Abundance of sulphate-reducing bacteria in fish farm sediments along the coast of Japan and South Korea

The abundance of sulphate-reducing bacteria (SRB) was investigated in the coastal marine sediments along the coast of Japan and South Korea. Sediment samples were collected from fish and shellfish farms between 2006 and 2008. As non-fish farming reference sites, sediments were also collected from highly eutrophic bays, a highly sulphidogenic saline lake, and the deep sea. A quantitative real-time PCR analysis that targeted the gene coding for a portion of the α-subunit of dissimilatory sulphite reductase (dsrA) was performed to assess the abundance of the SRB in the sediments. Between 2.8 × 10⁷ and 2.5 × 10⁹ copies of the dsrA gene per gram dry sediment were detected. There was no relationship between dsrA gene copy number and total bacterial count in the sediments, whereas organic matter contents (particulate organic carbon and nitrogen, ignition loss and chemical oxygen demand) and acid-volatile sulphide contents were significantly correlated with the dsrA copy number. The data presented demonstrate that organic enrichment of sediment may influence the abundance of SRB communities in coastal marine sediments and that the cell density of SRB may be used as a biological indicator for assessing pollution levels in sediments of marine fish farms.     

Bacterial community composition of sediments from a milkfish Chanos chanos Forsskål farm

Bacterial communities in sediments underneath milkfish cages and adjacent off‐cage areas in Bolinao, Lingayen Gulf, West Philippine Sea were characterized using PCR‐denaturing gradient gel electrophoresis to assess influence of the fish farming to the sediments. The sediments in the fish cage (FC) area showed anoxic conditions [redox potential of ?165 to ?213 mV and acid‐volatile sulphide‐sulphur (AVS‐S) of 0.55–1.88 mg g^?1 (dry weight)] compared to the relatively oxic off‐cage area [redox potential of 72–81 mV and AVS‐S of 0.09–0.14 mg g^?1 (dry weight)]. The composition of the microbial populations revealed influence of the fish feed sedimentation with higher dominance of putative sulphate‐reducing bacteria (SRB) in the FC area. Compositions of the bacterial taxa showed dominance of the Bacteroidetes group and Deltaproteobacteria. The results suggest that the fish feeds created a new suitable environment, in which reductive microorganisms such as SRB, ferric‐ion‐reducing bacteria and nitrate‐reducing bacteria can thrive. Organic load from the feed and quantity of its leftover constituents may be the key factors that influence the structure of the bacterial community in the sediments of the milkfish farms.     

Influence of fish food and faecal pellets on short‐term oxygen uptake,ammonium flux and acid volatile sulphide accumulation in sediments impacted by fish farming and non‐impacted sediments

Sediment cores were taken from impacted and non‐impacted areas and subjected to different incubations: (i) uninoculated, (ii) inoculated with fish feed and (iii) inoculated with gilthead seabream (Sparus aurata) faeces. After inoculation (or not), the cores were incubated for 8 h and the following biogeochemical fluxes were determined: sediment oxygen uptake (SOU), total ammonia nitrogen flux (TAN_f) and the production of acid volatile sulphides (AVS‐S_p). The results showed that the impacted sediments had a more pronounced benthic metabolism than non‐impacted sediments. Correlations between the variables and factorial analysis showed that oxygen consumption caused by the organic enrichment appeared as the trigger for subsequent biogeochemical alterations. The addition of faeces led to proportionally higher benthic rates of SOU, TAN_f and AVS‐S_p than those obtained in the feed incubations. Although the feed is relatively sterile and does not create an oxygen demand until colonized by bacteria, the faeces are already richly colonized with fish gut bacteria and could start to consume oxygen without the lag phase experienced in the incubations with feed. The TAN_f values measured after the addition of feed or faeces seem to be more related to the leaching velocity of TAN than with the benthic flux, given the short incubation time.     

Increased sulfate availability in saline water promotes hydrogen sulfide production in fish organic waste

The risk of hydrogen sulfide (H₂S) production can be a challenge in marine land-based recirculating aquaculture systems (RAS). Hydrogen sulfide is a toxic gas that can cause massive fish mortality even at low concentrations, and in addition, serious odour problems in the surroundings. It is a bacterial by-product originating from the degradation of organic matter in sulfur-rich waters such as marine waters. In order to hinder H₂S production in marine land-based RAS, more information on the H₂S production conditions and the associated microbiology is needed. In this study, the production of H₂S from rainbow trout (Oncorhynchus mykiss) organic waste was examined using a novel H₂S measurement method under a range of salinities (0, 5, 10, 15, 25 and 35 g/L) in anaerobic mixed reactors, and the microbial communities as well as abundance of sulfate reducing bacteria (SRB) were characterized. The maximum H₂S concentration increased from 23.1 ± 8.2 mg H₂S/L at 0 g/L salinity to 153.9 ± 34.1 mg H₂S/L at 35 g/L salinity. Similarly, the H₂S production rate increased from 5.6 ± 0.2 at 0 g/L salinity to 26.4 ± 12.7 mg of H₂S produced per day at 35 g/L salinity. The highest H₂S production was recorded after increased availability of volatile fatty acids, which were produced by fermentative bacteria from phyla Firmicutes and Bacteroidetes that dominated the microbial communities after day 5. The traditional sulfate reducing bacteria (SRB) were found only at 0 and 5 g/L salinity, while at higher salinities, H₂S production was carried out by novel unquantifiable SRB. The results demonstrate that H₂S can be a pronounced problem in marine RAS, although it can be controlled through preventing anaerobic conditions within the system.     

Quantifying Aquaculture‐derived Dissolved Organic Matter in the Mesocosms of Sanggou Bay Using Excitation‐emission Matrix Spectra and Parallel Factor Analysis

The cycling and fate of dissolved organic matter (DOM) in aquaculture systems are unique. Sanggou Bay, an aquaculture‐dominated system in China, was chosen to characterize the composition of DOM based on optical properties. Field incubation experiments of eight mesocosms containing various aquaculture organisms were conducted in July 2013 to explore the impact of aquaculture organisms on the DOM composition. Dissolved organic carbon (DOC) showed an increasing trend, especially in integrated mesocosms, suggesting the accumulation of DOM in the aquaculture ecosystem. The DOC concentration was positively correlated with a₂₈₀ (P < 0.01) rather than a₃₅₅, demonstrating that a₂₈₀ should be applied in the quantitative prediction of DOC in aquaculture systems. Parallel factor analysis was applied to identify the components of the excitation‐emission matrix spectra. Two humic‐like components and two protein‐like components were identified. The significant correlation between the wet weights of the organisms and the humic‐like component contents (P < 0.01) indicated that seaweeds and bivalves play important roles in the production of humic‐like matter. The variation of protein‐like materials was caused by the growth of aquaculture organisms and the decay of phytoplankton. The amount of bioavailable DOC (BDOC) derived from phytoplankton and organisms was estimated; bivalve organisms excreted more BDOC than did seaweeds. BDOC was significantly correlated with the protein‐like components (P < 0.05) in the microbial incubation experiment.     

L‐carnitine exerts a cytoprotective effect against H2O2‐induced oxidative stress in the fathead minnow muscle cell line

This study was conducted to investigate the protective effect of L‐carnitine (LC) against H₂O₂‐induced oxidative stress in the fathead minnow muscle cell line (FHM). The FHM cells were stimulated with 1 mM H₂O₂ for 1 h after LC pre‐treatment, and the cell viability and the activity and mRNA relative expression of antioxidant enzyme were measured to assess the antioxidant properties of LC. The results showed that the toxic effect of H₂O₂ on the viability of FHM cells was both dose‐ and time‐dependent. Furthermore, the viability of the 0.01–1 LC mM groups was significantly higher than those of the 1 mM H₂O₂ group. L‐carnitine protected the cells from H₂O₂‐induced oxidative damage, which was demonstrated by a significant reduction in the malondialdehyde and reactive oxygen species levels and increases in the intracellular total glutathione levels and the activities of total superoxide dismutase, catalase, glutathione peroxidase (GPx) and gamma‐glutamyl‐cysteine synthetase (γ‐GCS) in FHM cells pre‐treated with LC for 6 h compared with the 1 mM H₂O₂ group. In addition, the mRNA relative expression levels of the γ‐GCS catalytic subunit and nuclear factor nuclear factor erythroid 2‐related factor 2 were significantly higher than those of the 1 mM H₂O₂ group. It could be concluded that LC exerts a beneficial antioxidant effect against oxidative stress induced by H₂O₂ in FHM cells and that the appropriate treatment is 0.1–1 mM for 6 h in this study.     

Physico‐chemical characteristics of the improved extensive shrimp farming system in the Mekong Delta of Vietnam

Consecutive failure of the improved extensive shrimp farming system has deterred the economy of some coastal areas in Vietnam. To investigate pond physico‐chemical characteristics, a monitoring scheme was performed in the Cai Nuoc district of Southern Vietnam. Results show that the system was not optimal for shrimps. While ponds were not contaminated by organic loadings or major nutrients (N, P) and salinity and pH were most optimal for shrimp, more than 37% of dissolved oxygen (DO) measurements were lower than recommended. In the early morning hours, DO measurements were even much lower (0.84–2.20 mg L^?1). Sulphate (SO₄^2?) concentrations were most within the acceptable range. Total suspended solids (TSS) were above the acceptable limit (<50 mg L^?1). Iron, alkalinity and hydrogen sulphide were also higher than recommended. Pond sediment was anaerobic (redox potential ?422 to ?105 mV) and contained high amounts of organic matter (9.84–21.96%). Lethal DO levels, high TSS and anoxic sediment are the drawbacks in this system. Suggested measures to improve pond conditions are (1) allowing sedimentation before filling culture ponds, (2) covering dikes, (3) including no‐culture breaks between shrimp crops, (4) drying pond bottom, (5) removing sediment and (6) controlling pond's vegetation.     

Effects of Water Hardness and Calcium: Magnesium Ratios on Reproductive Performance and Offspring Quality of Macrobrachium rosenbergii

This study evaluated the effect of specific calcium and magnesium ratios at two hardness values on reproductive performance and offspring quality of Macrobrachium rosenbergii brood‐females. Hatchery water containing 110.5 mg/L CaCO3 hardness was considered baseline as it has been used successfully to hatch and rear larvae and was used as the control treatment. At each hardness value of 150 and 190 mg/L CaCO₃, four experimental water treatments were made in triplicate. Each treatment was adjusted using soluble salts (CaCl₂·H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O) to provide the hardness and calcium to magnesium ratios of 0:20, 20:80, 50:50, and 80:20 needed. Each of the experimental tanks (140 L) were stocked with six females and one male. The results indicated that both hardness and Ca:Mg ratios affect brood‐female reproductive qualitative parameters such as intermolt period, egg hatchability, egg dry weight, and egg‐clutch somatic index (ESI) parameters (P < 0.05) but not fecundity and eggs per spawn. The results revealed that brood‐females at 150 mg/L hardness showed greater reproductive performance than at 190 and 110.5 mg/L hardness. The findings also demonstrated that the treatment 50Ca50Mg at 150 mg/L hardness with 38.8 mg/L calcium and 12.9 mg/L magnesium had optimum reproductive performance and offspring quality for M. rosenbergii brood‐females.     

Somatic and physiological responses to cyclic fasting and re‐feeding periods in sobaity sea bream (Sparidentex hasta,Valenciennes 1830)

Different fasting and re‐feeding cycles were tested in a 60‐day trial in sobaity sea bream (Sparidentex hasta) juveniles to evaluate their effects on growth, physiological and biochemical parameters. Fish were exposed in triplicate to the following feeding regimes: control (fed everyday); F‐RF₁₊₁ (1 day of starvation followed by 1 day of re‐feeding); F‐RF₂₊₂ (2 days of starvation followed by 2 days of re‐feeding); F‐RF₃₊₃ (3 days of starvation followed by 3 days of re‐feeding); F‐RF₆₊₆ (6 days of starvation followed by 6 days of re‐feeding); and F‐RF₁₊₂ (1 day of starvation followed by 2 days of re‐feeding). A reduction in body mass between 10.0% (F‐RF₁₊₁) and 24.3% (F‐RF₆₊₆) was found in comparison with the control group after 60 days. As the length of fasting increased, the compensation coefficients in feed intake and weight gain decreased. Body lipid content decreased as fasting cycles increased. Haemoglobin, plasma protein, lysozyme and alkaline phosphatase activities were the most reliable biomarkers for assessing the nutritional condition in sobaity sea bream. A feeding strategy based on 1 day of starvation followed by 2 days of re‐feeding (F‐RF₁₊₂ group) may be advisable for on‐growing sobaity sea bream without reduction in growth and alteration of their haematological and physiological parameters.     

Evaluation of the immune response in rainbow trout fry,Oncorhynchus mykiss (Walbaum), after waterborne exposure to Flavobacterium psychrophilum and/or hydrogen peroxide

The immune response in rainbow trout fry against Flavobacterium psychrophilum was elucidated using an immersion‐based challenge with or without prior exposure to hydrogen peroxide (H₂O₂). Samples were taken from the head kidney 4, 48, 125 and 192 h after immersion, and the regulation of several genes was examined. Bacterial load was assessed based on the presence of 16S rRNA and correlated with gene expression, and the levels of specific antibodies in the blood were measured 50 days post‐infection. Separately, both H₂O₂ and F. psychrophilum influenced gene expression, and pre‐treatment with H₂O₂ influenced the response to infection with F. psychrophilum. Pre‐treatment with H₂O₂ also affected correlation between gene regulation and pathogen load for several genes. A delay in antibody production in H₂O₂‐treated fish in the early phase of infection was indicated, but H₂O₂ exposure did not affect antibody levels 50 days post‐infection. An increasing amount of F. psychrophilum 16S rRNA was found in the head kidneys of infected fish pre‐treated with H₂O₂ relative to the F. psychrophilum group. The results show that a single pre‐treatment with H₂O₂ impairs the response against F. psychrophilum and may intensify infection.     

Determination of Trace Lead in Fish Sauces by ID-ICP-MS After Mg(OH)2 Coprecipitation

A method of isotope dilution coupled with inductively coupled plasma mass spectrometry (ID-ICP-MS) after Mg(OH)₂ coprecipitation was employed to determine trace lead (Pb) in fish sauces. The pH values and the amounts of Mg²⁺ in the coprecipitation system and the amounts of isotopically enriched ²⁰⁶Pb reagent added in the measurement were optimized. Results showed that a recovery by adding standard was 92.0% with a relative standard deviation (RSD) of 0.39%. The detection limit estimated with the calculated method used in the study was 7.65 ng g^?1. Through the Mg(OH)₂ coprecipitation, more than 80% of matrix ions such as K⁺, Na⁺, and Ca²⁺ in the samples were effectively removed, and the trace Pb in fish sauces was largely enriched. The concentrations of Pb measured in 12 fish sauces ranged from 0.068 to 0.299 μg g^?1, which was completely within the Pb limit (0.50 μg g^?1), a hygienic standard for aquatic flavorings set in China (GB 10133-2005). It has been well demonstrated that the method of ID-ICP-MS coupled with Mg(OH)₂ coprecipitation is suitable for determining trace Pb in fish sauces containing high levels of salt matrices.     

Dietary ascorbic acid requirement for growth of striped catfish,Pangasianodon hypophthalmus (Sauvage, 1878) juveniles

A sixty‐day feeding trial was conducted to determine the ascorbic acid (AA) requirement for growth of striped catfish, Pangasianodon hypophthalmus juveniles. Seven iso‐nitrogenous and iso‐energetic (370 g protein per kg and 19.6 MJ/kg) purified diets were prepared with different levels of ascorbic acid such as control (0), T₁ (17.5), T₂ (35), T₃ (70), T₄ (175), T₅ (350) and T₆ (700) mg ascorbic acid (L‐ascorbyl‐2‐polyphosphate) equivalent per kg diet. Fish with a mean body weight of 3.2–3.4 g were stocked (fifteen fish per tank) in triplicates following a completely randomized design. Each group was fed to satiation twice a day for 60 days. Significant differences were observed in growth, survival, body composition and metabolic enzymes activities with different dietary ascorbic acid levels. Maximum weight gain, specific growth rate (SGR) and protein efficiency ratio (PER) were found in fishes fed with 35 mg AA per kg diet, supported by best feed conversion. Fish fed a diet containing vitamin C had the highest activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) compared to those fed with vitamin C‐depleted diets. In this study, based on using broken‐line regression analysis, the dietary vitamin C requirement for growth of P. hypophthalmus juveniles was estimated to be in the range of 46–76 mg AA per kg, depending on the criterion used, growth and liver storage. Our results will be helpful for the formulation of cost‐effective ascorbic acid incorporated diets for striped catfish, P. hypophthalmus.     

Reduction of in vitro growth in Flavobacterium columnare and Saprolegnia parasitica by products containing peracetic acid

Commercial products containing peracetic acid (PAA) are strong disinfectants with a wide spectrum of antimicrobial activity and have been suggested as potential therapeutic agents in aquaculture. The aim of this study was to compare the in vitro reduction of growth on two fish pathogens, Flavobacterium columnare and Saprolegnia parasitica, by seven commercial PAA‐containing products. Flavobacterium columnare was exposed to 1, 2, 4, 6, 8 and 10 mg L^?1 PAA and S. parasitica was exposed to 0.5, 1, 2, 4, 6, 8 and 10 mg L^?1 PAA in petri dishes for 24 h incubation. The reduction of growth was measured in comparison to a PAA‐free control. A reduction of the growth was observed for both pathogens with increasing PAA concentration. Hydrogen peroxide (H₂O₂) possibly has a role in the effectiveness of the products, since products with lower PAA concentrations had a higher concentration of H₂O₂. The commercial products with a low concentration of PAA and a low PAA:H₂O₂‐ratio were generally more effective against pathogens. The practical application of the products with low PAA concentration should be prioritized.     

Effects of feed restriction on compensatory growth performance of Indian major carps in a carp–prawn polyculture system: a response to growth depression

Effects of feed restriction on compensatory growth (CG) performance of Indian major carps, sediment loading and water productivity in a carp–prawn grow‐out production system were examined. The overall growth and crop performance were in the similar line in both T₁ (regular feeding, 2 times a day) and T₂ (4‐week feeding followed by 2‐week no feed). However, between T₁ and T₃ (8‐week feeding followed by 2‐week no feed), there was a significant (P < 0.05) variation in the overall growth and crop performance. This was probably due to the longer refeeding periods after cyclic food deprivation that successfully triggered compensatory growth response in T₃ (CG Index: 98–104%). Treatment‐wise sediment load ranged between 59.2 and 69.6 m³ t^?1 biomass. Higher the apparent feed conversion ratios, higher was the sedimentation rate. Higher the feed input, higher were the water exchange requirement, total water use and consumptive water use index. Cyclic food deprivation and refeeding also helped in maintaining water quality due to the restricted feed input (10.5% in T₂ and 2.0% in T₃), thus minimizes the input cost and improves production efficiency. Keeping the growth and yield performance, water productivity and economic efficiency in view, T₃ is considered the best feed management protocol followed by T₂ and T₁.     

The effects of bioturbation by the Venus clam Cyclina sinensis on the fluxes of nutrients across the sediment–water interface in aquaculture ponds

A mesocosm experiment was conducted to study the effects of bioturbation by the marine bivalve Cyclina sinensis in an aquatic system and to examine how the bioactivities of this clam alter the rate at which nutrients are exchanged across the sediment–water interface. A dark incubation experiment was performed to determine the fluxes of inorganic nutrients (NH₄ ⁺, NO₃ ^? + NO₂ ^? and PO₄ ^3?), benthic chlorophyll a (Chl a), organic matter and sediment oxygen consumption (SOC) on days 1, 10, 20 and 30. C. sinensis destroyed the initial sediment surface and partially enhanced oxygen penetration into the sediment. The clam also increased the water content and volume of the oxic sediment. The analysis showed that increases in the clam density and time period produced higher fluxes of all the nutrients (NH₄ ⁺, NO₃ ^? + NO₂ ^? and PO₄ ^3?) in the bioturbated chambers compared with the control (non-bioturbated chambers). The concentration of Chl a in the sediment increased significantly at the end of the experiment (day 30) (p < 0.05). The SOC rate increased significantly with the increase in density and with the time period from day 10 to day 30 (p < 0.05). As a result, the fluxes of nutrients increased with increased SOC, producing oxygen-induced sediment mineralization. Our findings suggest that the activities of the clams could positively influence SOC and cause an increase in the fluxes of inorganic nutrients. These effects may substantially improve the primary productivity and water quality of earthen pond ecosystems.     

Comparative study on the utilization of different lysine sources by channel catfish (Ictalurus punctatus)

In this study, five diets were formulated, namely positive control, negative control (lysine deficient) without or with the addition of crystalline l ‐Lys·HCl, l ‐Lys·H₂SO₄ and microcapsulated l ‐lysine·HCl (M‐Lys), and then fed to channel catfish with an initial body weight of 76.0 ± 0.3 g to investigate the effects of various lysine sources on the growth. After 8‐week feeding, the fish fed M‐Lys diet, but not Lys·HCl or Lys·H₂SO₄ diet, had a higher weight gain, a higher protein retention ratio and a lower feed conversion ratio than that fed negative control (P < 0.05), and showed a similar growth as positive control. The serum free amino acid level of Lys·HCl and Lys·H₂SO₄ group reached the plateau at the 2nd h after feeding, while the other three groups peaked at the 4th h. In Lys·HCl and Lys·H₂SO₄ groups, the activities of liver aspartate aminotransferase and alanine aminotransferase peaked at the 2nd h, but M‐Lys group peaked at the 6th and 4th h after feeding, respectively. The above results indicated that the supplementation of M‐Lys rather than Lys·HCl or Lys·H₂SO₄ in lysine‐deficient diet could improve the growth performance of channel catfish, due to the delayed absorption of supplemental lysine.     

Dietary magnesium did not affect calcium and phosphorus content in juvenile grouper,Epinephelus coioides

Most of magnesium (Mg) in fish is located in the bone. Dietary calcium (Ca) and phosphorous (P) has been reported to affect scales and vertebrae Mg dramatically in juvenile grouper, but the effect of dietary Mg on tissue Ca and P is unknown. This study was conducted to investigate the effect of dietary Mg supplement on growth, feed efficiency, morphometry, and the ash and Ca, P, sodium (Na) content in scales and vertebrae of juvenile grouper. Seven experimental diets were formulated to contain graded levels of Mg by supplementing the basal diet with 0, 200, 400, 600, 800, 1000 and 2000 mg kg^?1 Mg in the form of Mg sulphate (MgSO₄·7H₂O). Juvenile grouper with an initial body weight of 11.8 ± 0.1 g were fed to apparent satiation twice per day for 10 weeks. Dietary Mg supplement had no significant effect on growth, feed efficiency, and Mg concentration in scales and vertebrae of grouper, which indicates the Mg requirement of grouper was met in fish fed the basal diet. Mg supplements had significant effect on morphometry index such as body length, condition factor, viscera somatic index and mesenteric fat index. Extra dietary Mg supplement to the basal diet had no negative effect on ash, Ca and P concentrations in scales and vertebrae.     

Dose‐dependent protective effects of dietary selenium on abalone Haliotis discus hannai Ino against the toxicity of waterborne copper

This study was designed to assess the protective effects of dietary selenium (Se) on abalone Haliotis discus hannai Ino against the toxicity of waterborne copper (Cu). A 60‐day feeding trial was conducted in a static water system for abalone (initial weight: 3.17 ± 0.01 g) exposed to 0.02 mg L^?1 of waterborne Cu. The animals were fed one of the three experimental diets with 0.10, 1.31 and 4.20 mg kg^?1 of Se from Na₂SeO₃·5H₂O respectively. Results showed that the abalone fed 1.31 mg kg^?1 of dietary Se had the lowest Cu concentration in shell, muscle, mantle, gill, hepatopancreas and serum. Meanwhile, the significant lowest contents of malondiadehyde and protein carbonyl in hepatopancreas were also found in the treatment with 1.31 mg kg^?1 of dietary Se (P < 0.05). In addition, this treatment had significant higher glutathione content and thioredoxin reductase activity in hepatopancreas (P < 0.05). However, the activity of Se‐dependent glutathione peroxidase (Se‐GPx) was significantly decreased in the treatment with 4.20 mg kg^?1 of dietary Se (P < 0.05). In this treatment, the protein carbonyl content in hepatopancreas was significantly higher than that in the group with 1.31 mg kg^?1 of dietary Se (P < 0.05). In conclusion, in terms of anti‐oxidation and Cu accumulation, the protective effects of dietary Se on abalone against waterborne Cu were dose‐dependent. The 1.31 mg kg^?1 of dietary Se had this effect, but not 4.20 mg kg^?1 of dietary Se. Moreover, the latter increased the oxidative stress in abalone exposed to the waterborne Cu.     

Practical use of response surface methodology for optimization of veterinary antibiotic removal using UV/H2O2 process

Three of the most commonly used veterinary antibiotics—enrofloxacin (ENR), sulfamethoxazole (SMX), and oxytetracycline (OTC)—were chosen as representative antibiotics for UV/H₂O₂ treatments. The objective was to determine the optimization of UV/H₂O₂ to remove antibiotics from aquaculture discharge water using response surface methodology. The degradation of the antibiotics was investigated under varying UV/H₂O₂ conditions in environments with different levels of pH, water matrices, humic acid, and constituent ions. The degradation results demonstrated that increasing the H₂O₂ dosage facilitated ENR degradation at a neutral pH while facilitating degradation of SMX and OTC at a slightly acidic pH. The optimum removal conditions for ENR, which was used in all influential effect experiments and the contact tank experiments, was obtained at 10 mM H₂O₂, a pretreated COD of 87.51 mg L⁻¹, and an initial pH of 6.15. Among the tested anions, only the presence of Cl^- showed slight positive effects on ENR degradation, due to the generation of secondary active radicals. During the reaction, the hydroxyl radical (OH) was present at a higher pH while singlet oxygen (¹O₂) was slightly present at a lower pH. The experimental results from H₂O₂ sequential addition indicated that freshly added H₂O₂ could quench the recently generated OH and therefore a high H₂O₂ concentration with frequent adding was not necessary. Our contact system reduced the ENR concentration in both the effluent reservoir and in the UV irradiation zone. The overall results supported the use of the UV/H₂O₂ system to treat remnant antibiotics in the discharge water.