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Carbohydrates are a common and economical energy source in animal feeds. However, most fish show a persistent postprandial hyperglycemia after intake of a high-carbohydrate diet. Unfortunately, the mechanism of glucose metabolism in fish is still unclear. In the present study, tiger puffer (Takifugu rubripes) and turbot (Scophthalmus maximus) were intraperitoneally injected or orally administered with glucose or fructose (500 mg/kg body weight) to evaluate the ability of fish to utilize carbohydrates. Afterwards, serum glucose, fructose, pyruvate, insulin levels, and acute hypoxia tolerance were measured. Our results showed increased serum glucose level and then decreased post intraperitoneal injection with glucose, and reached a peak after 0.5 hours in turbot and 1 hour in tiger puffer. Tiger puffer had significantly lower liver glycogen, serum glucose, fructose, pyruvate, and insulin contents than turbot. Glucose and fructose only induced insulin secretion in turbot, but did not change serum insulin level in tiger puffer. Glucose was a stronger stimulator of insulin than fructose in the two marine species. Both intraperitoneal injection and oral fructose intake increased serum glucose level, while intraperitoneal or oral glucose also increased serum fructose level. Intraperitoneal injection of glucose promoted absorption and utilization of glucose in the blood more effectively than oral glucose intake. In addition, turbot and tiger puffer were intolerant to acute hypoxia, whereas supplementation with glucose or fructose improved hypoxia tolerance in the two marine fishes by activating anaerobic glycolysis. Taken together, our results provide important scientific information for understanding the mechanism for glucose and fructose utilization and improving hypoxia tolerance in fish. [ABSTRACT FROM AUTHOR]

Stagnating capture fisheries and increasing fish protein demand necessitate aquaculture production to bridge the gap. Lake Victoria is a potential water body for increasing fish production through cage farming. The sustainability of Lake Victoria for cage farming depends on timely and holistic site selection. However, current site selection methods involve complex, resource‐intensive field surveys that lack a holistic approach to integrate multiple factors. Accordingly, information regarding suitable sites for sustainable fish cage farming in Lake Victoria remains scarce. In this study, a transparent geographic information systems (GIS) and multicriteria evaluation (MCE) here after reffered to as GIS‐MCE was used to reveal potential sites to be permitted or avoided during cage aquaculture development in the Mwanza Gulf of Lake Victoria (Tanzania). Our analysis involved weighting and integration of sub‐models representing ecologically sensitive areas, physical environment, and socio‐economic and water quality variables into a single spatial model portraying different site suitability levels in the Mwanza Gulf. The results indicated that the sub‐models identified relatively larger suitable and most suitable sites compared to the overall model. No site maintained its status across all sub‐models. The overall model designated a small area (5.10 km2 or 1.52%) as the most suitable site, with 24.20 km2 (7.44%) as suitable, 64.47 km2 (19.82%) as less suitable, and 42.63 km2 (13.12%) as unsuitable for cage fish farming. The remaining area (188.84 km2 or 58.06%) was a constrained site to be avoided during cage aquaculture development. Taken together, the individual sub‐models are ineffective in designating potential sites for fish cage culture and thus should not be used solely. The GIS‐MCE general model provides a fast and timely method for identifying potential sites for cage farming in Lake Victoria. Fish farmers and managers should use the GIS‐MCE overall model in inland waters to facilitate site selection for complying with licensing requirements and decrease field extensive surveys. [ABSTRACT FROM AUTHOR]

Ammonia is a common environmental stress factor that constrains aquaculture industry development. This study evaluated the effect of carbohydrate levels and ammonia stress in oriental river prawn (Macrobrachium nipponense). The experiment had six treatments containing two water ammonia levels (0 and 5 mg/L) and three dietary carbohydrate levels (low carbohydrate diet (LCD, 10%), medium carbohydrate diet [MCD, 20%], and high carbohydrate diet [HCD, 30%]), and lasted six weeks. The results showed that the prawns fed on MCD had higher weight gain than those fed on LCD and HCD during ammonia stress. Moreover, the prawns fed on MCD had significantly lower acid phosphatase and alkaline phosphatase activities during ammonia stress. Feeding the prawns on the MCD increased B cells in the hepatopancreas during ammonia stress. Interestingly, the prawns fed on MCD had significantly lower superoxide dismutase activity compared to LCD and HCD during ammonia stress. Moreover, the prawns fed on MCD had significantly lower pyruvate kinase activity and pyruvate and lactic acid contents, while those fed on LCD had significantly higher succinic dehydrogenase, 6‐phosphogluconic dehydrogenase, and phosphoenol pyruvate carboxykinase activities during ammonia stress. The prawns fed on the MCD increased significantly glutaminase activity and decreased the ammonia content in the serum during ammonia exposure. In addition, feeding the prawns on MCD decreased significantly the expression of apoptosis and inflammation‐related genes. Taken together, the MCD supplied energy required to counteract ammonia stress, which increased growth, improved antioxidant capacity, facilitated ammonia excretion, and alleviated inflammation and apoptosis of the oriental river prawn. Highlights: Chronic ammonia stress inhibited growth and induced oxidative stress and apoptosis in prawns.Medium dietary carbohydrate alleviated oxidative stress and apoptosis of prawns.Medium dietary carbohydrate met the energy requirements of prawns and improved growth.Medium dietary carbohydrate enhanced ammonia excretion of Macrobrachium nipponense during ammonia stress.Prawns farmers should supplement 20% carbohydrate in the diets for M. nipponense juveniles. [ABSTRACT FROM AUTHOR]

Hypoxia is a common environmental stress factor in aquatic organisms, which varies among fish species. However, the mechanisms underlying the ability of fish species to tolerate hypoxia are not well known. Here, we showed that hypoxia response in different fish species was affected by lipid catabolism and preference for lipid or carbohydrate energy sources. Activation of biochemical lipid catabolism through peroxisome proliferator-activated receptor alpha (Pparα) or increasing mitochondrial fat oxidation in tilapia decreased tolerance to acute hypoxia by increasing oxygen consumption and oxidative damage and reducing carbohydrate catabolism as an energy source. Conversely, lipid catabolism inhibition by suppressing entry of lipids into mitochondria in tilapia or individually knocking out three key genes of lipid catabolism in zebrafish increased tolerance to acute hypoxia by decreasing oxygen consumption and oxidative damage and promoting carbohydrate catabolism. However, anaerobic glycolysis suppression eliminated lipid catabolism inhibition-promoted hypoxia tolerance in adipose triglyceride lipase (atgl) mutant zebrafish. Using 14 fish species with different trophic levels and taxonomic status, the fish preferentially using lipids for energy were more intolerant to acute hypoxia than those preferentially using carbohydrates. Our study shows that hypoxia tolerance in fish depends on catabolic preference for lipids or carbohydrates, which can be modified by regulating lipid catabolism. [ABSTRACT FROM AUTHOR]

Fish feeding habit determines the digestive tract structure and intestinal microflora. However, the relationship between feeding habit, digestive intestinal morphology, and microbial diversity of omnivorous, herbivorous, plankton feeder, and carnivorous fish from the same environment has not been compared. This study compared the digestive enzyme activities, intestinal morphology, and intestinal microflora of omnivorous (Carassius auratus), herbivorous (Ctenopharyngodon idellus), carnivorous (Siniperca chuatsi), and plankton feeder (Schizothorax grahami) fishes and predicted the potential functions of specific microflora on different nutrients. Twelve intestine samples were collected from each of the four fishes from Dianchi Lake. The composition and diversity of microbial communities were determined by using high‐throughput sequencing of 16S rDNA. The results showed that the carnivorous fish (S. chuatsi) had higher trypsin and pancrelipase activities in the hepatopancreas and enteropeptidase in the intestine, but lower amylase activities in the intestine. The carnivorous fish intestine had more microvilli branches and complex structures than other fish species in the order carnivorous > herbivorous > plankton feeder > omnivorous. The intestinal microflora diversity was higher in the omnivorous fish and followed the order omnivorous > herbivorous > plankton feeder > carnivorous. Acinetobacter species and Bacteroides species were the most dominant flora in the carnivorous and herbivorous fishes, respectively. Acinetobacter species and Pseudomonas species might help the host to digest protein, while Bacteroidetes species may help the host to digest cellulose. Taken together, feeding habit determines the digestive enzyme activities, intestinal tissue morphology, and differential colonization of fish intestinal flora. The knowledge obtained is useful in feed formulation and feeding practices for the studied fish species. [ABSTRACT FROM AUTHOR]

Ammonia is one of the common stress factors in aquaculture. However, the effect of chronic ammonia exposure in juvenile oriental river prawn (Macrobrachium nipponense) is currently unexplored. This study explored the effects of chronic ammonia on juvenile healthy oriental river prawns. Fifty prawns (0.123 ± 0.003 g) were exposed to 0, 5, and 15 mg/L total ammonia nitrogen (TAN) in triplicates for 28 days. The effects of chronic ammonia challenge were evaluated on growth, antioxidant capacity, hepatopancreas and gill morphology, and glucose and ammonia metabolism. The results showed that, the chronic ammonia exposure reduced significantly survival rate and weight gain of prawns. The prawns exposed to 15 mg/L ammonia had induced oxidative stress. However, the prawn exposed to 15 mg/L ammonia had significantly lower aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and acid phosphatase activities in the serum. Furthermore, exposure of prawns to 15 mg/L ammonia increased the activities of hexokinase, pyruvate kinase, pyruvate and lactic acid content, and glutamine synthase activity. However, the prawns exposed to 15 mg/L ammonia, reduced succinic dehydrogenase, 6‐phosphogluconic dehydrogenase, phosphoenolpyruvate carboxykinase, glutamate synthase, and glutamate dehydrogenase activities but increased ammonia content in serum. The exposure of ammonia deformed lumen, damaged basement membrane and decreased secretory cells in the hepatopancreas, disordered gill epithelial and pillar cells, and caused gill filament base vacuolation. Our study indicates that chronic ammonia stress impairs growth performance, tissue morphology, induces oxidative stress, and alters glucose and ammonia metabolism in juvenile oriental river prawns. [ABSTRACT FROM AUTHOR]

This study evaluated the presence of aflatoxin B1 in five different animal feeds collected from manufacturers, suppliers and consumers and its possible reduction by heating at 100°C for 180 min. A total of 160 animal feed samples were collected and analyzed by using lateral flow immunoassay method. The results revealed that all animal feeds analyzed were positive for aflatoxin B1 with 91% samples containing high concentrations ranging from 24.00 to 76.23 ng/g above the international allowable standard for animal feeds (20 ng/g). Maize bran (76 ng/g) and sunflower cake (63 ng/g) had higher aflatoxin B1 concentrations, correlating with higher moisture content. Upon heating the feeds, aflatoxin B1 was reduced to a concentration ranging from 2.24 to 9.78 ng/g (<20 ng/g). Our study suggests high potential health problems to animals and humans from aflatoxins requiring proper heating and frequent monitoring of the animal feeds for aflatoxin B1. [ABSTRACT FROM AUTHOR]

Arginine (Arg) is an important essential amino acid required for optimum fish growth. However, its role in plant‐rich diets on growth and the required level in juvenile Hemibagrus wyckioides are currently unknown. This study evaluated the effects of Arg supplementation in plant‐rich diets on growth, feed utilization, whole body composition, blood biochemical indicators and gene expressions of the target of rapamycin (TOR) signaling pathway in juvenile H. wyckioides. A total of 450 fish (6.40 ± 0.06 g) were randomized into six equal groups and fed on diets with graded Arg levels: 0 (control), 3, 6, 9, 12 and 15 g/kg of dry feed for eight weeks. The results revealed that specific growth rate (SGR) and feed conversion ratio of juvenile H. wyckioides were significantly improved and reduced, respectively in fish fed on 9 g/kg of Arg supplementation (p <.05). The optimum amount of dietary Arg content in plant‐rich diets for H. wyckioides was 63.77 g/kg diet based on SGR. Feeding fish with dietary Arg supplementation ranging from 9 to 12 g/kg improved significantly (p <.05) whole body protein contents and decreased lipid deposition. The mRNA levels of TOR, eukaryotic translation initiation factor 4E (4EBP) and ribosomal protein S6 kinase 1 (S6K1) in muscle and liver were significantly affected by increasing dietary Arg levels. Meanwhile, the mRNA relative expression levels of TOR and S6K1 in the liver and muscle increased significantly as Arg supplementation increased. On the other hand, the mRNA relative expression levels of 4EBP was significantly higher in fish fed on the 9 g/kg Arg diet compared to those fed on the control and 15 g/kg Arg diets. In conclusion, our current results indicate that dietary Arg supplementation in plant‐rich diets, might activate the TOR signaling pathway, which promotes protein synthesis and reduces lipid accumulation of H. wyckioides, resulting in improved growth. [ABSTRACT FROM AUTHOR]

The rearing of fish in intensive systems reduces their immunity leading to eruption of diseases, consequently prompting the use of antibiotics. Antibiotics are currently used in cultured fish globally to treat/prevent diseases. On the one hand, antibiotics used in aquaculture help to improve fish health by killing or inhibiting pathogenic bacteria proliferation. However, on the other hand, they cause multiple side effects. To date, information on systemic effects of antibiotics in cultured fish is scattered and their potential human health risk remains elusive. This review critically analyses and discusses the available information in the literature on the positive and negative effects of antibiotics in cultured fish and their potential human health risk via fish consumption. The review found 44 different antibiotics dominated by oxytetracycline were studied in various fish species worldwide. Antibiotics used in global aquaculture either decrease or increase fish growth and survival rates. They induce oxidative stress, which affect antioxidant and detoxification responses and cause host–microbiota dysbiosis. These changes compromise the fish immunity system, which ultimately lead to cellular damage. The toxicities generated inhibit the fish aerobic glycolysis, suppress lipogenesis and fatty acid β‐oxidation while increase energy demand by initiating gluconeogenesis and anaerobic glycolysis. Consumption of fish treated with antibiotics causes human health risk. Future studies are required on agents to restore dysfunctions induced by antibiotics in cultured fish, while attempts to limit their utilisation in aquaculture production are underway. [Correction added on 21 November 2020, after first online publication: The abstract has been amended to clarify the scope of the review.] [ABSTRACT FROM AUTHOR]

Swim bladder is an ideal source of collagen production in fish for improved human health. Proline (Pro) is the main proteinogenic amino acid needed for collagen production. However, the effects of Pro supplementation on the swim bladder collagen synthesis have rarely been evaluated in fish. We determined the effects of dietary Pro supplementation on swim bladder collagen synthesis and its possible signalling pathway in spotted drum, Nibea diacanthus. A total of 450 N. diacanthus (100 ± 3.05 g) were randomly assigned into six treatments and fed with diets supplemented with different levels of Pro (0, 2.5, 5, 7.5, 10 and 12.5 g/kg of dry diet, hereafter P0, P1, P2, P3, P4 and P5, respectively) for 8 weeks. At the end, we evaluated collagen synthesis in swim bladder and the expression of genes related to TGF‐β/Smad pathway in the fish. Dietary Pro levels increased significantly the contents of crude protein, total collagen (TC) and the levels of some amino acids in swim bladder than the control diet (p <.05). The optimum amount of dietary Pro inclusion in diets for swim bladder collagen synthesis in N. diacanthus was 7.6 and 7.5 g/kg based on crude protein and TC in swim bladder, respectively. Dietary Pro levels increased significantly the proline 4‐hydroxylase (P4H) content in fish serum, swim bladder, muscle and liver tissues than control (p <.05). The relative expression of collagen type I alpha 1 (COL1A1), alpha 2 (COL1A2) and mothers against decapentaplegic homolog 2 (Smad2) genes in liver and swim bladder initially increased significantly as the concentration of Pro and later decreased (p <.05). Similarly, the relative expression of transforming growth factor beta (TGF‐β), P4Ha2 and P4Ha3 genes in the swim bladder increased significantly as dietary Pro levels increased (p <.05). Using K‐means clustering analysis, dietary proline partly promoted collagen accumulation in swim bladder through upregulation of Smad2 and TGF‐βRT genes. Taken together, Pro affected the collagen metabolism in swim bladder, probably by regulating the TGF‐β/Smad pathway, most likely via transient overexpression of Smad2 gene. [ABSTRACT FROM AUTHOR]

Farming of red tilapia is increasing rapidly. However, its commercial farming development is challenged by lack of clear information on genetic basis for skin colour and pigmentation differences due to environmental changes. This study investigated the effects of photoperiod (light:dark, L:D) on the growth and skin colour variation of Malaysian red tilapia. A total of 180 fish weighing 150.48 ± 0.44 g were reared under natural photoperiod (13L:11D, control), prolonged lightness (24L:0D) and prolonged darkness (0L:24D) in three replicates for 78 days. The weight gain of fish cultured under both prolonged light and darkness were significantly higher than fish under natural photoperiod. The tyrosinase level in ventral skin was significantly higher for fish cultured under prolonged darkness condition than in the other two photoperiod regimes. Contrary, the cysteine level in the dorsal skin was significantly higher in the fish cultured under natural photoperiod than in prolonged light and darkness. The relative mRNA expressions of SRY‐related HMG‐Box 10 (sox 10), tyrosine (tyr), tyrosine‐related protein 1 (tyrp‐1) and solute carrier family 7 member 11 (slc7a11) genes were significantly higher in ventral skin of fish under prolonged darkness than the other two photoperiods. This study demonstrates that photoperiod has an impact on melanogenesis and growth of red tilapia. Understanding the effects of photoperiod on genetic basis of red tilapia will help in selective breeding programme of the important economic traits for the development of commercial red tilapia farming. [ABSTRACT FROM AUTHOR]

Organic matter (OM) such as organic nitrogen plays a substantial role in the global biogeochemical cycling of bio‐reactive components—amino acids (AA) in aquatic environments. Spatial and temporal variations in source, diagenesis, and fate of organic nitrogen such as AA in sediments of small tropical rivers and the role of oxbow/meandering loops under changing climatic conditions are poorly investigated. This study assessed the spatial and seasonal variations in OM composition, source, and diagenesis of a tropical small mountainous river—Netravati River, India, for 1 year. Water samples were determined for suspended particulate matter, and surface sediments were examined for bulk parameters, surface area (SA), and the L‐ and D‐enantiomers of AA. The L‐ and D‐enantiomers of AA displayed subtle seasonal variations in composition and depicted varying degrees of diagenesis. The concentration of D‐enantiomer of AA was high and showed substantial contributions from bacteria, terrestrial source, and in situ production. The D‐arginine was the most abundant D‐enantiomer of AA in the study area, possibly due to extracellular secretion by bacterial species and adsorption onto sediments, and thus, it was protected from degradation. Degradation index was more negative at the oxbow and meandering loop stations during the dry season suggesting that local geomorphologic settings steer the diagenesis of OM within the river. A negative relationship between gamma‐aminobutyric acid and organic carbon:surface area (OC:SA) ratio and a positive correlation between tyrosine and OC:SA ratio suggested accelerated loss of OM. Furthermore, the concentrations of most bulk parameters were higher in the lower reaches during monsoon and premonsoon seasons. Taken together, changes in seasons have an operational control in distinguishing the composition, source, and diagenesis of spatial OM distribution. Moreover, oxbows and river meandering loops influence the diagenetic processes in small tropical river systems. [ABSTRACT FROM AUTHOR]

Colonizing germ-free (GF) zebrafish with specific bacterial species provides the possibility of understanding the influence on host biological processes including gene expression, development, immunity, and behavioral responses. It also enlightens our understanding on the host-microbe interactions within the physiological context of a living host. However, the responses of GF zebrafish to various colonization conditions such as bacterial concentrations, colonization time points, and exposure duration remain unclear. To address this issue, we explored the responses of GF zebrafish by using two bacterial species at varying concentrations, colonization time points and exposure duration. Therefore, we mono-associated GF zebrafish with Escherichia coli DH5α or Bacillus subtilis WB800N at concentrations ranging from 102 to 107 CFU/ml either at 3 day post fertilization (dpf) or 5 dpf for 24 or 48 h. We evaluated the responses of GF zebrafish by analyzing the survival rate, colonization efficiency, nutrients metabolism, intestinal cell proliferation, innate immunity, stress, and behavior responses by comparing it to conventionally raised zebrafish (CONR) and GF zebrafish. The results indicated that the final bacteria concentrations ranging from 102 to 104 CFU/ml did not cause any mortality when GF mono-associated larvae were exposed to either E. coli DH5α or B. subtilis WB800N at 3 or 5 dpf, while concentrations ranging from 106 to 107 CFU/ml increased the mortality, particularly for 5 dpf owing to the decrease in dissolved oxygen level. The E. coli DH5α mainly induced the expression of genes related to nutrients metabolism, cell proliferation and immunity, while B. subtilis WB800N mainly upregulated the expression of genes related to immunity and stress responses. Moreover, our data revealed that GF zebrafish showed higher levels of physical activity than CONR and the microbial colonization reduced the hyperactivity of GF zebrafish, suggesting colonization of bacteria affected behavior characteristics. This study provides useful information on bacterial colonization of GF zebrafish and the interaction between the host and microbiota. [ABSTRACT FROM AUTHOR]