Fishes, Volume 8, Issue 1 (January 2023) – 57 articles

Fish rhabdoviruses are harmful single-stranded RNA viruses with high mortality rates which cause considerable economic losses in aquaculture. It is imperative to explore and develop new antiviral compounds against them. In recent years, in addition to inorganic antiviral substances, more than 50 different organic compounds have been confirmed to be effective in the prevention and treatment of rhabdovirus infection and its dissemination in fish. The main types of extracts or agents and their trial designs are here considered for review. This review reveals the reported antiviral activities of extracts from organisms, proteins, lipids, polysaccharides, nucleic acids, coumarin derivatives, arctigenin derivatives, and other antiviral organic molecules against fish rhabdoviruses, respectively. Additionally, their antiviral mechanisms of action include direct virucidal effects, inhibiting virus-induced host cell apoptosis, the blocking of the viral replication cycle, affecting gene expression and innate antiviral immune responses, and so on. This review also gives perspectives on how to comprehensively explore the potential applications of the candidate molecules, which lay the foundation for the future development of new compounds or strategies for the prevention and control of fish rhabdoviruses in aquaculture. Full article

Macrourus caml is a main by-catch in the Southern Ocean fishery and a main prey species of Antarctic toothfish Dissostichus mawsoni; it plays an important role in the Southern Ocean ecosystem. In this study, age estimation and stomach content analysis were conducted by using samples collected from the Cosmonauts Sea in 2021. The main objectives of this study were to estimate the age and diet of grenadier M. caml and explore the feeding habits of M. caml. Morphological analysis and molecular identification were conducted to determine the diet of M. caml in this study. Stomach content analysis showed that M. caml mainly fed on Malacostraca, Sagittoidea, Cnidaria and Algae, with the Malacostraca accounting for over 50%. The feeding habits of male and female M. caml were similar. The age of M. caml ranged from 9 to 19 years. Additionally, with the increase of body size, the proportion of Cnidaria was decreasing whereas the proportion of Malacostraca was increasing. The results would provide a reference for exploring the trophic level of M. caml and the food web in the Cosmonauts Sea. Full article

The Shoshone sculpin Cottus greenei is a micro-endemic species and an extreme habitat specialist, geographically restricted to the spring outlets that flow from the Snake River Plain Aquifer into the Snake River within the Hagerman Valley of south central Idaho. Although previous studies documented the range of the species and its relative abundance, no studies have assessed genetic diversity and structure. We sampled 20 populations from throughout the species range and genotyped 1311 with a panel of 12 microsatellite loci. Results indicate very high levels of genetic differentiation among most populations (average pairwise F_ST = 0.24), indicating limited gene flow. Preservation of the genetic diversity of this species will require the protection and preservation of multiple isolated populations. Full article

The present study evaluated a polyculture system with Pacific white shrimp (Litopenaeus vannamei) and the macroalga Gracilaria birdiae and its potential to remove nutrients. The experimental design consisted of a shrimp monoculture of 100 animals/m² (T0) and three multitrophic cultures with L. vannamei (100 animals/m²) and with G. birdiae at densities of 500 (T500), 1000 (T1000), and 2000 (T2000) g/m². Nitrogen and phosphorus concentrations decreased at the beginning of the experiment in the treatments with macroalgae, but this reduction was not maintained throughout the cultivation period. The stable values of G. birdiae biomass were perhaps related to the high turbidity of the water. There was an increase in shrimp biomass during cultivation, which reached the final individual averages of 7.5 g (T0), 7.6 g (T500), 5.9 g (T1000), and 7.5 g (T2000), with no significant differences between treatments. Nevertheless, the absence of macroalgae growth provides no added profit for the producer. Thus, there is no economic advantage in using G. birdiae in an integrated multitrophic system with L. vannamei at a high density and conditions of high water turbidity. Full article

Fish can go through periods of feed deprivation, either due to natural causes influenced by temperature or management techniques in animal production, affecting their energy metabolism differently, depending on the duration of fasting in days and water temperature. This study showed the effect of different days of fasting before slaughter in rainbow trout by analyzing the intermediary metabolic enzymes in the muscle and liver. For this purpose, a non-fasting group was compared with trout that fasted for 5, 10, and 20 days (55, 107, and 200 degree days (°C d), respectively). A first phase of increased activity of enzymes involved in glycolysis was observed, increasing hexokinase enzyme activity in muscle and pyruvate kinase enzyme activity in muscle and liver. As the fasting days progressed, enzymes involved in the gluconeogenic and glycogenolytic pathways in the liver such as lactate dehydrogenase and glycogen phosphorylase increased their activity regarding the no fasted group. After 20 days of fasting (200 °C d), lipogenic and protein related enzyme activity depletion was observed, leading to significant changes in energy metabolism. Therefore, prolonged fasting with high degree days duration may compromise the energy supply for the vital development of rainbow trout. Full article

The golden pompano (Trachinotus ovatus) is one of the most economically valuable marine fishes in South China. Streptococcus agalactiae, an infectious Gram-positive bacterium that is highly destructive for golden pompano culture, has recently caused massive losses to the golden pompano industry. This study aimed to investigate the dynamic immune response of golden pompano to S. agalactiae infection, using RNA-seq analysis at two different time points after infection. Abundances of differentially expressed genes (DEGs) gradually increased in the liver and spleen 48–120 h post-infection, whereas those in the head kidney were lower at 120 h than at 48 h. Pathway enrichment analysis of DEGs revealed that genes related to the complement system were continuously transcribed between 48 and 120 h. Metabolic and immune-regulation-related pathways were highly enriched in the liver 48 h after infection. Transcriptome analysis was verified using quantitative PCR for eight genes with similar expression trends. This study revealed the inflammatory response of golden pompano after S. agalactiae infection, including inflammation-related chemokines and signaling pathways. Our findings provide a theoretical basis for studying S. agalactiae resistance in golden pompano and provide a reliable resource for the genetic breeding of fish. Full article

Common sea stars (Asterias rubens) are at risk of physiological stress and decline with projected shifts in oceanic conditions. This study assessed changes in coelomic fluid (CF) blood gases, electrolytes, osmolality, and coelomocyte counts in adult common sea stars after exposure to stressors mimicking effects from climate change for 14 days, including decreased pH (−0.4 units, mean: 7.37), hypoxia (target dissolved oxygen ~1.75 mg O₂/L, mean: 1.80 mg O₂/L), or increased temperature (+10 °C, mean: 17.2 °C) and compared sea star CF electrolytes and osmolality to tank water. Changes in CF blood gases, electrolytes, and/or coelomocyte counts occurred in all treatment groups after stressor exposures, indicating adverse systemic effects with evidence of increased energy expenditure, respiratory or metabolic derangements, and immunosuppression or inflammation. At baseline, CF potassium and osmolality of all groups combined were significantly higher than tank water, and, after exposures, CF potassium was significantly higher in the hypoxia group as compared to tank water. These findings indicate physiological challenges for A. rubens after stressor exposures and, given increased observations of sea star wasting events globally, this provides evidence that sea stars as a broad group are particularly vulnerable to changing oceans. Full article

Abundance indices are essential data for the application of stock assessment models to obtain fish abundance estimates. Abundance indices have usually been derived from fishery-dependent data, yet the increase in fisheries-independent surveys is now offering new opportunities for these calculations. In this study, we explored the usefulness of ichthyoplankton indices derived from scientific surveys in estimating spawning biomass. In addition, we also investigated whether the strength of the year–class of the commercial cohort of Atlantic hake, as a determinant, could be defined at an early life stage. We used samples collected during the triennial mackerel and horse mackerel egg surveys (MEGS), which cover the hake spawning area in the Bay of Biscay. The biomass indices were determined as the abundance of eggs in the early development stage (stage 1) when transformed into egg production (EP) from 1995 to 2019 in the months of March and April—which is considered a period of high spawning activity for hake in this area. Additionally, we built a metric for larval abundance and converted larval length into age. This was in addition to constructing a pre-recruit year-class index (YCI) while using the EVHOE bottom trawl abundance database for hake for the period of 1997 to 2016. The results of regression analysis of egg production and spawning stock biomass indicate that both parameters are significantly correlated (r = 0.76). By connecting the abundance of eggs and larvae in the adjoining stages, we are able to identify two periods of high mortality associated with the transition from “yolk-sac-first” to “feeding larvae” and “late larvae-YCI10”, but we were unable to discover when the strength of the recruitment year–class is determined. As such, it appears that for the northern stock of hake, recruitment is established in the late juvenile stages. Full article

The study investigated the management practices that contribute to disease outbreaks in farmed tilapia in Lusaka and central and southern provinces in Zambia. It was a cross-sectional qualitative study undertaken from January to March 2021 in which questionnaires were administered to 49 farmers to assess their fish health management and biosecurity competence. Data were analysed using means, percentages, ratios, and logistical regression. The results showed that the majority of the farms had high stocking densities (>8 fish/m², 44.4%), reared Nile tilapia (67.7%), and sourced water for farming from rivers and streams (45.7%). A few farmers measured water quality parameters daily (16.7%) and removed dead fish from ponds daily (20.8%). The stocking density (p = 0.013), fish species (p = 0.031), dead fish disposal methods (p = 0.023), and control of predator birds (p = 0.016) influenced the total mortality recorded on farms, while pond type (p = 0.031 and p = 0.045), water source (p = 0.023), and stocking density (p = 0.027) influenced the duration of a mortality episode. It is evident that some fish health management practices and biosecurity concepts among tilapia farmers in the study area are inadequate and may not contain disease outbreaks or the spread of pathogens. Full article

Market demand for scallops has considerably increased in recent decades. Although natural populations of scallops are vulnerable, the queen scallop, Aequipecten opercularis, can represent a possible alternative to at-risk species. The aim of this study was to determine the effect of seawater parameters on the commercial quality, biological indices and nutritional quality of the scallop A. opercularis in 1900 L tanks in ex situ conditions. The condition index (CI) and meat yield (MY) peaked in autumn (89.92% and 40.29%, respectively). The muscle index (MI) showed the highest peak during the winter season (5.96%), while the gonadosomatic index (GSI) (34.06%) peaked in the spring months. Protein content (6.89–9.56 g/100 g), lipids (2.58–2.79 g/100 g) and carbohydrates (0.12–0.33 g/100 g) varied during the study period. Seasonal fluctuations in seawater temperature and pH negatively influenced the CI, MY and protein and lipid content, while positively affecting carbohydrate and moisture content. The most suitable period of the year for the consumption of the scallop A. opercularis was found to be the winter and spring periods, when the scallops achieved their highest nutritional value. It can be stated from this study that queen scallops in the Adriatic Sea have a high nutritional quality and that they can be proposed for higher human consumption. Full article

Food deprivation is a common stress in crustaceans that can affect their behavior and physiology. In this study, a video recording analysis system was used to compare the predation rate and behavior of the Chinese mitten crab, Eriocheir sinensis, foraging on the freshwater snail, Bellamya quadrata, under different degrees of food deprivation. The activities of lactate dehydrogenase, α-amylase, pepsin, and lipase in the hepatopancreas of crabs were determined after food deprivation for 0, 3, 9, and 15 days. The results showed that the predation and encounter rates of E. sinensis increased and then decreased with an increase in food deprivation time. The proportion of stationary time of E. sinensis initially decreased and then increased, whereas the proportion of searching and handling time increased initially and then decreased. There was a significant difference in the probability of capture upon encountering; however, food deprivation did not significantly affect the probability of consumption upon capture. Under food deprivation, the proportion of E. sinensis crushing tactics after nine-day food deprivation was significantly lower than that in the first nine days. Lactate dehydrogenase activity in the E. sinensis hepatopancreas after food deprivation was significantly higher than that in those not subjected to food deprivation, and the activities of α-amylase and pepsin in the hepatopancreas were consistent with the predation rate trend, showing an initial increase followed by a decrease. In conclusion, different degrees of food deprivation significantly affected the predation cycle of E. sinensis on B. quadrata. These results lay a solid foundation for further studies on the foraging behavioral ecology of E. sinensis and provide important information for improving E. sinensis production. Full article

The pelagic stingray (Pteroplatytrygon violacea), perhaps the only stingray to inhabit open ocean waters, is highly interactive with longline and purse seine fisheries. The threat to P. violacea posed by high bycatch mortality has received widespread attention. To date, the environmental preference of P. violacea, which is important in designing conservation and management measures, has not been well studied. Based on data collected during a 2016–2019 survey in the Pacific Ocean by national observers of tuna longline fisheries, the relationship between the presence of P. violacea and spatiotemporal and environmental variables was first analyzed using the Generalized Additive Model. The results showed that geographic location (latitude and longitude) was the most influential variable. Monthly, P. violacea is frequently present in the Pacific high sea from December to May. The El Niño–Southern Oscillation had a significant impact on the presence of P. violacea in the Pacific high sea, with both the cold (Ocean Nino Index <−0.5) and warm (Ocean Nino Index >1) phases leading to a decrease in its presence. Regarding the environmental factors, we found that high presence was associated with low salinity (33.0~34.5 psu), a relatively high concentration of chlorophyll (0.2–0.35 mg/m³), and warm water (>20 °C). P. violacea was most likely observed in the waters offshore, closer to seamounts, and with water depths between 4000 and 5000 m. Four areas, including those east of the Solomon Islands and east of Kiribati, areas west of the Galapagos Islands, and areas near the coastal upwelling of northern Peru, related to upwelling systems or seamounts, were identified as the potential key habitats of P. violacea. Predicted distribution maps showed a significant seasonal variation in the presence of P. violacea. Moreover, the yearly change in the presence of P. violacea in the Pacific high sea indicated a possible decreasing trend in recent years. The information first provided here is essential for developing conservation and management measures for P. violacea to prevent the unavoidable ecological consequences of bycatch or other anthropogenic factors. Full article

As an endangered animal species, the Chinese sturgeon (Acipenser sinensis) has been artificially cultured during recent years. In the present experiment, the performance of a common formulated feed and a mixed natural feed on the growth and blood physiology of Chinese sturgeon were compared during one year of indoor culture. In terms of specific growth rate, the formulated diet group showed a higher value (4.2%) compared with the natural food group (−1.8%) during one year of indoor culture. Alanine aminotransferase activities of the sturgeons in formulated diet group was significantly higher than that in the natural food group throughout whole experiment period (p < 0.05). The total protein albumin, albumin and globulin contents of the natural food group were significantly higher than that of the formulated diet group in February and May (p < 0.05). The C-reactive protein contents of the formulated diet group were significantly higher than that of natural food group in May and August (p < 0.05). The activities of total cholesterol, high-density cholesterol, and low-density cholesterol were significantly higher in the natural food group than those in the formulated diet group (p < 0.05). The activities of triglycerides were significantly higher in the natural food group than those in the formulated diet group in February and May (p < 0.05). Almost half of the biochemical indicators examined show significant seasonal fluctuations, indicating that seasons have a substantial impact on the Chinese sturgeon. Overall, these results indicate that natural food exerted a positive impact on physiological indicators compared to the formulated diet. Full article

Alterations to the functions and connectivity of mangrove–seagrass–patch reef (MSP) seascapes have the potential to impact the survival, foraging activities, and movement of reef-dependent invertebrates (e.g., crabs and shrimp) and fishes. In the current study, we examined carbon flow in the Guánica Biosphere Reserve in southwestern Puerto Rico using pigment analysis of particulate organic matter and stable isotope analysis of carbon (δ¹³C) and nitrogen (δ¹⁵N) in flora and fauna. Several lines of evidence pointed to N₂ fixers (cyanobacteria) being important for fueling primary productivity in this oligotrophic ecosystem including low (<0.7 µg L⁻¹) chlorophyll, prevalence of cyanobacteria based on pigment signatures, and the isotope signatures of seagrass and red mangrove leaf tissue (enriched δ¹⁵N values) and consumers (depleted δ¹⁵N values). Food web mixing models based on stable isotopes (δ¹³C and δ¹⁵N) revealed that multiple producers (phytoplankton, benthic microalgae, seagrasses, etc.) contributed organic matter to the consumers (zooplankton, invertebrates, and fishes) in the MSP seascape at the center of the reserve. Contribution estimates for common benthic invertebrates (crabs and shrimp) were taxon-specific, and the highest input was generally linked to particulate organic matter (POM) and benthic microalgae (BMA)/seagrass producer categories, although meaningful mangrove contribution was observed for some taxa. Similarly, contribution estimates for fishes were highest for POM and BMA/seagrass, with the latter producer category being more important for species known to migrate from mangroves or patch reefs to seagrass beds at night (bluestriped grunt, French grunt, and white grunt). Although all fish investigated were observed in mangrove prop-root habitats, input of organic matter from mangroves to these consumers was typically limited for most of the species examined. Understanding these complex seascapes contributes to our understanding of the ecology of these vital ecosystems. Full article

The recognition and elimination of invading pathogens are vital for host survival. Macrophages play a central role in host protection and cells functionally reminiscent of vertebrate macrophages are present in all multicellular organisms. A pattern responsible for bacterial recognition found on the surface of macrophages is CD14. These cells possess a repertoire of antimicrobial molecules stored in their granules and lysosomes. Polarization states observed in mammalian macrophages termed M1 and M2 also likely exist in fish macrophages. Markers for macrophage subtypes are slowly but definitively emerging in fish species. In the present study cell markers such as CD14, acetylcholine, alpha 7 acetylcholine nicotinic receptor (nAChR) subtype, the inducible nitric oxidase synthase (iNOS), and the antimicrobial peptide piscidin 1 are reported for the first time in the intestinal macrophages of both catfish Heteropneustes fossilis (Bloch, 1794) and the African bonytongue Heterotis niloticus (Cuvier, 1829) along the anterior and the posterior axis and the concentric muscle layers. Many antimicrobial effector responses of vertebrate macrophages including respiratory burst and NO induction are similar across the diverse animal taxa. Antibodies against calbindin coupled with ones to VAChT and tubulin revealed the localization of myenteric and submucosal plexuses, which are made up of enteric neurons, glial cells, and nerves near macrophages. Current studies allow for the elucidation of multiple roles of macrophages in disease models providing an insight into their in vivo function in fish. Full article

Submersion in the anaesthetic MS-222 is a well-established and effective method used during the euthanasia of fish, but the consequences of treatment with this anaesthetic for mitochondrial respiration are yet to be established. This is important to evaluate, as an increasing amount of research is conducting high-resolution respirometry to measure respiration across multiple species of fish, including looking at thermal sensitivity and mitochondrial responses to the warmer temperatures faced with climate change. Analysis often occurs after euthanasia with MS-222 without knowledge of how MS-222 itself affects any measured parameters of mitochondrial respiration, leaving potential for a misinterpretation of results. Here, high-resolution respirometry was conducted to explore how MS-222 affects oxidative phosphorylation in the brain and skeletal muscle of the three-spined stickleback, Gasterosteus aculeatus, which is a model species in evolutionary ecology. In the brain, differences in respiration were observed between three-spined sticklebacks euthanised with MS-222 and those where no anaesthetic was implemented. No differences between treatments were observed in the skeletal muscle, although variation between individuals was high and oxygen flux was lower than in the brain. Overall, this study highlights the need for a consistent method of euthanasia when conducting high-resolution respirometry in fish, as MS-222 may alter measures of oxidative phosphorylation. Full article

Aquatic surveys for fish in large water bodies (e.g., Laurentian Great Lakes of North America) often require a flexible approach using multiple methods, surveying different depths, and sampling across seasons, especially when the target species is elusive in its natural habitat. The round goby (Neogobius melanostomus) is an invasive, bottom-dwelling fish inhabiting rocky areas of all five Great Lakes. While trawl surveys are typically used for abundance assessments, angling has been demonstrated as a means of supplementing surveys with additional data. Yet, round goby abundance and distribution is still not well described. Recently, with considerable success, scientists have explored sampling environmental DNA (eDNA) to complement traditional monitoring techniques for population abundance estimates, early detection of invasive species, and spawning or migration events. Therefore, we collected eDNA from water samples alongside bottom trawls and hook and line angling in Lakes Huron and Michigan to detect round goby. eDNA samples were analyzed by both droplet digital PCR (ddPCR) and quantitative PCR (qPCR) to maximize the likelihood of detection. Overall, round goby was captured in 23% of the trawls, but the eDNA based methods detected round goby in 74% and 66% of samples by ddPCR and qPCR, respectively, mostly in samples collected at <30 m depths, and mostly in the fall. More studies comparing eDNA based methods to traditional monitoring, especially trawls in large open waters, may contribute to a better understanding of using eDNA in population assessments. Full article

Aquatic animals, which are ecologically important consumers in aquatic ecosystems and widely distributed in rivers, lakes, and seas, which occupy 70% of the earth’s surface, respond in unique ways to environmental changes at various temporal and spatial scales, and have optimized strategies for survival [...] Full article

Transient receptor potential vanilloid type 1 (TRPV1) has been investigated in humans and mammals; in recent years, some researchers have focused on this receptor in fishes. The present study aimed to identify TRPV1 receptors in cultures of RT-gill W1 cells and in the organs of rainbow trout (Oncorhynchus mykiss), in addition to evaluating the possible modulation induced by super critical fluid extract of basil (Ocimum basilicum), named F1-BEO. In vitro evaluation consisted of cell cultures and immunocytochemistry assays. During in vivo experimental sessions, eighty trout were divided into five groups that received a fish diet supplemented with 0, 0.5, 1, 2 and 3% w/w F1-BEO. Forty trout were euthanized after 15 and 30 days; organs were collected and processed according to the immunohistochemistry technique. Receptor expression was quantitatively measured using Image Pro Plus software. TRPV1 was identified in RT-gill W1 cells and in all organs, with a higher positivity in the muscle layers of the stomach, intestine and kidneys. F1-BEO induced an increased expression of TRPV1 in the stomach while a lower expression was appreciated in the bowel. No morphological alterations have been highlighted in the liver or kidneys. Further investigation will be necessary to evaluate the functionality of this receptor in rainbow trout. Full article

The effects of temperature manipulation, addition of sperm solution, and exposure to alkalized pH and/or hydrogen peroxide (H₂O₂) as possible spawning inducers in laboratory-conditioned and unconditioned adults of the yellow clam (Amarilladesma mactroides) were evaluated. In three trials, clams were laboratory-conditioned for 14 days and exposed to thermal shocks (from 20 °C to 23–29 °C), while clams from three additional trials were not conditioned but acclimatized for 45 min before spawning induction. Although conditioning advanced gonad maturity and increased the condition factor, none of the thermal treatments triggered spawning in these first trials. Histological analysis indicated that the gonads of conditioned clams were not mature. Alternatively, unfertilized and fertilized eggs, and larvae were observed after unconditioned clams were induced to spawn. The gonads of unconditioned clams were in an advanced stage of maturity. Exposure to temperature shocks, alone or in combination with the addition of sperm solution and with H₂O₂, resulted in spawning. Clams exposed to H₂O₂ kept their valves closed and had a high mortality rate. Temperature manipulation is the most promising stimulus to induce spawning in A. mactroides. As the success of conditioning depends on the stage of gonadal development at the time of capture in the wild, a period longer than 14 days may be necessary. Full article

Illegal, unreported, and unregulated (IUU) fishing in the disputed maritime areas causes significant damage to the marine ecology and authorized fisheries, increases the risk of conflicts among disputed states, and violates human rights at sea. Both unilateral measures and cooperative governance for IUU fishing are often inadequate in these areas. In light, this study aims to clarify the regulatory obligations of relevant states and explore feasible solutions based on international cooperation to promote IUU governance in disputed areas worldwide. The rapidly evolving international fisheries legal framework requires that states, such as coastal states, flag states, port states, or market states, fulfill their respective obligations to prevent and deter IUU and that the presence of disputes in a specific maritime area does not typically constitute grounds for derogation from these obligations or exemption from possible state responsibility. However, the implications of the conflicting claims in disputed maritime areas should be taken into consideration while interpreting and applying international legal rules. Therefore, this study suggests that regional and inter-regional cooperation is necessary for states to fulfill their obligations to regulate IUU fishing and prevent state responsibilities under international law. Parties to the dispute, as well as third parties, are encouraged to participate in the cooperative mechanism in order to coordinate legislative and enforcement measures and advance the institutionalization of IUU fishing regulation in the disputed maritime areas, which will not only advances the effective governance of IUU fishing but also reduces tensions among the disputing states and contributes to the peaceful settlement of the dispute. Full article

Mytella strigata (Hanley, 1843) is an invasive mussel species that has rapidly spread in China in recent years. Here, we tested the utility of three mitochondrial gene fragments, COI, 12S, and 16S, and two nuclear gene fragments, D1 28S and 18S-ITS1, for characterizing the levels of genetic diversity among and within populations using 191 M. strigata specimens collected in China to aid ongoing efforts to identify the origin of the invasion as well as molecular genetic studies. M. strigata exhibited two sex-associated haplogroups according to the COI and 12S sequences. The ratio of female-lineage to male-lineage COI and 12S sequences was 149:22 and 72:7, and the genetic distances between haplogroups were 6.56 and 9.17, respectively. Only one haplotype was detected among the 18S-ITS1 sequences (413 bp), and three haplotypes were detected among the D1 28S sequences (296 bp). The haplotype diversity of both the female-lineage COI and 12S sequences was greater than 0.5, and the nucleotide diversity of the 12S, 16S, D1 28S, and 18S-ITS1 sequences was less than 0.005 in all six populations in China. Our findings indicated that COI is the most useful gene fragment for genetic diversity studies of M. strigata populations; D1 28S and 18S-ITS1 sequences would be useful for species identification because of their low intraspecific diversity. Our genetic analysis of the COI sequences revealed Colombia as the most likely origin of M. strigata in China and showed that the invasive populations in China have recently experienced or are currently experiencing a population bottleneck. Full article

Japanese seabass (Lateolabrax japonicus) is an important species of cultured marine fish with high economic value in China. Nevertheless, from May to November 2019, mass mortality among cultured Japanese seabass occurred in Zhuhai City, Guangdong Province of China. Approximately 0.2–0.5% mortality was recorded daily, and the cumulative mortality was up to 30% during this disease outbreak. In this study, the clinical signs and pathological characteristics of diseased fish were investigated. Furthermore, the pathogenicity and antibiotic sensitivity of identified pathogenic bacteria from diseased fish were analyzed. The infected fish showed clinical signs of uncoordinated swimming; anorexia; pigment changes; and a number of 1–5 mm grayish-white nodules in the liver, spleen, and kidney tissues was also found. A bacterial strain, which was designated as ZHLJ2019, was isolated from the diseased fish. To ensure that ZHLJ2019 isolate was the causative agent, a Koch postulate trial was performed. Healthy Japanese seabass were infected by the intraperitoneal injection of 5 × 10⁴, 5 × 10⁵ and 5 × 10⁶ CFU/fish, and cumulative mortalities within 42 days were 75%, 90%, and 100%, respectively. The bacteria colony had traditional morphological and biochemical characteristics similar to that of Mycobacterium marinum. Phylogenetic molecular analyses of 16S rRNA, rpoB, hsp65, erp, and ITS genes confirmed that the isolated strain ZHLJ2019 was M. marinum. The granulomatous inflammation in internal organs of Japanese seabass naturally and experimentally infected with ZHLJ2019 isolate was consistent with the classic pathological features of mycobacteriosis. Drug susceptibility of ZHLJ2019 isolate to 11 antibiotics was determined by broth dilution method in vitro. The minimum inhibitory concentrations (MICs) of minocycline, rifampicin, ethambutol, isoniazid, streptomycin, doxycycline hydrochloride, kanamycin sulfate, levofloxacin, roxithromycin, and prothionamide against the strain ZHLJ2019 were 4, 2, 8, 4, 16, 8, 8, 8, 4, and 8 μg/mL, respectively. The results of this study suggest that M. marinum is the causal agent responsible for the morbidity and mortality of Japanese seabass cultured in intensive brackish water dirt ponds in southern China. Full article

Sipunculus nudus is an important intertidal aquaculture species that can ingest organic matter from the surface sediment and shows a high transportation capacity in sediment. However, little is known about the influence of intertidal aquaculture species on the sediment microbial community and the exchange of microbiota between the intestine and the surrounding sediment. In this study, the microbial communities in the intestine of S. nudus and three kinds of surrounding sediments were analyzed using high-throughput sequencing of the 16S rRNA gene amplicon, and the relationships between different communities were examined. Principal coordinate analysis and ANOSIM/Adonis analysis showed that the microbial communities of worm intestine samples were significantly different from those of surrounding sediments (p < 0.05). Meanwhile, compared with the sediment samples, the microbial α-diversity was significantly lower in the intestinal samples. Although the relative abundances of Proteobacteria and Cyanobacteria were high in all samples, three phyla (Bacteroidetes, Gemmatimonadetes, and Latescibacteria) showed a great difference between the four groups, as the abundances of the three phyla were significantly lower in the intestinal samples. Moreover, several microbial interactions were found between the worm intestine and surrounding sediments. BugBase functional prediction analysis indicated that the oxygen status of the sediment and the intestine was changed by bioturbation by the worm. Therefore, the microenvironment and microbial community in sediment were affected by the activity of S. nudus in the intertidal aquaculture zone. Full article

Optimal concentrations of three anesthetics for use with juvenile cobia (Rachycentron canadum) were determined using time-to-recovery and hematological datasets. Buffered MS-222, clove oil and 2-phenoxyethanol (2-PE) were examined. Juvenile cobia were exposed to three concentrations of each anesthetic at 24 °C. Based on time to recovery, optimal doses for MS-222 was determined as 120-mg L⁻¹, that for 2-PE, 0.4-mL L⁻¹ and, for clove oil, 5-mL L⁻¹. The hematological response of cobia to anesthesia included quantification of whole blood pH, pCO₂, pO₂, and Ca²⁺, K⁺, Na⁺, Cl⁻, hematocrit and glucose. Irrespective of anesthetic employed, cobia expressed metabolic acidosis, with changes in blood pH (p < 0.001) being matched by increases (p < 0.001) in pCO₂. Anesthesia tended to increase blood Na⁺, hematocrit, pO₂, Ca²⁺, and K⁺ although differential responses between anesthetics were recorded, suggesting different modes of action. A combination of recovery and hematological data indicated that when anesthesia is necessary, MS-222 represents the sedative of choice. Full article

To reveal the changes in the gut microbiota of yellow catfish after being infected by Edwardsiella ictaluri, 16S rRNA gene high-throughput sequencing technology was used to analyze the microbial composition and diversity of the healthy and diseased yellow catfish. The gut microbial richness and diversity of the diseased fish were significantly lower than those of healthy fish. The composition and predicted function of yellow catfish gut microbiota were drastically altered after infection by E. ictaluri. Fusobacteriota, Proteobacteria, and Firmicutes were the predominant bacterial phyla in the gut of the healthy fish, while Proteobacteria was the dominant phylum in the gut of the diseased fish. At the genus level, the gut of healthy fish was dominated by Cetobacterium, Plesiomonas, and Romboutsia, while the gut of diseased fish was overwhelmed by the pathogenic E. ictaluri (99.22 ± 0.85%), and Cetobacterium, Plesiomonas, and Romboutsia disappeared. This is the most characteristic feature of the intestinal microbiota composition of yellow catfish edwardsiellosis. The same sequence of E. ictaluri was detected in the intestine of the healthy fish and the liver and intestine of the diseased fish. The anaerobic and Gram-positive bacteria were significantly decreased, and the digestive system, immune system, and metabolic functions of the gut microbiota were significantly reduced in the diseased fish gut. This may be part of the pathogenesis of fish edwardsiellosis. Full article

The Subtropical Front (STF) plays a key role in the ecology of Chilean jack mackerel Trachurus murphyi. Nonetheless, there are few remote sensing studies of the STF in the open Southeast Pacific, and almost all of them have been conducted by satellite oceanographers in Russia and Ukraine to support respective large-scale fisheries of jack mackerel in this region. We reviewed these studies that documented long-term seasonal and interannual variability of the STF from sea surface temperature (SST) and sea surface height (SSH) data. We also mapped the STF from satellite sea surface salinity (SSS) data of the SMOS mission (2012–2019). The Subtropical Front consists of two fronts–North and South STF about 500 km apart–that border the Subtropical Frontal Zone (STFZ) in-between. The STF is density-compensated, with spatially divergent manifestations in temperature and salinity. In the temperature field, the STF extends in the WNW to ESE direction in the Southeast Pacific. In the salinity field, the STFZ appears as a broad frontal zone, extending zonally across the entire South Pacific. Three major types of satellite data-SST, SSH, and SSS-can be used to locate the STF. The SSH data is most advantageous with regard to the jack mackerel fisheries, owing to the all-weather capability of satellite altimetry and the radical improvement of the spatial resolution of SSH data in the near future. Despite the dearth of dedicated in situ studies of the South Pacific STFZ, there is a broad consensus regarding the STFZ being the principal spawning and nursing ground of T. murphyi and a migration corridor between Chile and New Zealand. Major data/knowledge gaps are identified, and key next steps are proposed to mitigate the data/knowledge gaps and inform fisheries management. Full article

Body condition indices are commonly used in the management of fish populations and are a surrogate to physiological attributes such as tissue-energy reserves. Relative condition factor (K_n) describes the condition of species relative to populations in a geographic area. We developed models to allow for the calculation of K_n in Montana, USA by using the weight–length data collected by Montana Fish, Wildlife & Parks. We generated log₁₀weight–log₁₀length relationships to obtain Montana specific parameter estimates for relative condition equations (W′) for 51 species and three subspecies. We developed separate models by water type (e.g., lotic and lentic) and sex for five species due to varying growth based on sexual dimorphism and varying ecosystem types. Relative condition offers the advantage of describing body condition relative to species in Montana, provides a condition index for species that do not have standard-weight models developed for relative weight (Wr), and affords more information for the global database on weight–length relationships of fishes. Full article