Juvenile Freshwater Research Articles

Resilience of Juvenile Freshwater Pearl Mussels to ThermalStress.

Climate change poses a significant threat to freshwater ecosystems by causing increases of average water temperatures, and more frequent and extreme heating events. Freshwater mussels are declining globally, and the distribution of the freshwater pearl mussel (Margeritifera margeritifera) has decreased dramatically over the past century. Even though it is likely that climate change is contributing to the decline of the species, little is known about the specific mechanisms involved. Here, we test how short episodes of water temperatures above the known thermotolerance range affect the survival and growth of the early post parasitic juvenile phase of freshwater pearl mussels. We also test if previous experience with elevated water temperatures can modify survival and growth responses to subsequent high-temperatures exposure. Mortality was very low in all treatments (< 5%) and not affected by the temperature treatments, while growth rate was positively affected by temperature. Our results suggest that juvenile mussels can survive short periods of heat stress when other environmental conditions are favourable. Future studies should therefore address how heat stress affects survival in combination with other stressors, such as reduced availability of dissolved oxygen.

Potential for juvenile freshwater mussels to settle onto riverbeds from field investigation

Freshwater mussel populations have been declining at an alarming rate around the world. Herein, we investigate whether changing flow conditions, as they affect juvenile freshwater mussel settling, could be a potential causative factor for this decline in the Dan River, North Carolina, USA. We deployed two uplooking velocity sensors on the riverbed between May and November 2019: one where mussels reside and another where they do not. From this data, we calculated shear velocity, which is a measure of the turbulence that acts to lift particles into suspension and acts against particle settling. We determined that a shear velocity less than 0.66 cm/s would be required to settle relatively large and dense juvenile mussels onto the riverbed; however, the lowest shear velocity we measured was 0.9 cm/s. Additionally, we estimated that juvenile freshwater mussels as large as 280-510 µm could always be suspended and not be able to settle onto the riverbed at these two locations. Therefore, the flow during May-November 2019 was high enough to prohibit recruitment of juvenile freshwater mussels at the sensor locations. Furthermore, we have identified that the magnitude of the lowest flows has increased since 2000, which may be exacerbating the decline in freshwater mussels.

Analysis of biological factors on affecting the growth performance and water quality of biofloc aquaculture system for freshwater barramundi

Biofloc technology is used to improve water quality and fish growth performance of aquaculture. The purpose of this research is to analyse the biological factors on freshwater barramundi in biofloc aquaculture system. Three set of experiments with 3 biological factors were carried out for freshwater barramundi to analyse the water quality and to evaluate the cultivated fish growth performance under the application of biofloc technology for 10 weeks. The biological factors involved are stocking density, carbon-to-nitrogen ratio and feeding rate. The water quality parameters were monitored weekly while the growth indices will be determined at the end of the experiments. The results revealed that stocking density has insignificant effect on the water quality but essential affected the growth rate of the freshwater barramundi. The best growth rate is observed at lowest stocking studied (10 fish/m3). The biofloc technology aquaculture system with C:N ratio of 16:1 and lowest stocking density (10 fish/m3) produced the best water quality and growth performance. Meanwhile the compatible feeding rate for the juvenile freshwater barramundi was identified at rate of 1% of fish body weight with feeding frequency once or twice a day in order to control the water quality and produced good growth performance of the juvenile.

Functional and molecular characterization of the Atlantic salmon gill epithelium cell line ASG-10; a tool for in vitro gill research.

Fish gills are not only the respiratory organ, but also essential for ion-regulation, acid-base control, detoxification, waste excretion and host defense. Multifactorial gill diseases are common in farmed Atlantic salmon, and still poorly understood. Understanding gill pathophysiology is of paramount importance, but the sacrifice of large numbers of experimental animals for this purpose should be avoided. Therefore, in vitro models, such as cell lines, are urgently required to replace fish trials. An Atlantic salmon gill epithelial cell line, ASG-10, was established at the Norwegian Veterinary institute in 2018. This cell line forms a monolayer expressing cytokeratin, e-cadherin and desmosomes, hallmarks of a functional epithelial barrier. To determine the value of ASG-10 for comparative studies of gill functions, the characterization of ASG-10 was taken one step further by performing functional assays and comparing the cell proteome and transcriptome with those of gills from juvenile freshwater Atlantic salmon. The ASG-10 cell line appear to be a homogenous cell line consisting of epithelial cells, which express tight junction proteins. We demonstrated that ASG-10 forms a barrier, both alone and in co-culture with the Atlantic salmon gill fibroblast cell line ASG-13. ASG-10 cells can phagocytose and express several ATP-binding cassette transport proteins. Additionally, ASG-10 expresses genes involved in biotransformation of xenobiotics and immune responses. Taken together, this study provides an overview of functions that can be studied using ASG-10, which will be an important contribution to in vitro gill epithelial research of Atlantic salmon.

Impacts of acute and chronic suspended solids exposure on juvenile freshwater mussels

Construction activities may affect adjacent water systems by introducing increased levels of suspended solids into the water body and may subsequently affect the survival and growth of freshwater mussels. We tested three sediment types from sites in Missouri, including Spring River sediment (SRS), Osage River bank clay soil (ORC), and quarried limestone from Columbia (LMT). We prepared series of suspensions of each sediment with total suspended solids concentrations ranging from 0 to 5000 mg/L. Juveniles from three mussel species, Fatmucket (Lampsilis siliquoidea), Arkansas Brokenray (Lampsilis reeveiana), and Washboard (Megalonaias nervosa) were exposed to these suspensions in both acute (96-h) and chronic (28-d) tests. No clear impact on survival was observed from the acute or chronic exposures, but chronic test showed that juvenile mussels' growth was strongly affected. Interestingly, growth was enhanced at lower levels of SRS and ORC (≤500 mg/L, p < 0.05), and the juvenile mussels exposed to 500 mg/L SRS exhibited approximately 60 % more dry weight than those reared in the control. LMT did not enhance growth. Growth was slowed by high concentrations (>1000 mg/L) of all three sediments, implying that high suspended solids levels could reduce survival in the long term. Our findings may help to inform regulations and guidelines for construction activities to minimize adverse effects on juvenile mussels.

Assessing the Toxicity of Sea Salt to Early Life Stages of Freshwater Mussels: Implications for Sea Level Rise in Coastal Rivers.

Sea levels across the planet are rising, particularly along the eastern coast of the United States. Climate-induced sea level rise can result in the inundation and intrusion of seawater into freshwater drainages. This would alter salinity regimes and lead to the salinization of coastal freshwater ecosystems. Increased salinity levels in freshwater can negatively affect freshwater-dependent species, including native mussels belonging to the order Unionida, which are highly sensitive to changes in water quality. Sea salt is largely made up of sodium and chloride ions, forming sodium chloride, a known toxicant to freshwater mussels. However, sea salt is a mixture that also contains other major ions, including potassium, sulfate, calcium, strontium, and magnesium, among others. Freshwater mussels exposed to sea salt would be exposed to each of the sea salt ions at the same time, resulting in a mixture toxicity effect. The mixture toxicity of these ions on early life stages of freshwater mussels is largely unknown because most research to date has evaluated individual salt ions in relative isolation. Therefore, we conducted acute toxicity tests on early life stages (glochidia and juvenile) of three freshwater mussel species that inhabit Atlantic Slope drainages (nonsalinity-adapted Atlanticoncha ochracea, salinity-adapted A. ochracea, Sagittunio nasutus, and Utterbackiana implicata). Glochidia and juveniles of each species were exposed to a control and six concentrations of Instant Ocean® Sea Salt (IOSS), a synthetic sea salt that closely resembles the ionic composition of natural sea salt. Exposure concentrations were 1 part(s) per thousand (ppt), 2 ppt, 8.5 ppt, 12.5 ppt, 17 ppt, and 34 ppt. We calculated the median effect concentration (EC50) for each of the eight acute toxicity tests and found that glochidia were more sensitive than juveniles to IOSS. At hour 24 EC50s for the glochidia ranged from 0.38 to 3.6 ppt, with the most sensitive freshwater mussel being the nonsalinity-adapted A. ochracea, exhibiting an EC50 of 0.38 ppt (95% confidence interval [CI] 0.33-0.44). Juvenile freshwater mussels exhibited EC50s at hour 96 ranging from 5.0 to 10.4 ppt, with the least sensitive freshwater mussel being the nonsalinity-adapted A. ochracea, exhibiting an EC50 of 10.4 ppt (95% CI 9.1-12.0). Our results show that acute exposure to sea salt adversely affects freshwater mussel viability, particularly glochidia. This information can be used to enhance freshwater mussel conservation strategies in regions that are or will be impacted by climate-induced sea level rise and associated freshwater salinization. Environ Toxicol Chem 2023;42:2478-2489. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Composition and apparent digestibility coefficients of essential nutrients and energy of cyanobacterium meal produced from Spirulina (Arthrospira platensis) for freshwater-phase Atlantic salmon (Salmo salar L.) pre-smolts

Composition and apparent digestibility coefficients (ADCs) were determined for whole-cell Spirulina meal produced from Arthrospira platensis (UTEX LB 2340). Spirulina meal contained 60 % crude protein, 20 MJ kg−1 gross energy, 16 % nitrogen-free extract (NFE), 10 % ash, 5 % moisture and 4 % crude lipid. Its protein was comprised of 25 % essential (EAAs) and 25 % non-EAAs. Spirulina meal protein demonstrated high EAA indices (1.0–1.3) relative to egg albumin and premium fishmeal. Spirulina meal was rich (mg 100 g−1) in chlorophyll a (1803) and c (369), β-carotene (141) and zeaxanthin (88) with low concentrations of antinutritional compounds crude fibre (4 %), trypsin inhibition activity (7 TUI mg−1) and phytate (17 mg g−1/ g) and undetectable heavy metal contaminants. A substitution digestion assay using cylindro-circular tanks (100L) equipped with faecal settlement columns was conducted with 164 juvenile (25 g) freshwater Atlantic salmon (Salmo salar L.) at 13 °C fed to apparent satiation with a reference diet (100 % basal mixture) or a test diet (80 % basal mixture and 20 % test ingredient) for 7 weeks. Single-ingredient ADCs for Spirulina meal were dry matter (75 %), ash (61 %), protein (81 %), lipid (73 %), NFE (63 %), energy (77 %), EAAs (average 91 %) and polyunsaturated fatty acids (PUFAs, 96 %). Digestible indispensable AA scores (DIAAS) for Spirulina meal were equal to or higher than 1 (range 1.0–4.6) showing Spirulina meal to be a high-quality protein for Atlantic salmon. Diet ADCs for the 20 % Spirulina meal diet were statistically the same as the reference diet for dry matter (73–74 %), ash (36–41 %), crude lipid (93–94 %), NFE (23–32 %) and energy (82–83 %), while crude protein ADC was slightly reduced from 92 to 90 %. Inclusion of 20 % Spirulina meal had no significant effects on diet ADC for the required EAAs (93–98 %), n-6 PUFA (96 %), n-3 PUFA (100 %) or essential n-3 long-chain PUFAs eicosapentaenoic acid and docosahexaenoic acid (100 %).

Laboratory-based comparison of screening materials for excluding juvenile freshwater fishes from New Zealand water intakes

ABSTRACT Growing demand for water requires resource managers to be innovative to minimise impacts on aquatic ecosystems. There are increasing concerns about fish damage and losses at water intakes, but few studies have examined the effectiveness of different screening material for excluding New Zealand fishes. We experimentally tested six screens (50–100 and 100–200 mm rock bunds, 3 mm woven mesh, 1.5, 2 and 3 mm wedge-wire), on two introduced and five native fish species. Bluegill bully (> 32 mm), common bully (> 30 mm), Canterbury galaxias (> 47 mm) and rainbow trout (> 40 mm) were screened effectively by 3 mm woven mesh and wedge-wire. Chinook salmon (> 43 mm) and īnanga whitebait (> 46 mm) were excluded by 2 mm wedge-wire, but shortfin elvers (< 80 mm) penetrated 3 and 2 mm wedge-wire, and glass eels (< 63 mm) penetrated 1.5 mm wedge-wire. Rock bunds were effective barriers for rainbow trout but were ineffective, and acted as habitat, for bluegill bully, Canterbury galaxias and shortfin eels. We recommend that 1.5 mm wedge-wire screens are used in the tidal zone of New Zealand rivers, 2 mm screens are used beyond this zone with an upstream transition to 3 mm screens dependent on catchment-specific fisheries values.

Immersion in sea cucumber’s steroid extract to increase male production of juvenile freshwater crayfish

One of the ways to increase the production for aquaculture is through the cultivation of monosexuals by ensuring genital reversal from which energy for reproduction is diverted towards growth. Masculinization has been identified as one of the most prominent techniques, where sex development was directed from female to male. This approach only altered the phenotype and not the genotype. The red claw crayfish (Cherax quadricarinatus) was a relatively new commercial commodity, and the males were known to grow faster than females. Hence, it was proposed to use monocultures comprising an all-male population to increase yield using steroid hormone, synthetic 17α-methyltestosterone. However, this technique generated residues that detrimentally affect human health, the environment, and cultivated organisms. Therefore, finding new safe natural steroid sources was essential, and one of which is exploring of natural hormones extracted from the viscera of sea cucumbers (Holothuria scabra Jaeger). This study focused on the determination of male formation and testosterone levels among juvenile crayfish, after immersing in sea cucumber steroid extract (SCSE). A completely random design with factorial was used with two variables, encompassing the varied doses (0, 2, 4 mg/L, 2 mg/L 17α-methyl testosterone as control group) and immersion times of 18 and 30 h. The result showed the dose-dependent ability of SCSE increase the male genital formation and promote the testosterone level of juvenile crayfish. In addition, the testosterone was influenced by dose and immersion duration time, with the highest level of testosterone observed in treatments of 4 mg/L SCSE with 30 h immersion was 0.248 ng/mL, while the male percentage was 77%. In conclusion, the combination of dose and immersion time significantly affected growth and testosterone levels.

Riparian detritus vs. stream detritus: food quality determines fitness of juveniles of the highly endangered freshwater pearl mussels (Margaritifera margaritifera)

Detritus is an important energy source of stream food webs. Being a mix of allochthonous and autochthonous sources, it is often unknown, which components contribute to the growth of stream organisms. This study focussed on the comparison of two different detritus types (riparian detritus and stream detritus) with respect to food quality and effects on growth as a fitness parameter of juvenile freshwater pearl mussels (FPM). We performed feeding experiments with juvenile FPM under laboratory conditions using the two detritus types from four different natural sources each. Food quality was determined by analysing the fatty acid composition. Stream detritus (conditioned to stream environment including autochthonous microbes) resulted in significantly higher growth rates of juvenile FPM than predominately terrestrial-based riparian detritus indicating higher food quality. Significantly positive correlations were found between mussel growth and different groups of polyunsaturated fatty acids (PUFA). This suggests that especially trace substances such as long-chained n-3 PUFAs and a high ratio of n-3 to n-6 PUFAs enhance the food quality of stream detritus for juvenile FPM. These results highlight the importance of instream conditioning of detritus for the food mix in headwater streams and the importance of PUFAs for the development of juvenile FPM.

Are Green Household Consumer Products Less Toxic than Conventional Products? An Assessment Involving Grass Shrimp (Palaemon pugio) and Daphnia magna.

Although it is generally assumed that green household consumer products (HCPs) contain individual compounds that are less toxic and/or more degradable than conventional HCPs, little research on this topic has been conducted. In our assessments, larval grass shrimp (Palaemon pugio) were used in a biodegradation study and juvenile freshwater cladocerans, Daphnia magna, were used in a photodegradation study. In each study, organisms were exposed to nondegraded and degraded treatments consisting of one green HCP and two conventional HCPs in six different categories (laundry detergent, dish detergent, mouthwash, insecticide, dishwasher gel, and all-purpose cleaner). Sensitivity to these products were assessed using 48-h static acute toxicity tests, and the median lethal concentrations (LC50s) then compared using an LC50 ratio test. For grass shrimp, only one green HCP (insecticide) was less toxic than both conventional HCPs. In one category (laundry detergent), the green HCP was the more toxic than either conventional HCP. Following a biodegradation treatment, none of the green product formulations became less toxic, whereas 44.4% of the conventional HCPs demonstrated decreased toxicity. For daphnids, green HCPs in three categories (dish detergent, insecticide, and all-purpose cleaner) were less toxic than both conventional products tested. Following a photodegradation treatment, two green product formulations (dish detergent and dishwasher gel) became less toxic (33.3%), whereas 87.5% of the conventional HCPs demonstrated decreased toxicity. The present study demonstrates that green HCPs are not necessarily less toxic and/or more degradable than their conventional counterparts. These results also suggest that the toxicity and degradability of end-product formulations need to be considered in the overall framework for green product evaluation. Environ Toxicol Chem 2022;41:2444-2453. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Experimental quantification of multiple point‐source pollution effects on juvenile freshwater mussels in a stream exposure gradient

Abstract Population declines in freshwater mussels (Unionida) resulting from failed recruitment, together with episodic water pollution potentially leading to juvenile mussel mortality, are often suspected (but rarely well documented), even in the most strictly protected aquatic areas. The aim of this study was to test a robust design for an in situ investigation of the water pollution effects on juvenile freshwater pearl mussel (FPM, Margaritifera margaritifera) in the protected Malše River (Czech Republic), which acts as a model system. A 30‐km river reach was delineated to include a section with previously recorded episodic multiple point‐source pollution events, as well as downstream and upstream control sections. Juvenile FPMs in open water mesh cages were exposed to river water at 15 sites in 42 exposure units (342 juveniles in individual chambers), and their survival and shell growth were assessed after a 33‐day period of low‐flow and high‐temperature conditions. The main physicochemical indicators related to municipal water pollution were measured weekly. The study results confirmed significantly impaired water quality indicated by episodic changes in total ammonia nitrogen (up to 1.037 mg L−1), total phosphorus (up to 0.516 mg L−1) and oxygen saturation (down to 75.0%) in the impaired section. While the growth of FPM (corrected for temperature effects) was significantly increased (shell length increment: 32.7 ± 9.7% – impaired, 26.4 ± 10.0% – control sections; mean ± SD), the survival (mean ± SD) of juveniles was significantly decreased in the impaired section (86.4 ± 12.5%) compared with the control sections (97.4 ± 5.7%). This study has demonstrated the capacity of applying a caged bivalve model at a fine spatial scale within a longitudinal river profile to document the impacts of water pollution. The methodology applied here may provide a useful tool for assessing and improving the level of water quality management and is applicable in FPM action plans and stream biotope conservation in general.

Effects of food abundance on juvenile freshwater mussel survival and growth in aquaculture, and comparison with growth in streams

Captive propagation has become an important tool in the conservation of imperiled freshwater mussels. Previous studies provide conflicting results about the effects of food abundance on survival and growth of juvenile mussels in aquaculture, and the extent to which growth in the hatchery reflects growth in the wild is unknown. We evaluated the effects of abundance of an algal-based diet on survival and growth of juvenile Cumberland Bean (Venustaconcha troostensis) in a recirculating aquaculture system. We compared food abundance (as fine particulate organic matter, FPOM) in our experimental food rations with FPOM in 14 streams to assess the similarity of hatchery and natural food sources. We compared growth in our experiments with previously published growth estimates of Cumberland Bean at 17 stream sites. Growth in the hatchery increased linearly with increasing food abundance from 3.5 to 27.6 mg/L algal dry mass (about 111,000–1,147,225 cells/mL), and mussel size after two weeks increased 2.9% for every doubling of algal dry mass within the range of our experimental rations. We observed no negative effects of increasing food abundance on survival, and ammonia concentrations remained below chronic effect concentrations in all treatments, even in food rations much higher than recommended by previous studies. FPOM in our experiments spanned a similar range of values as FPOM in streams. Growth in our experiments was similar to growth in streams, but our experimental temperatures were higher than in streams. When the probable effect of temperature was accounted for, growth in most experimental food rations was substantially lower than expected in streams despite similar FPOM. This suggests that food quality or other conditions are more favorable for mussel growth in the wild.

Environmentally friendly microbeads to model the dispersal of particulates in aquatic systems

The transport of particulate matter including the gametes, larvae and propagules of reproducing organisms and other organic matter involved in nutrient/contaminant transport are important processes, yet there are few environmentally friendly methods available to examine dispersal empirically. Herein we report on the development and application of a biodegradable and non-toxic physical model, based on alginate microbeads with modifiable size, density (ρ), and colour for use in dispersal studies. Specifically, the microbeads were designed to model the size and ρ of parasitic juvenile freshwater mussels (Unionidae; ρ = 1200 kg m−3), which undergo dispersal upon excystment from fish hosts. We released the juvenile-mussel and neutrally buoyant microbeads (ρ = 1000 kg m−3) in a local river and captured them in drift nets downstream. The concentration of microbeads declined with downstream distance, but neutrally buoyant microbeads were transported farther. Analysis of microbead capture rates could be described using the patterns of several mathematical models (negative exponential, power, and turbulent transport), which were consistent with the reported dispersal of mussel larvae and other benthic macroinvertebrates. These results support the use of alginate microbeads in dispersal studies, because their environmentally friendly and customizable properties offer improvements over non-biodegradable alternatives.

Functional Mechanism of Antimicrobial Peptide Bomidin and Its Safety for Macrobrachium rosenbergii.

Macrobrachium rosenbergii is an economically important source of crustacean seafood worldwide. Vibrio parahaemolyticus is an important aquatic pathogen that causes epidemics of acute hepatopancreatic necrosis in shrimp populations, which results in significant economic losses to aquaculture farmers. To prevent the antibiotics abuse, which has become a serious threat to human health, novel anti-infective strategies are urgently required to control V. parahaemolyticus. Antimicrobial peptides, which exhibit favourable germicidal activity compared to traditional antibiotics, can be used as a key method to prevent and treat bacterial diseases. Herein, an antimicrobial peptide, bomidin, was expressed through genetic engineering technology. The minimum inhibitory concentration (MIC) of bomidin showed a significant inhibitory effect on V. parahaemolyticus that was equivalent to that of ampicillin. Subsequently, the mechanism of action of recombinant bomidin was explored using PNP and ONPG assays to investigate the effects on membrane permeability. These assays indicated that bomidin penetrated the germ membrane and induced the release of cytoplasmic contents and ultimately interacted with DNA to form a bomidin-DNA complex that inhibits bacterial survival. Transmission electron microscopy and scanning electron microscopy revealed that bomidin could cause damage and dysfunction to the cell wall and membrane. Bomidin was nontoxic to mouse red blood cells within a concentration range that was much larger than the MIC. Toxicity assays revealed that 0.02mg/mL bomidin was safe for use with juvenile freshwater prawns of M. rosenbergii and significantly inhibited the growth of V. parahaemolyticus in cultured water. These results demonstrated that synthetic peptide bomidin had great antibacterial effect against V. parahaemolyticus and therefore a therapeutic potential in aquaculture.

Do Sand Smelt (Atherina presbyter Cuvier, 1829) Larvae Discriminate among Conspecifics Using Different Sensory Cues?

The ability of shoaling fish to recognise and differentiate between potential groupmates may affect their fitness and survival. Fish are capable of social recognition and multiple sensory cues mediate the recognition mechanisms. This has been comprehensively studied for juvenile and adult freshwater species. However, the recognition ability and mechanisms intervening during the larval phase of marine species are yet poorly understood. Fish larvae are capable of discriminating conspecifics from heterospecifics based on chemical and/or visual cues, but whether this recognition occurs at finer scales, such as discerning among conspecifics of different reefs, is yet understudied. Here, we tested the hypothesis that larvae of a marine fish species, the sand smelt (Atherina presbyter Cuvier, 1829), are able to recognise and associate with conspecifics of their natal reef versus conspecifics of a non-natal reef based on three sensory modalities—chemical, visual, and chemical and visual simultaneously. Results do not support our hypothesis, but still provide evidence of group cohesion and indicate large differences in the relative importance of the different senses when associating with conspecifics, with visual cues playing a more important role than chemical cues alone.

Effects of serotonin (5‐HT) on juvenile culture of narrow‐clawed crayfish Pontastacus leptodactylus (Eschscholtz, 1823)

Serotonin was used for the first time in this study as a feed additive in juvenile freshwater crayfish Pontastacus leptodactylus, (stage II-V) to investigate its effects on growth performance, survival and immune response based on total haemocyte count (THC). Serotonin was included in diets at levels of 0 (control), 5, 10, 20 and 40 mg kg−1. When the results were examined, a significant quadratic increase was observed in the values of final total length: FTL and final body weight: FBW, weight gain (WG), length gain (LG) and specific growth rate (SGR) with dietary serotonin amounts (Plinear and Pquadratic <0.05). The survival rates of crayfish showed a significant linear increase with doses of serotonin (Plinear = 0.001). THC values, on the other hand, were not affected by serotonin amounts in experimental diets. The broken line models estimated optimum dietary serotonin inclusions based on FBW and FTL as 20.03 and 20.44 mg kg−1, respectively. In conclusion, dietary serotonin can be used in growing juvenile P. leptodactylus during the developmental stages of II-V.

Modulation of growth, antioxidant status, hepatopancreas morphology, and carbohydrate metabolism mediated by alpha-lipoic acid in juvenile freshwater prawns Macrobrachium nipponense under two dietary carbohydrate levels

Carbohydrate is commonly used in aquatic organism as the cheapest energy source. However, most aquatic animals are low efficient in utilizing dietary carbohydrate for energy provision. Therefore, improving the utilization efficiency of high carbohydrate by aquatic organisms is important for sustainable aquaculture development. Alpha-lipoic acid (α-LA) is a cofactor of key enzymes involved in glucose metabolism. However, its role in regulation of carbohydrate metabolism in aquatic animals is currently unknown. This study investigated the effects of α-LA on growth, antioxidant status, hepatopancreas morphology, and carbohydrate metabolism of freshwater prawns Macrobrachium nipponense under two dietary carbohydrate levels. Six diets were formulated using casein and fish meal as the protein sources, fish oil and soybean oil as the lipid sources, and corn starch as the carbohydrate source, at two carbohydrate levels (15% and 30%) and three concentrations of α-LA supplementation (0, 700, and 1400 mg/kg). Each experimental diet was fed to juvenile prawns (mean weight 0.050 ± 0.003 g), twice daily to apparent satiation, in five replicates. In the 15% (low)-carbohydrate groups, weight gain was significantly reduced in prawns fed 1400 mg/kg α-LA compared with 0 or 700 mg/kg α-LA, but there was no significant effect in the 30% (high)-carbohydrate groups. Survival was significantly higher among prawns fed 700 mg/kg α-LA compared with 0 or 1400 mg/kg α-LA regardless of the carbohydrate level. The levels of dietary carbohydrate and α-LA also significantly affected the activities of key enzymes involved in glycolysis and the citric acid cycle. The activities of hexokinase and pyruvate kinase activities were highest in prawns fed l400 mg/kg α-LA, in both the low- and high-carbohydrate groups. Supplementation with 700 or 1400 mg/kg α-LA significantly increased the activities of 6-phosphofructokinase, pyruvate dehydrogenase, and succinate dehydrogenase regardless of the carbohydrate level. The level of malondialdehyde decreased significantly with increased α-LA supplementation; in contrast, the levels of superoxide dismutase, glutathione peroxidase, and glutathione were significantly higher in prawns fed 700 or 1400 mg/kg α-LA when compare with those fed no α-LA supplement. Dietary α-LA did not affect the overall morphology of the hepatopancreas, but 1400 mg/kg α-LA reduced the number of B (blister-like) cells. Thus, 700 mg/kg α-LA supplementation under either dietary carbohydrate level could improve the antioxidant status, carbohydrate metabolism, and morphology of the hepatopancreas in juveniles of M. nipponense. We conclude that α-LA supplementation can be used to improve the efficiency of carbohydrate utilization when a 30% carbohydrate diet is used for this prawn.

According to the issue of the giant freshwater prawn ((&lt;i&gt;Macrobrachium rosenbergii&lt;/i&gt;)

Purpose: study the biotechnical features of rearing juvenile giant freshwater prawn (Macrobrachium rosenbergii) using recirculating aquaculture systems (RAS).Materials and methods. Two fish-farming modules RAS and aquarian complex were used for the work. One of them has a total volume of 6.5 m3, the second - 14.5 m3. Larvae were reared in gasite cages of 0.021 m3 in an aquarian complex of two 200-liter aquariums. Larvae of one female prawn were used in an amount of 8500 units. At each stage of prawns' development we used different versions of feed of both animal and plant origin: artemia, minced fish, boiled chicken eggs (protein + yolk), beef liver and oat flakes.Results. Brood fish were kept at an average planting density of 6.2 individuals/m2, with a sex ratio of 1:4.5 (males: females). The planting density of larvae in cages was 2,125 units/cage or 101.2 units/liter. The average weight of juveniles during rearing of postlarvae at 130 days was 3.19 g. Juvenile yield was 49.9%. Specific growth rate of biomass varied from 4.87 to 3.68 %. Planting density of juveniles varied from 1775,6 units/m2 to 660,9 units/m2. As a result, the feeding coefficient was 5.24 units. Growing productivity was 362.7 pcs/m2 or 1156.8 g/m2 in the RAS module.Conclusion. There were established biotechnical peculiarities and production possibilities of growing young giant freshwater prawn (Macrobrachium rosenbergii) using fish-breeding RAS and aquarian complex. Modernization of fish-feeding RAS and use of some recommendations on feeding suggest the possibility of their use for breeding and rearing of juvenile giant freshwater prawns in already existing warm-water enterprises, initially aimed at other objects of aquaculture.

Coinfection of Chlamydia spp. and herpesvirus in juvenile farmed Siamese crocodiles (Crocodylus siamensis) in Thailand.

Background and Aim:For a decade, chlamydial and herpesvirus infections have caused significant morbidity and mortality in farmed crocodiles. In September 2017, a total of 160 juvenile freshwater Siamese crocodiles (Crocodylus siamensis) with conjunctivitis/pharyngitis lesions were admitted at the Veterinary Aquatic Animal Research Health Care Unit, Faculty of Veterinary Science, Mahidol University. All crocodiles did not respond well to antibiotics or supportive treatments and died. This study aimed to detect and identify the causative agents associated with conjunctivitis/pharyngitis and fatal outcomes in juvenile farmed Siamese crocodiles.Materials and Methods:A total of 138 pharyngeal and conjunctival swabs and conjunctival scrapes were collected from live crocodiles. All swab and scrape samples were DNA-extracted and amplified by polymerase chain reaction (PCR) using Chlamydiaceae- and herpesvirus-specific primers. Tissue samples (brain, lung, liver, heart, spleen, and intestine) were collected from two representative postmortem animals. All tissue samples were processed for molecular and pathological analyses.Results:PCR examinations identified chlamydial and herpesvirus DNA in 92% (126/138) and 100% (138/138), respectively, of the tested swab and scrape samples. Of those positive samples, 79% (26/33), 67% (4/6), and 98% (97/99) of the pharyngeal swabs, conjunctival swabs, and conjunctival scrapes, respectively, were positive for both chlamydial and herpesvirus DNA. Histopathological examination indicated necrosis and mononuclear cell infiltration in the liver, kidney, and intestine of the affected animals. The intracytoplasmic accumulation of Chlamydia was randomly observed in the examined tissue sample. Moreover, the presence of chlamydial and herpesvirus DNA was also detected in the tissue samples, including the heart, intestine, brain, lung, liver, and spleen, of the affected animals by PCR. Phylogenetic analyses revealed that Chlamydia spp. detected in the juvenile Siamese crocodiles was notably different from other known species in the Chlamydia genus, while the herpesvirus detected in the crocodiles was closely related to crocodyline herpesvirus 1.Conclusion:Based on histopathological and molecular examinations, this report provided the first evidence of coinfection of Chlamydia spp. and crocodyline herpesvirus 1 in juvenile Siamese crocodiles in Thailand.