Juvenile Fish Research Articles

БОЛЕЗНИ ПРОХОДНЫХ ЛОСОСЁВЫХ РЫБ ПРИ ИСКУССТВЕННОМ ВОСПРОИЗВОДСТВЕ В УСЛОВИЯХ КРАЙНЕГО СЕВЕРА ДАЛЬНЕГО ВОСТОКА

Replenishment of fish stocks by increasing the release of juveniles during artificial fish farming is currently an urgent problem in the Far North of the Far East. In 1995-2003; 2021, an epizootological survey of natural spawning grounds and fish farming enterprises located in the northern part of the Okhotsk Sea basin was conducted: Ola, Arman, Taui, Yana, Iret, Ola experimental production acclimatization base, Armansky, Taui, Yansky salmon hatcheries. The aim is to study bacterial and protozoal diseases of passing salmonids in artificial fish farming. The novelty of the research is that for the first time in the waters of the northern part of the Okhotsk Sea basin, bacterial and parasitic diseases were detected in passing salmon fish in natural reservoirs during anadromous migration and artificial fish farming. In pink salmon, chum salmon, coho salmon, sockeye salmon, Aeromonas hydrophila culture isolated from blood and internal organs turned out to be virulent. Aeromonosis was established for the first time in passing salmon fish of natural populations. As a result of bacteriological studies, Aeromonas hydrophila bacteria were isolated from different batches of fertilized eggs, yolk sac of larvae, ascitic fluid of the abdominal cavity of juveniles. Due to the detection of the invasion of juvenile fish Trichodina truttae and Myxosoma cerebralis, which amounted to 10.0-46.5%, trichodyniosis and myxosomiasis were registered. The ways of transmission of infection to fish farms have been established. Fertilized eggs are infected from producers on spawning rivers during the selection of sexual products. The epizootological situation of aeromonosis, trichodyniosis and myxozomiasis is recognized as unfavorable. The method of diagnosis of bacterial diseases of salmonids at fish-breeding enterprises of the region has been improved.

Hypoxia-acclimation adjusts skeletal muscle anaerobic metabolism and burst swim performance in a marine fish

Red drum, Sciaenops ocellatus, are a marine teleost native to the Gulf of Mexico that routinely experiences periods of low oxygen (hypoxia). Recent work has demonstrated this species has the capacity to improve aerobic performance in hypoxia through respiratory acclimation. However, it remains unknown how hypoxia acclimation impacts anaerobic metabolism in red drum, and the consequences of exhaustive exercise and recovery. Juvenile fish were acclimated to normoxia (n = 15, DO 90.4 ± 6.42 %) or hypoxia (n = 15, DO 33.6 ± 7.2 %) for 8 days then sampled at three time points: at rest, after exercise, and after a 3 h recovery period. The resting time point was used to characterize the acclimated phenotype, while the remaining time points demonstrate how this phenotype responds to exhaustive exercise. Whole blood, red muscle, white muscle, and heart tissues were sampled for metabolites and enzyme activity. The resting phenotype was characterized by lower pHe and changes to skeletal muscle ATP. Exhaustive exercise increased muscle lactate, and decreased phosphocreatine and ATP with no effect of acclimation. Interestingly, hypoxia-acclimated fish had higher pHe and pHi than control in all exercise time points. Red muscle ATP was lower in hypoxia-acclimated fish versus control at each sample period. Moreover, acclimated fish increased lactate dehydrogenase activity in the red muscle. Hypoxia acclimation increased white muscle ATP and hexokinase activity, a glycolytic enzyme. In a gait-transition swim test, hypoxia-acclimated fish recruited anaerobic-powered burst swimming at lower speeds in normoxia compared to control fish. These data suggest that acclimation increases reliance on anaerobic metabolism, and does not benefit recovery from exhaustive exercise.

Fine-scale movement response of juvenile brown trout to hydropeaking

Juvenile fish are known to be the most impacted during hydropeaking events due to stranding or uncontrolled drift resulting from changes to water depth and flow velocity. To shed light on their response to such hydraulic alterations, we coupled flume experiments with image-based fish tracking and quantified the fine-scale movement behavior of wild (n = 30) and hatchery-reared (n = 38) brown trout (Salmo trutta) parr. We exposed fish to two distinct hydropeaking treatments in a laterally inclined (14 %) flume section stocked with real cobbles to create refuge and heterogeneous hydraulic conditions. Fish were individually acclimated (20 min) to baseflow (Q = 1.6 L s-1) and then exposed to three consecutive hydropeaking events, reaching peakflows tenfold larger than baseflow (Q = 16 L s-1). We found that, within just minutes, fish exhibited fine-scale movement responses to cope with the change of hydrodynamic conditions. Fish moved perpendicular to the main flow direction to shallow areas as these became submerged during discharge increase, holding position at low velocity zones. This resulted in a significant difference (p < 0.001) in lateral occupancy of the experimental section between baseflow and peakflow. During peakflow, fish occupied specific positions around cobbles and exhibited swimming behaviors, including bow-riding and entraining, that allowed them to hold position while likely minimizing energy expenditure. As a result, swimming distance reduced 60–70 % compared to baseflow. During the decrease in discharge following peakflow, fish abandoned areas falling dry by moving laterally. In the treatment with the larger down-ramping rate, the time to initiate relocation was lower while the relocation speed was higher. This study shows that, for the conditions investigated here, brown trout parr is capable of swiftly deploying multiple behavioral responses to navigate rapid changes in hydrodynamic conditions. These findings can be incorporated into habitat modeling and improve our capacity to inform hydropeaking mitigation efforts.

Comparative analysis of edible oil quality in fish nugget frying: Vacuum vs. atmospheric conditions

Consumer awareness about safe and nutritional fried food leads to the development of vacuum frying which overcomes major limitations of traditional frying. In this study effect of vacuum (120◦C, 40kPa) and atmospheric frying (180°C) on the fried fish nuggets quality and frying oil was compared. Oils used for frying (soyabean and mustard oil) were repeatedly used for 25 h without any replenishment. Vacuum frying (VF) oils and fish nuggets show a slower degradation of polyunstaurated fatty acids (PUFA), lesser transfatty acid (TFA) formation and a low C18:2/C16:0 ratio as compared to atmospheric frying (AF). Soyabean oil used for vacuum frying fish nuggets show an increase from 2.14 % to 3.11 %, decrease from 45.25 % to 38.29 %, while as AF fish nuggets show an increase from 2.14 % to 5.48 % and decrease from 45.25 % to 22.19 % in TFA content and PUFA content respectively after 25 h of frying. Oil uptake was also found lower (34.89 %) in VF fish nuggets as compared to AF(37.45 %), while as water loss was higher in AF chips than VF nuggets by 1.42-fold after 10 minutes of frying. Sensory analysis revealed that VF fish nuggets show a higher retention of sensory attributes and overall acceptability but they were less crispy then AF fish nuggets. Overall, vacuum frying results in the production of safe and nutritious fried fish nuggets.

Cloning and expression profiling of peptide YY in the brain of common carp, Cyprinus carpio

Peptide YY (PYY) is an anorectic brain-gut pancreatic peptide that helps in feeding regulation by reducing appetite and is well characterized in mammals. The role of PYY in relation to brain is least studied in mammals as well as in lower vertebrates including fish, however high expression was evident in male reproductive tissue. In this regard, this study attempts to evaluate the significance of PYY in the brain of common carp, Cyprinus carpio. As a first step, the cDNA of PYY from brain of adult male carp was cloned. Following which expression analysis was performed using juvenile and adult fish. The differential distribution pattern in various regions of brain and ontogeny expression analysis indicated that PYY may involve in physiological processes related to brain-pituitary axis. In addition, a significant decrease in neuropeptide Y expression was observed upon PYY- endoribonuclease-prepared small interfering RNA transfection in brain cells, in vitro indicating plausible PYY-NPY interaction in brain-pituitary axis of common carp.

Quantitative impacts of hydroelectric dams on the trans‐Amazonian migrations of goliath catfish

AbstractHydropower expansion is increasingly responsible for connectivity and biodiversity loss in freshwater ecosystems. The Amazon basin, which supports the highest level of freshwater biodiversity globally, faces such unplanned expansion. Here, we demonstrate and quantify the impacts of two major hydroelectric dams on the Madeira River on the trans‐Amazonian movements of one apex predatory catfish (Brachyplatystoma rousseauxii) performing the longest migration known in freshwaters. Using otolith microchemistry, we show that above the dams, the former basin‐wide homing migration between the breeding grounds in the upper Madeira and the nursery in the Amazon estuary has now been replaced by residency. We found evidence suggesting downstream migration of juvenile fish past dams into the Amazon estuary and that some of them home back to the Madeira. However, we did not find evidence that the fish homing back from the estuary can access their breeding grounds in the upper Madeira; they remain blocked below the dams. Our results provide undisputable evidence that the conservation of the species primarily requires the reestablishment of connectivity with the construction of efficient fishways.

Pile driving noise impacts behavioral patterns of important East Asian juvenile marine fishes

The surge in renewable energy demand, particularly from offshore wind farm (OWF), raises concerns about underwater noise pollution during their construction. Despite extensive studies on underwater noise impacts in European and Western countries, local species targeted investigations are crucial for global application. We assessed how pile driving noise during OWF construction affected the behavior of three juvenile Korean fishes (Lateolabrax japonicus, Acanthopagrus schlegelii, and Platichthys stellatus) prevalent in East Asian seas. Pile driving noise playback induced rapid changes in L. japonicus and A. schlegelii swimming speed and group cohesion, with 40 % remaining un-habituated after 5 min. Notably, L. japonicus showed clear avoidance of the noise source, while P. stellatus behavior remained unchanged at all. Our findings confirm that even relatively low-intensity impulsive noise can alter fish behavior, potentially due to species-specific characteristics. Accumulated data will inform the development of strategies for smart OWF establishment, advancing sustainable energy practices.

Preparation of PBAT microplastics and their potential toxicity to zebrafish embryos and juveniles

The extensive use of traditional non-biodegradable plastics results in the generation of microplastics (MPs), forming a new pollutant that can pose significant environmental risks. Biodegradable plastics (BP) possess degradation properties and can partially replace conventional plastics, thereby reducing pollution. However, further investigation is needed into the toxicity of biodegradable microplastics (BMPs) on aquatic organisms. This study explores the toxic effects of PBAT microplastics (PBAT-BMPs) and microplastics produced from degradable PBAT/TPS (thermoplastic starch) composite film (PBAT/TPS-BMPs) on zebrafish embryos. Our findings indicate that the presence of microplastics on the embryo's surface increases with higher BMPs concentration. Nonetheless, PBAT-BMPs tend to aggregate and are blocked by the embryonic membrane, thus diminishing their toxic effects on the embryo. Acute toxicity experiments revealed that 30 mg/L of PBAT-BMPs significantly reduced the survival rate of zebrafish embryos, whereas PBAT/TPS-BMPs had a lesser effect on survival. Both types of BMPs influenced the hatching rate of the embryos, leading to prolonged incubation periods. Additionally, both types of BMPs impacted the locomotor behavior of zebrafish larvae, causing an increase in larval locomotor speed. However, these BMPs had little impact on larval body development and heartbeat behavior. Fluorescent microplastic tracer experiments demonstrated that PBAT-BMPs persisted in juvenile fish for at least 144 h and were difficult to metabolize and excrete. Our study aims to gain a better understanding of the potential effects of BMPs on aquatic ecosystems and biological health, as well as to propose effective strategies for reducing environmental pollution and protecting organisms.

Effectiveness of textured vegetable protein incorporation for partial fish meat substitution in fish cakes

SummaryExcessive consumption of seafood has resulted in a decline in fish stocks and the destruction of ecosystems worldwide. Textured vegetable proteins (TVPs) can be used in manufacturing fish products, including surimi‐based fish cakes, to prevent these problems. In this study, we aimed to incorporate TVP into fish cakes as an alternative to fish meat (surimi). Fish cake samples containing TVP (0, 5%, 10%, 15% and 20%) were prepared and cooked through boiling or frying. Texture profiles, volatile compounds and consumer acceptance of the fish cake samples were measured. An increase in TVP content enhanced the protein content of the samples, making them more suitable than fish meat is as a protein source. In the fish cake samples, the textural properties, including hardness, springiness, cohesiveness, gumminess and chewiness, increased with increasing TVP content. Analysis of the volatile compounds showed that hexanal and 2‐pentifuran, which are primarily responsible for the grassy or beany flavour of soy, increased with increasing TVP content in fish cakes. The levels of these components were significantly lower in the fried samples than in the boiled samples. Overall, fried fish cakes containing 5% TVP (FST5) exhibited acceptance ratings similar to those of the control. Moreover, FST5 scored the highest in appearance, odour, taste and overall liking. Therefore, fried fish cakes supplemented with 5% TVP were qualitatively similar to fried fish cakes containing 100% fish meat (surimi). We propose the partial substitution of fish meat with alternative products to potentially reduce overfishing.

On the Issue of Statistically Significant Differences between the Average Values of Plastic Features in Two Groups of Juvenile Fish and between the Average Values of Their Indices

On the Issue of Statistically Significant Differences between the Average Values of Plastic Features in Two Groups of Juvenile Fish and between the Average Values of Their Indices

Seasonal patterns of juvenile fish assemblages in the surf zones of tropical sandy beaches along Gaolong Bay, Hainan Island, China

AbstractAimSurf zones are crucial nursery habitats for the early life stages of fish species associated with typical coastal ecosystems. However, little is known about the temporal patterns and drivers of fish assemblages in tropical surf zones. This study aimed to assess the (1) main changes in fish community structure throughout 1 year, (2) seasonal dynamic patterns in fish assemblages, and (3) key factors influencing fish assemblages in the tropical surf zones.LocationGaolong Bay, Wenchang City, Hainan Island, China.MethodsFish sampling was conducted monthly from June 2021 to May 2022 using a beach seine net. Fish species were identified using both morphological and molecular analyses. Kruskal–Wallis test, analysis of similarity, non‐metric multidimensional scaling analysis, and similarity percentage analysis were used to investigate the temporal fish assemblage patterns. Generalised additive models and canonical correspondence analysis were used to assess how environmental variables influence fish assemblages.ResultsWe identified 83 fish species, which were grouped into three ecotypes based on their primary habitat: coral reef‐seagrass‐associated species (CS) (35), mangrove‐estuarine‐associated species (ME) (30), and common coastal‐estuarine‐associated species (CE) (18). Most captured individuals were juveniles, and fish abundance and diversity were highest in May. Most CS species were abundant between March and May. ME and most CE species were dominant from June to August, and Mugilidae (CE) was abundant between October and February. Furthermore, surf fish assemblages were substantially influenced by tidal level, water temperature, conductivity, pH, turbidity, and dissolved oxygen.ConclusionsJuvenile fish were abundant in May and fish species with three ecotypes alternate in the surf zones throughout the year. Counter to much current thinking, March maybe the spawn peak of most fish species in the studied area, and we suggest that the fishing ban period could start from March instead of May in the inshore areas of Hainan Island.

Can Puntius sophore breed artificially under controlled conditions? Tracing the life cycle of Puntius sophore through artificial captive breeding

The development of new strategies for breeding indigenous fish species is of utmost importance in the wake of unfavorable weather events, as a result of climate change. Therefore, an attempt has been made to achieve artificial breeding of an indigenous barb, Puntius sophore. Two groups of juvenile fish, collected from the wild, were reared till sexual maturation. One group was reared under a natural photothermal regime and the other was reared under strictly controlled conditions with photothermal stimulation till sexual maturation and subsequently, hormonal stimulation with OVAFISH was also done for inducement of spawning. The spawning efficiencies were analyzed and the results in terms of latency period (6.74 Hrs), ovulation rate (92.2 %), fertilization rate (90.6 %), hatching rate (89.9 %), and spawning efficiency coefficient (Se) (0.828) were found better in Puntius sophore reared under the indoor controlled condition with photothermal manipulation and hormone administration compared to the group of fish which was reared under a natural photothermal with a hormonal stimulation. The results of this study demonstrate the captive artificial breeding of Puntius sophore spawners reared under a natural photothermal regime and controlled photothermal regime in indoor conditions. The outcome of the present study can be used for developing key strategies for a climate smart aquaculture for fish farmers.

Otolith microchemistry identifies shallow, intertidal-dominated estuaries as important nurseries for sand flounder in New Zealand

Estuaries provide critical habitat, food, and refuge for juvenile fish. Elemental concentrations in otoliths can retrospectively identify estuarine nursery habitats that contribute disproportionately to adult populations, providing valuable information for fisheries and coastal ecosystems. The present study aimed to (1) compare elemental signatures of juvenile (age 0+) sand flounder Rhombosolea plebeia otoliths collected from 9 estuaries in east Otago, New Zealand, and (2) assess the application of otolith microchemistry for identifying the nursery habitats contributing to adult (age 1+) sand flounder from the coastal shelf population. Otoliths from juvenile flounder were collected in November 2020, and adults of the same cohort were collected in the winter/spring of 2022. Laser ablation inductively coupled plasma mass spectrometry quantified 12 element concentrations within the post-settlement region of juvenile and adult otoliths using depth-profiling and ablation transects, respectively. Significant differences in post-settlement elemental concentrations were detected among estuaries. Juvenile and adult sand flounder were classified to their nursery origin using canonical analysis of principal coordinates. Grouping estuaries by the New Zealand Estuary Trophic Index classification scheme improved the overall juvenile classification accuracy from 56.7% (51/90) to 82.2% (74/90). Adult sand flounder (n = 78) were classified to have originated from shallow intertidal dominated estuaries (62%), followed by Otago Harbour (32%) and shallow, short residence time river and tidal river with adjoining lagoon estuaries (6%). The results highlight how otolith microchemistry can provide information on the use of critical estuarine nursery habitats for a commercially important species.

Stable isotope analysis reveals fish juveniles as a temporal main resource consumed by invasive pumpkinseed (Lepomis gibbosus)

AbstractThe pumpkinseed Lepomis gibbosus (Linnaeus, 1758) is a small centrarchid fish species from North America that has invaded most European basins, with pronounced expected impacts. Analyses of pumpkinseed diet in its invasive range using gut content analysis (GCA) show macrozoobenthos as the most common dietary item, suggesting a competitive effect on native fish communities. Our study uses a combination of GCA and stable isotope analysis (SIA) to document pumpkinseed diet at two sites in its invaded range and relates pumpkinseed diet preferences with parasitic load. SIA revealed juvenile fish as a major prey item at one of the sites (63 and 50% of the diet of small and the large fish), while GCA showed pumpkinseed preying mostly on macroinvertebrates (chironomids, gastropods, Ephemeroptera, and Zygoptera larvae) at both sites. While infrequent infection by trophically transmitted parasitic nematodes could be related to low consumption of zooplankton, substantial infection by metacercariae of Posthodiplostomum centrarchi Hoffman1958 appears to reflect relatively high consumption rates of its intermediate host, physid snails. Using SIA allowed to demonstrate that pumpkinseed feeding in its non-native range can be based on piscivory, emphasising the need for combining multiple methods when studying the impact of non-native species on food webs.

In vivo multiscale analyses of spring viremia of carp virus (SVCV) infection: From model organism to target species.

Spring viremia of carp virus (SVCV) has a broad fish host spectrum and is responsible for a disease that generally affects juvenile fishes with a mortality rate of up to 90%. In the absence of treatments or vaccines against SVCV, the search for prophylactic or therapeutic solutions is thus relevant, particularly to identify solutions compatible with mass vaccination. In addition to being a threat to aquaculture and ecosystems, SVCV is a unique pathogen to study virus-host interactions in the zebrafish model. Establishing the first reverse genetics system for SVCV and the design of recombinant SVCV (rSVCV) expressing fluorescent or bioluminescent proteins adds a new dimension for the study of these interactions using innovative imaging techniques. The infection by bath immersion of zebrafish larvae with rSVCV expressing mCherry allows us to define the first SVCV replication sites and the host innate immune responses using different transgenic lines of zebrafish. The fins were found as the main initial sites of infection in both zebrafish and carp, its natural host. Hence, new insights into the physiopathology of SVCV infection have been described. We report that neutrophils are recruited at the sites of infection and persist up to the death of the animal leading to an uncontrolled inflammation correlated with the expression of the pro-inflammatory cytokine IL1β. Tissue damage was observed at the site of initial replication, a likely consequence of virus-induced injury or the pro-inflammatory response. Interestingly, SVCV infection by bath immersion triggers a persistent pro-inflammatory response rather than activation of the antiviral IFN signaling pathway as observed following intravenous injection, highlighting the importance of the route of infection on the progression of pathogenicity. Thus, this model of zebrafish larvae infection by rSVCV offers new perspectives to study in detail virus-host interactions and to discover new prophylactic or therapeutic solutions.

Growth optimalization of bileh fish seeds (Rasbora sp.) through different feeding frequencies

Bileh fish is a type of freshwater fish that is sought after by the people of Aceh because it has a delicious taste and is quite tasty. Bileh fish is a local fish species that has the potential to be developed as an aquaculture commodity and its population must be preserved from overfishing. The aim of this research was to determine the effect of different feeding frequencies on the growth of bileh fish fry (Rasbora sp.). This research used a non-factorial completely randomized design (CRD) method consisting of 4 treatments and 3 replications each, namely the frequency of feeding 1 time/day (P1), feeding 2 times/day (P2), feeding 3 times/day day (P3) and feeding 4 times/day (P4). The feed given is commercial feed PF 500 with 39% protein. The parameters observed included survival rate, length growth, weight growth, daily growth rate, feed efficiency and water quality. The results showed that different feeding frequencies had no significant effect on survival rate, absolute length and daily growth rate of bileh fish (Rasbora sp.). However, it has a real effect on weight growth and feed efficiency. The best feeding frequency to optimize the weight growth of bileh fish (Rasbora sp.) is in the P3 treatment with a frequency of 3 times/day.Keywords: Feed Efficiency; Feeding Frequency; Growth; Rasbora

The effect of the ratio of male to female Broodstock on the production of tilapia (Oreochromis niloticus) Seed

This research was conducted from November to December 2023 at the Production Centre of Pangkajene Fish Seed Institute, Sidenreng Rappang Regency, South Sulawesi Province. The objective of this study was to determine the effect of the ratio of male and female broodstock on tilapia seed production, and to determine the ratio of male and female broodstock that produce the most seed production. The design used was a completely randomised design with 4 treatments and 3 replications. The data obtained were presented in the form of graphs and tables. The effect of treatment was analysed using analysis of variance (ANOVA) followed by Tukey's test. The results of the analysis showed that the ratio of male to female broodstock had a significant effect on tilapia fry production (P &lt; 0.05) Sig = 0.034. The highest seed production was found in treatment C (1 male: 4 females) with an average production of 71,000 seeds. Treatment B (1 male: 3 females), 51,000 seeds, treatment D (1 male: 5 females), 34,000 seeds and treatment A (1 male: 1 female) with an average production of 21,000 seeds. It can be concluded that the ratio of male to female broodstock has a significant effect on the production of nila fish fry (Oreochromis niloticus). The highest fry production was obtained in the ratio 1 male; 4 females.Keywords: Broodstock; Production; Ratio; Seed; Tilapia

Technology for the production of extruded starter feed for juvenile fish

The latest advances in science, combined with the growing possibilities of modern technology, contributed to the improvement of fish feeding technology and fish farming in general. It is obvious that the expansion of the species composition of cultivated fish farming objects will continue, and the importance of feed and fish feeding technology will steadily increase. The developed recipes of starter feeds for juvenile fish and the technology of their production would make it possible to establish the production of these feeds for fish farms in Kazakhstan, as a result, the survival rate and growth rate of juvenile fish grown in industrial conditions would increase. The aim of the work was to develop recipes for starter feeds for pikeperch fry and technology for their production by extrusion, the development of these feeds to improve the efficiency of growing pikeperch in industrial conditions. According to the developed recipe, a starter feed for zander juveniles, balanced in terms of basic nutrients, was developed, a study was made of the effect of this feed on the efficiency and speed of growing zander juveniles. The dynamics of rearing juvenile pikeperch was studied when feeding the starter feed developed by the Kazakh Research Institute of Processing and Food Industry, with a feed coefficient of 1.28 and as a control foreign starter feed for trout “Aller Aqua” – 1.2. The materials of the article are of practical importance and the need for further research, they will help replenish the formulas of compound feed for the industrial cultivation of juvenile pike perch in fish farms of the Republic of Kazakhstan

Effect of alternative natural diet on microplastic ingestion, functional responses and trophic transfer in a tri-trophic coastal pelagic food web

The patchy distribution of microplastics (MP) and their size range similar to planktonic organisms, are likely to have major ecological consequences, through MP ingestion, food dilution, and transfer across trophic levels. Our study applied a community module using tritrophic food chain with zooplankton as prey, and a planktivorous seabass fry as predator. We conducted a series of feeding experiments and recorded the direct uptake of MP under six different concentrations ranging from 25 to 800 particles L−1. We also estimated the indirect transfer of MP via trophic link. The ingestion rates for Brachionus plicatilis, Mesocyclops isabellae, and Lates calcarifer, were 3.7 ± 0.3 MP ind−1 min−1, 1.69 ± 0.1 MP ind−1 min−1, and 3.51 ± 0.52 MP ind−1 h−1, respectively. In the presence of a natural diet, rotifers and copepods ingested significantly lower number, whereas, fish fry ingested a higher number of MP, suggesting further vulnerability to the consumers of MP-contaminated fish and potential biomagnification at higher trophic levels. Overall, the MP uptake rate increased with increasing concentration, and finally leveled off, indicating a type II functional response to MP concentration. The presence of natural diet led to a lower Km value. In the indirect transfer experiment, 74 % of B. plicatilis and 78 % of M. isabellae individuals were contaminated with MP, when offered as prey. Brachionid mastax and MP particles were observed in the gut of copepods. The fish fry gut content also recorded brachionid mastax, MP-contaminated copepods, and MP particles, showing direct evidence of trophic transfer pointing to a cascading effect on higher trophic levels including humans via piscivory.

Activin Signaling Pathway Specialization During Embryonic and Skeletal Muscle Development in Rainbow Trout (Oncorhynchus mykiss).

Activin signaling is essential for proper embryonic, skeletal muscle, and reproductive development. Duplication of the pathway in teleost fish has enabled diversification of gene function across the pathway but how gene duplication influences the function of activin signaling in non-mammalian species is poorly understood. Full characterization of activin receptor signaling pathway expression was performed across embryonic development and during early skeletal muscle growth in rainbow trout (RBT, Oncorhynchus mykiss). Rainbow trout are a model salmonid species that have undergone two additional rounds of whole genome duplication. A small number of genes were expressed early in development and most genes increased expression throughout development. There was limited expression of activin Ab in RBT embryos despite these genes exhibiting significantly elevated expression in post-hatch skeletal muscle. CRISPR editing of the activin Aa1 ohnolog and subsequent production of meiotic gynogenetic offspring revealed that biallelic disruption of activin Aa1 did not result in developmental defects, as occurs with knockout of activin A in mammals. The majority of gynogenetic offspring exhibited homozygous activin Aa1 genotypes (wild type, in-frame, or frameshift) derived from the mosaic founder female. The research identifies mechanisms of specialization among the duplicated activin ohnologs across embryonic development and during periods of high muscle growth in larval and juvenile fish. The knowledge gained provides insights into potential viable gene-targeting approaches for engineering the activin receptor signaling pathway and establishes the feasibility of employing meiotic gynogenesis as a tool for producing homozygous F1 genome-edited fish for species with long-generation times, such as salmonids.