Un-ionized Ammonia Levels Research Articles

Nile tilapia (Oreochromis niloticus) show high tolerance to acute ammonia exposure but lose metabolic scope during prolonged exposure at low concentration

Ammonia is a respiratory gas that is produced during the process of protein deamination. In the unionised form (NH3), it readily crosses biological membranes and is highly toxic to fish. In the present study we examined the effects of unionized ammonia (UIA), on the resting oxygen consumption (MO2), ventilation frequency (fV), heart rate (HR) and heart rate variability (HRV) in Nile tilapia (Oreochromis niloticus). Fish were either exposed to progressively increasing UIA concentrations, up to 97 µM over a 5 h period, or to a constant UIA level of 7 µM over a 24 h period. For both treatment groups resting MO2, HR and fV were recorded as physiological variables. Relative to the control group, the fish groups exposed to the incremental UIA levels did not exhibit significant changes in their MO2, HR and fV at UIA concentrations of 4, 10, 35, or 61 µM compared to control fish. Exposure to 97 µM UIA, however, elicited abrupt and significant downregulations (p < 0.05) in all three responses, as MO2, HR and fv decreased by 25, 54 and 76 % respectively, compared to control measurements. Heart rate became increasingly irregular with increasing UIA concentrations, and heart rate variability was significantly increased at 61 and 97 µM UIA. Prolonged exposure elicited significant changes at exposure 7 µM UIA. Standard (SMR) and maximum metabolic rate (MMR) were significantly reduced, as was the corresponding fV and HR. It is evident from this study that Nile tilapia is tolerant to short term exposure to UIA up to 61 µM but experience a significant metabolic change under conditions of prolonged UIA exposures even at low concentrations.

Model-based versus model-free feeding control and water-quality monitoring for fish-growth tracking in aquaculture systems

This paper proposes model-based and model-free control approaches to monitor the feeding rate and water quality for fish-growth tracking in aquaculture systems. The representative fish-growth model is revisited, which describes the total biomass change by incorporating the fish population density and mortality. Due to the challenging task of measuring the total fish biomass and population data, the new dynamic population model is validated with individual fish-growth data for tracking control. Ammonia exposure is a significant challenge in the fish-population growth tracking problem, affecting fish health and survival. To address this challenge, traditional and optimal controllers are first designed to track the weight reference within suboptimal temperature and dissolved oxygen (DO) profiles under various un-ionized ammonia (UIA) exposure levels by manipulating relative feeding. Then, a Q-learning approach is proposed to learn an optimal feeding-control policy from simulated data on fish-growth weight trajectories while managing ammonia effects. The proposed Q-learning feeding control prevents fish mortality and achieves good tracking errors for fish weight under UIA levels. However, it maintains a relative food consumption that potentially underfeeds fish. Finally, an optimal predictive algorithm that includes the temperature, DO, and UIA is proposed to optimize the feeding and water quality of the dynamic fish-population growth process, indicating that fish mortality is decreased and food consumption is reduced in all cases of UIA exposure.

Dactylogyrus extensus and Pseudomonas fluorescens dual infection in farmed common carp (Cyprinuscarpio)

Dactylogyrus extensus and Pseudomonas fluorescens are serious pathogens in Cyprinus carpio aquaculture causing severe impacts and substantial economic losses. During the early spring of 2021, abnormal mortalities were reported among farmed C. carpio. Moribund fish showed anorexia, respiratory distress, dermal ulcers, and septicemia. The water analysis revealed low dissolved oxygen (3.4 mg/L), and high un-ionized ammonia levels (0.65 mg/L). Seventy moribund C. carpio specimens were collected and subjected to parasitological and bacteriological examinations. The monogenetic trematode D. extensus was discovered in wet mounts from the gills of all the examined fish samples (100%). The identity of recovered parasites was confirmed by sequencing and alignment of the 28S rDNA gene. P. fluorescens was concurrently identified in the infested fish samples (58.5%) based on phenotypic characteristics using the API20 E. The identity of bacterial isolates was confirmed further by sequencing and alignment of 16S rRNA gene. The IL-1β and MHCII were upregulated in infested fish in tandem with the severity of infections. P. fluorescens isolates displayed high resistance to most of the tested antibiotics. The study is one of the earlier reports on D. extensus and P. fluorescens co-infections in farmed C. carpio and highlights the need of effective control programs to protect fish health and minimize losses.

Effects of different carbon sources on water quality, biofloc quality, and the productivity of Nile tilapia reared in biofloc-based ponds

Abstract The present study evaluated the effects of different carbohydrates materials used as carbon sources on water quality, biofloc quality, and growth and productive performance of Nile tilapia (Oreochromis niloticus) reared in biofloc (BFT)-based cement ponds (25 m x 10 m x 1.2 m; with 250 m3 volume). Nile tilapia fingerlings (44.9±1.9 g) were distributed into nine ponds at a density of 40 fish per 1 m3 (10000 fish/pond) to represent three treatments in triplicates. The control ponds received no carbon source addition; meanwhile sugarcane molasses (MO) and wheat flour (WF) were added to ponds. A commercial diet (30% crude protein) was offered to fish in each pond at levels of 3% and 2% of live body weight of fish in the control and BFT-based ponds, respectively, for 12 weeks. The amounts of feed were divided equally to three equal portions and offered to fish at 9:00, 13:00, and 17:00 h. The control ponds’ water was replaced by 50% every day with new water; meanwhile in MO and WF ponds, water loss via evaporation or leakage was compensated to reach the 1.0 m depth only. The pH value as well as unionized ammonia and nitrite levels, in the present study, were significantly lower, meanwhile nitrate and total suspended solids levels were significantly higher in MO and WF-treated ponds than the control one. The WF treatment resulted in significantly larger biofloc volume and higher total bacterial count compared to the MO treatment. The highest growth and production indices of Nile tilapia were observed in the BFT-based treatments as compared with the control group; particularly at the WF treatment followed by the MO treatment. In conclusion, the WF addition to cement fishponds is a more beneficial carbonaceous source for the efficient water quality, biofloc biomass, and growth and productivity of Nile tilapia reared in BFT-based system.

Effects of a commercial feed additive (Sanacore®GM) on water quality, productive performance and blood profile of gilthead seabream (Sparus aurata)

The present study evaluated the effects of the inclusion of commercial feed additive (Sanacore® GM; SAN) in diets on growth and productive performance, digestive enzymes, intestinal microbiota, intestinal histomorphometry and blood profile of gilthead seabream (Sparus aurata). For this purpose, four diets containing 0.0% (the control), 0.1%, 0.2% and 0.4% SAN were formulated and offered to triplicate groups of fish (20–23 g) reared in cages (30 × 10 × 3 m) for ten weeks. Water quality parameters were regularly monitored during the experimental period. No marked variations (p > 0.05) were observed in water temperature, dissolved oxygen and pH values; meanwhile, substantially decreases in unionized ammonia and nitrite levels were specifically detected at the treatment of 0.4% SAN. Feeding the fish on SAN-supplemented diets confirmed significant modulations in fish growth and production, haemato-biochemical profile, intestinal microbiota and intestinal histomorphometry. Fish growth, production and feed utilization indices extensively multiplied alongside with the increase in dietary SAN levels achieving their optimum values at the treatment of 0.4% SAN in contrast to the control group (0% SAN). Intestinal α-amylase, lipase and proteases activities were notably greater in fish fed with SAN-supplemented diets in particular at the 0.4% SAN diet. Feeding gilthead seabream on SAN-containing diets markedly increased red blood cell counts, haemoglobin level and haematocrit per cent mainly at the diet of 0.4% SAN. Compared with the control group, highest values of serum total protein, albumin and globulin accompanied with lowest values of alanine and aspartate aminotransferase were significantly recorded in fish fed on the 0.4% SAN diet. Intestinal microbiota were additionally modulated due to SAN administration to gilthead seabream. However, marked reductions in counts of Vibrio sp. and Escherchia coli alongside with high Bacillus sp. counts were obtained in fish mid-intestine mainly at the 0.4% diet. Feeding gilthead seabream on SAN-enriched diets confirmed higher villi length/width, absorption area and crypt depth than the control group with optimal values at the 0.4% SAN diet. According to the outcomes observed in this study, the SAN administration to gilthead seabream, especially at the 0.4% level led to considerable enhancements in overall growth and production performance via improving the secretion of digestive enzymes and prompting the intestinal morphometry and beneficial microbiota.

Administration of some probiotic strains in the rearing water enhances the water quality, performance, body chemical analysis, antioxidant and immune responses of Nile tilapia, Oreochromis niloticus

The performance, efficiency of consumed feed, body chemical composition, survival rate, antioxidant and immunity parameters of Nile tilapia (Oreochromis niloticus) reared in probiotic-treated water were studied. Two hundred apparently healthy Nile tilapia (20 ± 0.3 g) juveniles were reared for 70 days in five different treatments, with five replications as the control group (clean water) and four test groups with two probiotics strains (Bacillus toyonensis and Geobacillus stearothermophilus) at two different levels (1 or 2 × 105 CFU ml−1) applied in rearing water. Fish reared in water supplemented with G. stearothermophilus at low level demonstrated significantly enhanced (p < 0.05) growth performances in terms of final body weight (FBW), weight gain (WG), daily weight gain (DWG), specific growth rate (SGR), and relative growth rate (RGR) compared to the control group. In the same context, supplied fish rearing water a lower amount of G. stearothermophilus (GS1) remarkedly reduced feed conversion ratio values when compared to the control group. In contrary, all other feed efficiency parameters increased significantly when G. stearothermophilus (GS1) water was added at low amount in the compartment with the untreated group. Moreover, probiotic water additives significantly reduced the range and median levels of unionized ammonia (NH3) in water when compared to the untreated group. According to the findings of the body chemical composition, treated tilapia water with a high level of B. toyonensis had significantly higher crude protein and fat levels, as well as lower ash levels, than the control group. When compared to the control group, probiotic-water supplementation significantly improved oxidative status and immunological activity at all bacterial dosage levels, with the fish group enriched with a high level of G. stearothermophilus recording the maximum values of both antioxidant and immune activity. Finally, results reveal that water treated with B. toyonensis or G. stearothermophilus as a probiotic promoted Nile tilapia growth and health status, and this technology may be applied to stimulate tilapia productivity in culture farms.

Comparison of ammonia thresholds for survival and reproduction between two copepods: The planktonic calanoid Eurytemora affinis and the benthic harpacticoid Tigriopus japonicus

The planktonic species Eurytemora affinis and the benthic species Tigriopus japonicus are two copepods that are extensively employed in aquaculture operations, especially as a source of live feed during larval rearing. Compared to T. japonicus, E. affinis is difficult to keep in stable cultures and to mass produce, which largely limits its usage. Furthermore, high levels of un-ionized ammonia (NH3−N) can limit the productivity of aquatic organisms. However, the toxicity of NH3-N can be easily affected by environmental conditions. The planktonic and benthic growth features of E. affinis and T. japonicus may reflect different adaptations to NH3−N stress that could affect their reproductive performances. Hence, we investigated the effect of NH3−N on the survival and reproductive patterns of E. affinis and T. japonicus at both the individual and population levels. The median lethal concentrations for both the nauplius and copepodite stages, life history parameters, and population growths of each species were evaluated after acute (24-h) and chronic (21–28 days) NH3−N exposure. The results showed that E. affinis was more vulnerable to NH3−N stress than T. japonicus at all developmental stages. The nauplius and copepodite stages of E. affinis exhibited 14.7- and 33.7-fold lower 24-h LC50 doses, respectively, than those of T. japonicus. Chronic individual exposure to NH3−N concentrations over a specific threshold (≥ 0.2 mg/L for E. affinis and ≥ 14.6 mg/L for T. japonicus) affected survival rates, extended the duration of the nauplius and copepodite stages, and delayed maturation in both species. In contrast, batch culture showed that low concentrations of NH3−N were beneficial to the reproduction of T. japonicus, whereas such a trend was not clearly observed in E. affinis. Finally, we hypothesize that the differences in the NH3−N sensitivities of E. affinis and T. japonicus could be attributed to their evolutionary history in pelagic and benthic habitats, respectively. The low NH3−N tolerance of E. affinis indicates the importance of managing ammonia levels during their cultivation.

Biochar from Corn Waste as Biofilter in a Recirculating Aquaculture Systems

Abstract: The use of biofilter with the application of biochar technology for the improvement of water in a recirculating aquaculture system (RAS) provides a lot of advantages in aquaculture production. The research aimed to devise a biofilter system for the enhancement of TAN and un-ionized ammonia levels in a RAS using biochar from corn cobs for Nile tilapia Oreochromis niloticus production. It has five main parts: fish tank, biochar filtration tank, sediment filter, sludge filter and pump. The fish tank used is a 1 m 3 plastic cubical tank. The biochar filtration tank with a height of 85 cm and a diameter of 30 cm. The sludge filter has a height of 52 cm with a diameter of 13 cm. An electric water pump was used to recirculate the water. The system was fabricated and were able to effectively enhance the level of total ammonia nitrogen (TAN) at a rate of 0.56 ppm per hour for every 1kg biochar and 0.72 ppm per hour for the reduction of un-ionized ammonia. The devised biofilter proved to reduce the level of TAN by 9.45 ppm and un-ionized ammonia levels by 2.18 ppm in 6 hours and 30 minutes using corn cob biochar. Keywords: Biochar, Biofilter, Recirculating Aquaculture Systems (RAS), Total Ammonia Nitrogen (TAN), Un-ionized ammonia

Co-infection of Vibrio parahaemolyticus and Vibrio alginolyticus isolated from diseased cultured European seabass (Dicentrarchus Labrax)

This study was directed towards providing a comprehensive overview on the describing the clinico-pathological picture of the bacterial isolates affecting cultured seabass during episodes of mass mortalities in the private marine farm at Borg-El Arab, Alexandria province, Egypt and to make a full bacteriological investigation of the isolated Vibrio sp. Was done by morphological, colonial, biochemical characters, and VITEK 2 compact system. A total number of 100 apparently healthy European seabass were used in the experimental challenge with an approximate bodyweight of 30.0 ± 5.0 g, and an approximate average body length of 13.0 ± 2.0 cm was provided from the marine fish hatchery at Kilo 21 region - Agami, Alexandria province, Egypt. Fish were maintained in 1 m3 reinforced polyethylene ponds for acclimation to the new culture conditions for two weeks before the experiment. Random samples were collected for bacteriological examination to ensure that fish were not previously infected. This study concluded that, there is a close correlation exists between poor deteriorated water quality parameters and the incidence of Vibriosis in cage-farmed European seabass (Dicentrarchus labrax). In this case, several environmental parameters, such as the increased water temperature, un-ionized ammonia, and nitrite levels, in addition to decreased dissolved oxygen levels, triggered a devastating outbreak of Vibriosis in 40 cages of cultured European seabass. This finding confirms the nature of fish diseases as a “stress-related origin”. To sum up, from the findings mentioned above, we suggest further in vivo experiments for testing these antibiotics for treating Vibriosis in diseased European seabass additionally, developing more environment-friendly approaches and competent biosecurity strategies should also be evaluated for controlling and preventing such infections in mariculture.

Mitigation of transportation stress in common carp, Cyprinus carpio, by dietary administration of turmeric

Stress is an inevitable and unpredictable process, which can be interceded through various aquaculture practices. Transportation is one of those aqua-husbandry practices that induces stress and immunosuppression in cultured fish. The present study intended to evaluate the ameliorative effects of dietary turmeric on common carp, Cyprinus carpio, based on antioxidant, immunological and tissue health characteristics at pre- and post-transportation. Diets containing four different levels of turmeric [0% (CTL), 0.5% (0.5 T), 1% (1 T), and 2% (2 T)] were fed to common carp (average weight: 45.2 g) for 2 weeks; then, the fish were placed in plastic bags containing 2.5 L water and 5 L pure oxygen and transported for 3 h in a van. Samples of blood and water were collected before and after the transportation. Transportation led to deterioration of the water quality parameters, as evidenced by declines in dissolved oxygen and pH levels, but elevations in alkalinity, total ammonia and unionized ammonia levels. Fish from 1 T treatment exhibited significantly highest water dissolved oxygen post transportation. Significant decrements in plasma total antioxidant capacity (TAC) and total immunoglobulin (Ig) were observed due to transportation-induced stress. Whereas, plasma cortisol, glucose, lactate, alanine aminotransferase (ALT), aspartate aminotransferase (AST), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and lysozyme levels enhanced due to transportation-mediated stress in the fish. The transportation stress was mitigated in 0.5 T and 1 T treatments, which were reflected in terms of decrements in plasma cortisol, glucose, ALT, AST, ammonia, SOD (just in 1 T), CAT, and MDA levels, as well as increments in plasma total Ig and TAC levels in the fish. The above findings conclude that turmeric supplementation at 1% could be used as an excellent feed additive in order to ameliorate the adverse effects of transportation in common carp.

Expression of ion transport proteins and routine metabolism in juveniles of tropical gar (Atractosteus tropicus) exposed to ammonia

Tropical gar (Atractosteus tropicus) thrives in aquatic habitats with high levels of total nitrogen (TAN) and unionized ammonia (NH3). However, the tolerance of TAN and NH3, the excretion mechanisms involved, and the effects of these chemicals on routine metabolism are still unknown. Therefore, our objectives were to assess the acute toxicity of TAN and NH3 in A. tropicus juveniles after a 96-h exposure (LC50-96 h) to NH4Cl and after chronic exposure to two concentrations (15% and 30% of LC50-96 h TAN) for 12 days, as well as to evaluate the transcriptional effects associated with Rhesus proteins (rhag, rhbg, rhcg) and ion transporters (NHE, NKA, NKCC, and CFTR) in gills and skin; and to determine the effects of TAN and NH3 on routine metabolism through oxygen consumption (μM g-1 h-1) and gill ventilation frequency (beats min-1). LC50-96 h values were 100.20 ± 11.21 mg/L for TAN and 3.756 ± 0.259 mg/L for NH3. The genes encoding Rhesus proteins and ion transporters in gills and skin showed a differential expression according to TAN concentrations and exposure time. Oxygen consumption on day 12 showed significant differences between treatments with 15% and 30% TAN. Gill ventilation frequency on day 12 was higher in fish exposed to 30% TAN. In conclusion, A. tropicus juveniles are highly tolerant to TAN, showing upregulation of the genes involved in TAN excretion through gills and skin, which affects routine oxygen consumption and energetic cost. These findings are relevant for understanding adaptations in the physiological response of a tropical ancestral air-breathing fish.

The effects of acute and chronic exposure of ammonia on juvenile burbot (Lota lota) growth and survival

Burbot, Lota lota are a candidate species for commercial aquaculture because of their palatability and optimal growth at temperatures similar to those used in freshwater trout aquaculture. However, data on burbot environmental tolerances and requirements are sparse, especially with reference to water quality parameters relevant to aquaculture, such as un-ionized ammonia (UIA) concentration. We used a two-phased approach to evaluate the effects of un-ionized ammonia on the growth and survival of burbot. First, we measured the acute toxicity of ammonia to juvenile burbot (mean SL: 144 ± 6 mm; mean wet weight: 27.3 ± 3.4 g) and calculated a 96-h LC50 of 0.58 mg·L−1 UIA. We then measured the 60-d growth, food consumption rate, and performance of burbot (mean initial SL: 190 ± 6.9 mm; mean initial weight: 67.0 ± 4.5 g) reared in 0.00, 0.03, 0.06, 0.12, or 0.19 mg·L−1 UIA using a 20-tank flow-through system under optimal temperature (14.7 °C) and dissolved oxygen (DO >80% saturation) conditions. Elevated ammonia concentration significantly reduced daily food consumption and subsequent growth. Fish exposed to 0.03 and 0.06 mg·L−1 UIA showed temporal acclimation to UIA, achieving food consumption and growth rates on par with control fish after 30 days of exposure. The estimated effective UIA concentrations for 10 and 20% reductions in growth (EC10 and EC20) based on our data are: EC10 = 0.03 ± 0.006 mg·L−1 and EC20 = 0.050 ± 0.004 mg·L−1. We recommend rearing burbot under conditions that keep UIA levels ≤0.03 mg·L−1 based on our finding that above 0.03 mg·L−1 cause measurable reductions in growth rate.

The enrichment of diet with beneficial bacteria (single- or multi- strain) in biofloc system enhanced the water quality, growth performance, immune responses, and disease resistance of Nile tilapia (Oreochromis niloticus)

The present study examined the influences of dietary single strain (SSP; Lactobacillus plantarum) or multi-strain (MSP; Bacillus subtilis, L. plantarum, L. rhamnosus, L. acidophilus, L. delbrueckii) potential probiotics on Nile tilapia (Oreochromis niloticus) in biofloc (BF) and stagnant-renewal (SR) culture systems. Fish (8.63 ± 3.35 g) were allotted in six groups: T1, SR control; T2, SR + SSP; T3, SR + MSP; T4, BF + MSP; T5, BF + SSP; T6, BF control. After 112 days, water dissolved oxygen (O2), pH, electrical conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS), total ammonia nitrogen (TAN), un-ionized ammonia (NH3), and nitrite (NO2) levels were significantly increased while nitrate (NO3) concentrations were decreased under BF condition. Also, bacterial supplements showed significant effects on EC, TAN, NH3, NO2, and NO3 levels. The BF availability remarkably enhanced the activities of digestive enzymes and fish fed SSP-containing diet presented significantly superior weight gain and average daily growth over other diets. A significant effect on amylase activity was detected by probiotic and culture system interactions. Meanwhile, serum total protein, albumin, globulin, total immunoglobulin, superoxide dismutase (SOD), myeloperoxidase (MPO), and respiratory burst activity (RBA) were significantly higher and malondialdehyde and endotoxin were lower for fish stocked in BF system. Additionally, MSP-containing diet significantly promoted serum protease, SOD, catalase (CAT), alkaline phosphatase (AP), MPO, and RBA activities compared to other tested diets. Interestingly, serum alternative complement (ACH50) and lysozyme activities were merely affected by the main effect of probiotics. However, probiotics and culture system found to have individual or combined effects on the intestinal antioxidant enzymes, AP, and pro-inflammatory cytokines (tumor necrosis factor alpha and interleukin-1 beta). Further, tilapia challenged with Aeromonas hydrophila showed reduced mortality in BF groups fed probiotics. The results suggested that the effect of probiotics greatly differed upon the culture condition and the application of multiple strains probiotics had higher efficiency toward immunity than single strain probiotic.

Co-infection of Aeromonas hydrophila and Vibrio parahaemolyticus isolated from diseased farmed striped mullet (Mugil cephalus) in Manzala, Egypt – A case report

A sudden outbreak of disease associated with high mortality rates (75–85%) was reported in market-sized striped mullet (Mugil cephalus), farmed in earthen ponds in Manzala, Egypt, during the summer (July) 2019. We identified poor water quality parameters, including a sharp decrease in dissolved oxygen (DO) (3.5 mg/l) accompanied by elevated levels of unionized ammonia (0.90 mg/l), nitrite (0.05 mg/l), hydrogen sulfide (0.07 mg/l), nickel (0.7 mg/l), copper (0.6 mg/l), and iron (1.80 mg/l). Diseased and recently dead fish exhibited general septicemic signs. A. hydrophila and V. parahaemolyticus were isolated from diseased fish by culture on selective media and further identified by biochemical tests. PCR targeting the 16S rRNA gene and some virulence gene fragments of each bacterial isolate were performed, and genome sequencing and phylogenetic analysis confirmed the molecular identity of both isolates. The high molecular identity and close phylogenetic relationship confirmed that the isolates were genetically homologous to A. hydrophila and V. parahaemolyticus. Outbreaks involving multiple co-infecting pathogens have been reported in several fish species. The current study highlights a case report of synergistic interactions between poor water quality and the presence of aquatic microbial pathogens such as A. hydrophila and V. parahaemolyticus. This combination of factors resulted in the incidence of heavy mortalities in farmed striped mullet M. cephalus, during the summer season in Manzala Egypt.

Prey preference, environmental tolerances and ichthyotoxicity by the red-tide dinoflagellate Noctiluca scintillans cultured from Tasmanian waters

AbstractThe large phagotrophic dinoflagellate Noctiluca has become a prominent red tide organism in southeast Australian waters since the 2000s, raising concerns for beach tourism, grazing impacts as well as ichthyotoxicity for finfish aquaculture. Satisfactory culture growth rates (0.23–0.56 per day) were obtained by feeding with small Thalassiosira diatom and Tetraselmis flagellate diets, while optimal growth rates sustained for up to 8 months (0.69 per day) were achieved by feeding in a plankton wheel with the large chain-forming dinoflagellate Gymnodinium catenatum. Noctiluca was highly tolerant towards salinities from 20 to 35 and growth was stimulated by temperatures increasing from 10 to 23°C, which in combination with the key factor of prey abundance explains the incidence in southeast Australia of predominantly summer and spring but occasionally also winter blooms. Fatty acid biomarkers suggest that Tasmanian field populations indiscriminately feed on available diatom and dinoflagellate mixtures. Noctiluca exhibited very limited ichthyotoxicity, and only at the highest cell concentrations of 2 000 000/L (50% reduction in RTgill W1 cell viability). Only the densest red tide surface slicks contained acutely toxic levels of unionized ammonia of 242 to 510 μg/L while inshore slicks generated oxygen concentrations as low as 0–1.5 ppm. Lipid phycotoxins (eicosapentaenoic acid, docosahexaenoic acid) did not appear to contribute to Noctiluca ichthyotoxicity. The fatty acid 20:0 eicosanoic acid may serve as a potential Noctiluca biomarker in marine food webs and sediments.

Cytokines' gene expression, humoral immune and biochemical responses of common carp (Cyprinus carpio, Linnaeus, 1758) to transportation density and recovery in brackish water

The aim of the present study was to investigate the effects of stocking density during transportation and post-transportation salt treatment on stress, hydromineral, immunological and antioxidant responses in common carp (Cyprinus carpio). For this, the fish were transported in plastic bags for 4 h at two densities: 100 (LD) and 200 (HD) g/L and allowed to recover for 24 h in both freshwater (FW) and brackish water (3 g/L sodium chloride; BW). Water physicochemical parameters were determined after transportation. Blood stress, immunological and hydromineral responses, head kidney cytokine gene expression, and liver antioxidant responses were determined. The transportation led to significant decrease in water dissolved oxygen and pH, and increase in water total and unionized ammonia levels. Water dissolved oxygen was significantly lower, whereas, water total and unionized ammonia were significantly higher in the HD, compared to the LD group. Serum cortisol and glucose, and liver malondialdehyde levels, and expression of tumor necrosis factor-alpha, interleukin-1beta and interleukin-8 genes increased after transportation. Serum ion levels and liver superoxide dismutase and catalase decreased after transportation. All the above-mentioned changes, except for cortisol and catalase, were more severe in the HD compared to the LD group. There were no significant changes in serum total immunoglobulin and alternative complement after transportation, compared to before transportation values; but the LD group had significantly higher alternative complement than the HD group. Lysozyme and WBC significantly increase in the LD group; whereas, significantly decreased in the HD group, after transportation. Recovery in BW was useful to mitigate stress response, hydromineral imbalance, immunosuppression and oxidative stress caused by the transportation. Using sodium chloride is recommended during fish recovery from transportation, particularly when the fish are transported at high stocking density. The benefits of sodium chloride treatment seem to be mediated by restoration of hydromineral balance and oxidative status, which leads to healthier fish with higher immune responses.

Effect of Unionized Ammonia (UIA) on Virulence of Clostridium perfringens in Oreochromis niloticus

The present work was performed to study the effect of unionized ammonia (UIA) on mortality rate, clinical signs, postmortem findings, some biochemical and immunological parameters and histopathological findings of Oreochromis niloticus challenged with Clostridium perfringens type A . The experiment was carried out on 160 Oreochromis niloticus with average body weight 45±5 gram which were divided into 8 equal groups. Groups (1-4) were inoculated intraperitoneally with 0.2 ml/ fish of sterile cooked meat broth, while, groups (5-8) were inoculated intraperitoneally with 0.2 ml/fish of 24 hours old culture of Clostridium perfringens type A (0.5x10 7 CFU) on cooked meat broth. The groups (1 and 5) were used as a control (not subjected to UIA) but the groups (2 and 6), (3 and 7) and (4 and 8) were subjected to 0.53, 0.265 and 0.132 mg/L of UIA. The results revealed that the highest mortality rate was 80% and 70% in infected fish exposed to 0.53 and 0.265 mg/L of UIA, respectively. The fish showed nervous manifestation, effort to swallow air from the water surface and mortality occurred with open mouth with dark body coloration, hemorrhages on body and increased mucus secretion on skin and gills. The levels of serum alanine aminotransferase (ALT), creatinine and cortisol were significantly increased, while, the level of serum immunoglubulin M (IgM) was significantly decreased. Also, some histopathological changes were recorded in liver, kidney, gills and intestine. In conclusion, the elevated levels of UIA increased the virulence of Clostridium perfringens type A infection in Oreochromis niloticus.

Pre-sedation and transport of Rhamdia quelen in water containing essential oil of Lippia alba: metabolic and physiological responses.

The effects of transporting silver catfish (Rhamdia quelen) for 6 h in plastic bags containing 0 (control), 30 or 40 µL/L of essential oil (EO) from Lippia alba leaves were investigated. Prior to transport, the fish in the two experimental groups were sedated with 200 µL/L of EO for 3 min. After transport, dissolved oxygen, carbon dioxide, alkalinity, water hardness, pH, temperature and un-ionized ammonia levels in the transport water did not differ significantly among the groups. However, total ammonia nitrogen levels and net Na(+), Cl(-) and K(+) effluxes were significantly lower in the groups transported with EO of L. alba than those in the control group. PvO2, PvCO2 and HCO3(-) were higher after transporting fish in 40 µL/L of EO of L. alba, but there were no significant differences between groups regarding blood pH or hematocrit. Cortisol levels were significantly higher in fish transported in 30 µL/L of EO of L. alba compared to those of the control group. The metabolic parameters (glycogen, lactate, total amino acid, total ammonia and total protein) showed different responses after adding EO to the transport water. In conclusion, while the EO of L. alba is recommended for fish transport in the conditions tested in the present study because it was effective in reducing waterborne total ammonia levels and net ion loss, the higher hepatic oxidative stress in this species with the same EO concentrations reported by a previous study led us to conclude that the 10-20 µL/L concentration range of EO and lack of pre-sedation before transport are more effective.

Methanolic extract of Condalia buxifolia added to transport water alters biochemical parameters of the silver catfish Rhamdia quelen

The effects of the methanolic extract of Condalia buxifolia (MECB) were investigated in silver catfish (Rhamdia quelen) transported for 6 h in plastic bags at 0, 5 or 10 μL/L MECB. Prior to transport, the fish were sedated with 10 μL/L MECB for 5 min, except the control group. At the end of transport, dissolved oxygen, alkalinity, pH, temperature, and un-ionized ammonia levels in the transport water were not different between groups, but the control group presented the highest total ammonia levels. Net Na+, Cl− and K+ effluxes were highest in fish from the control group compared to those transported with MECB. PvO2, PvCO2 and HCO3− were higher after transport in fish transported with 5 μL/L MECB, but no significant difference between groups was found regarding blood pH and plasma cortisol levels. The metabolic parameters (glycogen, lactate, total amino acid, total ammonia and total protein) were lower or no significant difference was found in fish transported with MECB. There was no difference between treatments on the ecto-nucleoside triphosphate diphosphohydrolase, 5′-nucleotidase and acetylcholinesterase activities in the whole brain. The activity of all analyzed antioxidants increased in the gills and superoxide dismutase and glutathione-S-transferase also increased in the other analyzed tissues. In addition, lipoperoxidation (measured by thiobarbituric acid-reactive substances) and carbonylation of proteins (measured by protein carbonyl) decreased in most analyzed tissues, indicating lower ROS production. In conclusion, the use of MECB for the transport of silver catfish is advisable because MECB improves antioxidant defenses in several tissues and was effective in reducing waterborne total ammonia levels and ion loss.

The effects of ammonia and water hardness on the hormonal, osmoregulatory and metabolic responses of the freshwater silver catfish Rhamdia quelen

The aim of the present study was to assess the effects of ammonia and water hardness on endocrine, osmoregulatory and metabolic parameters in silver catfish (Rhamdia quelen). The specimens (60–120g) were subjected to six treatments in triplicate, combining three levels of un-ionized ammonia (NH3) (0.020±0.008mg/L [1.17±0.47μM], 0.180±0.020mg/L [10.57±1.17μM] and 0.500±0.007mg/L [29.36±0.41μM]) and two levels of water hardness (normal: 25mgCaCO3/L and high: 120mgCaCO3/L), and sampled after two exposure times (1 and 5 days post-transfer). Plasma cortisol, metabolites, osmolality and ionic values were determined concomitantly with the mRNA expression levels of different adenohypophyseal hormones (growth hormone, GH; prolactin, PRL; and somatolactin, SL). Previously, full-length PRL and SL as well as β-actin cDNAs from R. quelen were cloned. Exposure to high NH3 levels enhanced plasma cortisol levels in fish held under normal water hardness conditions but not in those kept at the high hardness value. The increase in water hardness did not alter plasma metabolites, whereas it modulated the osmolality and ion changes induced by high NH3 levels. However, this hardness increase did not lead to the decreased GH expression that was observed 5 days after exposure to 0.18mg/L NH3 in fish held at the normal water hardness level, whereas PRL expression was enhanced after one day of exposure under the increased hardness conditions. Additionally, SL expression decreased in specimens exposed for 5 days to 0.18mg/L NH3 and maintained at the high water hardness level. The results showed that increasing water hardness attenuated the hormonal parameters evaluated in R. quelen specimens exposed to high NH3 levels, although plasma metabolism do not appear to suffer major changes.