Fishes

14 pages, 1723 KB

Open AccessArticle

High Connectivity in the Deep-Water Pagellus bogaraveo: Phylogeographic Assessment Across Mediterranean and Atlantic Waters

by Martina Spiga, Giusy Catalano, Federica Piattoni, Alice Ferrari, Carolina Johnstone, Kenza Mokhtar-Jamaï, Montse Pérez, Fabio Fiorentino, Manuel Hidalgo and Alessia Cariani

Fishes 2025, 10(10), 527; https://doi.org/10.3390/fishes10100527 - 17 Oct 2025

Abstract

The Blackspot Seabream, Pagellus bogaraveo, is a commercially valuable species widely distributed in the northeastern Atlantic and Mediterranean. Its biology makes it vulnerable to overfishing, but its population structure and ontogenetic migration strategy remain unclear. Building on previous work based on microsatellite [...] Read more.

The Blackspot Seabream, Pagellus bogaraveo, is a commercially valuable species widely distributed in the northeastern Atlantic and Mediterranean. Its biology makes it vulnerable to overfishing, but its population structure and ontogenetic migration strategy remain unclear. Building on previous work based on microsatellite markers, we expanded the investigation by analysing the mitochondrial Control Region (CR) to complement nuclear data. We analysed 199 specimens from 13 sites and combined the new CR sequences with 129 published records to achieve the broadest coverage in terms of biogeographic and genetic data. We calculated genetic diversity and performed AMOVA, pairwise ΦST comparisons, and multivariate analyses. Eighty-eight haplotypes were identified, showing high haplotype diversity (Hd = 0.767–0.945) and moderate nucleotide diversity (π = 0.0026–0.0054). Most genetic variation occurred within populations, and overall analyses indicated genetic homogeneity. However, pairwise analysis and AMOVA confirmed significant differentiation of the Azores population. These results confirm extensive genetic connectivity throughout the Atlantic–Mediterranean range of P. bogaraveo, likely due to a combination of large larval dispersal and a common spawning migration strategy, but identify the Azores as a genetically distinct unit. This highlights the need to consider both large-scale connectivity and local divergence in fisheries management. Full article

(This article belongs to the Special Issue Conservation and Population Genetics of Fishes)

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13 pages, 1048 KB

Open AccessArticle

Comparative Critical Thermal and Salinity Maxima of a Threatened Freshwater Killifish and of the Global Invader Eastern Mosquitofish

by Yiannis Kapakos, Ioannis Leris, Nafsika Karakatsouli, Brian Zimmerman and Eleni Kalogianni

Fishes 2025, 10(10), 526; https://doi.org/10.3390/fishes10100526 - 16 Oct 2025

Abstract

Invasive fish species are a major driver of freshwater native fish biodiversity loss and their spread and impacts on the native fish are expected to increase within the current freshwater salinization and global warming crisis. In the current study, the upper thermal and [...] Read more.

Invasive fish species are a major driver of freshwater native fish biodiversity loss and their spread and impacts on the native fish are expected to increase within the current freshwater salinization and global warming crisis. In the current study, the upper thermal and salinity tolerance of the geographically range-restricted, threatened killifish Valencia robertae and its alien competitor, the globally invasive Eastern mosquitofish Gambusia holbrooki are compared in an experimental setting. Fish were exposed, after acclimation, to a continuous, dynamic temperature or salinity increase until predefined sub-lethal end points (loss of equilibrium and/or loss of buoyancy). The critical thermal and salinity maxima (CTMax and CSMax) were then calculated as the arithmetic mean of the combined thermal or salinity points at which the endpoint was attained. Finally, thermal and salinity safety margins for the two species were also calculated using abiotic data. Mosquitofish (females and males pooled) showed an average CΤmax of 35.85 °C and the killifish 36.27 °C (sexes pooled). Mosquitofish (male) showed an average CSmax of 40.25‰ and (male) killifish 42.64‰ (sexes also pooled). Killifish safety margins are much higher than those of the mosquitofish. Future impacts of global warming and salinisation on these species and on their interactions under current climate change scenarios are discussed. Full article

(This article belongs to the Section Biology and Ecology)

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15 pages, 2267 KB

Open AccessArticle

Thyroid Hormone (T3) Induces Male-like Reproductive Behavior in Female Tilapia

by Taiga Midorikawa, Ryo Kaneko, Sakura Inoue, Atsuhiro Tsutiya and Ritsuko Ohtani-Kaneko

Fishes 2025, 10(10), 525; https://doi.org/10.3390/fishes10100525 - 15 Oct 2025

Abstract

In most vertebrates, males and females display distinct reproductive behaviors. Some fish can change their sexual phenotype at various life stages, which involves alterations in their gonadal sex and changes in their reproductive behavior to align with the new gonadal identity. Although the [...] Read more.

In most vertebrates, males and females display distinct reproductive behaviors. Some fish can change their sexual phenotype at various life stages, which involves alterations in their gonadal sex and changes in their reproductive behavior to align with the new gonadal identity. Although the sex reversal phenomenon in reproductive behavior is well documented, the underlying mechanisms in the brains of these fish remain largely unknown. In the present study, we investigated the roles of the thyroid hormone (triiodothyronine (T3)) in the Mozambique tilapia as a potential regulator of male-specific nest-building behavior and gonadotropin-releasing hormone-3 (GnRH3) neurons, the regulatory neurons of male reproductive behavior, in the terminal nerve (TN) ganglion. T3 injection successfully induced nest-building behavior in mature female fish. T3 injection significantly elevated serum T3 concentrations in treated animals compared with those in controls. Through organotypic culture of brain slices that included the TN region, we demonstrated that T3 could stimulate an increase in the number of GnRH3 neurons, and the effect was inhibited by a thyroid hormone receptor (TR) inhibitor. Additionally, TRβ co-expression was observed in GnRH3 neurons. These findings highlight the crucial roles of T3 and GnRH3 in sex reversal processes within the fish brain. Full article

(This article belongs to the Special Issue Advances in Fish Reproductive Physiology)

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18 pages, 1589 KB

Open AccessArticle

Efficacy of Mango Leaf-Based Feed Additive on Growth Performance, Antioxidant Status and Digestive Enzyme Activities in Litopenaeus vannamei

by Hongjiao Cai, Haoye Zhang, Rongze Lu, Shaoyi Feng and Mao Lin

Fishes 2025, 10(10), 524; https://doi.org/10.3390/fishes10100524 - 15 Oct 2025

Abstract

Shrimp farming is one of the fastest-growing food-producing sectors worldwide. However, its rapid expansion has raised concerns about sustainability, particularly regarding the heavy reliance on antibiotics and synthetic additives. Mango leaf powder (MLP), a potential natural alternative to synthetic additives and antibiotics, was [...] Read more.

Shrimp farming is one of the fastest-growing food-producing sectors worldwide. However, its rapid expansion has raised concerns about sustainability, particularly regarding the heavy reliance on antibiotics and synthetic additives. Mango leaf powder (MLP), a potential natural alternative to synthetic additives and antibiotics, was evaluated as a dietary supplement in the aquaculture of Litopenaeus vannamei. This study aimed to assess the effects of MLP at 4% and 8% inclusion levels on shrimp growth, antioxidant status, digestive enzyme activities, and hepatopancreatic structure. A total of 540 shrimp were fed experimental diets for 42 days. Both MLP treatments significantly promoted weight gain and specific growth rate. They also enhanced antioxidant enzyme activity rates, such as superoxide dismutase, peroxidase, and catalase, and total antioxidant capacity, while decreasing malondialdehyde levels. The 8% MLP group also showed significantly increased digestive enzyme activities (amylase, trypsin, and lipase) compared to that in the control. These findings demonstrate the potential of MLP as a suitable feed additive that facilitates growth, antioxidant capacity, and digestive ability in shrimp. Importantly, this study reveals the potential of mango leaf powder as a novel feed additive for L. vannamei. Full article

(This article belongs to the Section Nutrition and Feeding)

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19 pages, 1579 KB

Open AccessArticle

Nutrient Analysis of Raw and Sensory Evaluation of Cooked Red Tilapia Filets (Oreochromis sp.): A Comparison Between Aquaculture (Red Kenyir™) and Wild Conditions

by Aswir Abd Rashed, Nurliayana Ibrahim, Nurul Izzah Ahmad, Mariam Marip, Mohd Fairulnizal Md Noh and Mohammad Adi Mohammad Fadzil

Fishes 2025, 10(10), 523; https://doi.org/10.3390/fishes10100523 - 14 Oct 2025

Abstract

The tilapia sector is advancing due to breakthroughs in aquaculture techniques and genetic enhancements. Comprehending sensory qualities is crucial for producers striving to meet market demands efficiently. As consumer preferences play a significant role in shaping the market, enhancing the sensory attributes of [...] Read more.

The tilapia sector is advancing due to breakthroughs in aquaculture techniques and genetic enhancements. Comprehending sensory qualities is crucial for producers striving to meet market demands efficiently. As consumer preferences play a significant role in shaping the market, enhancing the sensory attributes of both farmed and wild red tilapia will be key to ensuring their success in the competitive aquaculture industry. One of Malaysia’s most prominent aquaculture projects is the Como River Aquaculture Project located in Kenyir Lake, where tilapia fish farming, trademarked as Red Kenyir™, is conducted. Thus, this study aimed to evaluate the nutrient analysis of raw and five sensory attributes (appearance, texture, smell, taste, overall quality) of filets from Red Kenyir™ and wild red tilapia (Oreochromis sp.). Red Kenyir™ were fed three different commercial diets (A, B, and C) from fingerling to adulthood, while wild tilapia (W) was sourced from the market. Proximate and nutritional analyses were conducted based on the standard food analysis protocol by AOAC/AOCS. To the best of our knowledge, this is the first study to comprehensively document the nutrient analysis of raw and consumer sensory perception of cooked Red Kenyir™ aquaculture tilapia in direct comparison with wild red tilapia. The sensory evaluation was conducted using a consumer preference test. Statistical analysis was performed using SPSS. Nutrient analysis showed that Red Kenyir™ tilapia had lower fat (0.25–1.37 g/100 g vs. 4.30 g/100 g) and lower energy (77.38–113.46 kcal/100 g vs. 132.79 kcal/100 g) levels. Protein levels varied across groups (19–26.54 g/100 g vs. 22.95 g/100 g). The tryptophan content of the Red Kenyir™ tilapia samples ranged between 0.13 and 0.23 g/100 g, while the wild tilapia contained 0.19 mg/100 g. Sensory evaluation with 36 panelists revealed no significant differences in appearance, texture, or smell (p > 0.05). However, wild tilapia scored slightly higher in taste (4.14) than Red Kenyir™ (3.54–3.71) for steamed preparation (p < 0.05). In conclusion, these findings suggest that variations in the nutritional composition of Red Kenyir™ do not affect the sensory experience for consumer acceptance, making it a sustainable alternative for customers. Full article

(This article belongs to the Special Issue Seafood Products: Nutrients, Safety, and Sustainability)

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18 pages, 5648 KB

Open AccessArticle

Acoustic Estimation of Blue Mackerel (Scomber australasicus) Spawning Biomass in Yilan Bay, Taiwan: Integrating Depth Compensation and Fishery Data (2021–2024)

by Ting-Chieh Huang, Kuo-Wei Yen, Ruei-Gu Chen, Chia-Hsu Chih and Hsueh-Jung Lu

Fishes 2025, 10(10), 522; https://doi.org/10.3390/fishes10100522 - 14 Oct 2025

Abstract

The mackerel fishery is Taiwan’s most productive coastal fishery sector, with the blue mackerel (Scomber australasicus) being its primary target species. Given the economic and ecological significance of this fishery, considerable attention has been devoted to assessing stock status and promoting [...] Read more.

The mackerel fishery is Taiwan’s most productive coastal fishery sector, with the blue mackerel (Scomber australasicus) being its primary target species. Given the economic and ecological significance of this fishery, considerable attention has been devoted to assessing stock status and promoting sustainable use. Between 2021 and 2024, acoustic transect surveys were conducted in Yilan Bay during the blue mackerel spawning season, supplemented by hook-and-line sampling to confirm the identity of single-target acoustic signals. Acoustic detections within ±10 m of capture depth and ±10 min of capture time were used to establish a depth-compensated regression model linking target strength (TS) to fork length (FL). Validation revealed that over 80% of the hook-and-line samples were blue mackerel. After careful noise filtering, a depth-compensated regression model was established to relate TS to FL and sampling depth. The model incorporated both logarithmic body length and depth terms, effectively accounting for vertical variations in TS. The model improved alignment with biological sampling data by effectively accounting for depth-related variations in TS, thereby enhancing biomass estimation accuracy. Cross-validation with auction records from Nan-Fang-Ao Fishing Harbor confirmed that the acoustic biomass estimates closely mirrored commercial catch trends. These findings highlight the effectiveness of depth-compensated acoustic methodologies for obtaining reliable, fishery-independent spawning biomass estimates, supporting their continued application in long-term monitoring and spatial resource management. Full article

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18 pages, 835 KB

Open AccessArticle

Comparative Fulton’s Condition and Relative Weight of American Brook Lamprey (Lethenteron appendix) Larvae and Adults in Streams in Southeastern Minnesota, USA

by Neal D. Mundahl and Silas Bergen

Fishes 2025, 10(10), 521; https://doi.org/10.3390/fishes10100521 - 14 Oct 2025

Abstract

To reproduce successfully, non-parasitic brook lamprey must accumulate all nutrients needed for growth and reproductive development during a multi-year larval stage while feeding on low-quality detritus. We used total length and wet mass data of American brook lamprey (Lethenteron appendix) in [...] Read more.

To reproduce successfully, non-parasitic brook lamprey must accumulate all nutrients needed for growth and reproductive development during a multi-year larval stage while feeding on low-quality detritus. We used total length and wet mass data of American brook lamprey (Lethenteron appendix) in 14 streams across four watersheds in southeastern Minnesota, USA, to examine Fulton’s condition factors (Fulton K = [g wet mass/mm TL³] × 10⁶) of both lamprey ammocoetes (or larvae, n = 717) and spawning adults (n = 154) and developed preliminary standard mass equations for both life stages to allow for calculations of relative weights, a first attempt for any lamprey species. Condition factors and relative weights were most variable through the first year or two of the larval stage, with both condition factors and relative weights rising slightly through the remainder of the larval phase. Relative weights of most late-stage larvae ranged from 90 to 110% with condition factors at or slightly above 1.5. The standard mass equation for American brook lamprey larvae based on the top 25% heaviest individuals across the length range was: log₁₀ wet mass (g) = 2.7078 log₁₀ total length (mm)—5.115. Adult male American brook lampreys were slightly but not significantly longer than females at most of the sites examined, and condition factors and relative weights differed between the sexes only at one site. Overall, adult condition factors averaged 2.0, and relative weights averaged 86.9% and did not change significantly across the total length range (137 to 214 mm). The standard mass equation for American brook lamprey adults based on the top 25% healthiest or fittest individuals across the length range was: log₁₀ wet mass (g) = 2.7411 log₁₀ total length (mm)—5.047. American brook lamprey adults and ammocoetes approaching metamorphosis generally exhibited good condition factors and relative weights. Both adult and ammocoete condition factors and relative weights, along with adult lengths, differed significantly among streams. Length-wet mass data are needed from more populations of American brook lamprey across its range to build a more robust relative weight model for the species. Full article

(This article belongs to the Section Biology and Ecology)

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1 pages, 134 KB

Open AccessRetraction

RETRACTED: Li et al. Influences of Cr(VI) on SOD Activity, MDA, and MT Content in the Hepatopancreas and Gill of Portunus trituberculatus. Fishes 2024, 9, 407

by Lei Li, Chenshan Shao, Guodong Xv, Linlan Lv, Jiacheng Jiang, Weiyi Zou, Weiwei Su, Yanming Sui and Mei Jiang

Fishes 2025, 10(10), 520; https://doi.org/10.3390/fishes10100520 - 14 Oct 2025

Abstract

The journal retracts the article titled “Influences of Cr(VI) on SOD Activity, MDA, and MT Content in the Hepatopancreas and Gill of Portunus trituberculatus” [...] Full article

19 pages, 9110 KB

Open AccessArticle

Integrated Analysis of Phenotypic and Hepatic Transcriptomic Profiles Reveals Enhanced Cold Tolerance in Triploid Crucian Carp

by Suifei Tao, Zexun Zhou, Shandong Chen, Jialin Cui, Yude Wang, Kaikun Luo, Wei Liu, Qingfeng Liu, Wuhui Li and Shaojun Liu

Fishes 2025, 10(10), 519; https://doi.org/10.3390/fishes10100519 - 12 Oct 2025

Abstract

Cold stress poses a critical threat to fish survival by triggering metabolic dysfunction, oxidative damage, immune suppression, and apoptosis. However, hybrid polyploid fish triploid crucian carp (3nRCR, 3n = 150) demonstrate superior stress tolerance. In this study, we investigated the cold adaptation mechanisms [...] Read more.

Cold stress poses a critical threat to fish survival by triggering metabolic dysfunction, oxidative damage, immune suppression, and apoptosis. However, hybrid polyploid fish triploid crucian carp (3nRCR, 3n = 150) demonstrate superior stress tolerance. In this study, we investigated the cold adaptation mechanisms in different ploidy cyprinid fishes: triploid crucian carp compared to its diploid improved red crucian carp (Carassius auratus red var., RCC, 2n = 100, ♀) and improved allotetraploid (4nAT, 4n = 200, ♂) progenitors. Under controlled cooling, 3nRCR lost equilibrium at a significantly lower temperature (3.2 °C) than RCC (4.0 °C) and 4nAT (4.5 °C), confirming its superior enhanced cold resistance. Histological examination revealed minimal tissue damage in 3nRCR, characterized by reduced gill inflammation and cellular apoptosis. Transcriptomics revealed triploid-specific molecular strategies: 3nRCR uniquely activated retinol metabolism and metabolic rewiring (arginine/proline metabolism, oxidative phosphorylation). Notably, in the immune-related NLR signaling pathway, both nlrp1 and nlrp3 (key inflammasome components) were significantly downregulated in 3nRCR (p < 0.01). In contrast, genes involved in endoplasmic reticulum (ER) stress response, including chop and nrf2, were markedly upregulated, indicating a reinforced cellular stress resolution mechanism absent in both RCC and 4nAT. Our results demonstrate that triploid cold adaptation is orchestrated through a balanced interaction among mitochondrial apoptosis, ER stress, and inflammasome pathways. These findings provide novel insights into hybrid polyploid adaptation mechanisms and targets for cold-resilient aquaculture breeding. Full article

(This article belongs to the Special Issue Genetics and Breeding of Fishes)

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19 pages, 1320 KB

Open AccessArticle

Oral L-Dopa Disrupts Behavioral Self-Control in Male Fighting Fish (Betta splendens)

by Andrew Velkey, Kate Watson, Nathan White, Abigail Agi, Grace Doebler-Alligood, Isabella Tilmont, Brook Williams Sweeten and Kaitlyn Kinslow

Fishes 2025, 10(10), 518; https://doi.org/10.3390/fishes10100518 - 11 Oct 2025

Abstract

In their natural habitat, male Betta splendens are territorial resource defenders, whereas females are non-territorial opportunistic foragers. This ecological difference suggests that males may be more capable of delaying gratification for food rewards. The present study examined impulsive choice in Betta splendens through [...] Read more.

In their natural habitat, male Betta splendens are territorial resource defenders, whereas females are non-territorial opportunistic foragers. This ecological difference suggests that males may be more capable of delaying gratification for food rewards. The present study examined impulsive choice in Betta splendens through two experiments comparing subjects’ choices between a Smaller-Sooner (SS) reward (1 pellet immediately) and a Larger-Later (LL) reward (3 pellets after 15 s). In Experiment I, the choice distributions of males were more likely to stabilize on the LL option over the SS option, whereas females’ choice distributions were equally likely to stabilize on either option. These findings indicate that most males demonstrated spontaneous behavioral self-control without specialized training, while females were collectively indifferent. Experiment II investigated whether dopamine modulates this behavior by administering oral L-Dopa (60 mg/kg) to males before trials. Using the same procedures, only 30% of L-Dopa-treated males’ choice distributions stabilized on the LL reward, while 70% of experimental males’ choice distributions stabilized on the SS option; the choice distributions of control males were equally likely to stabilize on either reward. These results suggest that elevated dopaminergic activity increases impulsive choice in male Betta splendens. Future studies should examine dopamine agonists and antagonists, as well as female responses, to further clarify dopamine’s role in reward valuation and behavioral self-control in Betta splendens. Full article

(This article belongs to the Section Physiology and Biochemistry)

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16 pages, 1858 KB

Open AccessArticle

Trace Element Accumulation and Oxidative Stress in Three Populations of the European Eel Anguilla anguilla L. from Southern Italy

by Mariacristina Filice, Samira Gallo, Alessia Caferro, Gianni Giglio, Francesco Luigi Leonetti, Concetta Milazzo, Alfonsina Gattuso, Maria Carmela Cerra, Donatella Barca, Emilio Sperone and Sandra Imbrogno

Fishes 2025, 10(10), 517; https://doi.org/10.3390/fishes10100517 - 11 Oct 2025

Abstract

The European eel (Anguilla anguilla), a catadromous species currently listed as Critically Endangered by the IUCN, is undergoing a severe continental decline. Among the multiple contributing factors, chemical contamination of aquatic environments—particularly by heavy metals—plays a major role. This study analyzed [...] Read more.

The European eel (Anguilla anguilla), a catadromous species currently listed as Critically Endangered by the IUCN, is undergoing a severe continental decline. Among the multiple contributing factors, chemical contamination of aquatic environments—particularly by heavy metals—plays a major role. This study analyzed the concentrations of 16 trace elements in the muscle tissue of A. anguilla specimens collected from three ecologically distinct sites in Southern Italy: an estuary (Foce del Crati), a lagoon (Laghi di Gizzeria) and a stream (torrente Raganello). Correlations between trace element accumulation and the onset of oxidative stress were also examined. To assess eel health status, oxidative biomarkers were also analyzed in heart, liver, and gill tissues. Statistical analysis among populations revealed significant differences in the bioaccumulation of 10 of the 16 elements, with Cd and As being of particular concern. No significant correlations were found between these two elements and oxidative biomarkers, but Spearman analysis identified both positive and negative correlations with other elements varying by the site of collection. Oxidative biomarkers also showed site- and tissue-specific variation. In particular, SOD activity was highest in the liver and varied across sites; LPO and protein carbonyl levels were generally lower in eels from the Crati River, although heart values deviated from this trend, highlighting tissue-specific response patterns. These results underscore the complex interplay between chemical contamination and the physiology of the European eel, emphasizing the influence of environmental context in modulating tissue-specific oxidative responses. Full article

(This article belongs to the Special Issue The Impact of Contamination on Fishes)

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20 pages, 2753 KB

Open AccessArticle

Induction of Spawning in Captive Female Thicklip Grey Mullet (Chelon labrosus) Treated with Different GnRHa Delivery Systems

by Lambros E. Kokokiris, George Minos, Christos Simeonidis, Theofanis Karidas, Maria Papadaki and Constantinos C. Mylonas

Fishes 2025, 10(10), 516; https://doi.org/10.3390/fishes10100516 - 11 Oct 2025

Abstract

Thick-lipped grey mullet (Chelon labrosus) has important characteristics that make it a promising candidate species for diversifying Mediterranean aquaculture. However, spontaneous spawning in captivity has not been documented, mainly due to failure of females to spawn, highlighting the need for further [...] Read more.

Thick-lipped grey mullet (Chelon labrosus) has important characteristics that make it a promising candidate species for diversifying Mediterranean aquaculture. However, spontaneous spawning in captivity has not been documented, mainly due to failure of females to spawn, highlighting the need for further research on reproduction control. This study evaluated the efficacy of GnRHa administration, using repeated intramuscular injections or slow-release Ethylene–Vinyl Acetate (EVAc) implants combined with a dopamine antagonist (metoclopramide, Met), in terms of spawning performance and egg quality. Three groups were established: (a) saline injection (0.9% NaCl; Saline-INJ), (b) GnRHa [Des-Gly¹⁰, D-Ala⁶-ProNEth⁹-mGnRHa] injection at 10 μg kg⁻¹ BW (GnRHa-INJ), and (c) EVAc implant containing GnRHa at 50 μg kg⁻¹ bw (GnRHa-IMP). Over four weeks, Saline-INJ and GnRHa-INJ females received weekly saline or GnRHa, respectively. GnRHa-INJ and GnRHa-IMP females also received weekly Met (15 mg kg⁻¹ bw). GnRHa induced 11 spawns (1,768,680 eggs), nearly triple the Saline-INJ group (4 spawns, 394,400 eggs). Daily relative fecundity (DRF) and fertilization success were highest in GnRHa-INJ (56,982 eggs kg⁻¹ day⁻¹; 59.7%), followed by GnRHa-IMP (20,375; 18.8%) and Saline-INJ (13,061; 9.1%). Multiple injections showed a trend toward higher spawning performance and egg quality compared to implants, although variability was high and further replication is needed. Nevertheless, optimizing both GnRHa delivery methods could further enhance their effectiveness while maintaining operational benefits for aquaculture. Full article

(This article belongs to the Section Physiology and Biochemistry)

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18 pages, 8401 KB

Open AccessArticle

Identification of the Metallocarboxypeptidase M14 Gene Family in Lysiosquillina maculata, Odontodactylus scyllarus and Oratosquilla oratoria Based on the Full-Length Transcriptome

by Jiantong Zhang, Xiuqiang Dong, Xinyan Hu, Xiaowen Duan, Bin Xu and Fangrui Lou

Fishes 2025, 10(10), 515; https://doi.org/10.3390/fishes10100515 - 10 Oct 2025

Abstract

Metallocarboxypeptidase (MCP) is a crucial protein enzyme involved in food digestion and absorption in animals, which has a potential influence on the differentiation of the trophic niche. Considering that stomatopods have raptorial appendage-specific trophic niches, the present study screened and compared [...] Read more.

Metallocarboxypeptidase (MCP) is a crucial protein enzyme involved in food digestion and absorption in animals, which has a potential influence on the differentiation of the trophic niche. Considering that stomatopods have raptorial appendage-specific trophic niches, the present study screened and compared the MCP M14 gene family of three stomatopods (Lysiosquillina maculata, Odontodactylus scyllarus, and Oratosquilla oratoria) with different raptorial appendage morphologies based on full-length transcriptome information. There are 13 and 17 MCP M14 gene family members identified in L. maculata and O. scyllarus, respectively, which are classified as M14A, M14B, and M14D subfamilies. However, 15 MCP M14 family members have been identified in O. oratoria, all belonging to the M14A subfamily. The physicochemical properties, phylogenetic relationships, conserved motifs, and secondary and tertiary structures of the MCP M14 amino acid sequences were also analyzed in the present study. The results revealed that each amino acid sequence had unique physicochemical properties. Ten conserved motifs were further characterized across the MCP M14 amino acid sequences, and the type and number of motifs from the same subfamily remained highly conserved. Meanwhile, we found that most of the MCP M14 gene family members have critical residues (including Zn²⁺ binding sites [His69, Glu72, and His196], substrate-binding residues [Arg124, Arg127, and Arg145], and disulfide bond-forming residues [Cys138 and Cys161]) involved in disulfide bond formation and enzyme activity stabilization. Furthermore, the random coil is the predominant structural feature of the MCP M14 amino acid sequence. In conclusion, these results are undoubtedly valuable for exploring the evolution and regulation mechanisms of the trophic niche in stomatopods. Full article

(This article belongs to the Section Genetics and Biotechnology)

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22 pages, 1737 KB

Open AccessReview

Sustainable Aquaculture Through Enzymatic Hydrolysis of Raw Chitin from Crab By-Products: Functional Fish Feeds Targeting Fish Health with Implications for Human Health

by Ioannis Fotodimas, Kosmas L. Vidalis, John A. Theodorou, Panagiotis Logothetis and Grigorios Kanlis

Fishes 2025, 10(10), 514; https://doi.org/10.3390/fishes10100514 - 10 Oct 2025

Abstract

Valorisation of crab by-products by enzymatic hydrolysis (EH) is proving to be a promising strategy to promote sustainable aquaculture and support a circular economy for crustaceans. Crab processing generates significant amounts of by-products that, if not properly managed, pose an environmental and economic [...] Read more.

Valorisation of crab by-products by enzymatic hydrolysis (EH) is proving to be a promising strategy to promote sustainable aquaculture and support a circular economy for crustaceans. Crab processing generates significant amounts of by-products that, if not properly managed, pose an environmental and economic challenge. These by-products are rich in chitin, proteins, and bioactive compounds and offer significant untapped potential for the development of functional feed. This review focuses on the application of enzymatically hydrolysed crab by-products as functional feed additives in aquaculture and their effects on fish growth, health management, and, consequently, human health. Recent studies have shown that EH effectively recovers chitin and bioactive peptides and improves the digestibility and bioavailability of nutrients in aquaculture. The inclusion of crude chitin, along with residual proteins and calcium carbonate, in the diet of farmed fish has been associated with increased growth, improved immune responses, and greater disease resistance, emphasising their critical role in fish health management. In addition, these functional additives contribute to the development of innovative aquafeeds with high added value and improved nutritional quality, while reducing environmental waste. Overall, the utilisation of crustacean by-products through enzymatic hydrolysis represents a valuable tool for the sustainable development of crustacean aquaculture, promotes the circular economy, and supports the development of innovative functional feeds while improving the growth and health of farmed fish, which has a positive impact on human health through their consumption. Full article

(This article belongs to the Section Sustainable Aquaculture)

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10 pages, 1200 KB

Open AccessArticle

Estimating Whale Shark, Rhincodon typus, Length Using Multi-Stereo-Image Measurement

by Hiroto Yamamoto, Akira Sasaki, Tomoki Kanna, Yasushi Mitsunaga and Shinsuke Torisawa

Fishes 2025, 10(10), 513; https://doi.org/10.3390/fishes10100513 - 10 Oct 2025

Abstract

The whale shark Rhincodon typus is the largest known extant omnivorous fish species, reaching up to 17 m in length. Because of its slow growth and late maturity, R. typus is particularly vulnerable to human activities and is listed as endangered on the [...] Read more.

The whale shark Rhincodon typus is the largest known extant omnivorous fish species, reaching up to 17 m in length. Because of its slow growth and late maturity, R. typus is particularly vulnerable to human activities and is listed as endangered on the IUCN Red List. Understanding its biological characteristics, such as growth rate, is essential for their conservation. Non-invasive methods, including stereo-image measurements, have been used to measure the body length of the species over the years, which aggregates in coastal areas during specific life stages. This method enables us to estimate fish length by recording the target using a stereo camera, which commonly consists of two cameras. However, measurement errors increase in the setup as the target moves away from the camera. Therefore, we conducted a multi-stereo video shoot of a free-swimming whale shark in an aquarium tank and compared the performance of stereo cameras using two, three, and four cameras. The setups with three and four cameras outperformed the traditional two-camera stereo setup in terms of precision and accuracy, suggesting that a multi-stereo camera system can effectively estimate the body length of large animals such as whale sharks from a considerable distance. Full article

(This article belongs to the Special Issue New Technologies for Improving Fisheries and Aquaculture Production and Management)

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15 pages, 1104 KB

Open AccessArticle

Long-Term Trends in Brook Trout Habitat in Appalachian Headwater Streams

by Zac Zacavish and Kyle Hartman

Fishes 2025, 10(10), 512; https://doi.org/10.3390/fishes10100512 - 10 Oct 2025

Abstract

For lotic salmonids, pool habitats are critical to persistence and resilience. In the central Appalachians, brook trout (Salvelinus fontinalis Mitchill 1814) is an imperiled species that relies on pool habitats for refuge during drought and for spawning. We sought to study trends [...] Read more.

For lotic salmonids, pool habitats are critical to persistence and resilience. In the central Appalachians, brook trout (Salvelinus fontinalis Mitchill 1814) is an imperiled species that relies on pool habitats for refuge during drought and for spawning. We sought to study trends in pool habitats by studying habitat distribution and trends in 25 headwater systems over 18 years. Our analysis documented a significant decreasing trend in critical pool habitat (p = 0.006) and a significant increase in distance between these pools (p = 0.001) since 2003. Natural recruitment of large wood from second-growth riparian areas appears to be slower than losses. However, large wood recruitment from Superstorm Sandy in 2012, at least temporarily stabilized pool numbers. While salmonid populations can be highly resilient, disturbances can create unstable habitat conditions. These conditions could become more probable with projected alteration of flow regime due to climate change. These results highlight the need to further understand the potential impacts acute disturbances like drought, floods, debris flows, and other formidable events could have on temporal habitat availability. Full article

(This article belongs to the Special Issue New Conservation Strategies for Freshwater and Marine Fishes: Habitat Is the Key)

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13 pages, 1259 KB

Open AccessArticle

Effects of Time Interval and Speed Increments on the Critical Swimming Speed of Litopenaeus vannamei

by Yan Duan, Mengyao Li, Ming Sun, Aiyong Wang, Jie Liu and Xiumei Zhang

Fishes 2025, 10(10), 511; https://doi.org/10.3390/fishes10100511 - 10 Oct 2025

Abstract

Swimming ability is an important means for shrimp to survive in a water environment. To investigate the effects of different body lengths (L₁: 6.5 ± 0.25 cm, L₂: 8.8 ± 0.16 cm, and L₃: 11.5 ± 0.28 [...] Read more.

Swimming ability is an important means for shrimp to survive in a water environment. To investigate the effects of different body lengths (L₁: 6.5 ± 0.25 cm, L₂: 8.8 ± 0.16 cm, and L₃: 11.5 ± 0.28 cm) and different measurement methods on the measured critical swimming speeds (U_crit), this study used experimental ecology methods to determine the U_crit of three body length (BL) groups of whiteleg shrimp (Litopenaeus vannamei) at different time intervals (10, 20, 30, 40, and 50 min) and speed increments (1/2 BL s⁻¹, 3/4 BL s⁻¹, and BL s⁻¹) in a biological swimming channel. The results showed that the time interval and speed increment significantly affected the U_crit. In the small-body-length group (L₁), the U_crit of the shrimp decreased and then increased as the time interval increased, with no significant difference between time intervals or velocity increments. In the medium-body-length group (L₂), at the speed increment of 1/2 BL s⁻¹, the U_crit of the shrimp under the time interval < 40 min was significantly greater than that in the other treatment groups. At the speed increment of 1/2 BL s⁻¹, the U_crit of the shrimp decreased as the time interval increased. At the speed increment of 3/4 BL s⁻¹, the U_crit of the shrimp showed a trend of decreasing and then increasing with increasing time interval, and at a high-speed increment (BL s⁻¹), the time interval had no significant effect on U_crit. In the large-body-length group (L₃), at the speed increment of 1/2 BL s⁻¹, the U_crit of the shrimp under the time interval < 30 min was significantly higher than that in the other treatment groups. The effect of the time interval on U_crit was not significant at high-speed increments, and U_crit decreased with increasing time interval only at the speed increment of 1/2 BL s⁻¹. This study showed that, in the small-body-length group, the time increment has a more significant effect on the critical swimming speed, and, as the body length increases, both the time increment and velocity increment affect the critical swimming speed. When the time interval is 20 min and the speed increment is 1/2 BL s⁻¹, the measured U_crit is the closest to the appropriate value. Full article

(This article belongs to the Special Issue Biology and Culture of Marine Invertebrates)

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11 pages, 1110 KB

Open AccessArticle

Pulse Frequency and Water Velocity Determine Crossing Probability in Pulsed Direct-Current Fish Barriers

by Wanshuang Yi, Lu Cai, Yun Tan, Bo Xu, Jun Li, Lianwei Liu, Lanlan Xu, David Johnson, Shihong Zhu and Guosheng Yang

Fishes 2025, 10(10), 510; https://doi.org/10.3390/fishes10100510 - 10 Oct 2025

Abstract

Fish barrier technology by pulsed direct current has broad application potential to guide fish to suitable waters. The primary objective of this investigation was to study the effects of electric pulse frequency and water velocity on fish deterrence by pulsed direct current. The [...] Read more.

Fish barrier technology by pulsed direct current has broad application potential to guide fish to suitable waters. The primary objective of this investigation was to study the effects of electric pulse frequency and water velocity on fish deterrence by pulsed direct current. The test fish were adults of two common carp species, Hypophthalmichthys nobilis (bighead carp, standard length 0.460–0.545 m) and Cyprinus carpio (Eurasian carp, standard length 0.292–0.335 m). Experiments were conducted in the 20 m swimming chamber of a 50 m flume, with a pulsed electric barrier produced by vertical electrodes located in the middle of the swimming chamber. The effectiveness of the electric barrier in deterring fish from swimming upstream past the electrodes was tested. The electric pulse generator produces a square wave pulse, with a voltage of 150 V and width of 2 ms. There were four electric pulse frequency treatments (4 Hz, 6 Hz, 8 Hz, 10 Hz), and two water velocity treatments (0.2 m/s, 0.6 m/s), with 10 replicates of each treatment. There were four primary findings. (1) Of the 160 fish tested, no fish was stunned and only 4 trembled (lost the ability to swim) for more than 2 s after encountering the electric barrier. (2) At a given water velocity, the crossing probability decreased as pulse frequency increased, and the decrease was largest when the frequency increased from 8 to 10 Hz. (3) At a given electric pulse frequency, the crossing probability was higher at the high water velocity, and barrier efficiency was more sensitive to velocity at higher pulse frequencies. (4) H. nobilis, a stronger swimmer, crossed more often than C. carpio. This study can provide ideas for the management of invasive species. However, the study was conducted under controlled laboratory conditions, and field experiments should be carried out before field applications. Full article

(This article belongs to the Special Issue Adaptation and Response of Fish to Environmental Changes)

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22 pages, 4802 KB

Open AccessArticle

Comparative Analyses Reveal Potential Genetic Variations in Hypoxia- and Mitochondria-Related Genes Among Six Strains of Common Carp Cyprinus carpio

by Mohamed H. Abo-Raya, Jing Ke, Jun Wang and Chenghui Wang

Fishes 2025, 10(10), 509; https://doi.org/10.3390/fishes10100509 - 9 Oct 2025

Abstract

The ability of common carp to withstand both short-term and long-term oxygen deprivation has been well documented; however, the potential genetic mechanisms behind common carp’s hypoxia response remain unclear. Therefore, to understand the possible genetic foundation of their response to hypoxia, comparative genomic [...] Read more.

The ability of common carp to withstand both short-term and long-term oxygen deprivation has been well documented; however, the potential genetic mechanisms behind common carp’s hypoxia response remain unclear. Therefore, to understand the possible genetic foundation of their response to hypoxia, comparative genomic analyses were conducted among six common carp varieties: Color, Songpu, European, Yellow, Mirror, and Hebao common carps. We identified 118 single-copy orthologous positively selected genes (PSGs) (dN/dS > 1) in all common carps under study, with GO functions directly related to the cellular responses to hypoxia in Color and European common carp PSGs, such as oxygen transport activity, oxygen binding activity, respiratory burst activity, and superoxide anion production. The Bayes Empirical Bayes (BEB) technique identified possible amino acid substitutions in mitochondrial and hypoxic genes under positive selection. Exonic and intronic structural variations (SVs) were discovered in the CYGB2 hypoxia-related gene of Color and European common carps, as well as in several mitochondrial genes, including MRPL20, MRPL32, NSUN3, GUF1, TMEM17B, PDE12, ACAD6, and COX10 of Color, European, Songpu, Yellow, and Hebao common carps. Moreover, Color common carp and Songpu common carp were found to share the greatest percentage of collinear genes (49.8%), with seven Songpu common carp chromosomes (chr A2, chr A9, chr A13, chr B13, chr B15, chr B2, and chr B12) showing distinct translocation events with the corresponding chromosomes of Color common carp. Additionally, we found 570 translocation sites that contained 3572 translocation-related genes in Color common carp, some of which are directly relevant to mitochondrial and hypoxic GO functions and KEGG pathways. Our results offer strong genome-wide evidence of the possible evolutionary response of Cyprinus carpio to hypoxia, providing important insights into the potential molecular mechanisms that explain their survival in hypoxic environments and guiding future research into carp hypoxia tolerance. Full article

(This article belongs to the Section Genetics and Biotechnology)

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