Fish Stomach Research Articles

Effects of Substituting Fishmeal with Soy Protein Concentrate Supplemented with Essential Amino Acids in the Olive Flounder (Paralichthys olivaceus) Diet on the Expression of Genes Related to Growth, Stress, Immunity, and Digestive Enzyme.

This study identified the effects of substituting fishmeal (FM) with soy protein concentrate (SPC) supplemented with lysine and methionine in the olive flounder (Paralichthys olivaceus) diet on the expression of genes related to growth, stress, immunity, and digestion. Three experimental diets were prepared; the control diet (Con) contained 60% FM, and the experimental diets contained 25% (SPC25) and 50% (SPC50) FM replaced by SPC. After the 140-day feeding period, weight gain, specific growth rate, feed availability, biological indices, and chemical composition of the muscle were not significantly affected by the dietary treatments. The gene expression levels of growth-related genes (IGF, GFB-3), immune-related genes (IL-8 and caspase), and stress-related genes (SOD, GPX, PRX, TRX) were higher in Con fish than in those fed the SPC25 and SPC50 diets. Chymo-TRY2, TRY2, and TRY3 in the stomach of fish fed the SPC25 diet were higher than fish fed the Con or SPC50 diets. TRY2 and lipase of fish fed the SPC25 diet were higher than those of fish fed the other diets but TRY3 was not significantly affected by the treatments in the intestine. In conclusion, substituting 25% FM with SPC was the most effective diet for the expression of growth, immune, stress, and digestive enzyme genes.

How Japanese eels escape from the stomach of a predatory fish

Predation shapes diversity in the defensive tactics of prey. One specialized defensive tactic is to escape the digestive system of the predator after capture1,2,3,4,5,6,7,8. While most of these defensive tactics involve passive ejection alive from predators' mouths and vents1,2,3,4,5, active escape from the digestive tracts of predators has recently been observed in certain invertebrate species6,7 and fish8. However, no study has yet uncovered the behavioral patterns and escape routes of the prey within a predator's digestive tract. Here, we report the sequential escape processes of the Japanese eel Anguilla japonica from capture to escape via the gills of predatory fish Odontobutis obscura using an X-ray video system. All captured eels had at least one portion of their bodies swallowed into the stomach of the predator. Surprisingly, after being swallowed, most individuals attempted to escape by going back up the digestive tract towards the esophagus and gill, and some of them succeeded in escaping via the predator's gill. Some eels, whose entire bodies were completely inside the stomach, exhibited circling behavior along the stomach, seemingly searching for possible escape routes. An electro-anesthetization experiment revealed that eels utilize various escape routes through gill clefts, rather than just one.

The preliminary introduction of hydrogen peroxide into the stomach of aquarium fish increases their survival rate in conditions of acute hypoxia

BACKGROUND: A solution of 3% hydrogen peroxide is an over-the-counter oxygen-releasing antiseptic, which forms oxygen foam when interacting locally with the wound surface. Therefore, this drug is widely used for mechanical cleansing of the surface of chronic wounds from purulent masses. The release of oxygen during catalase cleavage of hydrogen peroxide indicates the possibility of achieving anti-ischemic and anti-hypoxic action. AIM: A study of the effect of intragastric hydrogen peroxide on the resistance of aquarium fish to acute hypoxia. MATERIALS AND METHODS: Experiments were conducted on 80 adult aquarium fish of the guppy, blue neon, tri-linear parsings, swordtail fish and zebrafish (Danio rerio) breeds. To create acute hypoxia, each fish was placed in a transparent plastic container containing 5, 10 or 20 ml of fresh water at a temperature of +25 - +26 °C together with the fish, after which the container was hermetically sealed. Then, the motor activity of the fish's body, the respiratory movements of the gill arches, the opening of the oral cavity, the fluctuations of the fins and the dynamics of their coloration were monitored until the complete final immobilization of the fish and their death. Immediately before the experiment, 0.05 or 0.1 ml of fresh water in the control series and 0.05 ml or 0.1 ml of 0.05% hydrogen peroxide solution in the experimental series were injected into the stomach of the fish. The liquid was injected into the fish's stomach using a gastric mini-probe connected to an insulin syringe. RESULTS: It is shown that aquarium fish retain their viability in a small volume of fresh water inside a hermetically sealed container for a limited period of time, since fish continuously consume oxygen dissolved in water, thereby deepening hypoxia. At the same time, after sealing the container, the fish very quickly assume a stationary state, in which they remain for a certain period of time until their death. However, just before death, the immobility of the fish is disturbed. At the same time, the fish suddenly appear convulsive body movements, active movements of pectoral fins, mouths and gill arches, pectoral fins change their color, after which the fish defecate into the water. The results showed that the preliminary injection of 0.05 or 0.1 ml of 0.05% hydrogen peroxide solution into the stomach of fish prolongs the period of immobility of fish in hypoxia by an average of 20%. In all likelihood, the immobile state of fish is part of the complex of their adaptive adjustment to the cessation of oxygen supply to the water and reflects the availability of reserves of adaptation to hypoxia. The fact is that the absence of muscle contractions stops the muscles from using oxygen, which they use to generate energy. It is assumed that inside the stomach, hydrogen peroxide is absorbed into the blood, where, under the action of the enzyme catalase, it is split into water and gaseous oxygen, which replaces oxygen in the gills in the absence of oxygen in the surrounding water. CONCLUSIONS: Under model conditions, it was shown that pre-administration of 0.05 or 0.1 ml of 0.05% hydrogen peroxide solution into the stomach of fish increases their survival in conditions of acute hypoxia. Therefore, hydrogen peroxide can be considered as a potential antihypoxant for prolonging life in various types of suffocation, including the final stage of COVID-19.

A belly full of jelly? DNA metabarcoding shows evidence for gelatinous zooplankton predation by several fish species in Greenland waters.

The waters of Greenland harbour a high species richness and biomass of gelatinous zooplankton (GZP); however, their role in the diet of the many fish species, including commercially exploited species, has not yet been verified. Traditionally, GZP was considered to be a trophic dead end, i.e. with a limited contribution as prey for higher trophic levels. We applied DNA metabarcoding of two gene fragments (COI, 18S V1-V2) to the stomach contents of seven pelagic and demersal fish species in Greenland waters, to identify their prey composition as well as the occurrence of GZP predation. We detected GZP DNA reads in the stomachs of all investigated fish species, with frequency of occurrences ranging from 12.5% (for Melanogrammus aeglefinus) to 50% (for Argentina silus). GZP predation had not yet been reported for several of these species. GZP were found to majorly contribute to the diet of A. silus and Anarhichas denticulatus, particularly, the siphonophore Nanomia cara and the scyphozoan Atolla were of a high importance as prey, respectively. The use of multiple genetic markers enabled us to detect a total of 59 GZP taxa in the fish stomachs with several GZP species being detected only by one of the markers.

Microplastic characterization in the stomachs of swordfish (Xiphias gladius) from the western Mediterranean Sea

In this study, we aimed to quantify the presence of microplastics (MPs) in the stomachs of large pelagic fish (swordfish, Xiphias gladius, Linnaeus, 1758) sampled in the western Mediterranean Sea, and assess temporal trends (2011–2012 vs. 2017–2019) in MP ingestion. MPs were extracted from stomachs and characterized by μ-Fourier transform infrared spectroscopy. Results highlighted the ingestion of MP in 39 out of 49 stomachs analysed. Ingested MPs consisted mostly of small (<1 mm) fibers (88.6 %, mean ± standard deviation = 2.5 ± 6.1 particles per stomach), with a greater frequency of occurrence (FO) in the second period (FO = 90 %, 3.3 ± 8.0 particles per stomach). The predominant colours were purple, black and blue, and polyethylene terephthalate was the most frequently detected polymer. These results are crucial for the development of management actions aimed at the conservation of swordfish in the Mediterranean Sea and the prevention of health risks to humans.

Insights into the diet and feeding behavior of immature polar cod (Boreogadus saida) from the under-ice habitat of the central Arctic Ocean.

Polar cod (Boreogadus saida) is an endemic key species of the Arctic Ocean ecosystem. The ecology of this forage fish is well studied in Arctic shelf habitats where a large part of its population lives. However, knowledge about its ecology in the central Arctic Ocean (CAO), including its use of the sea-ice habitat, is hitherto very limited. To increase this knowledge, samples were collected at the under-ice surface during several expeditions to the CAO between 2012 and 2020, including the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The diet of immature B. saida and the taxonomic composition of their potential prey were analysed, showing that both sympagic and pelagic species were important prey items. Stomach contents included expected prey such as copepods and amphipods. Surprisingly, more rarely observed prey such as appendicularians, chaetognaths, and euphausiids were also found to be important. Comparisons of the fish stomach contents with prey distribution data suggests opportunistic feeding. However, relative prey density and catchability are important factors that determine which type of prey is ingested. Prey that ensures limited energy expenditure on hunting and feeding is often found in the stomach contents even though it is not the dominant species present in the environment. To investigate the importance of prey quality and quantity for the growth of B. saida in this area, we measured energy content of dominant prey species and used a bioenergetic model to quantify the effect of variations in diet on growth rate potential. The modeling results suggest that diet variability was largely explained by stomach fullness and, to a lesser degree, the energetic content of the prey. Our results suggest that under climate change, immature B. saida may be at least equally sensitive to a loss in the number of efficiently hunted prey than to a reduction in the prey's energy content. Consequences for the growth and survival of B. saida will not depend on prey presence alone, but also on prey catchability, digestibility, and energy content.

Rediscovery, systematics and conservation of an enigmatic freshwater crayfish (Parastacidae) from the Australian monsoon tropics

AbstractFreshwater wetlands are among the world's most valuable ecosystems, supporting diverse biota and critical ecological services, yet these habitats have suffered extensive and pervasive anthropogenic disturbance. Northern Australia represents a rare example of a relatively unmodified, vast wetland habitat. The freshwater crayfishes of the region are poorly documented, with one enigmatic species, the nutcracker yabby Cherax nucifraga, described from a single individual sampled opportunistically from the stomach of a predatory fish. Here we report on the rediscovery of C. nucifraga from a relatively limited distribution in semi‐permanent coastal freshwater wetlands. Field studies were conducted to inform natural resource management and conservation. Genome skimming to recover mitogenomes, 18S–28S and histone sequences demonstrated a sister relationship with two congeners from the tropics, and moderate molecular genetic substructure was apparent within C. nucifraga between mainland and Melville Island locations. Cherax nucifraga is characterised by the presence of a strawberry‐coloured soft patch on the outer margin of the claw, uniquely present in both mature males and females. Meristic and multivariate morphometric comparisons are made with the co‐occurring redclaw Cherax quadricarinatus and the allopatric whiteclaw yabby Cherax bicarinatus, with a summary of diagnostic traits developed into a visual guide and key. Programs to further understand ecology, threats and traditional ecological knowledge will help to inform the future conservation management of the species in the face of increasing development and environmental change to northern Australian coastal freshwater wetlands. Specific conservation actions include identifying and protecting refuge habitats and preventing incursions by other Cherax species.

Increasing marine trophic web knowledge through DNA analyses of fish stomach content: a step towards an ecosystem-based approach to fisheries research.

Multispecies and ecosystem models, which are key for the implementation of ecosystem-based approaches to fisheries management, require extensive data on the trophic interactions between marine organisms, including changes over time. DNA metabarcoding, by allowing the simultaneous taxonomic identification of the community present in hundreds of samples, could be used for speeding up large-scale stomach content data collection. Yet, for DNA metabarcoding to be routinely implemented, technical challenges should be addressed, such as the potentially complicated sampling logistics, the detection of a high proportion of predator DNA, and the inability to provide reliable abundance estimations. Here, we present a DNA metabarcoding assay developed to examine the diet of five commercially important fish, which can be feasibly incorporated into routinary samplings. The method is devised to speed up the analysis process by avoiding the stomach dissection and content extraction steps, while preventing the amplification of predator DNA by using blocking primers. Tested in mock samples and in real stomach samples, the method has proven effective and shows great effectiveness discerning diet variations due to predator ecology or prey availability. Additionally, by applying our protocol to mackerel stomachs previously analyzed by visual inspection, we showcase how DNA metabarcoding could complement visually based data by detecting overlooked prey by the visual approach. We finally discuss how DNA metabarcoding-based data can contribute to trophic data collection. Our work reinforces the potential of DNA metabarcoding for the study and monitoring of fish trophic interactions and provides a basis for its incorporation into routine monitoring programs, which will be critical for the implementation of ecosystem-based approaches to fisheries management.

Enrofloxacin, Effective Treatment of Pseudomonas aeruginosa and Enterococcus faecalis Infection in Oreochromis niloticus.

Enrofloxacin is a broad-spectrum synthetic antimicrobial drug widely used in veterinary medicine. The present study aimed to determine the effective enrofloxacin dose for treating Pseudomonas aeruginosa and Enterococcus faecalis infection in Oreochromis niloticus. P. aeruginosa and E. faecalis isolates were verified using selective differential media and biochemically using the Vitek 2 test. Bacterial isolates were virulent for O. niloticus with LD50 equal to 2.03 × 106 and 2.22 × 107 CFU fish-1 for P. aeruginosa and E. faecalis, respectively. Infected fish suffered from decreased feed intake followed by off-food, tail erosion, darkening of the external body surface, exophthalmia, ascites, and loss of escape reflex. Internally, congested hemorrhagic hepatopancreas with engorged distended gall bladder were dominant. The posterior kidney was congested with enlarged spleen, and empty elementary tract. Pathologically, severe degenerative changes were dominant in the hepatopancreas, posterior kidney, spleen, stomach, and gills of infected fish. Antimicrobial sensitivity test indicated the high susceptibility of P. aeruginosa and E. faecalis to enrofloxacin with MIC estimated at 1 and 0.0625 µg/mL, respectively. Enrofloxacin effectively protected O. niloticus against E. faecalis and P. aeruginosa infection when used with medicated feed at doses of 10 and 20 mg kg-1 body weight.

Quantification of finfish assemblages associated with mussel and seaweed farms in southwest UK provides evidence of potential benefits to fisheries

Low trophic aquaculture, including shellfish and seaweed farming, offers a potentially sustainable food source and may provide additional environmental benefits, including the creation of new feeding, breeding and nursery areas for fish of commercial and ecological importance. However, quantitative assessments of fish assemblages associated with aquaculture sites are lacking. We used pelagic baited remote underwater videos (BRUVs) and hook and line catches to survey summer fish assemblages at 2 integrated blue mussel Mytilus edulis and kelp (predominantly Saccharina latissima) farms in southwest UK. We recorded at least 11 finfish species across the surveys, including several of commercial importance, with farmed mussels and/or kelps supporting significantly higher levels of abundance and richness than reference areas outside farm infrastructure. Farmed kelp provided temporary habitat due to seasonal harvesting schedules, whereas farmed mussels provided greater habitat stability due to overlapping interannual growth cycles. Stomach content analysis of fish caught at the farms revealed that some low trophic level species had high proportions of amphipods in their stomachs, which also dominated epibiont assemblages at the farms. Higher trophic level fish stomachs contained several lower trophic level fish species, suggesting that farms provide new foraging grounds and support secondary and tertiary production. Although not identified to species level, juvenile fish were abundant at both farms, suggesting potential provisioning of nursery or breeding grounds; however, this needs further verification. Overall, this study provides evidence that shellfish and seaweed aquaculture can support and enhance populations of commercially and ecologically important fish species through habitat provisioning.

Analisis Aspek Ekobiologi Ikan Kakatua (Scaridae) di Perairan Pulau Tikus Kota Bengkulu

The large potential of marine fisheries owned by the City of Bengkulu can be an economic source for the local community. The fish potential comes from pelagic fish and reef fish. One of the reef fish is the parrot fish (Scaridae). Parrot fish in Bengkulu City are obtained from Tikus Island which are sold on Malabero Beach. The purpose of this study was to analyze the ecobiological aspects of parrot fish (Scaridae) in Tikus Island waters, Bengkulu City. The results of this study are expected to provide information in the form of valid data regarding the ecobiological aspects of parrot fish (Scaridae) in Tikus Island waters, Bengkulu City. In this study, data collection to look at ecological or environmental aspects was carried out by direct observation in the field at 3 stations, while biological aspects, namely food habits (amount/type of food), were observed through a microscope in the laboratory. The results of water parameter measurements, namely the temperature at station 1 ranged from 28-29 0C, station 2 is 29 0C, station 3 is 29 0C. pH value at station 1 is 7.0-7.3, station 2 is 7.3-7.7, station 3 is 6.5-7.1. Salinity values at station 1 is 31 ppt, station 2 is 30 ppt and station 3 is 31 ppt. Dissolved oxygen (DO) at station 1 ranged from 5.6-6.3 mg/L, station 2 5.2-5.3 mg/L and station 3 5.6-6.1 mg/L. The water brightness at station 1 is 9.2 m, at station 2 is 6.6 m and at station 3 is 7.4 m. Current velocity at station 1 ranges from 0.09-0.11 m/s, station 2 are 0.08-0.14 m/s, and at station 3 ranges from 0.05-0.09 m/s. Water depth at station 1 is 9.2 m, station 2 is 7.3 and station 3 is 7.5 m. These results indicate that Tikus Island water have a good environment for survival and habitat of parrot fish (Scaridae) or other marine biota. Furthermore, the biological aspects studied are food habits. Based on the identification results, 4 groups of food types were found in the parrot fish stomach, namely phytoplankton, zooplankton, sand coral, and were not identified. The percentage of food groups found from phytoplankton, zooplankton, sand coral, and not identified were 53%, 3%, 15%, 29%, respectively.

Dietary metabarcoding of keystone sardine species reveals the importance of their ichthyoplankton prey in food webs of the Southern Brazilian Bight fisheries

AbstractClupeiform fishes are ecologically and economically important species contributing to industrial and artisanal fisheries worldwide. They represent key links in food webs, influencing the dynamic between trophic levels. The dietary interactions of these species are poorly studied in many regions, yet essential for fisheries management. To elucidate the role of these species in food webs of the Southern Brazilian Bight pelagic fisheries, we used metabarcoding analysis of fish stomach contents of Clupeiformes and possible predators. Onboard sampling from March to September 2016 allowed for processing of 87 stomach samples representing 31 species (including 12 samples representing three species of Clupeiformes). Links between trophic levels showed the predominance of Sardinella brasiliensis and Engraulis anchoita as important dietary items of a large range of fishes (28 species belonging to 18 families) and representing the majority of the total prey read abundance assigned to clupeiform fishes (~46% and ~32%, respectively). Opisthonema oglinum contributed to the diet of 16 species in 13 families and ~18% of total read abundance of clupeiform fishes as prey. The appearance of multiple clupeiform taxa in the diet of predators that are not commonly associated with pelagic prey indicates that ecosystem‐based fisheries management should not be separated between pelagic and demersal fisheries. The diet of Clupeiformes revealed an unexpectedly large diversity of fish species and a low proportion of invertebrates (&lt;5% of clupeiform prey reads). This was likely due to a combination of both a limitation of the metabarcoding method (primer bias and low success of invertebrate taxonomic identification) as well as a contribution of early life stages (ichthyoplankton) to the diet of these fishes. The potential role of clupeiform fish populations as a constraint to the recruitment from the ichthyoplanktonic phase of other ecologically or commercially important fishes should be considered as an important direction for future studies.

Isolation, identification, and monoclonal antibody development of largemouth bass virus

Largemouth bass virus (LMBV) poses a significant threat to largemouth bass farming, leading to substantial economic losses. In December 2022, massive largemouth bass juveniles died at a fish farm in the city of Xinxiang, China. Through a series of experiments, we conclusively identified LMBV as the causative pathogen. The affected fish displayed anorexia, lethargy, and hemorrhage at the pectoral and caudal fin base. No parasites or pathogenic bacteria were detected on the body surface or gills, or isolated from the diseased fish. Severe hemorrhage, lymphocyte infiltration, and extensive necrosis were observed in the liver, spleen, intestine, and stomach of the moribund fish. The tissue homogenate from the diseased fish induced epithelioma papulosum cyprini cells (EPC) cell death, while no such effects were observed in grouper spleen (GS) cells. Sequence similarity analysis of the major capsid protein (MCP) indicated the virus shared 100% similarity with the LMBV-FS2021 strain, placing it within the Ranavirus genus. Transmission electron microscopy (TEM) observations revealed plenty of hexagonal virions accumulated in the cytoplasm of infected EPC cells. Artificial infection demonstrated that LMBV-XX01 was highly fatal to Micropterus salmoides juveniles, with an LD50 of 103.081 TCID50/fish. RT-qPCR detection confirmed that LMBV appeared in all sampled tissues of the challenged largemouth bass, with significantly higher viral loads detected in the liver and heart compared to other tissues. Additionally, we successfully obtained a highly purified recombinant MCP of LMBV and developed two strains of monoclonal antibodies targeting MCP of LMBV-XX01. Overall, our findings provide valuable materials and insights for the design of prevention strategies and the development of detection methods for LMBV.

Oreochromis niloticus gastrointestinal microbiota affected by the infection with Staphylococcus haemolyticus and Providencia vermicola, two emerging pathogens in fish aquaculture

The rapid intensification of tilapia aquaculture is associated with losses due to emerging pathogens. The gastrointestinal microbiota plays a vital role in the host's health by modulating the immune system and several physiological functions. Recent studies suggest that bacterial pathogens may deleteriously affect the microbiota structure. This study analyzed the effect of challenging tilapia with two emerging bacterial pathogens: Staphylococcus haemolyticus and Providencia vermicola, on the stomach and intestinal microbiota. Immediately after infection, fish started showing disease signs, tilapia infected with S. haemolyticus and P. vermicola registered 40 and 67% survival after seven days, while no mortality was reported in the control group during the trial. Amplicon libraries constructed by amplifying the V4 region of the 16S rRNA gene were analyzed. Proteobacteria was the most dominant phylum in the stomach and intestine of all infection groups. Staphylococcus haemolyticus infection disrupted both stomach and intestine microbiota. For instance, Bacteroidetes abundance increased while Proteobacteria dropped in the stomach of fish infected with S. haemolyticus. Both alpha and beta diversity indexes showed a clear differentiation of this group from the control and P. vermicola-infected fish. The microbiota of the stomach and intestine of this last group was also affected, although the effects were not as severe as in the case of the S. haemolyticus challenge. Results revealed that both emerging pathogens could lead to dysbiosis, affecting the functioning of the tilapia gut microbiota.

Simple additive weighting – a recommended seeds selections system for nile tilapia fish farmer

Nile tilapias are known to be an economically important farmed fish in Indonesia. Due to its adaptability, this tilapia fish can thrive in various aquatic conditions, making them an important commercial fish to produce locally or export internationally. Because of this potential, this study aims to provide recommendations using the decision support system to facilitate fish farmer decision-making with the Simple Additive Weighting model. This approach is expected to provide recommendations to fish farmers, or the general public interested in having their own Nile tilapia brood stock. The fish in this research was selected randomly following six criteria, namely fish weight, length, movement, fin or body deformation, fish colour and fish stomach condition. The result-based decision making model in this study provides an accuracy of 86.6%.

Stream hydrology and a pulse subsidy shape patterns of fish foraging.

Pulsed subsidy events create ephemeral fluxes of hyper-abundant resources that can shape annual patterns of consumption and growth for recipient consumers. However, environmental conditions strongly affect local resource availability for much of the year, and can heavily impact consumer foraging and growth patterns prior to pulsed subsidy events. Thus, a consumer's capacity to exploit pulse subsidy resources may be influenced by antecedent environmental conditions, but this has rarely been shown in nature and is unknown in aquatic ecosystems. Here, we sought to understand the importance of hydrologic variation and a salmon pulse subsidy on the foraging and growth patterns of two stream salmonids in a coastal southeast Alaska drainage. To do this, we sampled fish stomach contents at a high temporal frequency (daily-weekly measurements) and analyzed fish consumption rates in relation to streamflow and pulse subsidy resource availability. We then explored the influence of interannual hydrologic variation on access to pulse subsidy resources (i.e. whether fish exceeded an egg consumption gape limit) in a bioenergetic simulation. Prior to Pink Salmon spawning, Dolly Varden and Coho Salmon displayed distinct and nonlinear flow-foraging relationships, where forage for both species consisted primarily of macroinvertebrates. During this time period, consumption maxima coincided with baseflow and the highest observed flow conditions, and consumption minima were observed at severe low-water and intermediate flow values. After salmon spawning began, forage was not significantly related to flow and consisted primarily of salmon eggs. Further, consumption rates increased overall, and foraging patterns did not appear to be affected by flow in either species. Bioenergetic simulations revealed that patterns of interannual hydrologic variation may shift Coho Salmon growth trajectories among years. Together, our results suggest that access to marine pulse subsidy resources may depend on whether antecedent hydrologic conditions are suitable for juvenile salmonids to grow large enough to consume salmon eggs by the onset of spawning.

Daily vertical distribution and diet of Cyclothone braueri (Gonostomatidae) in the Polcevera submarine canyon (Ligurian Sea, north-western Mediterranean)

Despite its abundance, the role of Cyclothone braueri in intermediate mesopelagic food webs has been poorly investigated, notably its trophic behaviour in areas characterized by peculiar oceanographic and ecological features, such as submarine canyons. In this study, we investigated the diel feeding pattern of C. braueri in the Polcevera submarine canyon, in the Ligurian Sea. Stratified sampling from the surface to 1300 m was undertaken with a BIONESS every 6 h during a 24 h period. Stomach contents of 244 C. braueri specimens from 11.6 to 27.5 mm SL were examined. Calanoid copepods were the dominant taxa in the fish stomachs (98% of all copepods), with Pleuromamma abdominalis, Neocalanus gracilis, Pleuromamma gracilis and Euchaeta acuta being the main preys. Among the 20 identified copepod prey species, about 20% were typical of the epipelagic zone, while the remaining 80% usually live in mesopelagic waters. The low number of prey per stomach (average = 1.4) and high vacuity index (53%) indicated that this species had very low metabolic requirements (trophic level in this study was 3.03). Most of the full stomachs were found during the morning and afternoon in the upper mesopelagic zone (200–400 m), indicating two main periods of feeding activity per day. This study confirmed high abundance and biomass of C. braueri in Polcevera canyon compared to those of open ocean waters and raised the question of how the presence of the canyon affects migratory and trophic behaviours of this mesopelagic fish. Further analyses aimed at investigating the link between the hydrodynamic regime of the Polcevera canyon and the behaviour and trophic ecology of C. braueri are needed to address this question.

The Occurrence of Microplastics in the Gut Contents of Selected Estuarine Fishes of Southern Kerala, India

This extensive study intends to assess the abundances of microplastics in estuarine fishes and to examine the spatial and temporal fluctuations in microplastic pollution in selected estuarine ecosystems, including those of the Thiruvananthapuram and Kollam districts. The presence of microplastics (those having a diameter of less than 5 mm) in the estuarine environment is a growing cause for alarm on both a national and international scale. To investigate this, between February 2020 and January 2022, we surveyed the seasonal deposition of microplastics in the stomachs of some estuarine fishes in Southern Kerala. Microplastics came in many forms that we were able to positively identify as polypropylene (PP), polyethylene (PE), polystyrene (PS), and others. Microplastics were extracted from fish samples taken at 16 sites across two years and categorised according to size, colour, type and polymer content. Microfibers of less than 1 mm in length were the most common type of microplastic discovered in fish; they likely originated in domestic washing machines or garbage. Fish in Southern Kerala may be at greater risk of contamination since microplastics are more readily available there than in most other studies across the world. To better understand the risks to fish and create effective control methods to prevent plastic usage and minimise its influence on the aquatic environment, we advocate for more research on microplastic collecting in estuarine environments. Elemental analysis of sediment samples gathered from these sites. The objective of this study is to identify the toxic elements may potentially be transmitted to fish through microplastics and humans eat plastic-tainted fish and are exposed to plastic particles which causes various health problems.

Description, molecular identification and pathological lesions of Huffmanela persica sp. nov. (Nematoda: Trichosomoididae: Huffmanelinae) from the daggertooth pike conger Muraenesox cinereus

BackgroundThe genus Huffmanela Moravec, 1987 (Nematoda, Trichosomoididae, Huffmanelinae), represents a group of nematodes that infect both marine and freshwater fish, and the main gross feature of infection with different species of the genus is the presence of noticeable dark spots or tracks within the parasitized tissues. The purpose of this study was to describe morphologically and morphometrically the eggs of a new marine species of Huffmanela (Huffmanela persica sp. nov.), which was found in the form of black spots in the ovary and the tunica serosa of the stomach of the daggertooth pike conger (Muraenesox cinereus). The new species differs from Huffmanela hamo, another species reported from musculature of this host in Japan, in egg metrics, eggshell features and targeted organ. Molecular identification and pathological examination of the lesions caused by the new species are also reported.MethodsNematode eggs with varying degrees of development were separated from the infected tissues (ovary and tunica serosa of stomach) and investigated using light and scanning electron microscopy. Different species-specific markers (small subunit ribosomal DNA, 18S; large subunit ribosomal DNA, 28S; internal transcribed spacer, ITS) were used for molecular identification and phylogenetic study of the new species. Infected tissues were fixed in buffered formalin for pathological investigations.ResultsThe fully developed eggs of H. persica sp. nov. are distinguished from those previously described from this host on the basis of their measurements (size, 54–68 × 31–43 µm; polar plugs, 6.4–9.7 × 8.4–12 µm; shell thickness, 3.5–6.1 µm) and a delicate but ornate uterine layer (UL) covering the entire eggshell including the polar plugs. Histopathological examination revealed a fibro-granulomatous inflammation in the ovary and the serosal layer of the stomach of infected fish. Maximum-likelihood (ML) phylogenetic analysis recovered a sister relationship between the new species of marine origin and Huffmanela species previously collected from freshwater hosts.ConclusionsThe present study is the first to report the molecular characterization and phylogenetic position of a teleost-associated marine species of the genus Huffmanela. A comprehensive list of nominal and innominate populations of Huffmanela is also provided.Graphical abstract

Improvement in spotted rose snapper growth and skin coloration after incorporation of shrimp head meal in diet

Four isonitrogenous (45% crude protein) and isoenergetic (20.29 – 20.47 kJ/g) experimental diets were formulated by replacing 0%, 10%, 20% and 30% of fish meal (FM) with shrimp head meal (SHM) as a source of protein and tested the rearing performance and skin coloration of spotted rose snapper Lutjanus guttatus. The SHM had a high content of protein and pigments (i.e., carotenes and xanthophylls), but also chitin which eventually could be an anti-nutritional constituent in the diet for some fish species. A total of 240 fish (initial average weight of 77 ± 0.5 g) were distributed in 12 fiberglass tanks (3000 L) (20 fish/tank) and were fed twice a day for 70 days. The fish feed diets containing SHM showed the highest growth rates (weight gained, WG; 82.8–88.2 g) and lowest feed conversion ratio values (FCR; 1.3 – 1.4) compared to the D-Control diet (WG; 62.1 g and FCR; 1.5). The chitinolytic enzymatic activity (CEA) significantly increased in the stomach of fish fed diets containing SHM. The fish fed diets containing 20% and 30% of SHM, showed higher redness and more reddish-orange tones than the fish fed with the D-Control diet. The FM replacement had improvements in final growth, chitinolytic enzymatic activity, and skin coloration of spotted rose snapper. Thus, the use of up to 30% SHM protein in practical diets for spotted rose snapper should be a good alternative to develop more efficient aquafeed production for these species, however, further research could be suggested to determine the effectiveness of SHM as a substitute for FM in diets for spotted rose snapper rearing at a commercial scale conditions.