Fishes

17 pages, 3157 KiB

Open AccessArticle

Isolation, Characterization, and Assessment of Probiotic Lactococcus lactis from the Intestinal Tract of Largemouth Bass (Micropterus salmoides)

by Xiaoyu Chen, Jiaonan Zhang, Jiaolin Zhang, Wenzheng Zou and Qingpi Yan

Fishes 2025, 10(6), 291; https://doi.org/10.3390/fishes10060291 - 16 Jun 2025

Abstract

The health benefits associated with microbial species inhabiting aquatic animals have garnered increasing attention, as it is expected that the colonization and efficacy of native probiotic bacteria adapted to the internal environment of the target species will be more active than non-native bacteria. [...] Read more.

The health benefits associated with microbial species inhabiting aquatic animals have garnered increasing attention, as it is expected that the colonization and efficacy of native probiotic bacteria adapted to the internal environment of the target species will be more active than non-native bacteria. In this study, six isolates were obtained from the intestinal tract of largemouth bass. Three of these isolates demonstrated higher growth ability compared to the others and were further characterized using in vitro assays. Lactococcus lactis LBM15 was found to exhibit antibacterial activity against common pathogens affecting largemouth bass; the adhesion inhibition capabilities of the isolates were systematically evaluated through competitive, repulsive, and substitutive adhesion assays. The strain inhibited adhesion to all six tested pathogen strains, with competitive adhesion inhibition rates ranging from 42% to 54%, the highest of which was observed against V. anguillarum. Repulsive adhesion inhibition rates ranged from 27% to 55%, with the highest rate noted for Edwardsiella tarda. Additionally, substitutive adhesion inhibition rates were found to range from 48% to 76%, with the highest inhibition observed against Aeromonas hydrophila. Furthermore, LBM15 exhibited favorable antimicrobial susceptibility profiles, showing sensitivity to 21 antibiotics tested. Notably, safety assessment trials were performed exposing fish to LBM15 at a concentration of 1 × 10⁹ CFU/mL by injection and at a concentration of 1 × 10⁸ CFU/mL by feed administration. No clinical abnormalities, behavioral alterations, or mortality were documented in either exposure group, confirming the safety of LBM15 for application in aquaculture. The results suggested that LBM15 isolates from largemouth bass have potential for further investigation and possible application as probiotic candidates. Full article

(This article belongs to the Section Welfare, Health and Disease)

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21 pages, 2253 KiB

Open AccessArticle

Enhancing African Catfish (Clarias gariepinus) Aquaculture in Uganda: Insights into Hatchery Propagation, Population Suitability, and Broodstock Management

by Gerald Kwikiriza, Sylvie Muwanga Tebitendwa, Philip Rwezawula, Waiswa Wilson Mwanja, Ivan Abaho and Harald Meimberg

Fishes 2025, 10(6), 290; https://doi.org/10.3390/fishes10060290 - 14 Jun 2025

Abstract

The African catfish, Clarias gariepinus, is among the most farmed fish species in Uganda’s rapidly growing aquaculture sub-sector. The enhanced growth performance, increased survival, and resilience to environmental stressors have driven a rising demand among farmers for improved African catfish broodstock and [...] Read more.

The African catfish, Clarias gariepinus, is among the most farmed fish species in Uganda’s rapidly growing aquaculture sub-sector. The enhanced growth performance, increased survival, and resilience to environmental stressors have driven a rising demand among farmers for improved African catfish broodstock and seed. Until recently, most studies of this species have focused on nutrition, physiology, and culture systems, with little known about the genetics, broodstock, and hatchery management of the cultured C. gariepinus populations. This knowledge gap has led to inbreeding depression, resulting in poor seed quality and reduced performance of the broodstock. To enhance catfish aquaculture production, a survey was conducted across multiple catfish hatcheries and farms in Uganda. Using semi-structured questionnaires, the study assessed broodstock management practices, hatchery propagation methods, the suitability of various populations, demographics, challenges, and prospects of hatchery operators. Responses were coded, and descriptive statistics such as frequency, percentages, and means were calculated. Results indicate that there are farmers who continue to source their broodstocks from the natural water bodies in addition to acquiring them from fellow farmers. The estimated effective population size (Ne) for the majority of the respondents was 133.33 and 178.22, with an average breeding coefficient of 0.4% and 0.3%, respectively. There is also a continuous use of shooters (fast-growing cannibalistic fish) by the farmers who hatch and select them to be used as broodstocks later, under the assumption that they have superior genetic traits. The reported hatchability rate was above 70%, with an average survival rate of 60% from larvae to fry. The study identified diseases, inadequate water supply, and electricity as the primary challenges for catfish breeding. While Uganda’s African catfish aquaculture industry is expanding rapidly, certain hatchery practices pose significant risks to its sustainability if not properly addressed. Full article

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13 pages, 2485 KiB

Open AccessArticle

Analysis of Peroxiredoxin 5 (SmPrx5) Function and Expression in Immune and Oxidative Stress Responses of Sepiella maindroni

by Chu Shao, Weiwei Song and Chunlin Wang

Fishes 2025, 10(6), 289; https://doi.org/10.3390/fishes10060289 - 13 Jun 2025

Abstract

In this study, we investigated the functional role of Peroxiredoxin 5 (SmPrx5) in the cuttlefish Sepiella maindroni. The full-length SmPrx5 cDNA is 934 base pairs (bp) in length, comprising a 31 bp 5′ untranslated region (UTR), a 330 bp 3′ [...] Read more.

In this study, we investigated the functional role of Peroxiredoxin 5 (SmPrx5) in the cuttlefish Sepiella maindroni. The full-length SmPrx5 cDNA is 934 base pairs (bp) in length, comprising a 31 bp 5′ untranslated region (UTR), a 330 bp 3′ UTR, and an open reading frame (ORF) of 573 bp that encodes a polypeptide consisting of 190 amino acids. Sequence analysis revealed the presence of a conserved peroxidase catalytic motif VPGAFTPGCSQTHLPG and the signature domain DGTGLTCSL, indicating that SmPrx5 belongs to the 2-Cys Prx subfamily. Quantitative real-time PCR (RT-qPCR) analysis demonstrated that SmPrx5 is broadly expressed across various tissues in S. maindroni, with particularly high expression levels observed in the testes, hemocytes, liver, and ovaries. Upon challenge with Vibrio alginolyticus, SmPrx5 expression was significantly upregulated in both the liver and hemocytes, peaking at 24 h post-infection and gradually returning to baseline levels within 48 h. Furthermore, the recombinant SmPrx5 protein exhibited notable antioxidant activity in vitro, suggesting its involvement in the oxidative stress response. These findings enhance our understanding of the molecular mechanisms underlying immune defense in marine cephalopods and highlight the potential role of Prx5 in host immunity. Full article

(This article belongs to the Section Genetics and Biotechnology)

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13 pages, 2529 KiB

Open AccessArticle

Cryopreservation of Ovarian Tissue at the Stage of Vitellogenesis from Yellow Drum (Nibea albiflora) and Its Effects on Cell Viability and Germ Cell-Specific Gene Expression

by Li Zhou, Feiyan Li, Zhaohan Sun, Jia Chen and Kunhuang Han

Fishes 2025, 10(6), 288; https://doi.org/10.3390/fishes10060288 - 12 Jun 2025

Abstract

The cryopreservation of ovarian tissues from fish has recently been carried out for several endangered and commercially valuable species. However, previous studies in this context have focused on the cryopreservation of immature ovaries—mainly through slow freezing and vitrification—which requires specialized freezing equipment or [...] Read more.

The cryopreservation of ovarian tissues from fish has recently been carried out for several endangered and commercially valuable species. However, previous studies in this context have focused on the cryopreservation of immature ovaries—mainly through slow freezing and vitrification—which requires specialized freezing equipment or higher cryoprotectant concentrations to keep cell viability. Therefore, the aim of this study was to explore a convenient, rapid, efficient and less toxic method for the cryopreservation of ovaries at the stage of vitellogenesis from yellow drum (Nibea albiflora), an economically important marine fish. The ovaries at the stage of vitellogenesis were isolated and cut into blocks of approximately 1 cm³, then cryopreserved with 15% propylene glycol (PG), fetal bovine serum (FBS) and 0.2 M trehalose as cryoprotectants. Finally, the samples were treated using three different freezing procedures, including a −80 °C refrigerator, liquid nitrogen, and their combination. After 7 days, the tissues were thawed and digested, and the cell survival rates and gene expression levels were detected using cell viability assay kits and qRT-PCR, respectively. The results of the viability assay showed that the procedure of ovarian tissue storage at −80 °C in a refrigerator for 1 h, followed by transfer to liquid nitrogen, resulted in the highest cell survival rate (>90%). Furthermore, the germ cells at various phases were of normal size; presented a full, smooth surface and regular shape; and did not show any signs of cell rupture, atrophy, depression, granulation or cavitation. Furthermore, the qRT-PCR results revealed that genes related to reproductive development, such as vasa, foxl2, zp3 and gsdf, were all down-regulated under the optimal protocol, while the expression of the nanos2 gene (which is specifically distributed in oogonia) maintained a higher level, similar to that in the control group. This indicated that the viability of germ stem cells (oogonia) was not weakened after freezing and that oogonia could be isolated from the cryopreserved ovaries for germ cell transplantation. The present study successfully establishes an optimal cryopreservation protocol for ovarian tissues from Nibea albiflora, providing reference for the preservation of ovaries at the stage of vitellogenesis from other species. Full article

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19 pages, 2747 KiB

Open AccessArticle

Assessing Thermal Stress in Silver Barb (Barbonymus gonionotus): Oxidative Stress and Biochemical, Hematological, Hormonal, and Operculum Responses Within Survival Temperature Range

by Kanokporn Saenphet, Supap Saenphet, Nathamon Tanasrivaroottanun, Phanit Srisuttha, Wikit Phinrub, Dutrudi Panprommin and Paiboon Panase

Fishes 2025, 10(6), 287; https://doi.org/10.3390/fishes10060287 - 11 Jun 2025

Abstract

This study investigates the biochemical and physiological responses of the economically important fish Barbonymus gonionotus to acute temperature fluctuations. Focusing on malondialdehyde (MDA) levels in serum and visceral organs, serum biochemical indices, hematological parameters, cortisol levels, and operculum movement, this research assessed the [...] Read more.

This study investigates the biochemical and physiological responses of the economically important fish Barbonymus gonionotus to acute temperature fluctuations. Focusing on malondialdehyde (MDA) levels in serum and visceral organs, serum biochemical indices, hematological parameters, cortisol levels, and operculum movement, this research assessed the impacts of thermal stress. Experimental conditions involved two thermal regimes: heat shock at 25–29 °C and 25–37 °C; as well as cold shock at 25–21 °C and 25–13 °C sustained over 24 (D1), 48 (D2), and 72 (D3) h. Serum MDA levels increased significantly. Notably, MDA in the gills, brain, and liver fluctuated under cold stress, particularly at 13 °C. Serum parameters showed significant alterations except for AST, total protein, and cholesterol, which remained unaffected by heat shock. Red blood cell (RBC) counts dropped to their lowest at 13 °C, while white blood cell (WBC) counts diminished significantly when temperatures dropped to 21 °C and then stabilized. Cortisol surged with temperature changes, peaking at 13 °C and 29 °C for cold and heat shock, respectively. Operculum movement was inversely affected by thermal changes, decreasing with cold and increasing with heat. These findings underscore the sensitivity of silver barb to thermal extremes, providing insights for optimized aquaculture management and enhanced resilience to environmental stressors. Full article

(This article belongs to the Section Physiology and Biochemistry)

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12 pages, 655 KiB

Open AccessArticle

Short-Term Anesthesia with Clove Oil and Propofol: Physiological Responses in Persian Sturgeon (Acipenser persicus)

by Milad Adel, Seyed Pezhman Hosseini Shekarabi, Piotr Gomułka, Alireza Babaalian Amiri, Cristiana Roberta Multisanti and Caterina Faggio

Fishes 2025, 10(6), 286; https://doi.org/10.3390/fishes10060286 - 11 Jun 2025

Abstract

Anesthesia is commonly used in sturgeon aquaculture to reduce stress and pain during handling and procedures. This study compared the effects of clove oil (rich in eugenol) and propofol—an anesthetic widely used in human and veterinary medicine—on Persian sturgeon (Acipenser persicus) [...] Read more.

Anesthesia is commonly used in sturgeon aquaculture to reduce stress and pain during handling and procedures. This study compared the effects of clove oil (rich in eugenol) and propofol—an anesthetic widely used in human and veterinary medicine—on Persian sturgeon (Acipenser persicus) fingerlings. A total of 405 fish (6.88 ± 0.90 g) were exposed to varying concentrations of clove oil (25, 50, 75, 100 mg L⁻¹), propofol (10.0, 12.5, 25.0, 50 mg L⁻¹), or no anesthetic (control) in triplicate. Hematocrit and monocyte levels remained unchanged across treatments, but the highest doses of both anesthetics significantly reduced leukocyte percentages (p = 0.049 and p = 0.043, respectively). While serum enzymes were stable, cortisol levels increased significantly at the highest concentrations of both clove oil (38.92 ± 5.1 ng mL⁻¹; p = 0.001) and propofol (36.48 ± 3.4 ng mL⁻¹; p = 0.035), indicating secondary stress responses. Propofol at 25 mg L⁻¹ showed fast induction and recovery times and induced milder stress compared to clove oil. Overall, short-term anesthesia with both agents triggered physiological stress, but propofol at 25 mg L⁻¹ appeared more suitable for minimizing adverse effects in Persian sturgeon fingerlings. Full article

(This article belongs to the Special Issue Use of Essential Oils in Aquaculture)

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20 pages, 2779 KiB

Open AccessArticle

Bioactive Substance Derived from Mealworm Larvae (Tenebrio molitor) Potentially Induces Immune Performance of Zebrafish (Danio rerio)

by Ibnu Bangkit Bioshina Suryadi, Muhammad Fariz Zahir Ali, Haruki Nishiguchi, Saita Akanuma, Chiemi Miura and Takeshi Miura

Fishes 2025, 10(6), 285; https://doi.org/10.3390/fishes10060285 - 10 Jun 2025

Abstract

Mealworm (Tenebrio molitor) larvae meal is a notable alternative protein source that is widely used in the aquaculture industry. Recently, it has also gained recognition for enhancing the immune performance of various aquaculture species. However, studies identifying the specific bioactive substances [...] Read more.

Mealworm (Tenebrio molitor) larvae meal is a notable alternative protein source that is widely used in the aquaculture industry. Recently, it has also gained recognition for enhancing the immune performance of various aquaculture species. However, studies identifying the specific bioactive substances responsible for the immunomodulatory effects of mealworm larvae meal remain limited. In this study, we isolated and purified a bioactive substance from mealworm and incorporated it into zebrafish (Danio rerio) diets at concentrations of 0, 10, and 100 µg/g; the zebrafish were fed this diet for 14 days. To assess the transcriptional changes induced by the bioactive substance, we performed RNA sequencing and qRT-PCR analysis on intestinal and liver tissues. Subsequently, zebrafish were challenged with Edwardsiella tarda via immersion in order to evaluate the protective effects of the bioactive substance. The results demonstrated that a dietary inclusion of 100 µg/g of the bioactive substance optimized the immune performance of zebrafish. Additionally, challenge tests revealed that the dietary inclusion of the bioactive substance from mealworms positively influenced pathogen resistance, although these effects were not consistently significant. Full article

(This article belongs to the Section Sustainable Aquaculture)

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14 pages, 1779 KiB

Open AccessArticle

Dietary Incorporation of Natural and Synthetic Reproductive Inhibitors: Exploring Their Impact on Sex Characteristics in Cyprinus carpio (Common Carp)

by Rafia Jamal, Farkhanda Asad, Shabana Naz and Syed Makhdoom Hussain

Fishes 2025, 10(6), 284; https://doi.org/10.3390/fishes10060284 - 9 Jun 2025

Abstract

The present study was designed to evaluate the effect of supplementation with papaya seeds (PSM), fish testes powder (FTP), and 17α-methyltestosterone (MT) on the reproductive parameters, growth performance, digestive enzymes, and histology of Cyprinus carpio. In the present study, fries (2–3 days [...] Read more.

The present study was designed to evaluate the effect of supplementation with papaya seeds (PSM), fish testes powder (FTP), and 17α-methyltestosterone (MT) on the reproductive parameters, growth performance, digestive enzymes, and histology of Cyprinus carpio. In the present study, fries (2–3 days old) were acclimatized for 2 days and then equally distributed into one control and six treatment groups and fed with one control and six experimental diets for 30 days, followed by a control diet for 60 days in each group with triplicates. These diets included control (T0), different levels of 17α-methyltestosterone (T1: 60 mg/kg; T2: 70 mg/kg), papaya seed powder (T3: 6 g/kg; T4: 7 g/kg), and fish (tilapia) testes powder (T5: 70%; T6: 80%). The treatment groups receiving papaya seed meal (PSM) showed significant improvements in growth performance, with a significant increase in final body weight. The best zootechnical performances (PER, SGR, and CF) were observed in fish fed with papaya seed compared to the control group. Reproductive analysis showed significant variations between treatment groups, with a large number of female C. carpio observed in the control group. Fish treated with T4 increased the sex percentage in favor of male fish by achieving 90% male phenotype followed by T6 with 88% male. Diets based on papaya seeds and fish testes powder significantly reduced the reproductive performance by reducing GSI, which affected the gonadal histology. The results revealed a visible effect of 17 α-MT and PSM feeding on the gonad structure. There were significant elevations in protease enzyme activity in T6 compared to the control (p < 0.05), and the highest amylase activity was observed in T3. Natural resources are not only more cost-effective but also environmentally friendly and readily available; they are a superior choice over synthetic alternatives for controlling the prolific breeding of C. carpio. Full article

(This article belongs to the Section Sustainable Aquaculture)

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21 pages, 10694 KiB

Open AccessArticle

Fecundity Study and Histological Analysis of the Gonads of the Sea Cucumber Holothuria tubulosa (Echinodermata: Holothuroidea) in the Central Aegean Sea, Greece: Insights into Reproductive Biology

by Athina Balatsou, Chrysoula Apostologamvrou and Dimitris Vafidis

Fishes 2025, 10(6), 283; https://doi.org/10.3390/fishes10060283 - 8 Jun 2025

Abstract

The Atlanto-Mediterranean sea cucumber Holothuria tubulosa is a species of great ecological and commercial importance, making it a primary target for collection in the Mediterranean region. This study investigated the reproductive biology of H. tubulosa (Gmelin, 1793) in a coastal area of the [...] Read more.

The Atlanto-Mediterranean sea cucumber Holothuria tubulosa is a species of great ecological and commercial importance, making it a primary target for collection in the Mediterranean region. This study investigated the reproductive biology of H. tubulosa (Gmelin, 1793) in a coastal area of the Central Aegean Sea (Eastern Mediterranean) over a one-year period, from June 2021 to May 2022. Monthly sampling was conducted via dives at depths up to 10 m, alongside the recording of environmental and biometric data. Histological analysis revealed a synchronous annual reproductive cycle, with gonadal maturation beginning in April and peak sexual maturity observed in July and August, followed by a single spawning event from August to September. The sex ratio was 1:1.31 (male: female), and the size at first maturity was 255.3 mm. These findings provide essential insights into the reproductive physiology of H. tubulosa and further contribute to the development of sustainable stock management strategies for sea cucumbers in the Hellenic Seas. Full article

(This article belongs to the Section Biology and Ecology)

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16 pages, 1656 KiB

Open AccessArticle

Effect of the Inclusion of Natural Pigments on the Performance and Gene Expression of Immune Response and Oxidative Stress of Oreochromis niloticus Cultured in a Biofloc System

by Andres Elias Castro-Castellon, Maria del Carmen Monroy-Dosta, Aida Hamdan-Partida, Martha Patricia Hernandez-Vergara, Jorge Castro-Mejía, German Castro-Mejia, Arnulfo Misael Martinez-Meingüer and José Antonio Mata-Sotres

Fishes 2025, 10(6), 282; https://doi.org/10.3390/fishes10060282 - 8 Jun 2025

Abstract

Tilapia (Oreochromis niloticus) is one of the most important species in aquaculture, so the optimization of its culture by using sustainable strategies is fundamental. The aim of this study was to evaluate the effects of incorporating natural pigments (carrot and beetroot [...] Read more.

Tilapia (Oreochromis niloticus) is one of the most important species in aquaculture, so the optimization of its culture by using sustainable strategies is fundamental. The aim of this study was to evaluate the effects of incorporating natural pigments (carrot and beetroot meal) as carbon sources in a biofloc system on the growth, immune response, and oxidative stress of O. niloticus. The experiment comprised four treatments: clear water as control (CT), biofloc with molasses (TBM), biofloc with carrot meal (TBC), and biofloc with beetroot meal (TBB). Results showed that biofloc helped to maintain optimal water quality and high survival rates, but specifically, TBC treatment achieved the highest growth rates and feed conversion ratio, along with elevated leukocyte counts, indicating improved health and immunity. Gene expression analysis revealed enhanced antioxidant activity (sod, gpx) and modulated immune responses (tnf-α, il-1β), particularly under thermal stress. Carrot meal emerged as an effective carbon source in biofloc systems, promoting growth, immune resilience, and oxidative stress resistance in tilapia, while beetroot meal improved pigmentation. These findings highlight the potential of natural pigments to enhance aquaculture sustainability and productivity. Full article

(This article belongs to the Special Issue Fish Hematology)

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19 pages, 2120 KiB

Open AccessArticle

Richness and Distribution of Mexican Pacific Cephalopods (Mollusca, Cephalopoda)

by Brian Urbano and Denise Arroyo-Lambaer

Fishes 2025, 10(6), 281; https://doi.org/10.3390/fishes10060281 - 7 Jun 2025

Abstract

Cephalopods have been widely studied around the globe. However, some areas are poorly understood. In Mexico, there is a significant lack of knowledge, particularly in the coastal zone of the eastern Pacific Ocean, where most studies have focused on commercial fisheries. An exhaustive [...] Read more.

Cephalopods have been widely studied around the globe. However, some areas are poorly understood. In Mexico, there is a significant lack of knowledge, particularly in the coastal zone of the eastern Pacific Ocean, where most studies have focused on commercial fisheries. An exhaustive review of documents (articles, books, theses, and regional reports) dealing with the cephalopods of the eastern Pacific in general and of Pacific Mexico in particular was undertaken along with an examination of malacological collections and databases available in Mexico and the USA. As a result, we obtained 3752 records corresponding to 3339 taxonomic records, featuring two superorders, six orders, 29 families, 60 genera, and 105 species. Of these, 89 species occurring in Mexican waters were confirmed, 76% pelagic, 21% in strictly benthic habitats, 2% benthopelagic, and 1% corresponding to demersal species. We proposed a modification for the distribution of 21 species and found 10 new records for Mexican waters. Full article

(This article belongs to the Section Taxonomy, Evolution, and Biogeography)

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14 pages, 862 KiB

Open AccessArticle

Quinolone Resistance and Prevalence of the Related Genes in Photobacterium damselae subsp. damselae Recovered from Diseased Fish in Eastern China

by Xiangyun Yang, Chen Shen, Suming Zhou, Liyun Jin, Yajun Wang and Fei Yin

Fishes 2025, 10(6), 280; https://doi.org/10.3390/fishes10060280 - 7 Jun 2025

Abstract

Photobacterium damselae subsp. damselae is a well-recognized marine animal pathogen. Herein, 70 P. damselae subsp. damselae isolates were investigated for quinolone susceptibility and prevalence of the genes including quinolone resistance-determining regions (QRDRs) and plasmid-mediated quinolone resistance (PMQR) genes. A total of 18/70 isolates [...] Read more.

Photobacterium damselae subsp. damselae is a well-recognized marine animal pathogen. Herein, 70 P. damselae subsp. damselae isolates were investigated for quinolone susceptibility and prevalence of the genes including quinolone resistance-determining regions (QRDRs) and plasmid-mediated quinolone resistance (PMQR) genes. A total of 18/70 isolates exhibited high-level resistance, and 23/70 isolates exhibited moderate resistance according to the MIC values. QRDR analysis showed that double mutants in both GyrA (Ser⁸³Ile) and ParC (6/17 Ser⁸⁰Phe or 11/17 Ser⁸⁰Tyr) were detected in 94.4% (17/18) high-level quinolone resistance P. damselae subsp. damselae strains. PMQR detection showed that 60.0% (42/70) carried at least one PMQR (1/42 qnrB coexistence with aac(6′)-Ib-cr, 1/42 qnrS coexistence with aac(6′)-Ib-cr, 44/46 qnrS). QnrA, QnrC, qnrD and qepA were not detected in all strains. Among the 42 PMQR-positive strains, 24 showed fluoroquinolones MICs ≤ 0.5 mg/L and 13 MICs ≥ 2 mg/L, all carrying QRDR mutations. For the twenty-eight non-PMQR strains, twenty-three showed fluoroquinolone MICs ≤ 0.5 mg/L without QRDR mutations, and five MICs ≥ 2 mg/L carrying QRDR mutations. In conclusion, qnrS (qnrS2 allele) is the major PMQR widespread in P. damselae subsp. damselae isolated from eastern China; however, QRDR mutation plays a marked role in mediating fluoroquinolone resistance. Full article

(This article belongs to the Section Fish Pathology and Parasitology)

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14 pages, 2423 KiB

Open AccessArticle

Assessing Fish Diversity in the Chishui River Using Environmental DNA (eDNA) Metabarcoding

by Jing Gao, Jing Zhang, Chengrong Pan, Sheng Xu, Yajie Wu, Wei Lv, Min Hong, Yuxin Hu and Yingru Wang

Fishes 2025, 10(6), 279; https://doi.org/10.3390/fishes10060279 - 7 Jun 2025

Abstract

Since 2017, a fishing ban in the Chishui River (China) has reduced human disturbances, yet the early-stage recovery of fish resources remains unquantified. Here, we applied environmental DNA (eDNA) metabarcoding to assess fish diversity and restoration status across its upper, middle, and lower [...] Read more.

Since 2017, a fishing ban in the Chishui River (China) has reduced human disturbances, yet the early-stage recovery of fish resources remains unquantified. Here, we applied environmental DNA (eDNA) metabarcoding to assess fish diversity and restoration status across its upper, middle, and lower reaches. An analysis of operational taxonomic units (OTUs) revealed higher unique than shared OTUs among reaches, indicating significant spatial partitioning of fish communities. The upper reaches exhibited the highest diversity due to reduced human activity, attributed to greater species richness, while the middle and lower reaches showed similar community structures. Key findings include the following: (1) the detection of rare endemic species (Schizothorax) and non-native Oreochromis DNA, suggesting invasion risks; (2) the investigation revealed a predominance of small-bodied fish species, indicating that large-bodied fish populations in the Chishui River (China) remained relatively scarce; (3) the recovery of demersal fish DNA from surface waters, confirming eDNA’s broad detection capacity. The results indicate that the fishing ban has contributed to the partial recovery of the fish community in the Chishui River (China). However, risks of biological invasion (e.g., Oreochromis species) remain, and large-bodied fish are still relatively scarce. To ensure effective conservation, it is critical to strengthen the monitoring and evaluation of the fishing ban’s effectiveness and implement timely measures to prevent invasive species proliferation. Full article

(This article belongs to the Section Genetics and Biotechnology)

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13 pages, 1348 KiB

Open AccessArticle

Morphometric, Nutritional, and Blood Analyses in Hybrid Striped Bass (Morone chrysops x Morone saxatilis, Walbaum 1972) Reared in a Recirculating Aquaculture System (RAS) Implant in Sicily, Italy

by Francesca Aragona, Syed Sikandar Habib, Francesco Fazio, Alessandro Zumbo, Antonino Costa, Kristian Riolo, Alessia Giannetto and Vincenzo Parrino

Fishes 2025, 10(6), 278; https://doi.org/10.3390/fishes10060278 - 6 Jun 2025

Abstract

Hybrid striped bass (HSB), a cross between white bass (Morone chrysops) and striped bass (Morone saxatilis), has garnered attention in aquaculture due to its adaptability, rapid growth, and high market value. This study investigates the morphometric, nutritional, and blood [...] Read more.

Hybrid striped bass (HSB), a cross between white bass (Morone chrysops) and striped bass (Morone saxatilis), has garnered attention in aquaculture due to its adaptability, rapid growth, and high market value. This study investigates the morphometric, nutritional, and blood characteristics of HSB reared in a recirculating aquaculture system (RAS) in Sicily, Italy, over a 22-month grow-out period. The fish were managed under standardized feeding and water quality protocols, with weekly monitoring of the physicochemical parameters. A total of 21 clinically healthy fish, averaging 571.33 ± 129.32 in body weight, were randomly sampled in the spring season from a commercial RAS facility equipped with biological filtration, UV sterilization, and seasonally regulated water parameters. The results revealed strong positive correlations between the morphometric parameters and blood indices, such as red blood cell (RBC) count, hemoglobin (Hb) levels, and hematocrit (Hct), highlighting their importance as health indicators. The proximate composition revealed an average moisture content of 75.55 ± 1.49, crude protein at 20.29 ± 0.26, total lipid at 4.25 ± 0.97, and ash content at 1.69 ± 0.17. Additionally, statistical analyses, including a principal component analysis (PCA), identified relationships between body size, nutritional content, and blood parameters, emphasizing the role of body size in influencing nutritional and health outcomes. The findings of this study are crucial for optimizing farming protocols and improving the health and productivity of HSB in RAS under Mediterranean conditions. Full article

(This article belongs to the Special Issue Fish Hematology)

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19 pages, 2384 KiB

Open AccessArticle

Effects of Dietary ARA/EPA Ratio on Growth Performance, Antioxidant Capacity and Lipid Metabolism-Related Genes of Juvenile Fat Greenling (Hexagrammos otakii)

by Fengzhi Lu, Yafeng Guo, Dandan Cui, Wenyuan Hua, Shuai Wang, Lei Peng, Yan Chen, Jian Han and Wei Wang

Fishes 2025, 10(6), 277; https://doi.org/10.3390/fishes10060277 - 6 Jun 2025

Abstract

Essential fatty acids are extremely important nutrients in the diet of fish, and the balance between arachidonic acid (ARA) and eicosapentaenoic acid (EPA) is crucial for the healthy growth of fish. Six isonitrogenous and isolipidic basal diets were given to 540 juvenile fat [...] Read more.

Essential fatty acids are extremely important nutrients in the diet of fish, and the balance between arachidonic acid (ARA) and eicosapentaenoic acid (EPA) is crucial for the healthy growth of fish. Six isonitrogenous and isolipidic basal diets were given to 540 juvenile fat greenling (Hexagrammos otakii) (31.4 ± 1.5 g) for 8 weeks to investigate the effects of dietary ARA/EPA ratio on growth performance, antioxidant capacity and lipid metabolism-related genes of juvenile H. otakii. The control group (A) had 7% fish oil added as the main fat source, while the experimental groups had 4% fish oil as the basic fat source, with varying proportions of ARA and EPA concentrates added to formulate five diets with varying ARA/EPA ratios (B 2.66; C 1.34; D 1.01; E 0.47; F 0.19). The experimental results revealed that adding ARA and EPA to the diet increased the percent weight gain (PWG) and feed conversion ratio (FCR) of juvenile H. otakii, and the PWG and FCR were greatest under Group E dietary conditions. The specific activities (U/mg protein) of superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (T-AOC) in the liver, as well as serum SOD and CAT were significantly higher in Groups D and E than those in other groups (p < 0.05). Malondialdehyde (MDA, nmol/g protein) content in the liver and serum was significantly lower in Group E than that in other groups (p < 0.05). Moreover, groups D and E exhibited significant increases in the specific activities (U/mg protein) of intestinal trypsin, lipase, and amylase, as well as in the intestinal villus length (p < 0.05). The incorporation of ARA and EPA into the feed reduced the expression levels of fat synthesis genes such as fas, scd1, accα, and srebp1, as well as the expression of lipolysis genes atgl and hsl. However, it also increased the expression of the lipolytic genes cpt1 and ppara. The ARA/EPA ratios in the dietary were 0.47 and 1.01, respectively, which are appropriate for enhancing growth efficiency, antioxidant enzyme activity, intestinal digestive enzyme activity and lipid metabolism regulation. Full article

(This article belongs to the Section Nutrition and Feeding)

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18 pages, 2242 KiB

Open AccessArticle

Catch Losses and Reduction of Bycatch for Jellyfish Using Marine Mammal Bycatch Reduction Devices in Midwater Trawl Gear

by Jung-Mo Jung, Hyun-Young Kim, Bong-Jin Cha, Sung-Jae Kim, Tae-Suk Kim, Gyeong-Cheol Hyun and Kyu-Suk Choi

Fishes 2025, 10(6), 276; https://doi.org/10.3390/fishes10060276 - 6 Jun 2025

Abstract

The National Institute of Fisheries Science in Korea is developing marine mammal bycatch reduction devices (BRDs) for midwater trawl gear. In this study, we tested two BRD-type guide nets (inclined net panel) with 30° and 45° tilt angles to prevent marine mammals from [...] Read more.

The National Institute of Fisheries Science in Korea is developing marine mammal bycatch reduction devices (BRDs) for midwater trawl gear. In this study, we tested two BRD-type guide nets (inclined net panel) with 30° and 45° tilt angles to prevent marine mammals from reaching the codend and facilitating their escape from the net. Fishing operations were conducted along the east and south coasts of South Korea, and cameras were installed in front of the BRDs to monitor their performance. The catch loss of herring with the 30° guide net was 13% and 11% in number and weight. The catch loss of hairtail was 53% and 51% in number and weight with the 30° guide net. Mackerel showed a 97% catch loss in number and weight with the 45° guide net. The 30° guide net resulted in lower catch loss for rudderfish and jack mackerel compared to the 45° guide net. The jellyfish discard rate of the BRD was 5% and 7% in number and weight with the 30° guide net and 12% and 11% with the 45° guide net, indicating that the 30° guide net was more effective at discarding jellyfish. Mesh selectivity was not strongly related to target species body length. Full article

(This article belongs to the Special Issue Sustainable Fisheries Dynamics)

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13 pages, 686 KiB

Open AccessArticle

Mercury and Selenium Trophic Transfer in the Mexican California Current Ecosystem Using a Top Predator as a Model

by Maria Emilia Rechimont, Felipe Amezcua, Jorge Ricardo Ruelas-Inzunza, Roberto Cruz-Garcìa, Juan Roberto Felipe Vallarta-Zárate and Felipe Amezcua-Linares

Fishes 2025, 10(6), 275; https://doi.org/10.3390/fishes10060275 - 5 Jun 2025

Abstract

Research on the trophic transfer of trace elements in food chains, particularly toxic elements like mercury (Hg) and essential elements like selenium (Se), is crucial for understanding their impact on human health. In this work, we assessed the transfer of Hg and Se [...] Read more.

Research on the trophic transfer of trace elements in food chains, particularly toxic elements like mercury (Hg) and essential elements like selenium (Se), is crucial for understanding their impact on human health. In this work, we assessed the transfer of Hg and Se in the blue shark (Prionace glauca), a top predator with economic importance. Muscle samples from sharks, as well as their main prey (squid, red shrimp, sardine, and mackerel), were analyzed for Hg and Se concentrations. The Hg levels of sharks were below the recommended legal limit for seafood consumption in Mexico (1 µg·g⁻¹ ww), while Se levels were significantly lower than previously reported for the species. Biomagnification was evaluated in this species by calculating biomagnification factors (BMF) for Hg and Se based on predator-prey element concentrations. Hg showed a BMF of 2.8, indicating biomagnification, while Se had a BMF of 0.2, suggesting biodilution. Trophic transfer factor models supported these findings, showing a positive correlation of Hg concentration with trophic level and a negative correlation with Se. However, while a hazard quotient under one does not pose a risk for consumption, a Se:Hg molar ratio under one estimated in the muscle tissue indicates that Hg levels along this food web should be approached with caution. Full article

(This article belongs to the Section Environment and Climate Change)

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14 pages, 3101 KiB

Open AccessArticle

A Hydroacoustic Assessment of the Density, Size, and Biomass of Fish in a Freshwater Reservoir After Non-Classical Biomanipulation

by Aihuan Guo, Qingping Lian, Pengcheng Sheng, Aiju Zhang, Julin Yuan and Kohji Iida

Fishes 2025, 10(6), 274; https://doi.org/10.3390/fishes10060274 - 5 Jun 2025

Abstract

Monitoring changes in fishery resources, such as the density and growth of fish, following large-scale fish stocking in a reservoir is important. In this study, BioSonics DT-X (201 kHz) was used to assess the seasonal changes in the density, size distribution, and biomass [...] Read more.

Monitoring changes in fishery resources, such as the density and growth of fish, following large-scale fish stocking in a reservoir is important. In this study, BioSonics DT-X (201 kHz) was used to assess the seasonal changes in the density, size distribution, and biomass of fish in Duihekou Reservoir, Zhejiang province, China, in 2020. The fish density was significantly lower in spring (3.33 ind./1000 m³) than in summer (75.24 ind./1000 m³), autumn (56.22 ind./1000 m³), and winter (20.37 ind./1000 m³) (p < 0.01). No significant difference in fish density was apparent between summer and autumn. Additionally, the average target strength (TS) values in spring (−41.05 dB) were significantly higher than in summer (−44.66 dB) and autumn (−45.55 dB) (p < 0.01), but significantly higher in winter (−38.12 dB) than in the other seasons (p < 0.01); no significant difference was observed between the summer and autumn values (p > 0.01). The fish biomass in winter (14.3 g/m³) was 13 times that in spring (1.1 g/m³). These results indicate that large-scale fish stocking can effectively adapt to reservoir habitats to achieve growth. The catch composition revealed silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) to be dominant species, mostly comprising young individuals. Stock enhancement plays a critical role in reshaping the fishery population structure in a reservoir. These findings enhance our understanding of fishery resource changes in reservoirs after non-classical biomanipulation and demonstrate how hydroacoustic techniques can be successfully used to quantify the density and size distribution of fish for more effective fishery management. Full article

(This article belongs to the Section Fishery Economics, Policy, and Management)

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19 pages, 3025 KiB

Open AccessArticle

Modelling the Spatial Distribution of Dosidicus gigas in the Southeast Pacific Ocean at Multiple Temporal Scales Based on Deep Learning

by Mingyang Xie, Bin Liu, Xinjun Chen, Wei Yu, Jintao Wang and Jiawen Xu

Fishes 2025, 10(6), 273; https://doi.org/10.3390/fishes10060273 - 5 Jun 2025

Abstract

With the advent of the big data era in ocean remote sensing and fisheries, there is a growing demand for finer temporal scales to predict spatial distribution of the jumbo flying squid (Dosidicus gigas). This can help reduce fuel costs and [...] Read more.

With the advent of the big data era in ocean remote sensing and fisheries, there is a growing demand for finer temporal scales to predict spatial distribution of the jumbo flying squid (Dosidicus gigas). This can help reduce fuel costs and provide higher quality and faster decision-making. Therefore, this study employed a deep neural network (DNN) model, using sea surface temperature, sea surface height, sea surface salinity, and photosynthetically active radiation as input factors, with catch per unit effort as the output factor. We construct five cases with temporal scales of 3, 6, 10, 15, and 30 days using data spanning 10 years (2012–2021). Additionally, the performance of DNN was compared with those of traditional methods such as generalized additive model (GAM), extreme gradient boosting (XGBoost), and artificial neural network (ANN). The results demonstrated that the DNN model had the best performance. As the temporal scale decreased, the mean squared error and the mean absolute error increased, whereas the area under the precision−recall curve decreased, indicating a decline in model performance. The interpretability analysis indicated that spatial and temporal factors significantly contributed to the model, with longitude exhibiting the highest contribution. To improve the accuracy of finer temporal scales, future research should focus on reducing noise in the data and address the presence-only nature of fishery data, particularly by cleaning the unsampled portions. Full article

(This article belongs to the Section Fishery Facilities, Equipment, and Information Technology)

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