and size-related changes in diet composition, which showed significant variations among size classes. Juvenile greater amberjack presumably feed on larger prey to meet their energy requirements. [ABSTRACT FROM AUTHOR]

Salinity is an important abiotic factor in aquaculture because of its significance in the multiple physiological progress of marine fish. The liver is the main organ involved in energy metabolism, supplying energy to other body tissues and organs. Greater amberjack (Seriola dumerili) is characterized by fast growth and is an important aquatic export product in China. In this study, the greater amberjack was cultured in varying salinity levels, i.e., from 5 to 40 ppt, for 72 h. Notably, all fish under 5 ppt salinity died within 24 h because of limited tolerance ability. A comparative transcriptome analysis was performed to explore the molecular response mechanism of the liver, a non-osmoregulatory organ, when fish was subjected to hypo- (10 ppt) and hyper-salinity (40 ppt) stress. A total of 100 and 5 DEGs were identified under hypo- (10 ppt) and hyper-salinity (40 ppt) stress, respectively. The DEGs were involved in lipid metabolism, glycine, serine, and threonine metabolism, and in various signaling pathways, including Calcium, PPAR and adipocytokine, and adrenergic signaling in cardiomyocytes. The mRNA expression levels of acsl5, lipin1, and apoeb in the liver were down-regulated under 10 ppt salinity, suggesting an elevation of fatty acids oxidation and energy requirement in response to the hypo-salinity stress. Similarly, there was a decrease in the expression levels of atp1b1b and cftr, responsible for the reduced Na+, K+ movement and Cl- ion secretion, under hypo-salinity stress. This study provides important basic data for the optimal artificial breeding of greater amberjack, and reveals the osmotic regulation mechanism of the liver in response to salinity stress.

Fishmeal and fish oil substitution in aquafeeds might have adverse effects on fish growth and health, mainly in carnivorous species, such as Mediterranean yellowtail (Seriola dumerili). Mediterranean yellowtail shows great potential as an alternative aquaculture species due to its fast growth and high price on the market, but the need for high-quality protein and fatty acid content in its diets is limiting its production. In order to improve the sustainability of its production, this study was conducted with 360 fish of 35 g to evaluate the effects on fish growth and health. Six diets were used: one control diet without replacement, three with FM replacement (FM66, FM33, and FM0) (33%, 66%, and 100% FM replacement), and two with FO replacement (FO50 and FO0) (50% and 100% FO replacement). The substitution of FM was with vegetable (VM) (corn gluten) and animal (AM) (krill and meat meal) meals. The reductions in FM and FO of up to 33 and 0%, respectively, did not affect the growth and survival of S. dumerili at the intestinal morphology level, except for the anterior intestine regarding the lower villi length and width and the posterior intestine regarding the lower width of the lamina propria. On the other hand, the substitution of fish ingredients in the diet affects liver morphology, indicating alterations in the major diameter of hepatocytes or their nuclei. Finally, diet did not affect the gut microbiota with respect to the control, but significant differences were found in alpha and beta diversity when FO and FM microbiota were compared. A 66% FM replacement and total FO replacement would be possible without causing major alterations in the fish.

Knowledge of the growth of stocks is essential to study the dynamics of fish populations, and thus to manage fisheries. For several species, it is not possible to carry out a sampling covering the totality of range size. Thus, an under-sampling coupled to a Bayesian approach could be realized for Seriola dumerili (Risso, 1810) to improve the growth parameters. A total of 166 individuals (89 females and 77 males) was monthly collected during one year, from August 2020 to July 2021, along the eastern coast of Tunisia (Mediterranean Sea, on coasts of Monastir, Sousse and Mahdia). The individual ageing data was carried out from the scales under binocular with transmitted light. For each sex, length-weight relationship (LWR; GW: gutted weight ± 1 g; TL: total length ± 0.1 cm) was estimated. For female and male LWR are presented as follow GW = 0.063TL2.524 (R2 = 0.948, p < 0.05) and GW = 0.056TL2.555 (R2 = 0.980, p < 0.05) respectively. For both sexes, the relationship exhibited allometric growth. The use of Markov Chain Monte Carlo chains was adopted to boost the estimation of Seriola dumerili growth parameters for both sexes. The comparison with Gompertz and Logistic growth models revealed the accuracy of the von Bertalanffy growth model. The estimated growth parameters for the population were TL∞ = 106.06 ± 5.54 cm, K = 0.19 ± 0.01 year–1. The enhancement of growth estimates for under-sampled will be useful in the stock assessment methods to sustain Seriola dumerili fishery. [ABSTRACT FROM AUTHOR]

Accurate identification of Seriola dumerili (SD) offers crucial technical support for aquaculture practices and behavioral research of this species. However, the task of discerning S. dumerili from complex underwater settings, fluctuating light conditions, and schools of fish presents a challenge. This paper proposes an intelligent recognition model based on the YOLOv8 network called SD-YOLOv8. By adding a small object detection layer and head, our model has a positive impact on the recognition capabilities for both close and distant instances of S. dumerili, significantly improving them. We construct a convenient S. dumerili dataset and introduce the deformable convolution network v2 (DCNv2) to enhance the information extraction process. Additionally, we employ the bottleneck attention module (BAM) and redesign the spatial pyramid pooling fusion (SPPF) for multidimensional feature extraction and fusion. The Inner-MPDIoU bounding box regression function adjusts the scale factor and evaluates geometric ratios to improve box positioning accuracy. The experimental results show that our SD-YOLOv8 model achieves higher accuracy and average precision, increasing from 89.2% to 93.2% and from 92.2% to 95.7%, respectively. Overall, our model enhances detection accuracy, providing a reliable foundation for the accurate detection of fishes.

In aquaculture, natural and eco-friendly resources are prioritized over synthetic inputs (e.g., antibiotics), and optimizing sustainable production methods is necessary. Probiotics have been well known for various potential functions in animal performance and health when supplemented as a single or mix of strain (s) in the diet. Consuming the right probiotic blend (synergistic types) is more advantageous than using each kind individually due to combining each species' functions. The present trial aimed to examine the potential impacts of two probiotic mixtures on the performance and well-being of amberjack juveniles (5.63 ± 0.04 g; Number = 300) for a 60-day feed trial. Three experimental diets (43.5 ± 0.50% total protein and 12.55 ± 0.17% total lipid) were formulated with no probiotics supplement for the control (CD1) or with probiotics mixture supplement. Probiotic mixtures were supplemented at 2 g/kg diet for groups D2 [Bacillus amyloliquefaciens TOA5001 (BA) + Streptococcus faecalis T-110 (SF)] and D3 [Bacillus amyloliquefaciens, Streptococcus faecalis T-110, Lactobacillus plantarum TO-A, Bacillus mesentericus TO-A] respectively. The analysis revealed no difference in all means of growth parameters, feed utilization, survival rate, biometric indices, whole-body composition, and blood parameters between control and probiotic-supplemented diet groups. Liver lysozyme activity, superoxide dismutase, peroxidase activity, and biological antioxidant (BAP) were significantly improved in fish fed D2 compared to CD1 (P < 0.05). The higher (P < 0.05) content of intestinal lactic acid bacteria was noted in fish group fed diet D2, with an improved intestinal histological structure such as increased villi length, cryptal depth, and goblet cells compared to those provided with CD1 and D3 diets. In conclusion, incorporating a mix of probiotic bacteria [BA+SF] at a 2 g/kg diet has remarkable effects on intestinal health, immune responses, and oxidative status of amberjack, S. dumerili, suggesting a potential probiotic candidate for this species.

By monitoring of fish in the Alekseev Bay of Popov Island with the long-time underwater video observation system, greater amberjack Seriola dumerili (Risso 1810) (Carangidae) was registered in the second time in Peter the Great Bay and several species were registered in the first time in the Alekseev Bay (Oplegnathus fasciatus, Pholis crassispina, Gymnogobius heptacanthus, Salangichthys microdon, and Liparis agassizii). The list of fish species for the Alekseev Bay is widened to 60 species.

This study provides the first socio-ecological overview of the Seriola dumerili fishery occurring in the Balearic Islands. This pelagic top-predator is among the five most valued fish resources of the Balearic community. Despite its ecological importance and potential vulnerability to aggregation fishing, few studies address the ecology of this large Carangidae species. Shining a light on its ecology is vital to ensure adequate species conservation and the sustainable and effective management of the fishery. Historical catches from 1950–1999, alongside detailed landing data for the last 21 years, were analysed to identify potential patterns in ecological and socio-economic factors. Significant inter-annual variability among the years was found in historical catches of greater amberjack, while catches and mean prices of the different size categories revealed significant results between seasons and months, respectively. Additionally, the purse seine fleet accounted for the highest percentage of S. dumerili catches. CPUE did not appear to change greatly between months and years after the annual 8-month fishing ban imposed in 2011 and therefore a re-evaluation of the closure was intended. Overall, this study suggests seasonality influences the S. dumerili fishery in the Balearic Islands, within which ecological influences show a higher regulating power than socio-economic factors. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate the effects of dietary fish oil replacement with a mixture of vegetable oils and probiotic supplementation on plasma biochemical parameters, oxidative stress, and antioxidant ability of Seriola dumerili. Specimens with an initial weight of 175 g were used. Four feeds were formulated with 0% (FO-100), 75% (FO-25), and 100% (FO-0 and FO-0+ with the addition of Lactobacillus probiotics) substitution of fish oil with a mixture of linseed, sunflower, and palm oils. After 109 days, no significant differences were observed in the activity of antioxidant enzymes in the liver, foregut, and hindgut, only glucose-6-phosphate dehydrogenase activity in the liver was higher in the fish fed the FO-100 diet than in those fed the FO-0 diet. No significant differences were observed in the total, reduced, and oxidized glutathione and the oxidative stress index in the liver. In addition, lipid peroxidation in the liver and red muscle values were higher in the fish fed the FO-100 diet than in the fish fed the FO-0+ diet, however, the foregut of the fish fed the FO-100 diet presented lower values than that of the fish fed the FO replacement diet, with and without probiotics. There were significant differences in cholesterol levels in the FO-100 group; they were significantly higher than those observed with the fish diets without fish oil. To sum up, fish oil can be replaced by up to 25% with vegetable oils in diets for Seriola dumerili juveniles, but total fish oil substitution is not feasible because it causes poor survival. The inclusion of probiotics in the FO-0+ diet had no effects on the parameters measured. [ABSTRACT FROM AUTHOR]

The greater amberjack (Seriola dumerili) is a gonochoristic fish with no sexual dimorphism in appearance, making sex identification difficult. Piwi-interacting RNAs (piRNAs) function in transposon silencing and gametogenesis and are involved in various physiological processes, including sex development and differentiation. Exosomal piRNAs can be indicators for the determination of sex and physiological status. In this study, four piRNAs were differentially expressed in both serum exosomes and gonads between male and female greater amberjack. Three piRNAs (piR-dre-32793, piR-dre-5797, and piR-dre-73318) were significantly up-regulated and piR-dre-332 was significantly down-regulated in serum exosomes and gonads of male fish, compared to female fish, consistent with the serum exosomal results. According to the relative expression of four marker piRNAs derived from the serum exosomes of greater amberjack, the highest relative expression of piR-dre-32793, piR-dre-5797, and piR-dre-73318 in seven female fish and that of piR-dre-332 in seven male fish can be used as the standard for sex determination. The method of sex identification can ascertain the sex of greater amberjack by blood collection from the living body, without sacrificing fish. The four piRNAs did not show sex-inclined expression in the hypothalamus, pituitary, heart, liver, intestine, and muscle tissue. A piRNA–target interaction network involving 32 piRNA-mRNA pairs was generated. Sex-related target genes were enriched in sex-related pathways, including oocyte meiosis, transforming growth factor-beta signaling pathway, progesterone-mediated oocyte maturation, and gonadotropin releasing hormone signaling pathway. These results provide a basis for sex determination in greater amberjack and improve our understanding of the mechanisms underlying sex development and differentiation in the species. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effect of dietary curcumin on non-specific immune responses and antioxidative ability in Seriola dumerili under ammonia stress and post-recovery. Three diets were prepared to contain 0, 75, and 150 mg/kg of curcumin. A total of 225 greater amberjack (initial weight: 100.90 ± 0.03 g) were distributed into nine cylindrical tanks, constituting an experimental design with three treatments and three replicates. After 56 days of feeding, plasma, intestinal, and hepatic enzyme activities were evaluated. Then, an acute ammonia challenge experiment was conducted. Ten fish per tank were subjected to acute ammonia stress (total ammonia-N: 1000 mg/L) for eight minutes followed by six minutes of recovery. The results indicated that dietary curcumin significantly promoted intestinal and hepatic alkaline phosphatase (ALP) and acid phosphatase (ACP) levels as well as hepatic antioxidative enzymes such as superoxide dismutase (SOD), total antioxidant capacity (T-AOC), reduced glutathione (GSH), and glutathione peroxidase (GSH-Px) of greater amberjack. In addition, curcumin addition improved the activities of antioxidant enzymes, such as SOD, T-AOC, GSH, GSH-Px, and catalase (CAT), and reduced malondialdehyde (MDA) content in liver, spleen, head kidney, and brain tissues after post-recovery. The indexes related to immunity and antioxidant enzymes in the liver, gill, and spleen rose again to some extent, but they showed the worst recovery ability in the head kidney and brain tissue samples. These results indicate that dietary curcumin supplementation could increase non-specific immune responses, antioxidant ability, and enhance resistance to high ammonia stress in juvenile S. dumerili. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Food Safety & Quality is the property of Journal of Food Safety & Quality Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Salinity is an important abiotic stress that has significant effects on the physiology and metabolism of marine fish. The greater amberjack (Seriola dumerili) is a large, fast-growing species with high commercial value in global aquaculture. To describe the molecular response of the greater amberjack liver to different salinity stresses, RNA-seq analysis was performed to identify the important genes and signaling pathways activated in response to salt stress. Greater amberjack juveniles were reared under different salinity stresses (20, 30, and 40 ppt) for 30 days to evaluate their tolerance, adaptability, and molecular responses. A total of 657 (426 up-regulated and 231 down-regulated) and 65 (17 up-regulated and 48 down-regulated) differentially expressed genes (DEGs) were identified in the group at 30 vs. 20 ppt and 30 vs. 40 ppt salinity, respectively. qPCR and transcriptomic analysis showed that salinity stress affected the expression of genes involved in lipid metabolism (pld2, pla2g7, acacb, and acsl4a), vitamin metabolism (cyp24a1 and cyp2r1), ion transporters (slc4a1a, slc4a4b, rhag, and rh50), and signal transduction (itpkcb, fgf19, and fgfr4). KEGG pathway enrichment analysis showed that the DEGs were primarily involved in metabolism, ribosome biogenesis in eukaryotes, and insulin signaling pathway. The identified candidate genes involved in metabolism pathways, ion transporters, and signal transduction, provide a basis for further study of the molecular mechanisms involved in salinity adaptation and transcriptional plasticity in the livers of marine fish.

El Niño–Southern Oscillation (ENSO) is a crucial oceanographic phenomenon that leads to interannual fluctuations in the climate and ecosystem productivity of tropical and subtropical areas. These fluctuations affect the suitability of habitats for many commercial fish species. However, detailed information on the effects of this major phenomenon and the resulting environmental changes on the habitat and catch rates of the economically and ecologically crucial species of the greater amberjack (Seriola dumerili) in the Taiwan Strait (TS) is lacking. In this study, we employed a weighted habitat suitability index (HSI) modeling method and used remotely sensed marine environmental data as well as data from recorders in Taiwanese fishing vessels (in 2014–2019) to understand the effects of ENSO events on the habitat suitability and catch rates for greater amberjack in the TS. Analysis of variance revealed that environmental factors substantially influenced greater amberjack habitats and catch rates during ENSO events across seasons. The catch rates were high in spring and summer in the southern and northern TS and in autumn and winter in the southern TS. The catch rates were higher in spring, summer, and autumn (>9.0 kg/h) in El Niño years, and in winter, the catch rates were higher in normal years (>12.0 kg/h) and lower in La Niña years. The predicted HSI for the southern and northern TS revealed that greater amberjack populations were predominantly distributed at 20–24°N and 24–28°N, respectively. Opposite habitat suitability was synchronously found in spring and summer during ENSO events, with higher HSI values recorded in spring in El Niño and normal years and higher HSI values recorded in summer in La Niña years. In winter, the HSI values of the southern and northern TS were higher in El Niño and normal years and substantially lower in La Niña years. Habitat suitability was extremely low in autumn. These findings imply that ENSO events play a key role in regulating environmental conditions and affect the catch rates and habitat suitability for the greater amberjack in the TS.

This study was conducted to determine whether curcumin has a positive effect in greater amberjack (Seriola dumerili), especially the ammonia nitrogen stress tolerance ability. The results showed that the stress recovery process of digestive enzymes amylase and trypsin, as well as absorptive enzymes Na+/K+-ATPase, γ-GT and CK, was accelerated. Lysozyme activity increased in the fish fortified with both curcumin diets. Aspartate aminotransferase activity restriction was activated at a low curcumin level. However, alanine aminotransferase activity restriction happened only at 0.02% dietary curcumin. Facilitation of lipid metabolism by curcumin was very clear, as triglyceride and total cholesterol content was basically maintained at the original level or even showed a slight decrease after recovery. HSP70 and HSP90 genes were not evidently stimulated to express in liver, kidney and spleen tissues. In addition, curcumin showed its inhibition capacity on IL1β and IFN-γ and a promoting effect on TGF-β1. The expression of NF-κB1 decreased in a higher degree in fish fed with 0.02% dietary curcumin, while 0.01% dietary curcumin accelerated the recovery pace of C3 and lgT after stress. This study showed that dietary curcumin supplementation can enhance ammonia nitrogen stress tolerance in greater amberjack, and its application prospect can be confirmed. [ABSTRACT FROM AUTHOR]

The environmental characteristics of the Taiwan Strait (TS) have been linked to variations in the abundance and distribution of greater amberjack (Seriola dumerili) populations. Greater amberjack is a commercially and ecologically valuable species in ecosystems, and its spatial distribution patterns are pivotal to fisheries management and conservation. However, the relationship between the catch rates of S. dumerili and the environmental changes and their impact on fish communities remains undetermined in the TS. The goal of this study was to determine the spatiotemporal distribution pattern of S. dumerili with environmental characteristics in the TS from south to north (20°N–29°N and 115°E–127°E), applying generalized additive models (GAMs) and spatiotemporal fisheries data from logbooks and voyage data recorders from Taiwanese fishing vessels (2014–2017) as well as satellite-derived remote sensing environmental data. We used the generalized linear model (GLM) and GAM to analyze the effect of environmental factors and catch rates. The predictive performance of the two statistical models was quantitatively assessed by using the root mean square difference. Results reveal that the GAM outperforms the GLM model in terms of the functional relationship of the GAM for generating a reliable predictive tool. The model selection process was based on the significance of model terms, increase in deviance explained, decrease in residual factor, and reduction in Akaike's information criterion. We then developed a species distribution model based on the best GAMs. The deviance explained indicated that sea surface temperature, linked to high catch rates, was the key factor influencing S. dumerili distributions, whereas mixed layer depth was the least relevant factor. The model predicted a relatively high S. dumerili catch rate in the northwestern region of the TS in summer, with the area extending to the East China Sea. The target species is strongly influenced by biophysical environmental conditions, and potential fishing areas are located throughout the waters of the TS. The findings of this study showed how S. dumerili populations respond to environmental variables and predict species distributions. Data on the habitat preferences and distribution patterns of S. dumerili are essential for understanding the environmental conditions of the TS, which can inform future priorities for conservation planning and management. [ABSTRACT FROM AUTHOR]

Female greater amberjack, Seriola dumerili reared in tanks have been inconsistent in entering or completing vitellogenesis. As a result, established spawning induction protocols employing gonadotropin-releasing hormone agonist (GnRHa) fail to induce oocyte maturation, ovulation and spawning. Males also exhibit reproductive dysfunctions resulting in low sperm production of relatively low quality. To ameliorate these problems, homologous Seriola dumerili single-chain recombinant Follicle stimulating hormone (sdrFsh) and Luteinizing hormone (sdrLh) were produced and administered to adult 4.8-year-old hatchery-produced (F1 generation) greater amberjack held in tanks, in order to enhance gametogenesis and increase reproductive performance (fecundity and fertilization success) upon spawning induction with GnRHa. Beginning at the onset of gametogenesis (27 April 2022), injections of sdrFsh and sdrLh were given for 6 consecutive weeks (a total of 7 treatments) in different combinations in males and females, and increasing doses. All fish treated with sdrFsh/Lh underwent complete gametogenesis, with females having oocytes in post-vitellogenesis and males producing releasable sperm at the time planned for the GnRHa spawning induction (6 June 2022). Furthermore, five of the six females initiated oocyte maturation prior to the GnRHa treatment, and at least one female also spawned spontaneously earlier (week 4). All but one untreated Control females did not complete vitellogenesis and exhibited follicular apoptosis/atresia, making them ineligible for GnRHa-induced spawning. Untreated Control males completed spermatogenesis and produced releasable sperm, but of somewhat lower spermatozoa density and significantly lower motility percentage and velocity compared to sdrFsh/Lh-treated males. GnRHa-induced spawning of the sdrFsh/Lh-treated fish enhanced mean daily relative fecundity and fertilization success, with embryo and larval survival >50%. These results are encouraging, and we expect that further optimization of dosage and administration timing can provide a reliable protocol for enhancing gametogenesis and promoting maturation in dysfunctional greater amberjack broodstocks maintained in aquaculture indoor facilities. • Untreated females did not complete vitellogenesis and underwent follicular atresia. • Seriola dumerili recombinant (sdr) Fsh and Lh promoted vitellogenesis and ovulation. • sdrFsh and sdrLh enhanced sperm motility and velocity. • Administration of GnRHa increased relative fecundity and fertilization. • sdrFsh and sdrLh may alleviate reproductive dysfunctions in greater amberjack. [ABSTRACT FROM AUTHOR]

The bacterial colonization of newly hatched fish is important for larval development and health. Still, there remains a lack of understanding regarding the early microbiota development in Seriola dumerili. In the present study, 16S rDNA sequencing was utilized to analyze the microbiota of S. dumerili larvae and their diets at various developmental stages. Proteobacteria emerged as the dominant phylum in larvae, exhibiting a "U"-shaped peak at DPH14. Conversely, Bacteroidetes, Firmicutes, and Cyanobacteria showed contrasting patterns over time. Alpha diversity followed a hump-shaped pattern, reaching its peak at DPH4, and subsequently declining to its lowest point at DPH30. Although the microbial community of diets was distinct to the larvae, limited impacts were displayed through the richness, diversity of microbial community, and correlation between diets and fish microbiota. Furthermore, these influences shifted with the fish development. The Neutral Community Model (NCM) explained the presence of a neutral process in the assembly of fish communities, but with the influence of random processes gradually diminishing as individual development progressed. These results indicated that diets do affect the fish microbiota assembly and succession, but not the critical driving factors. • The bacterial communities in larvae underwent dynamic changes as the fish developed. • The succession of microbiota surpassed the influence of diets in accordance with the course of larval ontogeny development. • The richness and diversity of fish microbial community sorely increased after fish turn to exogenous nutrition. [ABSTRACT FROM AUTHOR]

The study of fish digestive biochemistry is essential to understand factors that affect the net efficiency of food transformation and growth, and therefore aquaculture profitability. The aim of the present study was to assess the activity and functional characteristics of key digestive enzymes in juveniles of greater amberjack (Seriola dumerili), as well as the possible modulation of their relative importance by water temperature. For that, a combination of biochemical assays and substrate-SDS-PAGE were used. Under physiological conditions pepsin activity was negligible. Chymotrypsin was the most active enzyme in the digestive tract of the greater amberjack, while lipase was the enzyme with lower activity, though both enzymes in addition to trypsin were responsive to water temperature as revealed by discriminant analysis. Seriola dumerili showed to have pH-sensitive and, except for chymotrypsin, thermally robust proteases. Inhibition assays showed the major importance of serine proteases and revealed inverse trypsin and chymotrypsin responses to environmental temperature, with higher trypsin contribution in 26°C-fish while higher chymotrypsin contribution in 18°C-fish. Zymograms revealed three isotrypsin and three isochymotrypsin enzymes, with no variation in the presence of particular isoforms among rearing temperatures. However, they confirmed the role of chymotrypsin activity in providing digestive plasticity, with one of the isoforms being more active at lower temperatures. Thus, results indicate that variation in the relative contribution of chymotrypsin isoenzymes to a particular environmental temperature occurs due to different physic-chemical features of isoforms as a source of functional flexibility. This study assessed for the first time the effects of rearing temperature on greater amberjack digestive enzymes, increasing the knowledge on its digestive biochemistry, and aiding in the improvement of management practices for this species industrialization.

Greater amberjack (Seriola dumerili) is a fish species that has significant economic and cultural value. It has a large size and grows rapidly. However, the intolerance to hypoxia poses a major obstacle to the growth of its aquaculture industry. This study focuses on the gills and spleen, two organs closely associated with the response to acute hypoxic stress. By simulating the acute hypoxic environment and using Illumina RNA-Seq technology, we explored the gills and spleen transcriptome changes in the acute hypoxia intolerant and tolerant groups of greater amberjack. It was discovered that gill tissues in the tolerant group may maintain a stable intracellular energy supply by promoting glycolysis and β-oxidation compared to the intolerant group. Additionally, it promotes angiogenesis, enhances the ability to absorb dissolved oxygen, and accelerates oxygen transport to the mitochondria, adapting to the hypoxic environment. Anti-apoptotic genes were up-regulated in gill tissues in the tolerant group compared to the intolerant group, thereby minimizing the damage of acute hypoxia. On the other hand, the spleen inhibited the TCA and energy-consuming lipid synthesis pathways to supply energy under acute hypoxic stress. Pro-angiogenic genes were down-regulated in the spleen of individuals in the tolerant group compared to the intolerant group, which may be related to organ function. The suppressed reactive oxygen species (ROS) production and the impaired immune response function of the spleen were also found. The study explored the acute hypoxic stress response in greater amberjack and the molecular mechanisms underlying its tolerance to acute hypoxia. • Key differentially expressed genes of gills and spleen related to acute hypoxia in Seriola dumerili were identified. • Gills of acute hypoxia-tolerant individuals promote glycolysis, β-oxidation, and angiogenesis. • Spleen of acute hypoxia-tolerant individuals inhibits tricarboxylic acid cycle, lipid synthesis, and glycolysis suppression. • Gills increase oxygen uptake, while the spleen releases blood cells to transport oxygen to tissues. [ABSTRACT FROM AUTHOR]

The greater amberjack (Seriola dumerili) does not exhibit apparent sexual dimorphism in appearance, which makes it difficult to determinate its sex. MicroRNAs (miRNAs) can modulate the expression levels of targets through RNA silencing and post-transcriptional regulation and participate in various reproduction processes. Exosomal miRNAs can be signatures for the sex determination in fish. This study identified three miRNAs (abu-miR-30b, dre-miR-223, and dre-miR-133b-3p) that were significantly highly expressed in four tissues (serum exosomes, hypothalamus, pituitary, and gonad) in males compared to females, in line with the sequencing results of serum exosomes. Three miRNAs (abu-miR-30b, dre-miR-223, and dre-miR-133b-3p) could be used as signatures to detect the sex of greater amberjack with their expression levels in serum exosomes, providing an accurate and effective method. Furthermore, dre-miR-133b-3p could regulate the expression of its target gene (WW domain binding protein 2, wbp2). The negative regulation of dre-miR-133b-3p on wbp2 may modulate the gonadal development of greater amberjack. This study not only offers an effective method of sex determination in greater amberjack but also helps to understand the effect of sex-inclined miRNAs and their sex-related targets on gonad development within this species. • The miRNA profiles of serum exosomes were characterized between the sexes. • Three sex-inclined exosomal miRNAs were identified for sex determination. • Sex-inclined miRNAs were involved in the hypothalamus–pituitary–gonad axis. • Negative regulation of dre-miR-133b-3p on wbp2 may modulate the gonad development. [ABSTRACT FROM AUTHOR]

• Females reared in captivity lagged behind in reproductive development compared to the wild. • Multiple handling of the rearing cage at the DEVELOPING phase affected negatively reproductive development in both sexes. • Males exhibited a pronounced dysfunction when reared in captivity, even without any handling. We compared the endocrine status of the pituitary-gonad axis of wild and captive-reared greater amberjack (Seriola dumerili) during the reproductive cycle (April – July), reporting on the expression and release of the two gonadotropins for the first time in the Mediterranean Sea. Ovaries from wild females were characterized histologically as DEVELOPING in early May and SPAWNING capable in late May-July, the latter having a 3 to 4-fold higher gonadosomatic index (GSI). SPAWNING capable wild females exhibited an increase in pituitary follicle stimulating hormone (Fsh) content, plasma testosterone (T) and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P), while almost a 10-fold increase was observed in pituitary luteinizing hormone (Lh) content. An increasing trend of plasma 17β-estradiol (E 2) was also recorded between the two reproductive stages in wild females. Captive-reared females sampled during the reproductive cycle exhibited two additional reproductive categories, with REGRESSED females having extensive follicular atresia and fish in the REGENERATING stage having only primary oocytes in their ovaries. Pituitary content of Fsh and Lh, fshb and lhb expression and plasma levels of Fsh and Lh remained unchanged among the four reproductive stages in captive females, in contrast with plasma E 2 and T that decreased in the REGENERATING stage, and 17,20β-P which increased after the DEVELOPING stage. In general, no significant hormonal differences were recorded between captive-reared and wild DEVELOPING females, in contrast to SPAWNING capable females, where pituitary Lh content, plasma Fsh and T were found to be lower in females in captivity. Overall, the captive females lagged behind in reproductive development compared to the wild ones and this was perhaps related to the multiple handling of the sea cages where all the sampled fish were maintained. Between wild males in the DEVELOPING and SPAWNING capable stages, pituitary Lh content, plasma T and 17,20β-P, and GSI exhibited 3 to 4-fold increases, while an increasing trend of pituitary Fsh content, lhb expression levels and plasma 11-ketotestosterone (11-KT) was also observed, and an opposite trend was observed in plasma Lh. Captive males were allocated to one more category, with REGRESSED individuals having no spermatogenic capacity. During the SPAWNING capable phase, almost all measured parameters were lower in captive males compared to wild ones. More importantly, captive males showed significant differences from their wild counterparts throughout the reproductive season, starting already from the DEVELOPING stage. Therefore, it appears that captivity already exerted negative effects in males prior to the onset of the study and the multiple handling of the cage where sampled fish were reared. Overall, the present study demonstrated that female greater amberjack do undergo full vitellogenesis in captivity, albeit with some dysfunctions that may be related to the husbandry of the experiment, while males, on the other hand, may be more seriously affected by captivity even before the onset of the study. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate the effects of dietary fish oil replacement with a mixture of vegetable oils and probiotic supplementation on plasma biochemical parameters, oxidative stress, and antioxidant ability of Seriola dumerili. Specimens with an initial weight of 175 g were used. Four feeds were formulated with 0% (FO-100), 75% (FO-25), and 100% (FO-0 and FO-0+ with the addition of Lactobacillus probiotics) substitution of fish oil with a mixture of linseed, sunflower, and palm oils. After 109 days, no significant differences were observed in the activity of antioxidant enzymes in the liver, foregut, and hindgut, only glucose-6-phosphate dehydrogenase activity in the liver was higher in the fish fed the FO-100 diet than in those fed the FO-0 diet. No significant differences were observed in the total, reduced, and oxidized glutathione and the oxidative stress index in the liver. In addition, lipid peroxidation in the liver and red muscle values were higher in the fish fed the FO-100 diet than in the fish fed the FO-0+ diet, however, the foregut of the fish fed the FO-100 diet presented lower values than that of the fish fed the FO replacement diet, with and without probiotics. There were significant differences in cholesterol levels in the FO-100 group; they were significantly higher than those observed with the fish diets without fish oil. To sum up, fish oil can be replaced by up to 25% with vegetable oils in diets for Seriola dumerili juveniles, but total fish oil substitution is not feasible because it causes poor survival. The inclusion of probiotics in the FO-0+ diet had no effects on the parameters measured.

This study provides the first socio-ecological overview of the Seriola dumerili fishery occurring in the Balearic Islands. This pelagic top-predator is among the five most valued fish resources of the Balearic community. Despite its ecological importance and potential vulnerability to aggregation fishing, few studies address the ecology of this large Carangidae species. Shining a light on its ecology is vital to ensure adequate species conservation and the sustainable and effective management of the fishery. Historical catches from 1950–1999, alongside detailed landing data for the last 21 years, were analysed to identify potential patterns in ecological and socio-economic factors. Significant inter-annual variability among the years was found in historical catches of greater amberjack, while catches and mean prices of the different size categories revealed significant results between seasons and months, respectively. Additionally, the purse seine fleet accounted for the highest percentage of S. dumerili catches. CPUE did not appear to change greatly between months and years after the annual 8-month fishing ban imposed in 2011 and therefore a re-evaluation of the closure was intended. Overall, this study suggests seasonality influences the S. dumerili fishery in the Balearic Islands, within which ecological influences show a higher regulating power than socio-economic factors.

The greater amberjack (Seriola dumerili) is a gonochoristic fish with no sexual dimorphism in appearance, making sex identification difficult. Piwi-interacting RNAs (piRNAs) function in transposon silencing and gametogenesis and are involved in various physiological processes, including sex development and differentiation. Exosomal piRNAs can be indicators for the determination of sex and physiological status. In this study, four piRNAs were differentially expressed in both serum exosomes and gonads between male and female greater amberjack. Three piRNAs (piR-dre-32793, piR-dre-5797, and piR-dre-73318) were significantly up-regulated and piR-dre-332 was significantly down-regulated in serum exosomes and gonads of male fish, compared to female fish, consistent with the serum exosomal results. According to the relative expression of four marker piRNAs derived from the serum exosomes of greater amberjack, the highest relative expression of piR-dre-32793, piR-dre-5797, and piR-dre-73318 in seven female fish and that of piR-dre-332 in seven male fish can be used as the standard for sex determination. The method of sex identification can ascertain the sex of greater amberjack by blood collection from the living body, without sacrificing fish. The four piRNAs did not show sex-inclined expression in the hypothalamus, pituitary, heart, liver, intestine, and muscle tissue. A piRNA–target interaction network involving 32 piRNA-mRNA pairs was generated. Sex-related target genes were enriched in sex-related pathways, including oocyte meiosis, transforming growth factor-beta signaling pathway, progesterone-mediated oocyte maturation, and gonadotropin releasing hormone signaling pathway. These results provide a basis for sex determination in greater amberjack and improve our understanding of the mechanisms underlying sex development and differentiation in the species.

In this study, we investigated the effect of dietary curcumin on non-specific immune responses and antioxidative ability in Seriola dumerili under ammonia stress and post-recovery. Three diets were prepared to contain 0, 75, and 150 mg/kg of curcumin. A total of 225 greater amberjack (initial weight: 100.90 ± 0.03 g) were distributed into nine cylindrical tanks, constituting an experimental design with three treatments and three replicates. After 56 days of feeding, plasma, intestinal, and hepatic enzyme activities were evaluated. Then, an acute ammonia challenge experiment was conducted. Ten fish per tank were subjected to acute ammonia stress (total ammonia-N: 1000 mg/L) for eight minutes followed by six minutes of recovery. The results indicated that dietary curcumin significantly promoted intestinal and hepatic alkaline phosphatase (ALP) and acid phosphatase (ACP) levels as well as hepatic antioxidative enzymes such as superoxide dismutase (SOD), total antioxidant capacity (T-AOC), reduced glutathione (GSH), and glutathione peroxidase (GSH-Px) of greater amberjack. In addition, curcumin addition improved the activities of antioxidant enzymes, such as SOD, T-AOC, GSH, GSH-Px, and catalase (CAT), and reduced malondialdehyde (MDA) content in liver, spleen, head kidney, and brain tissues after post-recovery. The indexes related to immunity and antioxidant enzymes in the liver, gill, and spleen rose again to some extent, but they showed the worst recovery ability in the head kidney and brain tissue samples. These results indicate that dietary curcumin supplementation could increase non-specific immune responses, antioxidant ability, and enhance resistance to high ammonia stress in juvenile S. dumerili.

Epitheliocystis is a fish gill disease caused by a broad range of intracellular bacteria infecting freshwater and marine fish worldwide. Here we report the occurrence and progression of epitheliocystis in greater amberjack reared in Crete (Greece). The disease appears to be caused mainly by a novel Betaproteobacteria belonging to the Candidatus Ichthyocystis genus with a second agent genetically similar to Ca. Parilichlamydia carangidicola coinfecting the gills in some cases. After a first detection of the disease in 2017, we investigated epitheliocystis in the following year's cohort of greater amberjack juveniles (cohort 2018) transferred from inland tanks to the same cage farm in the open sea where the first outbreak was detected. This cohort was monitored for over a year together with stocks of gilthead seabream and meagre co-farmed in the same area. Our observations showed that epitheliocystis could be detected in greater amberjack gills as early as a month following the transfer to sea cages, with ionocytes at the base of the gill lamellae being initially infected. Cyst formation appears to trigger a proliferative response, leading to the fusion of lamellae, impairment of gill functions and subsequently to mortality. Lesions are characterized by infiltration of immune cells, indicating activation of the innate immune response. At later stages of the outbreak, cysts were no longer found in ionocytes but were observed in mucocytes at the trailing edge of the filament. Whole cysts appeared finally to be expelled from infected mucocytes directly into the water, which might constitute a novel means of dispersion of the infectious agents. Molecular screening indicates that meagre is not affected by this disease and confirms the presence of previously described epitheliocystis agents, Ca. Ichthyocystis sparus, Ca. Ichthyocystis hellenicum and Ca. Similichlamydia spp., in gilthead seabream. Prevalence data show that the bacteria persist in both gilthead seabream and greater amberjack cohorts after first infection. [ABSTRACT FROM AUTHOR]

In order to understand the effects of dietary curcumin on the growth and digestive performance of Seriola dumerili, this study was conducted under laboratory conditions. The control group was added with 0% curcumin, and two treatment groups were added with 0.01% and 0.02% curcumin, respectively. Fish were fed with experimental diet for 8 weeks. The growth data, growth genes, intestinal digestive enzymes, tissue parameters, and blood lipid-related indicators were measured, and the correlation between digestive indicators, growth gene indicators, and growth characteristic indicators was analyzed. The results showed that the survival rate, visceral ratio, hepatosomatic ratio, and condition factor of Seriola dumerili increased first and then decreased with the increase of curcumin content in feed. The feed conversion ratio of the control group was significantly higher than that of the treatment group. With the increase of curcumin content in feed, lipase and trypsin increased first and then decreased with the increase of curcumin content. Compared with the control group, curcumin significantly increased the muscle thickness and the number of goblet cells of Seriola dumerili. High and low contents of curcumin can reduce the content of serum total cholesterol and triglyceride, and a low dose (0.01%) of curcumin has the strongest lipid-lowering effect. The relative gene expression of IGF1 and IGF2 reached the maximum in the 0.02% treatment group. The results showed that the addition of curcumin in feed could theoretically improve the survival rate, feed efficiency, and other growth characteristics of Seriola dumerili, improve intestinal digestion and structure, promote intestinal health, and reduce blood lipid levels. The best effect was achieved in the 0.01% treatment group. The results of this study provide a theoretical reference for the feasibility of adding curcumin to Seriola dumerili feed in production and realize the optimal proportion of feed additives for this species, which is beneficial to the sustainable development of aquaculture.

The histological process of gonadal differentiation, together with the endocrine changes of sex steroid hormones and some of their precursors, was studied in hatchery-produced greater amberjack Seriola dumerili from 101 until 408 days post-hatching (dph), with samplings conducted every 50 days. Histological processing showed that sex differentiation began at 101 dph with the formation of the ovarian cavity in females, while the presumptive males did not yet contain any germ cells in their gonad. At 150 dph, we observed the first germ cells in the developing testes. Sex differentiation in almost all sampled individuals was complete at 408 dph. No size dimorphism was observed between the sexes, and the sex ratio was 1:1, suggesting that there was no influence of early rearing in captivity on sex differentiation. Plasma concentrations of adrenosterone (Ad), androstenedione (Δ4), 11-ketotestosterone (11ΚΤ), testosterone (Τ), estradiol (Ε2), progesterone (P4) and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were measured in males and females with the use of liquid chromatography tandem mass spectrometry (LC–MS/MS) to examine their role in the sex differentiation process. From the seven hormones, the only one that exhibited differences between the sexes was 11-KT and the plasma 11-KT concentration was found to be a useful indication of greater amberjack sex. Variations were observed in the mean values of Ad, Δ4, 11-KT, T, P4 and 17,20βP over time in one or both sexes, indicating their involvement in the sex differentiation process. [ABSTRACT FROM AUTHOR]

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• No sexual size dimorphism was observed in up to 5-year-old greater amberjack. • Puberty occurred in 3-year-old hatchery-produced male greater amberjack. • Puberty occurred in 5-year-old hatchery-produced female greater amberjack. • Gonadal size was significantly smaller than mature, reproductively active fish in the wild. • Spawning induction with GnRHa was not effective, suggesting a dysfunction in females. We evaluated the onset of puberty of first-generation (F1) hatchery-produced greater amberjack (Seriola dumerili) reared in sea cages for 5 years. Fish were sampled every year in June, at the expected peak of the spawning period in the Mediterranean Sea. No sexual dimorphism in body weight was observed in the study. The ovaries of 1 and 2-year-old (yo) females consisted of primary oocytes only, while at the age of 3-yo early vitellogenic (Vg) oocytes were also identified, but with extensive follicular atresia. At the age of 4-yo, late Vg oocytes were observed, but again extensive follicular atresia characterized the ovaries of 50 % of females. At the age of 5-yo, follicular atresia of Vg oocytes was very limited. In males, gametogenesis was evident already in 1- and 2-yo fish, and 100 % of sampled 3-yo males produced collectable viable sperm. Plasma testosterone (T), 17β-estradiol (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) remained similar in 3 – 5-yo females, with T and E2 levels being highest in females in advanced vitellogenesis or with significant follicular atresia, compared to immature females. In males, plasma T declined over the years, while 11-ketotestosterone (11-KT) and 17,20β-P were highest in 4 and 5-yo males, with spermatozoa motility characteristics being improved from the 4th year onwards. The administration of GnRHa implants to 5-yo fish induced only two spawns, albeit no fertilized eggs were obtained. The results indicate that hatchery-produced greater amberjack males mature well and within the same age observed in the wild, however with smaller gonad size. On the contrary, females mature later than in the wild, also with a smaller gonad size. Spawning in response to GnRHa treatment was not effective, suggesting that Mediterranean hatchery-produced broodstocks may be dysfunctional, and further research is needed to document any improvement as the fish get older, or to determine if the results may be related to the specific stock of fish. [ABSTRACT FROM AUTHOR]

The environmental characteristics of the Taiwan Strait (TS) have been linked to variations in the abundance and distribution of greater amberjack (Seriola dumerili) populations. Greater amberjack is a commercially and ecologically valuable species in ecosystems, and its spatial distribution patterns are pivotal to fisheries management and conservation. However, the relationship between the catch rates of S. dumerili and the environmental changes and their impact on fish communities remains undetermined in the TS. The goal of this study was to determine the spatiotemporal distribution pattern of S. dumerili with environmental characteristics in the TS from south to north (20°N–29°N and 115°E–127°E), applying generalized additive models (GAMs) and spatiotemporal fisheries data from logbooks and voyage data recorders from Taiwanese fishing vessels (2014–2017) as well as satellite-derived remote sensing environmental data. We used the generalized linear model (GLM) and GAM to analyze the effect of environmental factors and catch rates. The predictive performance of the two statistical models was quantitatively assessed by using the root mean square difference. Results reveal that the GAM outperforms the GLM model in terms of the functional relationship of the GAM for generating a reliable predictive tool. The model selection process was based on the significance of model terms, increase in deviance explained, decrease in residual factor, and reduction in Akaike’s information criterion. We then developed a species distribution model based on the best GAMs. The deviance explained indicated that sea surface temperature, linked to high catch rates, was the key factor influencing S. dumerili distributions, whereas mixed layer depth was the least relevant factor. The model predicted a relatively high S. dumerili catch rate in the northwestern region of the TS in summer, with the area extending to the East China Sea. The target species is strongly influenced by biophysical environmental conditions, and potential fishing areas are located throughout the waters of the TS. The findings of this study showed how S. dumerili populations respond to environmental variables and predict species distributions. Data on the habitat preferences and distribution patterns of S. dumerili are essential for understanding the environmental conditions of the TS, which can inform future priorities for conservation planning and management.

Fish (175 g of initial weight) were fed in triplicated groups with four diets formulated by 0% (FO 100), 75% (FO 25) and 100% (with and without probiotics, FO 0 and FO 0+) of fish oil replacement consisting of a mixture of linseed, sunflower and palm oils. After 109 days, growth and nutritional parameters were not affected by the treatment; however, fish fed with 0% of fish oil showed the lowest survival rate and without differences between the same diet with probiotics. As for biometric parameters, significant differences in the viscerosomatic index (VSI) were observed between fish fed the FO 0+ diet and the FO 100 and FO 25 diets. Results obtained from histological analysis did not detect inflammation in gut samples, while liver samples showed a remarkable steatosis in all four treatments. Total fish oil replacement produced a significant difference in the width of the lamina propria. The dietary inclusion of probiotics in the FO 0+ diet seems to favour a recovery of intestine histology. In addition, as fish oil substitution increased, the width of the lamina propria also increased. In conclusion, it is possible to affirm that the four diets administrated to Seriola dumerili did not compromise the correct development of the animals. [ABSTRACT FROM AUTHOR]

An 84-day trial was performed to assess the use of alternative protein sources in Seriola dumerili. Three diets were used, FM100 diet, as a control diet without fishmeal substitution, and FM66 and FM33 diets with a fishmeal replacement of 330 g/kg and 660 g/kg, respectively. At the end of experiment, fish fed the FM66 diet showed the no differences in growth, nutritional parameters and fatty acid composition. Heavy metals present some differences but are always lower than risk levels.In sensory analysis, differences between diets appeared in pH and color, and also in some texture parameters between FM33 and the other two diets. No differences appeared between diets related to flavor.In summary, long periods of feeding with high fish meal substitution diets, affects Seriola dumerili growth; despite this the quality of the fillet was not affected even with a 66 % of substitution.

Epitheliocystis is a fish gill disease caused by a broad range of intracellular bacteria infecting freshwater and marine fish worldwide. Here we report the occurrence and progression of epitheliocystis in greater amberjack reared in Crete (Greece). The disease appears to be caused mainly by a novel Betaproteobacteria belonging to the Candidatus Ichthyocystis genus with a second agent genetically similar to Ca. Parilichlamydia carangidicola coinfecting the gills in some cases. After a first detection of the disease in 2017, we investigated epitheliocystis in the following year’s cohort of greater amberjack juveniles (cohort 2018) transferred from inland tanks to the same cage farm in the open sea where the first outbreak was detected. This cohort was monitored for over a year together with stocks of gilthead seabream and meagre co-farmed in the same area. Our observations showed that epitheliocystis could be detected in greater amberjack gills as early as a month following the transfer to sea cages, with ionocytes at the base of the gill lamellae being initially infected. Cyst formation appears to trigger a proliferative response, leading to the fusion of lamellae, impairment of gill functions and subsequently to mortality. Lesions are characterized by infiltration of immune cells, indicating activation of the innate immune response. At later stages of the outbreak, cysts were no longer found in ionocytes but were observed in mucocytes at the trailing edge of the filament. Whole cysts appeared finally to be expelled from infected mucocytes directly into the water, which might constitute a novel means of dispersion of the infectious agents. Molecular screening indicates that meagre is not affected by this disease and confirms the presence of previously described epitheliocystis agents, Ca. Ichthyocystis sparus, Ca. Ichthyocystis hellenicum and Ca. Similichlamydia spp., in gilthead seabream. Prevalence data show that the bacteria persist in both gilthead seabream and greater amberjack cohorts after first infection.

Greater amberjack (Seriola dumerili) is a very promising candidate for the diversification of the Mediterranean aquaculture due to its high demand, excellent flesh quality and high market prices. Its production expansion has, however, failed so far, due to several bottlenecks mainly related to pathology. This review addresses the major pathogens, which hinder the culture of greater amberjack with special focus in the Mediterranean region, and highlights possible treatment solutions. Among the important recorded pathogens of caged greater amberjack in the Mediterranean, the gill monogenean Zeuxapta seriolae seems to be the most problematic, causing significant losses. While formalin immersions are inefficient to combat this parasite, baths with hydrogen peroxide are extremely effective and praziquantel administration could be a more practical in‐feed treatment solution. The digenean blood flukes, Paradeontacylix spp., also account for important losses in greater amberjack farms in the same region. Dietary administration of praziquantel constitutes an effective therapeutic measure against those infections. Vibrio harveyi is also a bacterial pathogen severely affecting fish maintained both in land‐based facilities and in cages, whereas Epitheliocystis is a disease reported frequently that can be fatal when it occurs at early stages. Skin flukes such as Benedenia seriolae and Neobenedenia girellae as well as other parasites bacteria and viruses mentioned herein, which have caused substantial losses in Asian enterprises, but have not been identified yet in greater amberjack farmed in the Mediterranean, should be considered as potential threats. [ABSTRACT FROM AUTHOR]

Appropriate binders have not yet been determined in pellet feed for amberjack Seriola dumerili juveniles. This study aimed to assess the influence of binders (activated gluten [AG], guar gum [GG], and carboxymethylcellulose [CMC]) on growth, feed ingestion, gastric emptying time (GET), digestibility, intestinal histology, body composition, and blood chemical constituents of amberjack juvenile. Dry pellets bound by supplementing different binders (3% AG, 2.5% AG combined with 0.5% GG [AG + GG], and 3% CMC) were fed to fish (mean body weight ± SD = 52.5 ± 0.6 g) for 30 days. After feeding, fish fed the AG diet exhibited growth, protein and dry matter digestibility, and feed utilization levels significantly (p <.05) higher than those of fish fed the AG + GG and CMC diets. Moreover, GET in fish fed the AG + GG and CMC diets were slower than those from fish in the AG group. These responses appeared to be associated with the viscosity of binders and diets. In fish fed the AG + GG and CMC diets, several blood indices were significantly (p <.05) lower than those in fish fed the AG diet. These results suggest that AG is a candidate binder in pellet feed for amberjack juvenile. [ABSTRACT FROM AUTHOR]

Jaw malformations are a serious problem in fingerlings of the greater amberjack, Seriola dumerili. To establish a countermeasure against these malformations, we conducted a larval behavioural test to identify their root cause, and we investigated the ability of low‐brightness rearing tank walls to control their occurrence. Larval distribution was examined in a horizontally illuminated rectangular transparent aquarium (20 cm × 100 cm × 25 cm), and their distribution was biased towards the light source after this lighting was provided from 3 to 13 days post hatching (dph), indicating positive phototaxis; this response disappeared on 22 dph (there are no data between 13 and 22 dph). Larvae were observed to swim phototactically towards the light source and repeatedly collided with the tank wall (walling behaviour). To investigate the ability of wall brightness to control the incidence of jaw malformations, we compared their incidence in a rearing trial with different Munsell colour values for the tank walls: 2.11 (black), 5.85 (grey) and 9.52 (white). The incidence rate of jaw malformations at 25 dph was significantly lower in the tanks with lower‐brightness walls, that is, 5.8%, 22.5% and 26.8% for black, grey and white respectively. Larval walling behaviour was most intense for white, followed in order by grey and black. These results indicate that positive phototaxis elicits larval walling behaviour, causing jaw malformations, and that low‐brightness tank walls control this process. [ABSTRACT FROM AUTHOR]

Marine heatwaves (MHWs) have increased in frequency, intensity, and duration in recent years causing significant impacts on marine organisms and fisheries. This study explores the physiological changes of juvenile greater amberjacks (Seriola dumerili) that cope with MHWs. Results showed that physiological parameters were significantly affected by the intensity, duration of MHWs or interaction of two factors (P < 0.05). Repeated MHWs in which water temperatures were increased (24 °C to 28 °C and 32 °C) resulted in changes in enzyme activity levels (catalase (CAT), superoxide dismutase (SOD), and glutathione (GSH)), as well as the level of malondialdehyde (MDA) for antioxidant defense, immune function (acid phosphatase (ACP), alkaline phosphatase (ALP), and lysozyme (LYZ)), and energy metabolism (including triglycerides (TG), glucose (GLU), aspartate aminotransferase (GOT), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), and succinate dehydrogenase (SDH)). The activities of enzymes, including those associated with antioxidant defense, immune function, and energy metabolism, changed significantly in relation to short-term MHWs, indicating a thermal stress response. When S. dumerili were exposed to repeated-MHWs, thermal stress responses increased at 28 °C (T28) and decreased at 32 °C (T32). These results exhibited the inability of S. dumerili to acclimate to severe thermal stress from MHWs. This study examined S. dumerili responses to MHWs and assessed the physiological adaptation of juvenile greater amberjacks to MHWs. • Physiological parameters were significantly affected by the intensity, duration of MHWs or interaction of them. • The activities of enzymes changed significantly in relation to short-term MHWs, indicating a thermal stress response. • When exposed to repeated-MHWs, inability of S. dumerili were found to acclimate to severe thermal stress from MHWs. [ABSTRACT FROM AUTHOR]

Fishmeal and fish oil substitution in aquafeeds might have adverse effects on fish growth and health, mainly in carnivorous species, such as Mediterranean yellowtail ( Seriola dumerili ). Mediterranean yellowtail shows great potential as an alternative aquaculture species due to its fast growth and high price on the market, but the need for high-quality protein and fatty acid content in its diets is limiting its production. In order to improve the sustainability of its production, this study was conducted with 360 fish of 35 g to evaluate the effects on fish growth and health. Six diets were used: one control diet without replacement, three with FM replacement (FM66, FM33, and FM0) (33%, 66%, and 100% FM replacement), and two with FO replacement (FO50 and FO0) (50% and 100% FO replacement). The substitution of FM was with vegetable (VM) (corn gluten) and animal (AM) (krill and meat meal) meals. The reductions in FM and FO of up to 33 and 0%, respectively, did not affect the growth and survival of S. dumerili at the intestinal morphology level, except for the anterior intestine regarding the lower villi length and width and the posterior intestine regarding the lower width of the lamina propria. On the other hand, the substitution of fish ingredients in the diet affects liver morphology, indicating alterations in the major diameter of hepatocytes or their nuclei. Finally, diet did not affect the gut microbiota with respect to the control, but significant differences were found in alpha and beta diversity when FO and FM microbiota were compared. A 66% FM replacement and total FO replacement would be possible without causing major alterations in the fish.

The article provides description of spontaneous granulomatous aerocystitis by Phoma herbarum in a wild greater amberjack. Topics discussed include information on the Phoma herbarum Westend as a saprophytic fungus mostly recognized as a plant pathogen; discussions on the pathogen causing a chronic progressive and lethal visceral mycosis; and the infections by P. hebrarum in fish characterized by lethargy and erratic swimming.

• GnRHa implants were more effective than injections in inducing spawning. • High fecundity and good egg quality was produced by both hormonal treatments. • GnRHa implants also supported vitellogenesis. The greater amberjack (Seriola dumerili) is one of the most promising finfish species for aquaculture, due to its cosmopolitan distribution and acceptability, high growth rates and large size. However, lack of reproduction control has been one of the main bottlenecks for its commercialization. The study examined two endocrine methods for the induction of oocyte maturation/ovulation and spawning, which are based on the induction of endogenous Luteinizing Hormone (LH) release from the pituitary, through the use of Gonadotropin Releasing Hormone agonist (GnRHa) either in the form of sustained-release delivery systems (implants) or injections (acute release). The stock (n = 28) consisted of wild fish captured in 2011 and each GnRHa administration method was conducted in two replicates, with 6 and 8 fish per tank, respectively, at a 1:1 sex ratio. Fish were given a GnRHa injection once a week (three administrations), or a GnRHa implant every 2 weeks (two administrations). Mean daily relative fecundity was significantly higher (t 1.3 = −5.24, P = 0.012) in the implanted fish (15,170 ± 2,738 eggs kg−1 female day−1) compared to the injected fish (6,119 ± 2,790 eggs kg−1 female day−1). Total relative fecundity was also significantly higher (t 1.3 = −9.93, P = 0.003) in the implanted fish (102,402 ± 20,337 eggs kg−1 female) compared to the injected ones (26,517 ± 9,938 eggs kg−1 female), but there were no differences in the quality of eggs in terms of fertilization, 24-h embryo survival, hatching and 5-d larval survival. The number of females with fully vitellogenic oocytes eligible for induction of spawning decreased from the initial to the final sampling, from 7 to 6 females for the GnRHa implant treatment and from 7 to 3 females for the GnRHa injection treatment. In addition to apparently promoting the proper endocrine changes leading to multiple cycles of oocyte maturation, ovulation and spawning, and thus producing larger numbers of eggs; the use of GnRHa implants may be more appropriate in greater amberjack than multiple injections because (a) it also stimulates vitellogenesis and (b) involves less handling of the fish. [ABSTRACT FROM AUTHOR]

Lancefield group C Streptococcus dysgalactiae causes infections in farmed fish. Here, the genome of S. dysgalactiae strain kdys0611, isolated from farmed amberjack (Seriola dumerili) was sequenced. The complete genome sequence of kdys0611 consists of a single chromosome and five plasmids. The chromosome is 2,142,780 bp long and has a GC content of 40%. It possesses 2061 coding sequences and 67 tRNA and 6 rRNA operons. One clustered regularly interspaced short palindromic repeat, 125 insertion sequences, and four predicted prophage elements were identified. Phylogenetic analysis based on 126 core genes suggested that the kdys0611 strain is more closely related to S. dysgalactiae subsp. dysgalactiae than to S. dysgalactiae subsp. equisimilis. The genome of kdys0611 harbors 87 genes with sequence similarity to putative virulence‐associated genes identified in other bacteria, of which 57 exhibit amino acid identity (>52%) to genes of the S. dysgalactiae subsp. equisimilis GGS124 human clinical isolate. Four putative virulence genes, emm5 (FGCSD_0256), spg_2 (FGCSD_1961), skc (FGCSD_1012), and cna (FGCSD_0159), in kdys0611 did not show significant homology with any deposited S. dysgalactiae genes. The chromosomal sequence of kdys0611 has been deposited in GenBank under Accession No. AP018726. This is the first report of the complete genome sequence of S. dysgalactiae isolated from fish. [ABSTRACT FROM AUTHOR]