Fish Blood Research Articles

Influence of Thermal Pollution on the Physiological Conditions and Bioaccumulation of Metals, Metalloids, and Trace Metals in Whitefish (Coregonus lavaretus L.).

The Kola nuclear power plant, which discharges warm water into one of the bays of subarctic Lake Imandra, significantly changes fish habitats. The temperature gradient of the lake is between 2 and 8 °C, which makes it significantly different from the natural temperature of the lake water. The stenothermal cold-water native species (lake whitefish (Coregonus lavaretus L.)), living for more than 40 years under conditions of thermal pollution, has adapted to this stressor. Moreover, this population differs favorably from the population in the natural-temperature environment in terms of its physiological state. Firstly, the hemoglobin concentrations in the fish blood are in the range of the ecological optimum, and secondly, it has a higher somatic growth, as estimated by Fulton’s condition factor. One of its main adaptive mechanisms of ion regulation is an intense metabolism of Na due to the high respiratory activity of the whitefish in warmer water. An increased accumulation of Rb and excretion of Se, Mo, and Si are associated more or less with that feature. Under conditions of an increased water temperature, the main metabolic need is due to a deficiency of Se in fish. The intensive metabolism of selenoproteins may involve risks of toxic effects and the bioaccumulation of Hg, As, and Cu in cases of increased existing stressors or the appearance of new ones.

Selection of assay, organism, and approach in biomonitoring significantly affects the evaluation of genotoxic potential in aquatic environments.

In this study, few different evaluation concepts were used for the assessment of genotoxic potential at the stretch of the Danube River identified as a significant hotspot of pollution originated through the untreated wastewaters. Three sites were chosen: one site upstream of the wastewater outlet in Novi Sad (Serbia), one at the outlet of wastewaters, and one site few kilometer downstream. Ex situ approach comprised prokaryotic SOS/umuC test on Salmonella typhimurium TA1535/pSK1005 and comet assay on human hepatoma cell line (HepG2). In situ approach was based on the active monitoring (cage approach) using freshwater mussels Sinanodonta woodiana and fish Cyprinus carpio. The comet and micronucleus assays were selected for evaluation of DNA damage in mussel haemocytes and fish blood cells. Within the ex situ part of the study, our results indicated that the eukaryotic model system is more sensitive compared to the prokaryotic one. In situ bioassays are recommended for obtaining a better insight into ecosystem status and in the case of our study the complete insight of genotoxic pressure. However, the choice of animals as bioindicators also has a significant impact on the quality of the obtained information. Differential response between fish and mussels was observed at the highly polluted site suggesting possible involvement of additional protective mechanism such as valve closure in mussels.

КОСВЕННЫЙ ОТБОР САМОК ФОРЕЛИ КАК СЕЛЕКЦИОННЫЙ ПРИЕМ ПОВЫШЕНИЯ ИХ ПРОДУКТИВНОСТИ И РЕЗИСТЕНТНОСТИ

The scientific work considers the selection method of selection in a herd of producers of rainbow trout Kamloops, taking into account values of positive correlation of some morphometric characteristics and degree of development of their reproductive products, as well as the features of natural protective functions of their body at the age of three. It is established that the somatic structure and, development of postorbital region largely determine the functional features of trout, as well as their reproductive qualities. In the indirect selection of three-year-old breeders, taking into account morphometry and correlation, females with a size of postorbital head region greater than 55 mm exceeded by 29.2% the live weight and by 40.4% the weight of trout caviar with a length of this head region less than 55 mm. When comparing the resistance of two experimental groups of three-year-old breeder flock, certain differences in immune proteins and hemoglobin content in blood were revealed. Note that in the selected group of fish, a large degree of saturation of red blood cells with hemoglobin is observed, which indicates increased share of oxygen absorption by the body, as well as the intensity of redox processes of metabolism. Indicators of serum proteins of trout in experimental groups vary ambiguously. So in the experimental group, producers had an average total protein in blood of 63.26 g / l, which is significantly 17.5% more than in the blood of fish in the control group. This can be explained by the relationship of the globulins with the immune status of fish of experimental group and its resistance by raising the level of globulin fraction, a high amount of Ig M` protein (by 42.9%) in the blood of trout in the experimental group suggests more aggressive immune system in these fish to viral, invasive and other infections, indicating improved adaptability of selected herds.

Nuclear and Cellular Abnormalities of Erythrocytes in Response to Thermal Stress in Common Carp Cyprinus carpio.

As a consequence of global warming, increase of water temperature is likely to alter physiological functions of fish. Hence, we examined the effects of high temperature on blood glucose, hematological parameters [hemoglobin (Hb), red blood cell (RBC), and white blood cell (WBC)], and nuclear and cellular structure of blood cells of common carp (Cyprinus carpio) after exposure to three temperature regimes (27, 31, and 35°C) for 14 days. Fish were sacrificed on 3, 7, and 14 days of exposure. The blood glucose level increased significantly in the fish exposed to 35°C compared to 27 and 31°C. The Hb and RBC contents decreased but WBC increased significantly in the blood of fish exposed to 35°C compared to 27 and 31°C at 7 and 14 days of exposure. Consequently, the frequencies of erythroblasts (Ebs), erythrocytic nuclear abnormalities (ENA), and erythrocytic cellular abnormalities (ECA) were found to be increased in the blood of fish exposed to 35°C compared to 27 and 31°C. There was a significant increase in neutrophils and decrease in lymphocytes in the highest temperature (35°C). With increasing temperature, dissolved oxygen (DO) decreased but free CO2 increased significantly during the study period. The present study demonstrated that common carp are better adapted to 27 and 31°C environmental temperatures, while the higher temperature 35°C is likely stressful to this fish species.

In vivo phagocytosis and hematology in Astyanax altiparanae, a potential model for surrogate technology.

Although the potential of surrogate propagation technology for aquaculture and conservation of Neotropical fish, the poor understanding of the host immune system may results in rejection and destruction of the donor material. Thus, it is necessary to study and to develop methods to evaluate the effects of immunosuppressive drugs employment and to evaluate the immunocompatibility between donor and receptor. Thus, the present study aimed to optimize a methodology to assess in vivo phagocytosis in Astyanax altiparanae using Saccharomyces cerevisiae and to evaluate their hematological response resultant from the inflammatory induction. To this, S. cerevisiae were labeled with Congo red and injected in the coelomic cavity of A. altiparanae at the concentration of 2.5 x 106 cells mL-1. A PBS solution and a non-injected group were kept as control. Fish blood was sampled and the phagocytic capacity and index were determined at 1, 2, 3 and 6 h post-injection (hpi). The yeast injection successfully stimulated phagocytosis, with the best result for phagocytosis assessment after 2 hpi. Moreover, it was achieved a high traceability of phagocytized and non-phagocytized yeast under optic microscopy analysis due to the Congo red labeling. The hematological profile was similar to usually observed in early infections, indicating lymphocyte migration to inflammatory site and increase in number of circulating phagocytes due to natural response to inflammatory stimulus. In conclusion, our method was efficient to assess in vivo phagocytosis in A. altiparanae and will be an important tool to evaluate the efficacy of immunosuppressive drugs in this species. Additionally, these results may serve as support for further studies in fish immunocompetence, both in laboratory and in field conditions.

Histology, serum biochemistry and haematological profiles of Clarias gariepinus fed diets containing Luffa cylindrica seedmeal

Abstract. A 56-day feeding trial was conducted to evaluate the effect of processing time, inclusion level and/or their interactions on serum biochemistry, haematology and histology of the liver and kidney of Clarias gariepinus fed diets containing Luffa cylindrica seedmeal. The five formulated diets were designated as control (CTR) and tested, replaced at 15 and 30% by 5- and 10-min toasted Luffa cylindrica seedmeal (D515T, D530T, D1015T and D1030T). The experimental design followed a 2×2 factorial experiment in a completely randomised design; the processing time of 5- and 10-min toasting and inclusion level of 15 and 30% serves as factors. Triplicate groups of each treatment were made. Blood sampling, harvesting of organs, serum biochemistry, histology and haematological studies followed standard procedures. The results of the study showed that the effect of processing time, inclusion level and their interactions had significant impact (p<0.05) on Clarias gariepinus. A decrease in RBC, PCV and Hb was observed when compared with control for inclusion level, processing time and/or their interaction. Total protein, albumin and globulin of the blood of fish fed diet CTR was not significantly different (p>0.05) from that of the blood of the fish fed D1015T. Mild to moderate vacuolation of the hepatocytes were recorded among the livers of fish fed control and test dietary treatments except those fed D1030T that recorded very severe vacuolation of the hepatocytes. The kidney, being the excretory organ, was also affected. However, normal cell architecture was recorded in fish fed CTR, D530T and D1030T.

COMPOSITION OF LEUKOCYTES IN BLOOD OF GOLDFISH INFECTED BY LIGULA (DIGRAMMA) INTERRUPTA (CESTODA: PSEUDOPHYLLIDEA)

The tapeworm Ligula interrupta of the genus Ligula (Digramma) (Cestoda: Pseudophyllidea) is a specific parasite of freshwater cyprinid fish; its plerocyrcoids are localized in the body cavity causing heavy parasitic pathology. With parasitosis, an important role in the regulation of the pathological process is assigned to the participants of the organism’s protective reactions, among which a special pool of immunocompetent cells – leukocytes – is distinguished. In the literature, there are single data on hemo- and immunopoiesis goldfish with digrammosis. In our work, new data were obtained on the leukocyte composition of the blood of goldfish Carassius auratus (Linnaeus, 1758), infected with Ligula interrupta in conditions of the native range (Shilen Lake and Cheremukhovoe Lake, Lake Baikal basin). All fish specimens caught with seine nets, both infested and noninfested with L. interrupta, were identical by the size and age composition (age +3…+5, body length 145–237 and 150–180 mm, respectively, weight 100–184 and 120–174 g). Hematological studies were carried out according to the Sbornik [2]. To quantify the individual types of leukocytes, the leukocyte profile, expressed in absolute terms, was calculated. Three groups of cells were revealed in the blood of all goldfish species: blast forms, granulocytes (neutrophils, pseudobasophils) and agranulocytes (lymphocytes, monocytes). The decrease in the blood of infected fish of the total number of leukocytes and their various types at all stages of development, the violation of the proliferation and differentiation of lymphoid and granulocytic elements in the studied organs, the formation of vacuolated and atypical cells, the absence of circulating basophils and eosinophils were established. It has been shown that in this parasitic system, partner relations are reduced to the launch of L. interrupta mechanisms that regulate the host's protective immunological processes by the type of inhibition of the acute inflammatory response and the development of mild chronic inflammation.

Inorganic mercury and dietary safe feed additives enriched diet impacts on growth, immunity, tissue bioaccumulation, and disease resistance in Nile tilapia (Oreochromis niloticus)

Little is known about the impacts of dietary exposure to inorganic mercury (Hg) for a long duration on the health indicators, growth, and disease resistance in Oreochromis niloticus. Accordingly, the current study was designed to assess the effects of Hg contaminated diets on blood biochemistry, growth, chemical composition, Hg bioaccumulation in the tissues, histopathology of liver and head kidneys, and disease resistance to Aeromonas hydrophila of O. niloticus. Also, the efficiency of citronella oil, geranium oil (GO), curcumin (CUR), Bacillus toyonensis (BT), and Bacillus subtilis (BS) as dietary supplements on reversing the negative impacts of Hg were assessed. A total of 240 tilapia fingerlings were assigned to eight dietary treatments fed on the basal diet (G1), G1 diet contaminated with 50 ppm Hg (G2), whereas the other groups fed the G2 diet and enriched with 400 mg CO (G3), 400 mg GO (G4), 200 mg CUR (G5), 7 × 107 cells BT (G6), 7 × 107 cells BS (G7), and 7 × 107 BT + BS/ kg diet (G8) for 16 weeks. The obtained results showed that fish fed on the G2 diet had significantly impaired growth performance indicators, blood parameters, and resistance to bacterial infection compared with fish in the control group. Additionally, distinct pathological perturbations in liver and head kidneys were observed. In contrast, fish groups G3 to G8 had a significant enhancement in the growth performance, Hg bioaccumulation in fish tissues, blood biochemistry, and resistance against A. hydrophila infection compared with fish in the G2 group. Maximum improvement was recorded in G5, G6, and G8. Conclusively, from both health and an economic point of view, these results suggested that several benefits might be gained by adding these additives, especially CUR, BT, and BT + BS, on growth enhancement and ameliorating Hg negative impacts in O. niloticus.

Molecular detection of apicomplexan blood parasites of coral reef fishes from free-living stages of ectoparasitic gnathiid isopods.

Gnathiid isopods are marine ectoparasites that feed on the blood of fishes that have been implicated as vectors of blood parasites, with transmission possibly occurring through biting during their parasitic life-stages, or through ingestion by fishes. However, evidence for their role as vectors is limited, reflecting the small number of research groups working on them. Here, we used a molecular barcode approach to identify fish hosts and apicomplexan parasites in free-living gnathiids from the eastern Caribbean Sea, with the goal of further evaluating their potential role as reservoirs and/or vectors for these parasites. Apicomplexa were only identified in 8% of the Gnathia analyzed, and in four cases we could identify both Apicomplexa and fish host DNA. The results further suggest that Gnathia spp. in this region may serve as reservoirs for Apicomplexa, but whether they are vectors for this parasite remains uncertain.

Estimating degradation of individual essential amino acids in fish meal and blood meal by rumen microbes in a dual-flow continuous-culture system

Current feeding systems are based on the assumption that the AA profile of rumen undegraded protein is similar to that of the original feed. The objective of this experiment was to determine rumen bacterial degradation of individual essential AA in fish meal (FM) and blood meal (BM). Eight dual-flow continuous-culture fermentors were used in a completely randomized block design with a factorial arrangement of treatments and 3 replicated periods. Fermentors were supplied with 95 g of dry matter/d of isonitrogenous diets. Treatments contained a nonprotein N source (urea and tryptone) that was substituted with increasing proportions of FM or BM (0, 33, 67, or 100%). Diets consisted of 22.0% crude protein, 35.2% neutral detergent fiber, 34.6% nonfiber carbohydrates, 2.0% ether extract, and 9.2% ash. We hypothesized that the increase in the flow of individual AA would be attributed to the increase in the supply of the AA from each protein supplement. True organic matter degradation was decreased by increasing levels of FM or BM, but did not affect degradation of neutral detergent fiber and acid detergent fiber, total volatile fatty acids (VFA) concentration, or the molar proportion of propionate. There was a substrate by level of inclusion interaction in acetate molar proportion and branched-chain VFA. Butyrate concentration decreased linearly with increasing levels of FM and BM in treatment. Changes in branched-chain VFA reflected differences in content of branched-chain AA between supplements and the level of inclusion, although the quadratic effect suggests that other factors were involved. Ammonia-N concentration showed a substrate by level of inclusion interaction. Total dietary N and AA flows increased with increasing levels of FM or BM in treatment. The efficiency of bacterial crude protein synthesis was not affected by treatment, but the flow of bacterial N decreased in FM diets as the level of FM increased. Flows of AA increased linearly with increasing levels of the respective AA from supplements. Arginine, Ile, Met and Phe were more degradable, while His was more resistant to bacterial degradation. Results suggest that the resistance to rumen bacterial degradation of individual AA varies within FM and BM protein and may affect the estimates of dietary supply of individual AA to the small intestine.

Genotoxic Consequences in Common Grass Carp (Ctenopharyngodon idella Valenciennes, 1844) Exposed to Selected Toxic Metals.

The primary aim of the current study was to recognize the biomarker approach as the finest tool to identify the geno-toxicological effects of copper, chromium, and lead inside the blood of grass carp using micronucleus test and comet assay. The induced micronuclei frequency in response to the administered concentrations of LC50 metals was discovered in the erythrocytes of metal-exposed fish at four-time intervals. The genotoxic effect of these metals with respect to the formation of micronuclei was ranked as chromium > lead > copper. Percentages of other cellular and nuclear abnormalities were also determined in the exposed blood films. Equally, the genotoxic studies in terms of comet assay in fish blood revealed significant deviations p < 0.05 against each of the studied metal at their respective time interval as compared with the healthy fish group. However, induced frequency of micronuclei and the calculated DNA damage were not found to be duration dependent. Consequently, copper, chromium, and lead have been explored as cytotoxic elements that can be responsible for inducing genotoxic effects in fish existing aquatic habitats.

Genotoxicity in the rivers from the Brantas catchment (East Java, Indonesia): occurrence in sediments and effects in Oreochromis niloticus (Linnæus 1758).

This paper reports the first data from an integrated study investigating genotoxicity in the Brantas River, Java, Indonesia. Results showed that organic sediment extracts from the sites in the Brantas Delta retained genotoxic compounds identified using the SOS Chromotest and that the Aloo River and, to a lesser extent, the Surabaya River were the most contaminated studied sites. This genotoxicity was attributable to compounds that did not require any bioactivation under the test conditions. Occurrence of genotoxic effects was further investigated in erythrocytes from Nile tilapia, Oreochromis niloticus. High numbers of micronuclei were counted, especially in fish sampled in the rivers of the Brantas Delta. Moreover, cytoplasmic alterations which could be indicative of the presence of lipofuscin were found in the cytoplasm of the fish blood cells, especially in fish from the Aloo, Surabaya and Kalimas rivers. Altogether, our data showed that genotoxicity is occurring in fish living in rivers of the delta of the Brantas River and suggest that sediments from these sites may constitute a major source of pollution and hazard for species living or feeding in the area.

Reduced access to cleaner fish negatively impacts the physiological state of two resident reef fishes

Many “client” coral reef fishes have their ectoparasites removed by the “cleaner” wrasse Labroides dimidiatus in mutualistic interactions. Clients regularly receiving cleaning services reportedly benefit from increased growth and cognitive performance, but the underlying physiological changes that covary with such benefits are unknown. Here, we tested whether reduced access to cleaning services affects physiological state in two species of damselfish, Amblyglyphidodon curacao and Acanthochromis polyacanthus. We performed an in situ removal experiment on the Great Barrier Reef, Australia, whereby 47% of cleaners on a natural reef were removed. Since cleaners occupy defined territories (called “cleaning stations”), this removal created areas where small, resident clients, including A. polyacanthus and A. amblyglyphidodon, had no access to cleaning services. One month following cleaner removal, we measured body condition and collected blood samples from both damselfish species from territories with and without access to cleaners. Blood was used for estimating haematocrit levels, hormonal analyses, and immune cell counts. We tested for correlations among all these parameters to explore potential trade-offs in terms of growth, aerobic capacity, immune activation, and/or reproduction as a result of the loss of cleaning benefits. In both species, we found that fish without access to cleaners had lower haematocrit, testosterone levels, and lymphocyte counts than fish with access. There were no significant changes in fish body condition, leukocytes, granulocytes, or plasma cortisol levels between fish with access to cleaners or not. However, testosterone levels correlated negatively with the proportion of granulocytes in the blood of fish with access to cleaners. Our results suggest that even a relatively short-term reduction in access to cleaning services can have negative physiological outcomes for clients. Thus, the presence of cleaners on coral reefs appears to have important benefits for coral reef fish community health.

The Efficacy of Poppy, Papaver nudicaule extract as an Anesthetic for the Common Carp, Cyprinus carpio

Aqueous extract of poppy plant) Papaver nudicaule) with five concentrations (50, 100, 150, 200 and 250) mg/l were used to anesthetize fingerlings of the common carp Cyprinus carpio (Mean total length 8.91 ± 0.31 cm and mean total weight 7.72 ± 1.19 gm) instead of the traditional use of MS-222. Results showed that extracted solution of poppy have partial and overall anesthesia effect on these fishes with inverse relationship between the concentrations used and the time needed to reach partial and overall anesthesia, and also direct relationship between concentrations used and time needed for fish recovery. Best results were obtained by using a concentration of 250 mg/l, where time for partial anesthesia was 8 ± 1.52 min., time for overall anesthesia was 10 ± 1.70 min., time needed for partial recovery was 25 ± 2.43 min. and time needed for overall recovery was 35 ± 2.23 min. Fish behavior observations revealed a difference ranging from slow swimming with increasing in breathing rates movements to vertical swimming near the surface, then laying at bottom and too much decrease in breathing rates movements. Results appeared that there were no significant differences (p≥0.01) between glucose concentration in fish blood plasma after recovery and control fishes. So it was concluded that these. The results showed also that there were no significant differences (p≥0.01) in ALP, AST, ALT, LDH and CK among fishes after recovery comparing with the control fishes. Experimental fishes exhibited no stress during anesthesia by using poppy extracted solution. This indicated that the treated fishes exhibited no physiological effects stress which might lead to poor health condition later. The study demonstrated that poppy can be used as an effective anesthetic, as we obtained acceptable induction and recovery times. The poppy can be recommended as suitable anesthetics for fishes (200 or 250 mg/l).

Significance of Glutamate Racemase for the Viability and Cell Wall Integrity of Streptococcus iniae

Streptococcus iniae is a pathogenic and zoonotic bacterium responsible for human diseases and mortality of many fish species. Recently, this bacterium has demonstrated an increasing trend for antibiotics resistance, which has warranted a search for new approaches to tackle its infection. Glutamate racemase (MurI) is a ubiquitous enzyme of the peptidoglycan synthesis pathway that plays an important role in the cell wall integrity maintenance; however, the significance of this enzyme differs in different species. In this study, we knocked out the MurI gene in S. iniae in order to elucidate the role of glutamate racemase in maintaining cell wall integrity in this bacterial species. We also cloned, expressed, and purified MurI and determined its biochemical characteristics. Biochemical analysis revealed that the MurI gene in S. iniae encodes a functional enzyme with a molecular weight of 30 kDa, temperature optimum at 35°C, and pH optimum at 8.5. Metal ions, such as Cu2+, Mn2+, Co2+ and Zn2+, inhibited the enzyme activity. MurI was found to be essential for the viability and cell wall integrity of S. iniae. The optimal growth of the MurI-deficient S. iniae mutant can be achieved only by adding a high concentration of D-glutamate to the medium. Membrane permeability assay of the mutant showed an increasing extent of the cell wall damage with time upon D-glutamate starvation. Moreover, the mutant lost its virulence when incubated in fish blood. Our results demonstrated that the MurI knockout leads to the generation of S. iniae auxotroph with damaged cell walls.

Response of kutuklin hemaglutinin protein adhesion in koi fish (Cyprinus carpio) infected by Myxobolus sp.

Koi fish (Cyprinus carpio) cultivation is quite easy to maintain if it can look carefully at fish health well. The Difficulty in maintenance due to parasitic attacks is Myxobolus sp., and this parasite is capable of causing death in fish. Treatment of parasites attached to koi fish can be done by giving chemicals such as Pyrethrum. This research aims to determine the reaction of kutuklin hemagglutination adhesin to koi fish infected by Myxobolus sp. The method used is an explorative and descriptive by conducting an In-Vivo test on koi fish. The treatment is, healthy fish without drug as a control, healthy fish with a drug dose of 1 µl/g feed, and fish were infected with a drug dose of 1 µl/g. Observation is done by taking fish blood plasma in each treatment. The results showed that kutuklin was able to contribute to treating Myxobolus sp. However, it cannot restore such a healthy state. This is indicated by high (up to 1/1024 dilution) in the hemagglutination (HA) test of koi fish blood plasma. So, that kutuklin can be used as an immune suppressor (immunosuppressor).

Screening of Biomarkers Related to Ovarian Maturation and Spawning in Blunt Snout Bream (Megalobrama amblycephala) Based on Metabolomics and Transcriptomics.

In fish breeding practices, gamete maturity of females is vital to reproductive success. For some species, it is possible to estimate the female maturation status based on abdomen observation, but quite difficult for some species which mature at big size. To screen out the potential biomarker in fish blood relating to female maturation, we employed the approach integrating the UPLC-MS/MS and RNA-seq techniques to investigate the metabolites and genes reflecting the sexual maturation and spawning of female blunt snout bream Megalobrama amblycephala. The study included four groups, 1-year-old immature female individuals, 2-year-old immature female individuals, 2-year-old sexually mature female individuals, and 2-year-old sexually mature female individuals after 24h of successful spawning. The upregulated metabolites in mature females were involved in "steroid hormone biosynthesis," "metabolic pathways," "glycerophospholipid metabolism," etc. compared with those of immature individuals. As the key intermediate of steroid hormone biosynthesis, 17α-hydroxypregnenolone exhibited the highest level in 2-year-old mature females than in the immature females. Meanwhile, the metabolites (i.e., dodecanoic acid and myristic acid) participating in fatty acid synthesis exhibited much lower levels in the females after spawning than those before spawning. In addition to the metabolites, the genes involved in ovarian steroidogenesis were significantly upregulated in the 2-year-old immature females compared to the 1-year-old immature females, indicating that the ovarian steroidogenesis plays important roles in ovarian development of M. amblycephala at the early stages. The significant upregulation of genes (i.e., itpr1, camk2, and mekk2) involved in the "GnRH signaling pathway" was observed in the mature females compared with the immature females, which indicated that the estrogen levels increased after female maturation in M. amblycephala. Moreover, many genes (e.g., gck, creb1, tf2-9, ryr2, asgr1, and creb1) regulating insulin secretion and thyroid hormone synthesis were significantly downregulated after female spawning. The dynamics of gene expression and metabolites observed in this study provide novel cues for guiding fish practical artificial reproduction.

Hematological and biochemical blood indices of rainbow trout depending on the level of protein in feeds

Protein nutrition of fish is one of the main factors of ensuring their active growth. Finding the optimal concentration of protein is an actual direction of research. The purpose of the experiment was to establish the effect of different protein nutrition levels in commercial rainbow trout feeding on hematological and biochemical parameters of their blood. For this purpose, five experimental groups were formed by the method of analogs. The experiment lasted 210 days and was divided into two periods: equalization (10 days) and main (200 days). During the equalization period, the feeding ration was the same for fish in the control and experimental groups. In the main period, the level of protein in experimental feeds for different experimental trout groups ranged from 44 to 52% per 1 kg. It was found that different levels of rainbow trout’s protein nutrition did not cause significant changes in blood morphological composition. It is proved that rearing trout using compound feeds with a crude protein content of 50% and 52% promotes the increase of red blood cells, hemoglobin, white blood cells and phagocytic activity in blood. The use of 44% and 46% low crude protein diets in fish feeding reduces the morphological components in blood. As a result of studies on the phagocytic activity of neutrophils in fish blood, a slight increase was revealed under the influence of the studied factor. The analysis of the obtained results showed that with increasing levels of crude protein in the diets of rainbow trout, the concentration of total protein and its fractions in blood serum increased. Accordingly, the amount of total protein in blood of fish in the control group was 60.0 g/L, in the experimental groups – it was within the range of 59.6- 65.3 g/L. The increase in the level of rainbow trout’s protein nutrition in the experimental groups 4 and 5 caused an increase in the number of albumins, β-globulins and γ-globulins compared to control. As a result of experimental studies, an increase in the mineral status of rainbow trout blood during use of feeds with the crude protein content of 50-52 % was established. No differences were found during the assessment of trout white blood cell counts. The use of the obtained results during the production of compound feed will allow having a positive effect on the hematological parameters of commercial rainbow trout

Antioxidative, histological and immunological responses of rainbow trout after periodic and continuous exposures to a peracetic acid-based disinfectant

Peracetic acid (PAA)-based disinfectants are considered as sustainable alternatives in aquaculture due to their harmless residues from spontaneous decay. The key components of PAA-based disinfectants are PAA and hydrogen peroxide (H2O2). Little is known if the exposure to exogenous PAA and H2O2 from PAA-based disinfectants interferes with endogenous reactive oxygen species (ROS) regulation and innate immunity in fish. In the present study, rainbow trout (Oncorhynchus mykiss) were exposed to a PAA-based disinfectant for 6 weeks in flow-through systems by either periodic (pulse) or continuous modes. For the periodic exposure, a single dose of 1 mg L−1 PAA (and 1.4 mg L−1 H2O2) was applied biweekly and spontaneously degraded within hours. For the continuous exposure, a constant drip was applied which aimed to maintain 0.2 mg L−1 PAA (and 0.28 mg L−1 H2O2) in the inflow water but was counteracted by escalating degradation by the second week. The exogenous PAA/H2O2 elevated the level of endogenous total free radicals (TFR), probably through diffusion at the gill, as well as stress-activated endogenous generation (by periodic exposure only at the higher PAA/H2O2 dose). In response, the total antioxidant capacity (TAC) in gill and serum was significantly elevated. Liver showed no significant changes in the levels of TFR and TAC. Epidermal mucous cell density was significantly lower in response to persistent scarce exogenous PAA/H2O2 of the continuous exposure compared to the control. This sensitive response was absent in the periodic exposure probably due to rapid epidermal recovery during the exposure intervals. In contrast, the branchial structural adjustment of trout in response to exogenous ROS was less sensitive. Minimal hyperplasia of lamellae was present only in the periodic exposure. Enzymes responsible for innate cutaneous and humoral immunity including lysozyme, alkaline phosphatase, myeloperoxidase and esterase were not influenced by either exposure. However, ceruloplasmin was highly sensitive to exogenous PAA/H2O2; it was significantly elevated in fish skin, independent of the exposure modes, suggesting potential antioxidant protection of ceruloplasmin in fish skin. In serum, ceruloplasmin reduction was positively correlated to the reduction of antiprotease activity which indicates that ceruloplasmin may have anti-proteolytic function in fish blood. In conclusion, both exposure modes of the PAA-based disinfectant triggered mild antioxidant defenses in rainbow trout. To minimize the risk of oxidative damage while applying PAA-based disinfectants, sufficient intervals between periodic applications might be a better option than the persistent low PAA/H2O2 concentration of the continuous application.

Rising CO2 saves lives

Anthropogenic climate change is a multi-faceted problem. Rising CO2 levels in the atmosphere cause a warming of global temperatures, acidify the oceans and may ultimately deplete aquatic oxygen, leading to hypoxia. By itself, any one of these conditions can pose a real challenge to an animal, but how the stressors interact is still largely unexplored. Aquatic hypoxia may be especially intricate and, unlike the hypoxic conditions that one might experience when climbing a mountain, is almost always caused by organismal respiration in the water and, thus, is associated with an additional, simultaneous increase in CO2. The linkage between oxygen and CO2 levels in water has long been known, but how fish are affected by the combined challenge is poorly studied.To address the issue, Daniel Montgomery and his colleagues at the University of Exeter, UK, set out to test the effect of rising CO2 on the hypoxia tolerance of European seabass. They measured the oxygen consumption of the fish while lowering the available oxygen in the water; the point at which the animal can no longer extract oxygen from the depleted water and their oxygen consumption starts to decline is a popular indicator of hypoxia tolerance in fish. Knowing that higher levels of CO2 tend to acidify the blood of fish – compromising the ability of haemoglobin to bind oxygen and hindering the fish's ability to extract oxygen from the water – Montgomery then supplemented one of the treatments with a simultaneous increase in CO2, expecting that the combined challenge would render the fish more susceptible to hypoxia.However, contrary to these predictions, CO2-treated fish excelled at extracting oxygen from the water and outperformed the low-CO2 group in terms of hypoxia tolerance. When Montgomery took a closer look at the fish's blood, he found no difference in blood pH between the treatments, indicating a remarkable capacity of the seabass to counteract the acidifying effect of elevated CO2; surely this is good news for fish that must cope with global rises in CO2. In addition, fish in the rising CO2 treatment had a higher haemoglobin–oxygen affinity compared with the low-CO2 group – a surprising finding, given the common blood pH in the two groups – and this may explain their improved ability to tolerate hypoxia. Haemoglobin is housed within red blood cells, which may actively alter their internal environment to modulate oxygen transport. Whether this is part of the mechanism by which CO2-exposed seabass increased their haemoglobin–oxygen affinity remains to be seen.Studying the effects of climate change is complicated as numerous factors may interact to challenge an organism. Understandably, researchers often choose to study single factors in isolation, as this simplifies the interpretation of the data. However, Montgomery and colleagues show that overlooking interaction effects may limit our ability to predict the response of animals to climate change in the wild. In European seabass it appears that the combined condition of a decreasing oxygen level and an increasing CO2 level in the water, as is found in nature, improves hypoxia tolerance. To account for such effects in future work, current methods to assess hypoxia tolerance in fish should be revised to control for, or at least measure and report, CO2 levels in the water. Rising CO2 levels receive a lot of bad press and, in the context of climate change, rightfully so. However, at least for seabass that find themselves gasping for oxygen, the natural rise in CO2 that comes with aquatic hypoxia may actually save lives.