Fishing Research Articles

Economic evaluation of barriers to minimize reservoir sport fish escapement

AbstractObjectiveBarriers can be an effective method for reducing escapement of reservoir sport fish; however, whether the financial benefits of a barrier outweigh the costs of a barrier is unknown. We sought to quantify the costs and benefits associated with constructing barriers to reduce fish escapement while explicitly accounting for variability and uncertainty.MethodsWe developed a framework using simulation modeling and discounted cash flow techniques to quantify the costs and benefits of barrier construction on Brushy Creek Lake, Iowa, where a barrier was constructed in 2020 to reduce escapement of stocked Walleye Sander vitreus and Muskellunge Esox masquinongy. We then incorporated this framework into an interactive Shiny application to enable cost–benefit evaluations across a wide range of barrier types, system types, species, and escapement rates.ResultThe present value of the parallel‐bar barrier on Brushy Creek Lake, Iowa, over 10 years was US$69,576 (range = $64,484–$73,976), whereas the present value of escaped fish was $316,416 ($253,459–$378,823), indicating a net benefit of $246,840 ($188,975–$304,847) associated with barrier construction. The benefit–cost ratio of barrier construction was 4.55 after 10 years, indicating that for every $1 in present value spent on barrier construction, we saved $4.55 by preventing fish escapement. There was a 99% probability of a positive mean net benefit of the barrier after 3 years.ConclusionOur results indicate that barriers can be a cost‐effective option to minimize fish escapement, and barrier costs are more predictable compared with the cost of escapement. Quantifying the value of escaped fish and barrier construction on an economic scale enables the use of formal decision‐making tools to address complicated and multifaceted issues associated with reservoir fisheries management.

Neutral processes and taxonomic scale drive beta species-genetic diversity correlations in a submesophotic tropical reef fish.

If similar evolutionary forces maintain intra- and interspecific diversity, patterns of diversity at both levels of biological organization can be expected to covary across space. Although this prediction of a positive species-genetic diversity correlation (SGDC) has been tested for several taxa in natural landscapes, no study has yet evaluated the influence of the community delineation on these SGDCs. In this study, we focused on tropical fishes of the Indo-Pacific Ocean, using range-wide single nucleotide polymorphism data for a deep-sea fish (Etelis coruscans) and species presence data of 4878 Teleostei species. We investigated whether a diversity continuum occurred, for different community delineations (subfamily, family, order and class) and spatial extents, and which processes explained these diversity patterns. We found no association between genetic diversity and species richness (α-SGDC), regardless of the community and spatial extent. In contrast, we evidenced a positive relationship between genetic and species dissimilarities (β-SGDC) when the community was defined at the subfamily or family level of the species of interest, and when the Western Indian Ocean was excluded. This relationship was related to the imprint of dispersal processes across levels of biological organization in Lutjanidae. However, this positive β-SGDC was lost when considering higher taxonomic communities and at the scale of the entire Indo-Pacific, suggesting different responses of populations and communities to evolutionary processes at these scales. This study provides evidence that the taxonomic scale at which communities are defined and the spatial extent are pivotal to better understand the processes shaping diversity across levels of biological organization.

Does the microplastics ingestion patterns and polymer composition vary across the oceanic zones? A case study from the Indian coast

This study explores microplastic (MP) presence in the gastrointestinal tracts of deep-sea fish from the Central Indian Ocean, off the Indian coast. Among the 27 species examined, 19 showed MP contamination, averaging 2.68 ± 0.30 (±SE) MPs per individual. Polymer analysis via FTIR and micro-Raman identified several types, including polyethylene terephthalate (PET), polyvinyl alcohol (PVA), polypropelene (PP), polyvinyl acetate (PVC), polyurethane (PU), polytetrafluoroethylene (PTFE), polyaniline (PANI), polymethyl methacrylate (PMMA), and polyethersulfone (PES), with PET being the most prevalent (33.33 %). MP ingestion was higher in benthopelagic fish and those at higher trophic levels, as indicated by comparisons across oceanic zones. Niche partitioning analysis suggests feeding behaviour as a primary influencer of MP ingestion in deep-sea fish rather than habitat or trophic level. The study proposes the potential use of deep-sea fish as indicators for assessing microplastic pollution across oceanic zones and deep-sea regions through bycatch monitoring.

Extraction of virgin deep-sea fish oil (Lepidocybium flavobrunneum and Ruvettus pretiosus) and their potential as immunostimulants

Extraction of virgin deep-sea fish oil (Lepidocybium flavobrunneum and Ruvettus pretiosus) and their potential as immunostimulants

The impact of oceanographic factors on the composition and abundance of mesopelagic fish communities in the central and equatorial Atlantic

This paper presents an overview of the composition and abundance of pelagic fish communities collected during the 43rd cruise of the R/V ′Akademik Sergey Vavilov' on the transect in the central Atlantic, from the Azores to the Equator, in autumn 2016. Samples were taken only at night with a Samyshev-Aseev modified Isaacs-Kidd non-closing midwater pelagic trawl (SAMT) at 18 stations from two depth of 0–200 and 0–700 m. The study recorded 112 species of juvenile and adult mesopelagic fishes belonging to 20 families at the sampled stations. The statistical analysis indicated notable disparities in the fish communities that were caught at depths of 0–200 and 0–700 m. Our study suggests that there are notable differences in pelagic fish associations between the North Atlantic anticyclonic gyre zone and the equatorial jets region, at both depths analyzed. These differences are most likely the result of variations in hydro-physical and other environmental parameters. It has been observed that deep-sea fish communities in the equatorial and central North Atlantic are capable of inhabiting at the same time multiple habitats that exhibit varying physical and chemical structures of water masses. This phenomenon highlights the remarkable ecological adaptability of the species that make up mesopelagic deep-sea communities, as well as their wide geographical distribution. The higher abundance and diversity of mesopelagic fishes observed at stations located above the Mid-Atlantic Ridge may be due to a general decrease in depth over the ridge compared to the surrounding regions and/or local circulations occurring over its crests. Thus, the tops and slopes of seamounts may become unique concentrations of mesopelagic fishes for a limited time due to their topography.

Utilizing environmental DNA and imaging to study the deep-sea fish community of Takuyo-Daigo Seamount

The increase in interest of mining at seamounts means there is a critical need to establish baseline inventories through environmental survey, with the aim of promoting the conservation and stewardship of these remote habitats. To efficiently evaluate fish biodiversity around a seamount, we compared environmental DNA (eDNA) methods using seawater and sponge samples against methods using imagery obtained with a remotely operated vehicle (ROV) and a free-fall deep-sea camera lander called the Edokko Mark I on the Takuyo-Daigo Seamount (153.0°E, 23.5°N) in the northwestern Pacific Ocean. We detected a total of 18 fish families by these methods. The fish fauna detected on the seamount included many families commonly found in deep-sea areas and were similar to the fish fauna of other seamounts located at similar latitudes in the northwestern Pacific. Significant differences in the patterns of detection of fish families between the eDNA and imaging methods is attributed to the differing powers of detection of some fish groups between methods (related to primer compatibility and fish size). For deep-sea fish, the difference in fish composition at the family level between seawater and sponge eDNA methods was not significant, but the difference between Edokko Mark I and ROV methods was significant; the latter difference is likely due to whether or not bait is used to attract fish. Although the eDNA workflow implemented here requires improvements, the use of eDNA and imaging methods in combination provided better insight into the biodiversity of deep-sea fishes in the deep-sea around a seamount, where our knowledge of the fish fauna has been extremely limited. Our recovery of eDNA from seawater and sponge samples around the seamount demonstrates the potential of these methods for facilitating environmental baseline surveys and impact assessments of mining activities to obtain results not previously possible with the use of visual methods only.

Unraveling the ecological impacts of alewife in a large Midwest reservoir decades after introduction

Alewives Alosa pseudoharengus are native to the Atlantic Coast but have been introduced to inland waters as forage for sportfish populations. Alewife introductions have benefitted sportfish growth and body condition but have also negatively influenced larval fish survival through predation or competition for zooplankton. In 1986, alewives were stocked into Lake McConaughy, Nebraska, and became abundant and self-sustaining shortly thereafter. It has since been hypothesized that the alewife introduction altered zooplankton size and species composition and potentially negatively influenced Walleye recruitment. However, no studies on alewife distribution or food habits have been conducted on Lake McConaughy to date to investigate the potential influences of alewife on the fish and zooplankton communities. We collected alewives in the nearshore areas of Lake McConaughy during May–July 2022 and 2023 using short-term (about 1 h) small mesh horizontal gill net sets. We spatially assessed alewives by sampling the north and side south sides in addition to four classified quadrants of the reservoir. Total lengths (mm) were recorded, and stomachs were collected from up to 20 alewife per net. Prey were identified and food habits were summarized as percent composition by number. Zooplankton consumption was also paired with vertical Wisconsin zooplankton net tows taken at each site to assess prey selectivity. There was no evidence of piscivory suggesting that alewife predation is not influencing fish recruitment in Lake McConaughy. Alewives almost exclusively consumed zooplankton throughout the study period, suggesting the potential for interspecific competition with young-of-year fish. Our research provides a greater understanding of how introducing a non-native prey species to benefit sport fishes may have unintended negative consequences.

Polychlorinated biphenyls and incident coronary heart disease-related outcomes in Great Lakes fish consumers

BackgroundExposure to polychlorinated biphenyls (PCBs) has been linked to risk factors for cardiovascular disease such as increased inflammation, accelerated atherosclerosis, diabetes, and sex hormone dysregulation. Furthermore, there is increasing evidence suggesting associations between internal dose of PCBs and cardiovascular outcomes. ObjectivesThe purpose of this study is to investigate longitudinal associations of PCBs with coronary heart disease (CHD)-related outcomes in a cohort of Great Lakes sport fish consumers. MethodsThe Great Lakes Sport Fish Consumer cohort was established in the early 1990's. Eight hundred nineteen participants were followed from 1993 to 2017. Serum PCBs were measured in 1994/1995 (baseline), in 2001, and in 2004, while health history questionnaires were administered in 1996, 2003, 2010, and 2017. Cox models were used to prospectively investigate associations of total PCBs and PCB groupings, based on aryl hydrocarbon receptor activity, with incident self-reported physician diagnosis of coronary heart disease (CHD), myocardial infarction (MI), and angina pectoris. ResultsA 2-fold increase in phenobarbital-type PCBs was associated with a 72% increase in likelihood of self-reported incident diagnosis of CHD (HR=1.72, 95% CI: 1.06–2.81; p=0.0294). Similar results were observed for total PCBs (HR=1.68, 95% CI: 1.05–2.69; p=0.0306) and mixed methacholine/phenobarbital type (mixed-type) PCBs (HR=1.60, 95% CI: 1.02–2.52; p=0.0427), but not methacholine-type PCBs. PCBs were not strongly associated with risk of MI or angina. ConclusionsThis study presents evidence that exposure to PCBs increases the risk of developing coronary heart disease. Given the large number of risk factors and causal pathways for CHD, future research is required to better understand biological mechanisms of action for PCBs on CHD.

Smallmouth Bass and Walleye predation on stocked age‐0 Walleye in Lake Oahe, South Dakota

AbstractObjectiveWalleye Sander vitreus are important sport fish that are commonly stocked to supplement populations. Increases in Smallmouth Bass Micropterus dolomieu abundance have prompted concerns regarding potential predation by these and other piscivores on stocked Walleye. Our objectives were to assess the timing and duration of predation on stocked Walleye, the frequency of occurrence and percent composition of Walleye in predator diets, and the percentage of stocked Walleye consumed.MethodsWe collected Smallmouth Bass, adult Walleye, Largemouth Bass M. nigricans, and Northern Pike Esox lucius diets in May (prestocking) and June–September (poststocking) 2019 and 2021 from three bays in Lake Oahe, South Dakota. We stocked two bays with Walleye (30–32 mm; 255–1649 Walleye/ha), whereas one bay was unstocked and served as a reference. We estimated Smallmouth Bass population abundance using Schnabel capture–recapture models, and we used bioenergetics to estimate the percentage of stocked age‐0 Walleye consumed.ResultWe found age‐0 Walleye in up to 11.4% of Smallmouth Bass diets and 14.6% of adult Walleye diets during the poststocking period. A single Largemouth Bass consumed one Walleye at 3 days poststocking (DPS), whereas we did not identify Walleye in Northern Pike diets. Daily mean percent composition by weight (±95% confidence interval) of age‐0 Walleye in diets peaked at 43.2 ± 35.1% at 3 DPS for Smallmouth Bass and 49.8 ± 97.7% at 14 DPS for adult Walleye. Following the peaks, age‐0 Walleye percent composition by weight rapidly declined and was generally 0% after 25 DPS. Smallmouth Bass abundance was 0.4–5.6 fish/ha, whereas recaptures of other predator species were insufficient for reliable population estimates. We estimated that Smallmouth Bass consumed 29,930 age‐0 Walleye in 2019 and 12,535 age‐0 Walleye in 2021 (up to 14.7 ± 4.7% of stocked fish), potentially representing an important source of stocking mortality.ConclusionOur research provides insights into the effects of poststocking predation on age‐0 Walleye by Smallmouth Bass and, to a lesser extent, Walleye, Largemouth Bass, and Northern Pike. Managers should consider predation on stocked fingerling Walleye from resident predators and should contemplate alternative stocking locations or timing to reduce potential predation.

Fish Tissue Mercury in Lakes and the Moderating Effects of Selenium

Fish mercury concentrations result in fish consumption advisories. However, selenium : mercury molar ratios >1 are protective to wildlife and humans. Therefore, we sampled total selenium (TSe) and total mercury (THg) concentrations and molar ratios in sport fish from 50 Idaho (ID) lakes >20 ha and 67 northeastern USA (NE) lakes >1 ha. Sample lakes were selected at random, to obtain unbiased estimates of mean fish tissue levels, with known confidence limits, for target populations of 95 ID lakes >20 ha in surface area and 12,557 NE lakes >1 ha. Bass and salmonids presented the greatest potential mercury toxicity risk to consumers based on their higher mercury content, desirability as game fish, and widespread distributions. Fish tissue THg exceeded safe consumption criteria in an estimated 20–80% of the lakes in the two regions and TSe exceeded safe consumption thresholds in an estimated 0–20% of the lakes in the two regions. However, the Se : Hg molar ratio was >1 in an estimated 90–97% of fish tested from NE and ID lakes. Therefore, we concluded that Se levels in these systems are usually sufficient to limit disruption of selenoprotein activities by Hg, and that fish consumption advisories based on Hg alone are unnecessarily restrictive.

At-sea application of the comet assay to a deep-sea fish

Given the go ahead, deep-sea mining operations are likely to continue for decades on a substantial spatial scale and the resulting sediment plumes combined, are likely to extend beyond the licenced mining areas, and could lead to the chronic exposure of deep-sea organisms to a mixture of metals, even mobile species, such as fish, that could conceivably display avoidance behaviour. The metal concentrations, often substantially below lethal doses, mean that individual mortality is too blunt a measure to allow assessment of “serious harm”. Commonly used cellular biomarkers of exposure in ecotoxicology include DNA damage using the Comet assay. True deep-sea ecotoxicological studies with fish are rare and to our knowledge, there are no published data or method optimizations for deep-sea fish. Coryphaenoides ssp. were collected during SMARTEX expedition 1 (Feb/Mar, 2023) to the Clarion Clipperton Zone (CCZ) in the Eastern Pacific Ocean using a baited trap deployed between 4580–4,732m depth for 24–48 h. Blood and gill tissue were removed and processed for the Comet assay. In order to reduce artefactual DNA damage from cryopreservation observed previously, two sets of samples were prepared: a cryopreservative (10% DMSO) was added to one set of samples and stored at −80 °C; the second set was used to perform a Comet assay within hours of collection. A custom-built gimble table enabled horizontal electrophoresis at sea after which Comet assay slides were dried and stored at room temperature until further analysis. The Comet assay was also assessed in freshly sampled and frozen rainbow trout cells as a proxy control in order to evaluate potential artefacts from the collection and sampling procedure of the deep-sea fish. The blood samples processed at sea had a significantly reduced level of DNA damage compared to the frozen samples. There was no significant difference between the fresh deep-sea and rainbow trout samples. However, the freshly prepared gill samples in Coryphaenoides ssp. showed substantial artefacts, possibly as a consequence of barotrauma. These results represent the first effort at establishing baseline DNA damage data for deep-sea fish, an essential component in understating and quantifying the impact of deep-sea mining.

Estimating Age and Growth of Largemouth Bass in Southwestern Reservoirs by Using Otoliths and Scales

Abstract Age and growth data are frequently used to monitor and manage important North American sport fishes such as Largemouth Bass Micropterus salmoides. Continental and regional growth standards have been developed for this species to assess fish growth over time and across space. However, Largemouth Bass age and growth data are infrequently collected in Arizona and the reliability of age estimates derived from typical structures (e.g., scales, otoliths) in the Southwest is uncertain. Our objectives were to 1) compare precision and bias of age estimates from scales with those from otoliths and 2) estimate Largemouth Bass growth in several southwestern warmwater reservoirs by using otoliths. We collected Largemouth Bass from three Arizona reservoirs—Alamo, Peña Blanca, and Roosevelt—by boat electrofishing in spring 2021. We removed scales and sagittal otoliths from fish and then prepared and independently aged them three times. We compared differences in precision and bias between scales and otoliths using reader agreement percentages, confidence ratings, average coefficients of variation, and age-bias plots. We used age estimates from Largemouth Bass otoliths to calculate mean lengths-at-age at capture and relative growth indices based on published growth standards in each reservoir. Largemouth Bass scale age estimates were less precise, overestimated ages of younger fish, and underestimated age of older fish compared with those of otoliths. Growth was lower in Peña Blanca Lake than in the other two reservoirs according to mean length-at-age estimates, and relative growth indices suggested that Largemouth Bass growth in all three reservoirs was above average at younger ages, but less so at older ages. The results from this study add to a growing body of literature supporting the use of otoliths for estimating age and growth of Largemouth Bass.

Child Labour in Saurashtra Region of Gujarat State

Child labour is one of the most pressing social problems which the international community has been facing. Children are an important asset not only for their country but for the whole of mankind. They are not merely future adults. They are tiny apostles of peace and above all very much human beings though weak and immature. In almost all societies, children work in some way, though the types of work they do and the forms of their involvement vary. But many millions of children work under abusive and exploitative conditions that are clearly dangerous to them. There are still a large number of children who are employed in rag picking, collection of raw hides and skins, leather flaying and tanning, accompanying their parents for deep sea fishing, fish processing and storage, collection of minor forest produce, etc., that have not been brought within the ambit of the prohibited category.

Sport fish movement responses to a littoral zone coarse woody habitat addition

AbstractObjectiveFish movements and distributions throughout an ecosystem are important for understanding ecological interactions, conservation, and management. Coarse woody habitat (CWH) additions are a popular habitat enhancement tool that can influence movements and distributions of fishes; however, behavioral responses in relation to CWH additions are understudied. The objectives of our study were to test for changes in habitat use and behavioral responses of Muskellunge Esox masquinongy, Smallmouth Bass Micropterus dolomieu, and Walleye Sander vitreus to CWH additions in a small inland northern lake over 3 years and to evaluate two common forms of fish tracking to estimate daily movement of these fishes.MethodsWe used passive integrated transponder tag data collected continuously at 10 littoral sites and radiotelemetry data collected biweekly during the summer–fall months prior (2017) and following (2018–2019) CWH addition to examine movement behaviors and estimate daily probability of movement for the three species among lake habitats using multistate models.ResultWalleye were the most likely to remain near CWH, followed by Smallmouth Bass and Muskellunge. All species were more likely to move away from the modified and unmodified littoral zones and were more likely to remain in the offshore zone. Increased movement of fish may be in response to CWH creating a refuge for forage fish and subsequent increases in prey search times.ConclusionOur results suggest that CWH additions may alter established species‐specific annual movements, distributions, and habitat use to differing degrees in ecosystems, as our results differ from other CWH studies. Methodologically, radio‐tagging was most effective for offshore tracking but most labor intensive. Novel passive integrated transponder arrays (less labor intensive once installed) worked well to monitor movement between habitat types in shallow littoral areas. Long‐term monitoring of behavioral changes will be essential to assessing the stability changes caused by these habitat alterations.

Trimethylamine-N-oxide depletes urea in a peptide solvation shell

Trimethylamine-N-oxide (TMAO) and urea are metabolites that are used by some marine animals to maintain their cell volume in a saline environment. Urea is a well-known denaturant, and TMAO is a protective osmolyte that counteracts urea-induced protein denaturation. TMAO also has a general protein-protective effect, for example, it counters pressure-induced protein denaturation in deep-sea fish. These opposing effects on protein stability have been linked to the spatial relationship of TMAO, urea, and protein molecules. It is generally accepted that urea-induced denaturation proceeds through the accumulation of urea at the protein surface and their subsequent interaction. In contrast, it has been suggested that TMAO's protein-stabilizing effects stem from its exclusion from the protein surface, and its ability to deplete urea from protein surfaces; however, these spatial relationships are uncertain. We used neutron diffraction, coupled with structural refinement modeling, to study the spatial associations of TMAO and urea with the tripeptide derivative glycine-proline-glycinamide in aqueous urea, aqueous TMAO, and aqueous urea-TMAO (in the mole ratio 1:2 TMAO:urea). We found that TMAO depleted urea from the peptide's surface and that while TMAO was not excluded from the tripeptide's surface, strong atomic interactions between the peptide and TMAO were limited to hydrogen bond donating peptide groups. We found that the repartition of urea, by TMAO, was associated with preferential TMAO-urea bonding and enhanced urea-water hydrogen bonding, thereby anchoring urea in the bulk solution and depleting urea from the peptide surface.

Population demographics and angler exploitation of Suwannee Bass in two Georgia rivers

AbstractObjectiveSuwannee Bass Micropterus notius are a unique black bass that are endemic to riverine systems in Georgia and Florida, USA. Despite their “near threatened” status by the International Union for Conservation of Nature's Red List, Suwannee Bass are a popular sport fish that can be harvested throughout their range under a single harvest regulation with all black basses (genus Micropterus). However, a single harvest regulation may have disproportion effects on Suwannee Bass because of their rarity, limited distribution, and sex‐specific growth patterns.MethodsBoat electrofishing was used to collect Suwannee Bass and Largemouth Bass M. nigricans from both the Withlacoochee and Ochlockonee rivers to assess population demographics and angler exploitation. Common fisheries assessment metrics were calculated and annual exploitation rate was estimated from high reward (US$100) tags under simulated variability in tag loss and angler reporting rates.ResultWe observed different relative abundance and size structure among river systems. Electrofishing catch per unit effort of Suwannee Bass was higher in the Withlacoochee River (6.89 fish/h) than the Ochlockonee River (2.01 fish/h). Length‐frequency histograms suggested a wide breadth of lengths and presumed ages except for a lack of stock size Suwannee Bass in the Ochlockonee River. Eight percent of monetary reward tags were returned from anglers, yielding an overall exploitation estimate of 3.2%.ConclusionAnnual angler exploitation rates of Suwannee Bass and Largemouth Bass were low (<9.1%) in the Withlacoochee and Ochlockonee rivers of Georgia. Low exploitation coupled with a wide breadth of lengths and ages suggest these populations are currently not at risk of overexploitation.

Improved traits of proximate composition, liver antioxidant capacity and feeding habits in diploid hybrids from female Micropterus salmoides × male Lepomis cyanellus

Distant hybridization has been widely used as an effective strategy for improving fish germplasm. The largemouth bass (Micropterus salmoides, LB) is a popular fish worldwide due to its excellent performance in aquaculture, edibility, and sport fishing. However, the carnivorous nature of LB increases the cost and difficulty of culture and poses a threat to wild fishery resources. At present, there is a lack of research on improving the germplasm of LB. In this study, hybrid offspring (LG) were produced by crossing female LB and male green sunfish (Lepomis cyanellus, GS). The biological characteristics of the LG, such as muscle proximate composition, liver antioxidant enzyme activity, and pharyngeal tooth structure, were analyzed to evaluate their potential for aquaculture. The proximate composition analysis revealed that LG has a higher crude protein content of 20.07% compared to LB (18.1%) and GS (18.7%) (P < 0.05), and a lower crude fat content of 0.57% than LB (1.17%) (P < 0.05). Furthermore, LG had a significantly higher essential amino acid content (7.20%) than LB (6.43%) (P < 0.05), but not significantly different from GS (6.82%) (P > 0.05). In terms of fatty acid content, LG had significantly lower levels of saturated fatty acids (0.083%) compared to LB (0.153%) and GS (0.169%) (P < 0.05). Additionally, the amount of arachidonic acid (C20:4n6, ARA) in LG (0.058%) was significantly higher than LB (0.019%) and GS (0.043%) (P < 0.05). Regarding antioxidant enzyme activities in the liver, LG exhibited significantly higher superoxide dismutase (SOD) activity than LB and GS (P < 0.05). Electron microscopic observation of the pharyngeal tooth showed that the tooth number of LG (160.67 ± 3.93) was significantly lower than that of LB (181.67 ± 4.97) (P < 0.05) and significantly higher than that of GS (108.00 ± 3.58) (P < 0.05), while the tooth diameter of LG (0.076 ± 0.023) was significantly higher than that of LB (0.057 ± 0.016) (P < 0.05) and significantly lower than that of GS (0.108 ± 0.044) (P < 0.05). In conclusion, this study found that LG exhibited improved traits in proximate composition and hepatic antioxidant enzyme activity. The pharyngeal tooth characteristics indicated that LG may have different food selection and processing capabilities. This is the first report on biological characteristics in offspring produced from a distant hybridization between LB and GS, providing new insights into the genetic improvement and germplasm innovation of LB.

Unveiling taxonomic diversity in the deep-sea fish genus Notacanthus (Notacanthiformes: Notacanthidae) with description of Notacanthus arrontei n. sp.

Notacanthid fishes constitute a common part of benthopelagic deep-sea fish communities on seamounts and continental slopes around the world. However, their highly conserved morphology and the usual lack of information on deep-water organisms make it difficult to appropriately address their biodiversity. A multidisciplinary approach combining morphological data with a DNA-based species delimitation analyses was used to explore the taxonomy of Notacanthus species. For this purpose, morphological and molecular data were obtained from 43 individuals, and the resulting information was combined with the available data. The results showed the occurrence of Notacanthus arrontei n. sp. from the Iberian Peninsula and highlighted several taxonomic conundrums regarding the Notacanthus genus. For instance, no significant differences were found between Notacanthus indicus and the recently described Notacanthus laccadiviensis, questioning its taxonomic status. Similarly, the result of the species delimitation molecular analysis coincided with previous DNA barcoding studies supporting the snubnosed spiny eel Notacanthus chemnitzii as a species complex that requires further research. Moreover, two unidentified records from the Indian Ocean were confirmed to belong to an unknown species pending formal description, and barcoding data show for the first time the occurrence of the shortfin spiny eel Notacanthus bonaparte in the Australia-New Zealand area. This research confirms the existence of important gaps in the knowledge of notacanthid fishes and represents a step forward toward a better understanding of their biological diversity.

Trophic niche overlap of deep-sea fish species revealed by the combined approach of stomach contents and stable isotopes analysis in the Central Tyrrhenian Sea

Understanding the trophic ecology of marine ecosystems is a key challenge given that they are subject to anthropogenic pressures that can alter the integrity of the food web. The bathyal zone of the Central Tyrrhenian Sea is characterized by an high level of community biodiversity, heavy anthropogenic pressure and thus represents a fundamental environment for the study of trophic relationships between demersal fish species which live in sympatry, but this basin still remains data deficient. To fill this information gap, we investigated the trophic niche overlap of four deep-sea fish species, Galeus melastomus, Helicolenus dactylopterus, Lepidorhombus boscii, and Trisopterus capelanus, in the Central Tyrrhenian Sea using an integrated approach of stomach content and stable isotopes analysis (δ13C and δ15N). Our analysis revealed that the blackmouth catshark G. melastomus displays a wide trophic niche with considerable overlap with other fish species, as it consumed diverse prey including fish, crustaceans, and cephalopods, thus proving a generalist and opportunistic feeding behavior. The blackbelly rosefish H. dactylopterus exhibits a narrower isotopic trophic niche comprising mainly benthic crustaceans and so suggesting a marked specialism in feeding strategy. The diet of the four-spotted megrim L. boscii showed a marked overlap with that H. dactylopterus, as these species shared a similar benthic habit and relied upon a similar pool of resource. The poor cod T. capelanus showed a diverse diet comprising both prey captured close to the bottom, especially decapod and mysid crustaceans, and bathypelagic prey, mainly Osteichthyes, Myctophidae, and amphipod Hyperiidae, with an intermediate partially segregated isotopic niche width. The combination of stomach content analysis and stable isotopes analysis provided the first characterization of the trophic relationships, shedding light on the trophic niche overlap of these four ecologically important deep sea fish species. The diets of the four investigated species showed similarities in the composition of prey, but also differences which allows them to partially reduce competition. This information may be of crucial relevance for the development of effective management and conservation strategies for the bathyal Mediterranean environment.

First evidence of sexual dimorphism in olfactory organs of deep-sea lanternfishes (Myctophidae).

Finding a mate is of the utmost importance for organisms, and the traits associated with successfully finding one can be under strong selective pressures. In habitats where biomass and population density is often low, like the enormous open spaces of the deep sea, animals have evolved many adaptations for finding mates. One convergent adaptation seen in many deep-sea fishes is sexual dimorphism in olfactory organs, where, relative to body size, males have evolved greatly enlarged olfactory organs compared to females. Females are known to give off chemical cues such as pheromones, and these chemical stimuli can traverse long distances in the stable, stratified water of the deep sea and be picked up by the olfactory organs of males. This adaptation is believed to help males in multiple lineages of fishes find mates in deep-sea habitats. In this study, we describe the first morphological evidence of sexual dimorphism in the olfactory organs of lanternfishes (Myctophidae) in the genus Loweina. Lanternfishes are one of the most abundant vertebrates in the deep sea and are hypothesized to use visual signals from bioluminescence for mate recognition or mate detection. Bioluminescent cues that are readily visible at distances as far as 10 m in the aphotic deep sea are likely important for high population density lanternfish species that have high mate encounter rates. In contrast, myctophids found in lower density environments where species encounter rates are lower, like those in Loweina, likely benefit from longer-range chemical or olfactory cues for finding and identifying mates.