Young Fish Research Articles

Effect of An Additional Amount of Fish and Fermentation Time on The Sensory Properties of The Lemea

Lemea, a traditional fermented food of the Rejang people in Bengkulu, is made from young bamboo and fish. The fish commonly used in the making Lemea is Mozambique tilapia or Mujair (Oreochromis mossambicus). The fermentation process typically lasts between 3 to 7 days. This study aimed to assess the sensory characteristics, including taste, color, texture, and aroma, of Lemea, based on the preferences of panelists. The variations examined were fermentation duration, and the amount of Mujair fish added. The research followed a completely randomized design, incorporating three fermentation durations (24, 96, and 144 hours) and three fish quantities (250 grams, 500 grams, and 750 grams). Sensory evaluations were conducted on the fermented samples, encompassing taste, aroma, texture, and color. The data revealed that the most favored taste and texture of Lemea were achieved with 500 grams of fish and a fermentation duration of 144 hours (J2W3). Likewise, the preferred aroma and color were observed in the sample with 750 grams of fish and 24 hours of fermentation (J3W1). The data analysis indicated that the sample with 500 grams of fish and a fermentation duration of 144 hours (J2W3) exhibited the most favorable sensory characteristics (taste, aroma, texture, and color). Thus, the quantity of fish added and the duration of fermentation influenced the sensory attributes of Lemea.

Thyroid neoplasia associated with nutritional deficiency in cultured jade perch in Hong Kong.

Non-neoplastic thyroid hyperplasia is common in terrestrial animals, secondary to nutritional imbalances or other goitrogenic compounds. Thyroid hyperplasia is relatively common in teleost fish; however, malignant thyroid neoplasia is rarely reported. We diagnosed cases of thyroid neoplasia in a population of jade perch (Scortum barcoo). The 3,000 affected fish had grossly apparent, bilateral pharyngeal swellings. Histologic examination confirmed proliferative thyroid lesions ranging from hyperplasia to well-differentiated follicular cell carcinoma. In addition, the younger population of animals on the farm also had bacterial septicemia and mild Dactylogyrus sp. gill infections. Feed analysis revealed a severe deficiency of iodine and vitamin C in the homemade fish diet used on the farm. The concentrations of other minerals, such as zinc, were also on the lower end of the recommended requirements for freshwater fish. The farm was using surface water in its recirculating aquaculture system. We recommended a switch to a commercial aquaculture diet, as well as to use well water rather than surface water to avoid any contaminants, and to treat the younger fish with an antibiotic for bacterial septicemia. Our case provides evidence of progression from nutritional-associated thyroid hyperplasia to neoplasia in farmed teleost fish.

Breeding of whitefish Coregonus Lavaretus L. at the Knyazhegubsky fish hatchery

The article describes whitefish Coregonus lavaretus L., 1758 (Baltic environmental type) breeding results at the Knyazhegubsky fish hatchery (Murmansk region, Russia). Since 2017, the major goal of this fish hatchery has been the breeding of freshwater type of whitefish. Technology for whitefish breeding was tested in 2018-2019. A number of problems encountered by fish breeders were identified. Live fertilized Baltic whitefish eggs at the “eye pigmentation” phase are purchased every year from OOO “Forvat” fish farm (Sosnovo settlement, Priozersky district, Leningrad region, Russia) and transported to the Knyazhegubsky fish hatchery. Major fish-farming activities subsequently performed at the fish hatchery include: eggs incubation in Weiss machines, summer and winter rearing of juveniles in rearing facilities, in trout ditches, and at equipped summer site as well as release of young whitefish aged under one year into the Kovdozerskoe water reservoir. The average mass of a single young fish in the first batch released in 2019 was 0.5 grams. Juvenile fish is available for release on a partial basis into water bodies of the Murmansk region for fish-stocking purposes under contracts with business entities. Currently, technology is being worked on for rearing and formation of the breeding stock. In general, the results of the work performed indicate that Baltic whitefish (freshwater type) rearing conditions at the Knyazhegubsky fish hatchery are favorable.

Effects of Vitamin C on Growth and Non‐Specific Immune Response of Labeo gonius Fry in Density‐Dependent Biofloc Rearing

Biofloc technology offers a viable choice for the rearing of fish seed by offering a safe and protected habitat for young fish. Nevertheless, it is crucial to establish a standardised stocking density and implement effective ameliorative steps in order to successfully utilise this technology. In this study, a 90‐day investigation was conducted to assess the effect of stocking density and dietary vitamin C (Vit C) levels on the growth and immunity of Labeo gonius fry (1.03 ± 0.01 g) reared in a biofloc system. Three stocking density groups (5, 10 and 15 fish per 50 L) were established, and each experimental group was supplemented with three levels of Vit C (0, 500 and 1000 mg kg−1). The highest survival rate was observed in the lowest density group (five fish per 50 L) fed with 1000 mg kg−1 Vit C. A better feed conversion ratio and significantly higher protein efficiency ratio were found in the moderate stocking density group (10 fish per 50 L) fed with 500 mg kg−1 Vit C. Total leukocyte count (TLC), haemoglobin, and packed cell volume improved in Vit C‐fed groups. The total erythrocyte count (TEC) increased in groups fed Vit C and stocked at lower densities (5 and 10 fish per 50 L). Total serum protein (TPP) content increased when Vit C was added at a rate of 500 mg kg−1. Serum glucose and cortisol levels were significantly reduced in Vit C‐supplemented groups. Supplementation of Vit C at 500 mg kg−1 resulted in a significantly lower value of malondialdehyde (MDA). Thus, the findings confirm that the incorporation of Vit C in the basal diet promotes the growth and health status of L. gonius fry reared in the biofloc system at high‐density rearing.

Enhancement of eicosapentaenoic and docosahexaenoic acid contents in a Japanese flounder, Paralichthys olivaceus, by low-temperature rearing

This study tested the enhancement of omega-3 long chain polyunsaturated fatty acid content in a Japanese flounder, Paralichthys olivaceus, through low-temperature rearing. The young fishes (age: 160 days) were reared at water temperatures of 7, 10, 15, 20, and 23 °C for four to seven months. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents in their muscle and body weights were observed during the rearing. The rates of increase in both EPA and DHA contents as rearing progressed were higher at lower temperatures. However, the increase in the inventory (total mass in muscle per fish) of these FAs was similar between temperatures except for 7 °C because the growth of body weight offset the influence of temperature.

Spatial and temporal diversity of fish captured by light traps in various habitats in coastal waters in the oldest marine protected area in Vietnam and its implications for conservation

Abstract Vietnam's oldest marine protected area, the Con Dao Archipelago, hosts a high diversity of fishes, but they are not taken into account in its management. Knowledge of the spatial and temporal diversity of fishes is critical to identify the ecological functions of protected habitats, including as nurseries and feeding grounds. One way to assess diversity is using light traps that target young fish stages. Fish were collected monthly from June 2016 to May 2017 using light traps in three main habitats: seagrass beds, coral reefs and the harbour. Morphometry and DNA barcoding were used to identify the species caught. A total of 11,293 fish were collected, of which 1,248 were barcoded and assigned to 158 species belonging to 81 genera and 34 families, evidence that coral reefs and seagrass beds in Con Dao marine protected area (MPA) are home to a highly diverse and abundant community of fish species. Species richness and Shannon diversity indices did not differ significantly among sampling sites, but both species composition and diversity indices differed in the wet and dry seasons. The abundance of fish was related to sea water temperatures, which varied significantly depending on the month. During the dry season, fish diversity peaked in April, when the water temperature was highest. Conserving fish in Con Dao MPA is important not only for the characterization of the trophic network in coral reefs and seagrass beds but also for preservation of coral reef ecosystems and endangered species. Ensuring connectivity between coral reefs and seagrass beds in Con Dao MPA would facilitate fish conservation but, at present, the MPA only focuses on protecting fragmented habitats that are home to a number of endangered mammal species. Local authorities should establish a continuum of protected areas along coastal habitats and seasonal controls on fishing as part of sustainable management of MPAs.

Economic evaluation of Arapaima gigas production in earth ponds: Case study of a small fish farm at San Martin-Peru

Arapaima gigas is an Amazon specie with great commercial demand and high production performance, but its feasibility is variable. The current study aimed to perform an economic evaluation of the production of A. gigas on earth ponds in San Martin, Peru. Three hundred young fish (19 ± 0.01 cm and 68.32 ± 0.01 g) were stocked (ten fish·m–2 in three ponds of 1000 m2 for 390 days). Growth performance was evaluated based on the survival, feed conversion rate (FCR), final mean weight, final average length, weight gain, specific growth rate, and productivity. Investment, costs, indicators, and feasibility were determined. Arapaima gigas has a profitable production performance in earth ponds in Peru, fish presented a weight gain (kg) of 11 kg in 390 days and productivity of 3,265.70 kg·ha–1. Food and fingerlings were the most important items in the production cost. This production is a low-investment and high-profitable business, with an incremental investment of US$3,287.15, profit of US$ 3,977.38·cycle–1, Net Present Value of US$ 22,149.37, and an Intern Rate Return of 32.28%. This could be a way of increasing the income of small producers through the diversification of their production.

Efficacy of otolith morphometry for rapid discrimination of cryptic fishes

The cryptic external morphology of fishes poses challenges for accurate species identification. This study assessed whether the morphometry of otoliths (and body length) could be used as a method to distinguish among closely related, morphologically similar species that are highly valued by commercial or recreational fishers. The otolith morphometry of fishes within four genera (Centroberyx, Lethrinus, Polyprion and Sillago) were compared. Canonical Analysis of Principal Coordinates that included combinations of morphometric variables (i.e., otolith length, width, thickness, weight, and fish length) produced highly accurate species prediction rates ranging from 92.5 to 99.9% across all genera. When different combinations of morphometric variables were modelled, changes in species prediction accuracy rates were minimal (i.e., up to 3%) for the Centroberyx, Polyprion and Sillago species. The exclusion of otolith weight from the multivariate analysis did not significantly decrease prediction accuracy within all four genera. In contrast, the prediction accuracy of the two lethrinids reduced by 7–25% when fish length was excluded, which may be attributable to the larger size attained by L. nebulosus in comparison to its congener L. punctulatus, as well as the very similar ovate shaped otoliths in younger fish of both species. Simplifying data collection to only length-based otolith measurements (and fish length for lethrinids) would provide a more rapid and cost-effective method for discrimination and be more practical when sampling at sea where obtaining accurate weight measurements of otoliths is typically unfeasible. Spatial variation in otolith morphometrics was evident for C. gerrardi, L. punctulatus, P. oxygeneios and S. vittata, which might be attributed to the differences in length distributions of fish samples from different regions. The misclassified specimens within the species groups were notably smaller individuals, suggesting the complexity of otolith shape increases with ontogeny. Hence, further investigation of variations in morphological characteristics, other than otoliths, may be required for the discrimination of cryptic species during the juvenile stage. This study highlights the robustness of multivariate analysis of otolith morphometric data for discriminating closely-related, cryptic species.

Juvenile Striped Bass consume diverse prey in Chesapeake Bay tributaries

AbstractObjectiveAnadromous Striped Bass Morone saxatilis are dominant predators in estuaries and coastal areas along the U.S. Atlantic coast, with the potential to exert top‐down control on prey populations. Although Striped Bass diets have been studied previously, spatiotemporal patterns of diet across ontogeny remain poorly understood, especially for young fish in shallow nursery habitats.MethodsWe collected and examined gut contents from adult, juvenile, and young‐of‐year (age‐0) Striped Bass from nine rivers across the Maryland and Virginia portions of Chesapeake Bay during summer and fall 2018. We compared the use of traditional morphological inspection and new amplicon‐based next‐generation sequencing methods for identifying gut contents.ResultStriped Bass in shallow tributary habitats of Chesapeake Bay had diverse diets that varied strongly with ontogeny and salinity zone. In particular, the diet of age‐0 Striped Bass varied greatly from those of juveniles and adults when age‐0 fish foraged in freshwater habitats. Although our results on prey consumed aligned with previous surveys, we identified additional taxa as important prey for these young fish, including dipteran insects, Banded Killifish Fundulus diaphanus, Inland Silverside Menidia beryllina, bay barnacle Amphibalanus improvisus, and grass shrimp Palaemon spp. Comparison of methodologies indicated that 40% of prey by weight could not be identified with morphological analysis, while 76% of mitochondrial cytochrome oxidase I sequences could be assigned binomial names, allowing for high‐resolution taxonomic comparisons.ConclusionThis study adds to the growing body of evidence that amplicon‐based next‐generation sequencing methods are far superior to traditional morphological analyses of gut contents for fine‐scale taxonomic resolution of prey.

The robustness of our assumptions about recruitment: A re-examination of marine recruitment dynamics with additional data and novel methods

Recruitment is the number of young fish entering a population and is an essential process in age-structured stock assessment models. Many of the models on which stock assessments are based assume some level of influence of spawning biomass on recruitment, and estimation of this functional relationship has been a focus of substantial research. However, recruitment is also influenced by environmental fluctuations that induce autocorrelated patterns, trends, and shifts in deviations from the stock-recruitment relationship. Consequently, previous meta-analyses of stock-recruitment relationships have had trouble calibrating the relationship. We revisited the findings of Szuwalski et al. (2015) to determine if their results are robust to the addition of data to the RAM Legacy Stock Assessment database and choice of analysis method (the PELT algorithm, MARSS models, and Bayesian change point detection). Since the publication of Szuwalski et al. (2015), the number of stocks in the database has doubled. We determined the primary influence of spawning biomass on recruitment and examined the recruitment time series for regime shifts for 432 stocks. Our results indicated that 57% of stocks did not have a significant correlation between spawning biomass and recruitment over the observed biomasses. Environmental conditions played a larger role in recruitment variation than spawning biomass. The presence, location, and number of regime shifts in recruitment time series was highly dependent on the detection method, with Bayesian change point detection identifying the fewest regime shifts. Despite the sensitivity to the detection method, 46% of stocks without a significant correlation between spawning biomass and recruitment are estimated to have experienced at least one regime shift as determined by the PELT algorithm Our analyses suggest that effective methods for modeling and forecasting large variations in recruitment over time are needed, particularly given that climate change is predicted to impact the frequency and magnitude of regime shifts.

Disrupting the Repeat Domain of Premelanosome Protein (PMEL) Produces Dysamyloidosis and Dystrophic Ocular Pigment Reflective of Pigmentary Glaucoma.

Pigmentary glaucoma has recently been associated with missense mutations in PMEL that are dominantly inherited and enriched in the protein's fascinating repeat domain. PMEL pathobiology is intriguing because PMEL forms functional amyloid in healthy eyes, and this PMEL amyloid acts to scaffold melanin deposition. This is an informative contradistinction to prominent neurodegenerative diseases where amyloid formation is neurotoxic and mutations cause a toxic gain of function called "amyloidosis". Preclinical animal models have failed to model this PMEL "dysamyloidosis" pathomechanism and instead cause recessively inherited ocular pigment defects via PMEL loss of function; they have not addressed the consequences of disrupting PMEL's repetitive region. Here, we use CRISPR to engineer a small in-frame mutation in the zebrafish homolog of PMEL that is predicted to subtly disrupt the protein's repetitive region. Homozygous mutant larvae displayed pigmentation phenotypes and altered eye morphogenesis similar to presumptive null larvae. Heterozygous mutants had disrupted eye morphogenesis and disrupted pigment deposition in their retinal melanosomes. The deficits in the pigment deposition of these young adult fish were not accompanied by any detectable glaucomatous changes in intraocular pressure or retinal morphology. Overall, the data provide important in vivo validation that subtle PMEL mutations can cause a dominantly inherited pigment pathology that aligns with the inheritance of pigmentary glaucoma patient pedigrees. These in vivo observations help to resolve controversy regarding the necessity of PMEL's repeat domain in pigmentation. The data foster an ongoing interest in an antithetical dysamyloidosis mechanism that, akin to the amyloidosis of devastating dementias, manifests as a slow progressive neurodegenerative disease.

Effects of Formulated Diet and Frozen Fresh Fish on Growth, Serum Biochemical Indexes, Liver Antioxidant, and Lipid Metabolism of Juvenile Cobia (Rachycentron canadum)

Feed is the main source of material and energy for farmed fish, and its nutritional value and balance are important factors affecting fish’s growth rate and physical health. In order to explore the effects of two different feed sources on the growth, serum biochemical indexes, liver antioxidant capacity, and lipid metabolism of young cobia fish, 300 young cobia fish with an initial body weight of 43.14 ± 1.25 g were selected for the experiment and randomly divided into two treatments. Each treatment had five replicates, and each replicate had 30 fish. They were fed with formulated feed and frozen fresh fish, respectively, for 12 weeks. The results showed that the weight gain rate, specific growth rate, and feed conversion rate of juvenile cobia fish fed with formulated diet were extremely significantly lower than those of the frozen fresh fish group ( P < 0.01 ), and condition factor was significantly lower than that of the frozen fresh fish group ( P < 0.05 ). However, protein efficiency rate, hepatosomatic index, and viscerosomatic index were significantly higher than those of frozen fresh fish group ( P < 0.05 ). The content of water, crude protein, and crude ash in the whole fish had no significant difference ( P > 0.05 ), while the content of crude lipid decreased significantly ( P < 0.05 ). The serum aspartate aminotransferase activity and sugar content of cobia in the formulated diet group were significantly higher than those in the frozen fresh fish group ( P < 0.05 ). In contrast, the total cholesterol, triglyceride content, alkaline phosphatase activity, and phosphorus content were significantly lower than those in the frozen fresh fish group ( P < 0.05 ). Compared with the frozen fresh fish group, the antioxidant enzyme activities in the liver of the formulated diet group were significantly decreased ( P < 0.05 ) except malondialdehyde (MDA) and the activity of fatty acid synthase, while there was no significant difference in the malate dehydrogenase. The study showed that under the experimental conditions, frozen fresh fish was more suitable for feeding juvenile cobia, and the formulated diet had adverse effects on the liver of juvenile cobia. Therefore, the nutritional composition of frozen fresh fish and the metabolic characteristics of cobia were used for reference to optimize and adjust the nutritional formula of juvenile cobia.

Creating new littoral zones in a shallow lake to forward-restore an aquatic food web

Current rates of habitat loss require science-based predictions on how to restore or newly create lost habitat types. In aquatic ecosystems, littoral zones are key habitats for food web functioning, but they are often replaced by unnatural steep shorelines for water safety. To reverse this trend, knowledge is needed on how to successfully (re)create littoral zones. We quantified the response of an aquatic food web to the large-scale creation of new heterogeneous littoral habitats in shallow lake Markermeer, the Netherlands. Lake Markermeer was formed by dike construction in a former estuary, which created a heavily modified homogeneous 70,000 ha turbid lake lacking littoral habitat. Fish and bird populations declined over the last decades, but classical restoration via return to former marine conditions would compromise water safety and the large spatial scale prohibited biodiversity offsets. Therefore, an innovative “forward-looking restoration” approach was adopted: a 1000 ha archipelago called “Marker Wadden” was constructed without using a historic reference situation to return to. This aimed bottom-up stimulation of the aquatic food web by adding missing gradual land-water transitions and sheltered waters to the lake. After four years, new sheltered shorelines had become vegetated if they were constructed from nutrient-rich sediments. Exposed and sandy shorelines remained free of vegetation. Zooplankton community diversity increased in sheltered waters due to bottom-up processes, which increased food availability for higher trophic levels, including young fish. The creation of sheltered waters increased macroinvertebrate densities threefold, with sediment type determining the community composition. The archipelago became new nursery habitat for 13 of the 24 fish species known to occur in the lake, with up to 10-fold higher abundances under sheltered conditions. We conclude that modifying abiotic conditions can stimulate multiple trophic levels in aquatic food webs simultaneously, even in heavily modified ecosystems. This provides proof-of-principle for the forward-looking restoration approach.

Growth patterns and feeding characteristics in early developmental stages of Takifugu rubripes cultured in a recirculating aquaculture system

The growth patterns and feeding characteristics of Takifugu rubripes at different developmental stages (0–50 days after hatching, DAH) were investigated under artificial breeding conditions using ecological and traditional biological methods. The results revealed rapid growth in head length, head height, and eye diameter from hatching to 50 DAH, and the inflection point for body length growth occurred at 27 DAH. From 27 to 50 DAH, the growth rate slowed. In the swimming organs, the inflection points for tail, pectoral, dorsal, and anal fin growth occurred from 29 to 31 DAH. The growth rate for fins slowed after this period, suggesting the preferential development of important organs related to sensation, locomotion, and feeding during early development, with varied developmental periods. An investigation of the feeding rhythm of T. rubripes larvae, juveniles, and young fish showed that feeding activities mainly occurred during the daytime, a behavior typical of daytime feeders. The average daily feeding rate of T. rubripes was 12.61% for the early-stage larvae at 6 DAH, 43.89% for the late-stage larvae at 15 DAH, 40.05% for juveniles at 30 DAH, and 28.46% for young fish at 46 DAH. In addition, the satiation time for juveniles tended to decrease with increasing age, whereas the time for digestion tended to increase. These data can be used as a reference for the daily feeding of T. rubripes at different developmental stages. Comprehensive understanding of the growth and feeding characteristics of early-stage T. rubripes developed in this study will be useful for the management of artificially bred fry and will aid in promoting the growth and survival rates of aquaculture fish larvae.

About non-target-sized pollock in the northeastern part of the Sea of Okhotsk during the winter-spring special fishery: from observations to fishing rules

In the Pollock fishery in the northeastern of the Sea of Okhotsk, it is not uncommon for non-target fish bycatch to exceed the 20% limit established by the Fishery Rules and can reach significant values (over 90%). Specifying in the message sent to the territorial department of Rosrybolovstvo the total amount of bycatch of young fish (in %), in case of exceeding the allowable bycatch, will allow to react quickly to such situations and temporarily close the fishing areas directly during the fishing season. The specialists of KamchatNIRO prepared the corresponding proposals for amendments of clauses 38,4 and 38,5 of the new edition of the Fishery Rules for the Far Eastern Fishery Basin in 2020 which came into force on September 1, 2022.

Количественные характеристики гидробионтов и молоди рыб шельфовой зоны Северного Сахалина (обзор) Часть 2.

The article presents a review of published materials and results of specialized ecological and fishery research for the period 1950-2021, containing data on abundance and biomass of the main groups of hydrobionts (phytoplankton, zooplankton, zoobenthos), larvae and young fish in different shelf areas of northern and northeastern Sakhalin Island. Regularities of distribution of different plankton groups by shelf areas and by different water, horizons are considered. Quantitative indicators of systematic groups of hydrobionts and juvenile fish of different shelf areas are compared. The work summarizes the materials on the Zapadno-Shmidtovsky and Deryuginsky license areas, Yuzhno-Kirinsky hydrocarbon field and others.

Biological Diversity of Sula River (Ukraine) Under Different Hydrological Conditions

Abstract Hydrobiological research of the main components of the biota of the lower reaches of the Sula River was conducted. The river flows into the Kremenchutsk Reservoir. Zoobenthos, zooperiphyton, vascular water plants, and ichthyofauna in lotic and lentic microbiotopes were studied. Species and communities of protected status were stated. It was shown, that a significant share (about 30%) consists of rheophilic species. 28 species of fish were registered in the studied area, of which eight are invasive species and 10 are under protection. The biotopic distribution of different fish species, and the intensity of the downstream migration of juvenile fishes in spatial, temporal, and species aspects were estimated. It was identified, that about 12 million young fish migrate from the researched part of the Sula River to the Kremenchuk reservoir during the season.

Connecting Suborganismal Data to Bioenergetic Processes: Killifish Embryos Exposed to a Dioxin-Like Compound.

A core challenge for ecological risk assessment is to integrate molecular responses into a chain of causality to organismal or population-level outcomes. Bioenergetic theory may be a useful approach for integrating suborganismal responses to predict organismal responses that influence population dynamics. We describe a novel application of dynamic energy budget (DEB) theory in the context of a toxicity framework (adverse outcome pathways [AOPs]) to make quantitative predictions of chemical exposures to individuals, starting from suborganismal data. We use early-life stage exposure of Fundulus heteroclitus to dioxin-like chemicals (DLCs) and connect AOP key events to DEB processes through "damage" that is produced at a rate proportional to the internal toxicant concentration. We use transcriptomic data of fish embryos exposed to DLCs to translate molecular indicators of damage into changes in DEB parameters (damage increases somatic maintenance costs) and DEB models to predict sublethal and lethal effects on young fish. By changing a small subset of model parameters, we predict the evolved tolerance to DLCs in some wild F. heteroclitus populations, a data set not used in model parameterization. The differences in model parameters point to reduced sensitivity and altered damage repair dynamics as contributing to this evolved resistance. Our methodology has potential extrapolation to untested chemicals of ecological concern. Environ Toxicol Chem 2023;00:1-14. © 2023 Oak Ridge National Laboratory and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Loss of sea ice and intermittent winds alter distributions and diet resources of young forage fish in the Chukchi sea

Loss of sea ice alters habitat for organisms that function as energetic links in Arctic food webs. To address the impacts of such changes on lower trophic levels we focus on forage fish during the early life stages (polar cod: Boreogadus saida and saffron cod: Eleginus gracilis) and copepods (Calanus spp. and Pseudocalanus spp.) in the Chukchi Sea with differing reliance on sea ice environments. We assess distributions throughout years of varying ice extent (2010–2013, 2015, 2017–2018) and diet resources during unprecedented warm years (2017, 2018) using stable isotope analyses (bulk δ13C and δ15N and δ13C compound-specific isotope analysis of amino acids). Calanus spp. and polar cod were found at relatively higher latitudes in closer proximity to recent sea ice, whereas saffron cod were rare and Pseudocalanus spp. were ubiquitous. Polar cod juveniles, but not larvae, were more common in open water, suggesting that low ice and northward ocean currents interact to influence juvenile distributions. Low summer sea ice also coincided with northward expansion of warm Pacific-origin water across the shelf. Stable isotope δ13C values reflected this latitudinal variation in water masses as well as inshore-offshore gradients due to convergence of ocean currents. When summer sea ice was absent during 2017, juvenile polar cod were dispersed across the shelf, abundances were low for both copepod taxa, isotopic niche was reduced for polar cod, and carbon sources for some larval polar cod reflected boreal-associated phytoplankton. Distributions and isotopic patterns suggest that under low ice conditions, along-shelf wind reversals and weak currents can lead to dominance of Pacific-origin water, mixing of organisms from various source locations, and reductions in sea ice-influenced environments. Northward expansion of subarctic water masses and organisms across the Chukchi shelf alters basal resources for lower trophic levels and modifies pelagic habitats to more uniformly resemble lower latitude marine ecosystems.

აკვაკულტურის განვითარების როლი საქართველოს სამცხე-ჯავახეთის რეგიონის ეკონომიკის ზრდის საქმეში

The article presents the analytical description of the current situation of aquaculture development in Samtskhe-Javakheti region and in Georgia in general. The data about sector development natural potential are provided, the indicators of the fish production dynamics are analyzed in the paper. Water resources have a great potential and their ecological-sound use enables Georgia to meet not only an internal demand of the country on the fresh water fish, but also due to specifics of the local waters, produce export product. Internal water resource of fresh water for fishery production includes total water surface of 16,900 ha of 860 lakes. Samtskhe-Javakheti region is distinguished with the specific water resources compared to other regions. The regions is rich with the hydro-resources, including the R. Mtkvari water-collecting basin, the basin of the rivers Uraveli, Paravani, Borjomistskali and Gujaretistskali with total size 6,250 m2, with the total water resource of 3, 475 mln m3. The region territory covers 15 non-drying, 25 drying and 64 little lakes, 5 water reservoirs transforming into the swamp of the hydro-resource objects. The total size of the basin of the main lake exceeds 983 m2, the volume of the water reaches to 400 million m3. The water reservoir located in the Lirbalakhi basin in the region includes 2.08 million m3, and the size of the swamps is 817 ha in the region. The article studies the dynamics of the land plots occupied by aquaculture. According to the data, there is 23% of growth of the land plots occupied by aquaculture in entire Georgia; while the situation is different in the target region, there is 10% of reduction, followed by reduction of the share of aquaculture land from 11.1% until 10.6%. Study of the aquaculture fodder supply demonstrated that use of combined fodder is increasing in Georgia; average rate of the growth consists of 5-7 % in the country, while the rate is higher in Samtskhe-Javakheti region, where use of combined fodder achieved 35% of growth. There is tendency of growth in use of all kind of fodder. The index of the fodder expenses reached 1.30 throughout entire country, while it is 1.38 in Samtskhe-Javakheti, indicating strengthening of the fodder basis and intensive development of the field. The analysis of fish production dynamics is also an indicator for the further development of the aquaculture. In 2021 compared to 2019, there is 16% of growth in production of the fish, comprising 2,861 tons. The growth achieved 24% in the same period in the region what can be considered as a positive phenomenon in fishery production in Georgia, where the share of the fish farms (family-run) was increased up to 60% with growing engagement of the farmers aged 25-45 from 20% up to 29%. The rate of fish production is in compliance with the increased rate of water stock. The study revealed the specific problems (fish structure, diversification of the fodder, veterinarian service, growing of young fish) requiring solution to increase development of fresh water fish breeding, making financial sustainability of farming and economic growth of the region.