Grey Mullet Research Articles

Bottlenose dolphin predation on flathead grey mullets using barrier feeding techniques: a visual and acoustic case study in the Mediterranean Sea

We report first-time evidence of barrier feeding techniques in the population of common bottlenose dolphin (Tursiops truncatus) at the estuary of the Tiber River (Rome, Italy), used to prey on the flathead grey mullet (Mugil cephalus). We describe an event that occurred in summer 2023, consisting of dolphins forcing schools of mullets against different types of barriers, i.e. sea surface, coastal breakwater blocks and other dolphins. We provide the first visual and acoustic account of this predation modality in the Mediterranean Sea, showing that bottlenose dolphins adopted techniques to fragmentate prey assemblages and then to limit prey escape routes by forcing them against barriers. In this way dolphins were able to catch the mullets both in air and in the water. Such a technique possibly depends on the ability of sensing each other in the hunting group and of exchanging information through different types of vocalizations.

The Growth Performance, Haematological Parameters and Serum Biochemistry of the Flathead Grey Mullet Mugil cephalus Under Recirculating Aquaculture System and Traditional Culture Systems.

The present investigation explored the growth performance, haematological parameters and serum biochemistry of flathead grey mullet under recirculating aquaculture system (RAS) and traditional culture systems. Nine hundred healthy fish, weighing 43.80 ± 3.55 g and length 16.54 ± 0.82 cm were randomly distributed to three treatments of RAS and traditional culture systems (T1: 20% of water changed daily; T2: once-through system 250 L/h; T3: RAS-20% of water changed weekly) in nine concrete tanks of 4000 L at stocking density of 100 fish/tank and each treatment had three replicates. Fish were fed (33.1% crude protein, 3 mm pellets) twice a day at a rate of 3% for 12 weeks. These findings suggest that the T3 followed by T2 led to notable improvements in growth performance compared to other culture systems. Significantly elevated values of weight gain, length gain, specific growth rate, average daily gain and survival % were observed in T3. The RBCs exhibited a significant decrease under T2. Haemoglobin concentrations and WBC counts significantly increased under RAS. Significant values of mean cell haemoglobin and mean cell haemoglobin concentration were recorded in T2. Total protein, albumin and globulin enhanced significantly under RAS, whereas the highest values of cortisol were observed in T2 and T3. These findings demonstrate that the RAS followed by once-through system significantly improve growth performance, feed efficiency and survival, as well as enhancing the haematology and serum biochemical status of flathead grey mullet. In conclusion, RAS provides ideal conditions for optimizing physiological functions, growth performance and fish health.

Resistance patterns, virulence determinants, and biofilm genes of multidrug-resistant Pseudomonas aeruginosa isolated from fish and fish handlers

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic bacterium that is widely distributed in aquatic environments and causes major economic losses in fish and public health hazards.This study aimed to identify the occurrence of P. aeruginosa in samples collected from fish and fish handlers, and to investigate the antimicrobial susceptibility, virulence determinants, and biofilm genes of P. aeruginosa isolates. A total of 276 samples were cross-sectionally collected from Nile tilapia (53), Golden grey mullet (52), Mediterranean horse mackerel (50), Striped red mullet (71), and fish handlers (50) at five different retail fish markets in Damietta Governorate, Egypt. Pseudomonas species (spp.) were biochemically identified in 57.9% of the total examined samples. Peudomonas aeruginosa were the most prevalent species isolated from the fish and human samples via PCR technique. Peudomonas aeruginosa isolates exhibited full resistance (100%) to tobramycin (TOB), gentamicin (CN), and colistin (CL), with a high level of susceptibility (88.5%) to imipenem (IPM) using the disk diffusion method. Most P. aeruginosa isolates (84.6%) exhibited drug resistance, with 61.5% were multidrug resistance (MDR) and 23.1% were extensive drug resistance (XDR). Most isolates had at least four virulence-associated genes (lasB, toxA, exoU, and oprL) and three biofilm genes (psIA, peIA, and lasR) by using uniplex PCR. The lasI, and rhlR Quorum Sensing (QS) genes were identified in 84.6% and 61.5% in the examined P. aeruginosa isolates, respectively. The highest mortality rate in Nile tilapia experimentally infected with P. aeruginosa isolate encoding most of virulent genes. Multivariate analyses revealed high heterogeneity among the examined isolates. This study revealed the emergence of virulent and drug resistant P. aeruginosa isolates in fish, poses high risks to consumers and food. Thus, strict hygienic measures should be considered when catching, handling, and storing fish, in addition to the routine application of antimicrobial susceptibility testing.

Impacts of dietary Ajwain (Trachyspermum ammi L.) on growth, antioxidative capacity, immune responses, and intestinal histology of grey mullet (Liza ramada)

This study investigated the impacts of dietary supplements with ajwain seed extract (ASE) on the growth, biochemical parameters, digestive enzymes, antioxidant activity, immunity, and intestine histology of Liza ramada. Juveniles (N = 450) with an initial weight of 40.12 ± 0.14 g were fed six experimental diets enriched with ASE at 0 (control), 0.2, 0.4, 0.6, 0.8, and 1.0 g/kg diet for 60 days. Results revealed that fish-fed diets containing ASE at levels of 0.6 g/kg or higher exhibited significantly improved growth parameters including final weight, weight gain percentage, and specific growth rate, along with enhanced feed conversion efficiency compared to lower ASE levels and the control diet. Survival rates remained similar across all experimental groups. Digestive enzyme activity, particularly lipase, was highest in groups fed higher ASE levels (≥ 0.4 g/kg diet). Histomorphological analysis of the intestine showed improved villi structures with increasing ASE supplementation, reaching an optimal appearance at 0.8 g/kg. Blood biochemical analysis indicated higher total protein and globulin concentrations, and lower total cholesterol levels in groups with higher ASE intake (≥ 0.4 g/kg diet). Immune parameters increased with increasing ASE concentrations, including lysozyme activity, bactericidal percentage, and nitroblue tetrazolium levels. Antioxidant status, measured through superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and malondialdehyde (MDA) levels, showed significant improvements with ASE supplementation, with optimal dietary ASE levels for maximizing SOD (0.73 g/kg), CAT (0.74 g/kg), GPx (0.83 g/kg), and minimizing MDA (0.73 g/kg) identified through polynomial regression analysis. These findings suggest that ASE supplementation (0.6–0.8 g/kg) positively influences the growth performance, digestive function, gut health, immunity, and antioxidant status of L. ramada, highlighting its potential as a beneficial dietary additive in aquaculture.

Determination of body length regression formulas for the golden grey mullet (Chelon auratus, Risso 1810) based on otoliths found in the feces of the Caspian Seal (Pusa caspica Gmelin, 1788)

The Caspian Seal, the sole mammal endemic to the Caspian Sea, is listed in the IUCN Red List as a species facing the threat of extinction, a status similarly recognized and/or assigned in all countries in the Caspian region.The study of seal nutrition using caprological methods is of great interest for understanding animal adaptation to deteriorating habitat conditions and assessing the adequacy of their food base in the sea. This method involves analyzing the contents of feces from ichthyophages to detect undigested fish otoliths.The results of studying the seal's diet during periods of haulout on breeding grounds showed that the frequency of occurrence of Chelon auratus otoliths ranged from 2-3% to 27.7% of all fish otoliths detected in feces.This study aims to assess changes in Chelon auratus otoliths as they pass through seals' gastrointestinal tracts and estimate formulas for recovering the linear dimensions of fish consumed by these seals.The research indicates that otolith growth slows with fish growth but does not cease entirely. Allometry is evident in the different ratios of otolith length and width to fish length in various size groups and the change in otolith shape as fish grow.To recover the body length of fish consumed by seals based on otoliths found in their feces, applying inverse calculation formulas obtained when studying the relationship between otolith growth and fish body growth using collection material obtained directly from fish is possible.Further research should focus on refining the recovery formula for the length of large fish by dividing the length into several segments, each described by separate formulas describing the relationship between fish body length and otolith length and width growth.

Variation in the Local Grey Mullet Populations (Mugil cephalus) on the Western Pacific Fringe

Background: Understanding population genetic structures is crucial for planning and implementing conservation programmes to preserve species’ adaptive and evolutionary potential and thus ensure their long-term persistence. The grey mullet (Mugil cephalus) is a globally distributed coastal fish. Its populations in waters surrounding Taiwan on the western Pacific fringe are divided into at least two stocks (migratory and residential), but questions remain regarding their genetic divergence and gene flow. Methods and Results: To cast more light on this, allozyme variations at 21 presumptive gene loci of 1217 adult grey mullets from 15 localities in Japan, Taiwan and mainland China, and four gene loci from 1470 juveniles from three localities in Taiwan were used to investigate patterns of genetic variation. The mean expected heterozygosity (He) was 0.128—ranging from 0.031 (Matsu) to 0.442 (Kaoping)—and the mean observed heterozygosity (Ho) was 0.086—ranging from 0.017 (Kaohsiung) to 0.215 (Kaoping). Both AMOVA and the high overall mean FST of 0.252 indicated enormous genetic differentiation among populations and the positive mean value of FIS was 0.328, indicating a deficiency of heterozygotes. PCoA indicated that the samples of M. cephalus could be split into three groups and STRUCTURE analysis showed that all individuals were grouped into three genetic clusters. The results of mutation-drift equilibrium tests did not suggest that the populations experienced any recent genetic bottleneck. The results from all localities in the present investigation showed significant change in the GPI-A genotype frequencies with latitudes—e.g., increases in GPI-A*135/135 homozygote frequencies and GPI-A*100/100 frequencies were highly correlated with latitudinal cline. All migratory populations with the GPI-A genotype were almost exclusively the GPI-A*100/100 homozygote. During the life history of M. cephalus, the GPI-A*100/135 heterozygote frequency significantly decreases with age. Conclusions: Based on these data, we suggest that each GPI-A genotype represents trait combinations of higher fitness in some portions of the environment. Furthermore, the genotypic frequencies change in accordance with life stages, suggesting that selection occurs throughout the life span.

Metazoan parasite fauna of grey mullet (Mugilidae) from the coastal waters of Vietnam

A total of 201 fishes of the family Mugilidae caught off central Vietnam (Nha Trang Bay) were examined for parasites. Eight species of Mugilidae were identified based on cytb and 16S rRNA sequences. Protozoa were not revealed. The metazoan parasites belong to six higher taxa. Myxozoa Grassé, 1970 is represented by six genera, three of which were first found in grey mullets off Vietnam. The specimens of Monogenea Van Beneden, 1858 belong to two genera: Ligophorus Euzet et Suriano, 1977 and Metamicrocotyla Yamaguti, 1953. Twelve species of the former were recorded for the first time both in the coastal waters of Vietnam and in the East Sea. Trematoda Rudolphi, 1808 is represented by the members of the four families, of which only three species, Haplosplanchnus pachysoma (Eysenhardt, 1892), Pseudohaploporus planilizum Atopkin, Besprozvannykh, Ha, Nguyen, Nguyen & Chalenko, 2019 and Spiritestis arabii Nagaty, 1948, were identified. The latter was first recorded in the East Sea. Acanthocephala Rudolphi, 1808 specimens belong to the species Neoechinorhynchus dimorphospinus Amin & Sey, 1996. Crustacea Brünnich, 1772 are represented by five families, of which only the copepod Lernanthropsis mugilii (Shishido, 1898) and the isopod Nerocila orbignyi (Guérin, 1832) were identified. Hirudinea Savigny, 1822 were not determined to genus and species level. A total of 25 species of parasites were found in the Mugilidae fishes examined in Nha Trang Bay. In general, 96 species of parasites are currently documented in these fishes in the East Sea, 55 of which occur off Vietnam. As a result of this study, carried out off central Vietnam, 16 parasite species were recorded in grey mullet for the first time in Vietnamese coastal waters and 15 for the first time in the East Sea. Thus, extending the geographical range of the studies may result in new records of parasites in these fishes.

Investigating dynamics, etiology, pathology, and therapeutic interventions of Caligus clemensi and Vibrio alginolyticus co-infection in farmed marine fish

This study investigated a disease outbreak characterized by caligid copepod infestations and subsequent secondary bacterial infections in European seabass (Dicentrarchus labrax) and flathead grey mullet (Mugil cephalus) cultivated at a private facility in the Deeba Triangle region of Egypt. Moribund fish displayed brown spots on the skin, tongue, and gills, along with lethargy and excess mucus. The fish suffered severe infections, exhibiting external hemorrhages, ulcers, and ascites. The fish had pale, enlarged livers with hemorrhaging. Comprehensive parasitological, bacteriological, molecular, immunity and histopathological analyses were conducted to identify the etiological agents and pathological changes. Caligid copepod infestation was observed in wet mounts from the buccal and branchial cavities of all examined fish, and the caligids were identified as Caligus clemensi through COI gene sequencing and phylogenetic analysis. Vibrio alginolyticus was confirmed as a secondary bacterial infection through biochemical tests, recA gene sequencing, and phylogenetic analyses. Antibiotic susceptibility testing revealed resistance to β-lactams, aminoglycosides, and trimethoprim-sulfamethoxazole in V. alginolyticus isolates. Upregulation of the inflammatory marker IL-1β in gill and skin tissues indicated a robust cell-mediated immune response against the pathogens. Histopathological examination revealed severe tissue damage, hyperplasia, hemorrhage, and congestion in the gills, along with hepatocellular degeneration and steatosis in the liver, providing initial insights into this outbreak. A comprehensive therapeutic regimen was implemented, comprising prolonged hydrogen peroxide immersion baths, followed by the application of the nature-identical plant-based compound Lice-less and probiotic Sanolife Pro-W supplementation. This integrated approach effectively eliminated C. clemensi infestations, controlled secondary bacterial infections, and restored fish health, reducing morbidity and mortality rates to minimal levels.

Effect of Replacement of Soybean Meal with Fermented Rice Bran as Protein Source on Growth Response, Feeding Utilization, Body Composition, Intestinal Microbiota and an Economic Evaluation of the Grey mullet, Mugil cephalus

Effect of Replacement of Soybean Meal with Fermented Rice Bran as Protein Source on Growth Response, Feeding Utilization, Body Composition, Intestinal Microbiota and an Economic Evaluation of the Grey mullet, Mugil cephalus

Population dynamics of the flathead grey mullet (Mugil cephalus Linnaeus 1758) in the Narmada estuary on the west coast of India

The population dynamics of flathead grey mullet, Mugil cephalus, were evaluated using length-frequency data collected from the Narmada estuary monthly between January 2018 and December 2019. The population parameters were assessed and calculated using the FiSAT-II software tool (FAO-ICLARM Stock Assessment Tools) after the estimation data were divided into 10 mm class intervals. A total of 419 specimens were collected, with an average length range of 171.14±58.15 mm and an average weight of 58.15±45.65 g, respectively. The length-weight relationships were established as W = 0.0105 L2.979. Length-frequency data revealed that length groups 140–149 (15.75 %) and 130–139 mm (13.37 %) dominated the commercial catches of M. cephalus at the Narmada estuary. Different growth parameters were estimated as L∞ = 309.75 mm, K = 0.41 yr−1 and t0 = −0.0013 years. The estimated values of mortality coefficients Z, M, and F were 1.06 yr−1, 0.52 yr−1 and 0.54 yr−1, respectively. The value of exploitation ratio (E) by using the length-converted catch curve method was established as 0.51, which was found to be a little high from the optimum value (0.50). The recruitment was found to be continuous almost throughout the year, with two peaks, once during February to May and another during August to October. The maximum sustainable yield (MSY) was estimated at 970.218 t if the suggested length at first capture (Lc = 123.44 mm TL) is maintained throughout the capture periods. The fishing pressure was found to be slightly excessive for the current stocks, which should be considered for proper management of the fishery in the Narmada estuary.

Effects of water temperature on growth, health and digestive processes of the thicklip grey mullet Chelon labrosus

This study aimed to identify the effects of water temperature on the rearing of the omnivorous teleost Chelon labrosus and to determine the optimal temperature for the culture of this interesting candidate for the diversification of European aquaculture. The fish (initial weight 26.81 ± 6.2 g) were held at four water temperatures (18, 22, 26 and 30 °C) in triplicate for 90 days in 100 L recirculating tanks (n = 14 / tank). The effects of said temperatures were assessed on growth, intestinal health and the digestive processes of the fish. At 18 °C, energy consumption was low, leading to a high accumulation of reserves and slow growth, a typical overwintering strategy. The best growth results were obtained at 22 °C, followed closely by 26 °C, which resulted in low energy reserves. The fact that the fish at 26 °C grew less than the ones at 22 °C while having similar energy consumption, suggested that this temperature was close to the end of the optimal range, but no signs of stress were detected. However, at 30 °C the fish had lower energy reserves but grew significantly less, which can be considered indicative of stress. Health impairment at this temperature was confirmed by the epithelial lesions found in this group. The growth and energy availability of the different groups is discussed in the light of the activities of α-amylase, pepsin and alkaline proteases. As an integration of all these results, a quadratic regression model resulting from growth values (SGR) in relation to water temperature was performed, and it allowed predicting an actual optimal water temperature of 22.8 °C for growth of C. labrosus. This is the first assessment of the optimal water temperature for the culture of C. labrosus, and it will be highly valuable for the development of its intensive culture.

Effective complete replacement of fish oil by linseed oil in diets for thick-lipped grey mullet (Chelon labrosus) juveniles reared at three environmental salinities

One of the major challenges for fish oil replacement by alternative oils is the limited capacity of marine fish species to convert 18C fatty acids into long-chain poly unsaturated fatty acids (LC-PUFA). Since salinity markedly affects this conversion capacity, euryhaline species, such as thick-lipped grey mullet (Chelon labrosus), may have a good potential to use diets without inclusion of fish oil. To test this hypothesis, thick-lipped grey mullet juveniles were fed two different diets based on fish oil (FO diet) or linseed oil (LO diet) at three different salinities: 46 ppt, 35 ppt, and 16 ppt. At the end of the trial, the biochemical and fatty acid composition of whole-body, liver, and muscle, as well as the relative expression of the genes codifying for the elongase Elovl5 and the desaturase Fads2 in liver, were determined. The results showed the good capacity of mullet juveniles to convert 18C fatty acids into LC-PUFA, which was enhanced by the replacement of FO by LO and the reduction of salinity to an isosmotic level (16 ppt). Besides, these juveniles efficiently used diets with complete replacement of FO by LO with growth performance, body composition, and LC-PUFA fatty acid profiles similar to those of fish fed FO, particularly when reared at 16 ppt.

Food and feeding habits of Grey mullet, Rhinomugil corsula (Hamilton, 1822) in the Sitakunda coast of Bay of Bengal, Chattogram, Bangladesh

Food and feeding habits of Grey mullet, Rhinomugil corsula (Hamilton, 1822) in the Sitakunda coast of Bay of Bengal, Chattogram, Bangladesh

Chemical Composition of Two Grey Mullet Species (Chelon auratus, Mugil cephalus): A Comparative Study on Wild and Aquaculture-Adapted Species

This study assessed the chemical composition of wild and culture-adapted golden grey mullet (Chelon auratus) and flathead grey mullet (Mugil cephalus). Wild samples were collected seasonally from Trabzon shores and compared to those adapted to aquaculture conditions for one year. Both species had high levels of glutamate, aspartate, alanine, leucine, and isoleucine. Mugil cephalus was a high protein source for adults, with a digestible indispensable amino acid score (DIAAS) score above 100 in both wild and culture forms. However, a DIAAS score exceeding 100 was only detected in wild Chelon auratus in the winter and spring. Both species had high levels of EPA and DHA, with Mugil cephalus having the highest lipid quality. Despite seasonal variations, cultured fish maintained a good nutritional profile similar to wild fish, especially in the autumn and summer.

Microbial Communities Associated with the Intestinal Tract of Grey Mullets from a Mediterranean Aquatic Environment

Introduction: Grey mullets comprise different species that represent the most ubiquitous teleost families in the planet’s coastal waters. They are an important proportion of the Mediterranean lagoon’s production and have been recently considered cultivated marine fish. This study aimed to explore the intestinal microbial communities of grey mullets to understand their possible ecological role for fish and the aquatic environment. Methods: Thirty-four wild-caught mullets were sampled from a Mediterranean lagoon during four seasons and the V3-V4 hypervariable regions of 16S rRNA (Illumina MiSeq) of the fish gut were sequenced. Parameters of the aquatic environment were detected: temperature, salinity, DO, PO4, NH4, NO3, NO2, SiO, DIN, and Chla. Results: The results indicated a high bacterial diversity (mean Shannon index: 4.74 ± 1.12; Simpson index: 0.93 ± 0.08) and variations among seasons. Sixty prokaryotic phyla were identified and the most abundant ones were: Proteobacteria (mean relative abundance 35.4% ± 17.9), Actinobacteriota (mean relative abundance 16.4% ± 9.9), and Firmicutes (mean relative abundance 10.1% ± 10.9). Bacteria belonging to the phylum Chloroflexi were relevant in autumn, Spirochaetota, Verrucomicrobiota, Fusobacteriota, and Cyanobacteria were particularly abundant in winter while Bacteroidota characterized summer fish. A total of 332 prokaryotic families were identified with 26 most abundant ones; Rhodociclaceae (Proteobacteria) were dominant in autumn, Brevinemataceae (Spirocheaetota) and Fusobacteriaceae (Fusobacteriota) were especially present in winter and the Staphylococcaceae (Firmicutes) prevailed in spring. Conclusion: This study sheds light on the variation in the complex gut microbial community structure of Mediterranean grey mullets and their potential ecological role in protecting fish and preserving the aquatic environment.

Optimizing nutrient utilization, hydraulic loading rate, and feed conversion ratios through freshwater IMTA-aquaponic and hydroponic systems as an environmentally sustainable aquaculture concept

Water quality in land-based fish production can be controlled through either instantaneous water exchange or costly wastewater treatment followed by recirculation. Agricultural-aquaculture integration is an excellent alternative technique for reducing nutrient discharge levels, boosting profitability, and converting fish culture wastewater into valuable products. The current study employed a solar energy system to power two separate IMTA-aquaponics systems (Nutrient Film Technique, NFT, and Floating Raft Systems, FRS) for the cultivation of Nile tilapia, African catfish, thin-lipped grey mullet, freshwater crayfish, freshwater mussels, and a variety of vegetables. Tilapia and catfish were fed exclusively on diets under the IMTA system. All wastewater from tilapia and catfish ponds, both dissolved and solid, flows sequentially to ponds containing other cultivated species. The water then flows through the IMTA system's terminal point to the NFT and FRS systems before returning to the tilapia and catfish ponds, allowing complete control of the nutrient flow throughout this entire circular system. Two 147-day production cycles were concluded. The results from the second production cycle are reported. Total biomass gain for aquatic species in the IMTA system was 736.46 kg, compared to 145.49 kg in the tilapia and 271.01 kg in the catfish monoculture systems. The current IMTA system had a cumulative feed conversion ratio (FCR) of 0.90, while the FCRs for tilapia and catfish were 1.28 and 1.42, respectively. Nile tilapia and catfish consumed 571.90 kg of feed containing 25.70 kg of nitrogen (N) and 9.70 kg of phosphorus (P), reflecting, and gaining 11.41 and 3.93 kg of dietary N and P, representing 44.40 and 40.46% dietary N and P retention, respectively. In the IMTA system, the addition of mullet and prawn as detrivores aquatic animals improves dietary N and P utilization efficiency to 59.06 and 51.19%, respectively, while the addition of mussels as herbivore animals improves dietary N and P utilization efficiency to 65.61 and 54.67%, respectively. Finally, using FRS and NFT as hydroponic systems increased dietary N and P efficiency to 83.51% N and 96.82% P, respectively. This study shows that the IMTA-Aquaponic system, as a bio-integrated food production system, can convert the majority of fish-fed residues into valuable products suitable for desert, rural, and urban areas in impoverished and developing countries.

Comparative metabolomic analysis of minced grey mullet (Mugil cephalus) pasteurized by high hydrostatic pressure (HHP) during chilled storage

The beneficial antimicrobial effects of high hydrostatic pressures (HHP) treatments on chill-stored seafood are well documented. Less attention has been given to their impact on the metabolic profile of the seafood, which can offer valuable insights into the preservation mechanisms of these treatments. To address this gap, the present work describes the effects of HHP on the metabolome of chill-stored grey mullet using 1H-NMR. Samples were treated with HHP at 0, 400, 500, and 600 MPa for 10 min and stored at 2–4 °C. HHP effectively inactivated Lactobacillus spp., E. coli, Pseudomonas spp., total Coliforms, and sulfite-reducing anaerobic bacteria (AB), and significantly (p < 0.05) reduced the total mesophilic bacteria (TMB). Additionally, the microbiological shelf-life of grey mullet was extended from 9 to 35 days with the application of 600 MPa HHP. Unsupervised hierarchical cluster analysis and robust Principal Component Analysis (rPCA) revealed the overall changes in metabolites’ profile caused by HHP. HHP treatment significantly reduced the formation rate of decay-related metabolites, including hypoxanthine, trimethylamine (TMA), and biogenic amines, which significantly (p < 0.05) positively correlated with all considered microorganisms. A metabolic pathway analysis revealed several pathways that may underly the spoilage of grey mullet, including tyrosine metabolism, pyruvate metabolism, lysine metabolism, glycolysis/gluconeogenesis, butanoate metabolism, citrate cycle (TCA cycle), phenylalanine metabolism, and sulfur metabolism. Interestingly, among these pathways, lysine metabolism remained unaffected by the considered HHP treatments. These findings provide a better understanding of the mechanisms underlying the effects of HHP on chilled grey mullet.

Infection dynamics and shedding kinetics of RSIV in red sea bream (Pagrus major) using immersion and cohabitation challenge models

Red sea bream iridovirus (RSIV) poses a significant threat to global aquaculture and wild fish populations, leading to substantial economic and ecological losses. Despite its recognition as a major viral disease, our understanding of the dynamics of RSIV infection and transmission in naturalistic conditions remains limited. Therefore, the present study aimed to investigate the kinetics, shedding, and interspecies transmission of RSIV in red sea bream (Pagrus major) through immersion and cohabitation challenge models. The primary objectives were to (1) elucidate the pathogenicity of RSIV in red sea bream through naturalistic immersion challenges, (2) analyze the viral load and shedding dynamics in RSIV-infected fish, and (3) assess the risk of horizontal transmission to other species. Our results indicated that red sea bream exposed to high doses of RSIV (101–107 RSIV copies/mL) experienced rapid cumulative mortality, particularly at 25 °C. Notably, red sea bream infected by immersion at 25 and 15 °C showed a significant increase in RSIV shedding into seawater when the viral load exceeded approximately 102.48 RSIV copies/mg, highlighting a critical threshold for understanding disease spread in aquaculture settings. Histopathological analysis revealed that the spleen and kidney were primarily affected, with significant lesion scores correlating with viral loads. We observed a strong correlation between viral load and histopathological infection grades, particularly in these primary tissues. Furthermore, cohabitation experiments highlighted the risk of RSIV transmission to other fish species, including rock bream (Oplegnathus fasciatus) and flathead grey mullet (Mugil cephalus), indicating the possibility of horizontal spread in multi-species farming systems. These findings emphasize the importance of continuous surveillance and robust biosecurity measures in aquaculture systems to manage RSIV infection effectively. Overall, this study contributes to understanding RSIV dynamics in red sea bream, offering insights into the impact of this virus in aquaculture environments, particularly concerning viral shedding and transmission.

Po-210 in plankton and fish from coastal waters (gulf of Trieste, northern Adriatic Sea)

The activity concentrations of Po-210 were determined in seawater (<0.45 μm), suspended particulate matter (0.45–20 μm), fractionated plankton (20–50 μm, 50–200 μm, >200 μm) and tissues from four fish species, namely European seabass (Dicentrarchus labrax), Golden grey mullet (Chelon auratus), Gilt-head bream (Sparus aurata) and Common pandora (Pagellus erythrinus), collected in the Gulf of Trieste (northern Adriatic Sea). The activity concentration of Po-210 in seawater varied from 0.4 to 2.2 mBq/L in the dissolved phase (<0.45 μm) and from 0.4 to 0.8 Bq/L in suspended particulate matter (0.45–20 μm). Plankton fractionation showed the levels of 62–395 Bq/kg Po-210 in the >200 μm mesoplankton fraction, 65–459 Bq/kg in 50–200 μm and 52–537 Bq/kg in 20–50 μm microplankton fractions. No significant differences were found between fractions. The Po-210 distribution trend in fish tissues was in order: liver > stomach with intestine > kidney > spleen > gonads > gills > muscle. Bioaccumulation factors were determined for fish tissues indicating that the amount of Po-210 mostly depends on fish feeding habits. Hence, the main pathway entry of Po-210 is through ingested food. The highest estimated average total annual effective ingestion doses of Po-210 are obtained via the consumption of Common Pandora (7.1 μSv/year to 16.5 μSv/year) while the lowest doses are due to the consumption of European seabass (0.32 μSv/year to 0.76 μSv/year). Comparison with levels reported for other Mediterranean and Atlantic areas showed that only activitiy concentrations of Po-210 in fish appear significantly different, most likely because different fish species were analysed. The human dose exposure via fish consumption in the area is rather low.

CALIGUS TURKIYENSIS N. SP. (COPEPODA: CALIGIDAE) ON THE FLATHEAD GREY MULLET, MUGIL CEPHALUS (LINNAEUS) (MUGILIFORMES: MUGILIDAE) FROM THE SEA OF MARMARA, TURKEY

Caligus turkiyensis n. sp. is described from the body surface and fins of the flathead grey mullet, Mugil cephalus Linnaeus, 1758, collected in the Sea of Marmara in Turkey. The new species is easily distinguished from its congeners by the ratio of genital complex length/ abdomen length, number of segments in abdomen, length of tines in the sternal furca, number of teeth on the mandible, position of the posterolateral corners of the genital complex relative to the abdomen, status of the recurved terminal claw of the antenna and postantennal process, ratio of length and anterior margin of the maxillule endopodite, process on myxal surface of maxilliped, ratio of first/third spine on fourth leg and existence of denticles on first spine of fourth leg in the female; total body length, process on myxal surface of maxilliped, number of plates and spine at terminal segment of antenna in the male. This study also includes records of Caligus apodus (Brian 1924) and Caligus pageti Russel, 1925 on two mugilid species from the Sea of Marmara, Turkey. The Sea of Marmara is considered as a new locality for C. pageti.