Intensive Fish Farming Research Articles

Environmental factors can affect the relationship between Nile tilapia and its parasites in cage systems culture

Parasites represent a serious obstacle in Brazilian intensive fish farming, and then, monitoring parasitic infestations in aquaculture is a duty of every tilapia producer. The objective of this study was to identify the branchial ectoparasites of Nile tilapia, evaluate the correlation between parasitic intensity, host biometrics, and limnological variables, as well as to identify gill histological changes in fish. Thus, fish representing the three phases (I, II, and III) of production were collected in two commercial fish farms - 1 and 2, necropsied, and their parasites quantified and identified. The gill alterations were processed for histological analysis. Cichlidogyrus sclerosus and Scutogyrus longicornis (Monogenoidea), and Lamproglena monodi (Lernaeidae) have been identified in the tilapia gills. The highest intensities of Monogenoidea infestation were in summer and autumn in both fish farms, with a positive correlation between parasites and water temperature. Infestation by L. monodi occurred only in Fish farm 2, with greater infestations in winter and spring, with a negative correlation between water temperature and parasitism. There was also an increase in parasitism according to the weight and length of the fish in the two fish farms. Histological changes such as hyperplasia, lamellar hypertrophy, and the presence of basophilic cysts on the secondary lamellae were detected in tilapia. Thus, water quality parameters and season of the year, which are closely related, can affect communities of parasites that infest Nile tilapia grown in cages. These findings are important to assist in planning disease control and prevention strategies for Nile tilapia fish farming, to reduce economic losses resulting from fish diseases and death.

Regulation of Rhesus glycoprotein-related genes in large-scale loach Paramisgurnus dabryanus during ammonia loading.

Waterborne ammonia is one of the crucial issues that limited production and animal health in aquaculture. Ammonia-tolerant varieties are highly desired in intensive fish farming. Screening for the key regulatory genes of ammonia tolerance is essential for variety breeding. According to the previous hypothesis, Rh glycoproteins play an important role in ammonia excretion in teleosts. However, the ammonia defensive mechanisms are not well described at present for large-scale loach (Paramisgurnus dabryanus), a typical air-breathing and commercially important fish in East Asia. Here we show that the transcription of Rh glycoprotein-related genes was significantly affected by ammonia exposure in this species. Probit analysis showed that 96h-LC50 of NH4Cl at 23℃ and pH 7.2 was 92.64mmol/L. A significant increase of Rhcg expression in gills was observed after 48h of 60mmol/L and 36h of 80mmol/L NH4Cl exposure, suggesting that Rhcg present on the apical side of the branchial epithelium facilitates NH3 excretion out of gills. A high concentration of acute ammonia exposure induced elevated Rhbg transcript in the gills of large-scale loaches, while a slight change in Rhbg expression was observed in response to lower ammonia, suggesting that transcriptions of Rhbg genes are activated by a considerably high level of ambient ammonia to eliminate excessive endogenous nitrogen. The Rhag mRNA level in gills of large-scale loaches increased markedly with the prolonging of exposure time from 0 to 36h of ammonia loading, suggesting Rhag localized in gills may be primarily associated with ammonia handling. During 7-21 days of ammonia exposure, the expression of most Rh glycoproteins-related genes in the gills decreased, indicating that the functional role of Rh glycoproteins is not primarily associated with ammonia defense over a long period (more than 7 days). Although a significant transcript of Rhbg was found in the skin of a large-scale loach, the lack of Rhcg and down-regulation of Rhag may indicate that the skin is not an essential location of ammonia excretion, at least when submerged to high levels of ammonia in the environment. In conclusion, Rh glycoproteins localized in gills as ammonia transporters play a momentous role in ammonia detoxification in this species during acute ammonia loading. However, it does not show a positive function during long-term ammonia exposure. Furthermore, the physiological function of Rh glycoproteins localized in the skin is still unclear and deserves further study.

Antagonism of cysteinyl leukotriene receptors by zafirlukast modulated acute inflammatory reaction in tilapia, Oreochromis niloticus

To identify activation pathways and effector mechanisms of innate immunity in fish has become relevant for the sanitary management of intensive fish farming. However, little is known about the blocking of cysteinyl leukotrienes receptors (CysLTRs) and their effects in teleost fish. Our study evaluated the anti-inflammatory effect of 250 and 500 μg zafirlukast (antagonist of CysLTRs)/kg b.w., administered orally in the diet, during acute inflammatory reaction induced by Aeromonas hydrophila bacterins in Oreochromis niloticus. 80 tilapia were distributed in 10 aquariums (100L of water each, n = 8) to constitute three treatments: Control (inoculated with A. hydrophila bacterin and untreated); Treated with 250 μg or 500 μg of zafirlukast/kg b.w. and inoculated. To be evaluated in three periods: 6, 24 and 48 h post-inoculation (HPI), totaling nine aquariums. A tenth group was sampled without any stimulus to constitute reference values (Physiological standards). Tilapia treated with zafirlukast demonstrated dose-response effect in the decrease of accumulated inflammatory cells, strongly influenced by granulocytes and macrophages. Zafirlukast treated-tilapia showed decrease in blood leukocyte counts (mainly neutrophils, and monocytes) and reactive oxygen species production. Treatment with zafirlukast resulted in down-regulation of ceruloplasmin, complement 3, alpha2-macroglobulin, transferrin and apolipoprotein A1, as well as up-regulation of haptoglobin. Our study provided convincing results in the pathophysiology of tilapia inflammatory reaction, considering that treatment with zafirlukast, antagonist of cysteinyl leukotriene receptors, resulted in a dose-response effect by suppressing the dynamics between leukocytes in the bloodstream and cell accumulation in the inflamed focus, as well as modulated the leukocyte oxidative burst and the acute phase protein response.

Treating performance of a commercial-scale constructed wetland system for aquaculture effluents from intensive inland Micropterus salmoides farm

In intensive inland fish farming, discharge of untreated effluents adversely affects adjacent water bodies and causes water pollution. Thus, it is highly necessary to treat the effluents from inland fish farm. In this study, we built a commercial-scale integrated constructed wetland (CW) system with vertical subsurface flow, and monitored the purifying effect. During fish farming and discharge of effluents periods, the water samples were collected to detected the total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3--N), nitrite nitrogen (NO2--N) and chemical oxygen demand (CODMn). Results showed that the system was stable and significantly improved water quality from fish pond. During the fish farming period, the removal efficiency for TN, TP, NH4+-N, NO3--N, NO2--N, and COD was 24.93–43.72%, 61.92–72.18%, 56.29–68.63%, 56.66–64.81%, 56.42–64.19% and 28.37–42.79%, respectively. Similarly, these parameters were also markedly decreased by the integrated CW system during sewage discharge period, and the average total removal rate for TN, TP, NH4+-N, NO3--N, NO2--N, and COD was 50.24%, 64.48%, 61.36%, 62.65%, 56.16% and 37.32%, respectively. It was worth noting that three key parameters for effluents detection TN, TP and COD values were below the threshold values of water quality of Class II in freshwater sewage discharge standard of China (SCT9101-2007). In conclusion, this study evidently demonstrated that application of CW system was an environmental sustainable sewage treatment strategy in intensive inland fish farming.

Humoral antibody response in Arctic charr (Salvelinus alpinus) against Aeromonas salmonicida ssp. achromogenes following vaccination with a novel autogenous vaccine

The bacterium Aeromonas salmonicida ssp. achromogenes (Asa) causes atypical furunculosis in salmonids that may lead to extensive financial losses in intensive fish farming. The commercially available vaccine commonly used against the ssp. achromogenes in the production of Arctic charr in Iceland has been developed for Atlantic salmon (Salmon salar) against the subspecies salmonicida which causes typical furunculosis, but it has insufficient efficacy in Arctic charr. In response to this, a novel vaccine against Asa in Arctic charr was developed in cooperation with Spanish vaccine company; HIPRA, and the antibody response of Arctic charr against Asa investigated using enzyme-linked immunosorbent assay. Fish used for testing were vaccinated using the novel, monovalent autogenous experimental vaccine and a commercially available vaccine Alpha Ject® 3000 developed for Atlantic salmon that was used as a comparison. The study was conducted in commercial production units where the fish were continually exposed to natural outbreaks of atypical furunculosis. Blood samples were collected from the fish prior to vaccination and thereafter at approximately ten-week intervals in each production unit throughout the production period until the fish reached harvesting size. Fish growth and mortality was recorded throughout the study. The results indicated that both vaccines induced antibody response in fish against Asa antigens and that antibody titers obtained during the first weeks following vaccination were maintained throughout the production period. However, significantly higher antibody titers were observed in fish vaccinated with the experimental novel vaccine and fish mortality was significantly lower in production units containing fish vaccinated with the novel vaccine in comparison to the Alpha Ject 3000® vaccine. These results suggest that the novel vaccine may be a promising candidate for protective immunity against atypical furunculosis caused by Asa in Arctic charr.

Dietary emamectin benzoate induces dose-dependent variations in haemato-biochemical and erythrocyte-metric parameters of Oreochromis niloticus (L.)

Intensive fish farming often leads to the emergence of infectious and parasitic diseases, which require aquadrugs to control them. The present study evaluated the effects of 1× (50 μg/kg biomass/day) and 3× (150 μg/kg biomass/day) dietary emamectin benzoate (EB)-dosing on healthy Oreochromis niloticus for 7 consecutive days in comparison with control. Dietary EB caused a significant dose-dependent reduction in feed intake and an increase in mortalities. The total erythrocyte counts (TECs), monocyte counts (MCs), haemoglobin (Hb), haematocrit (Ht), and mean cell haemoglobin concentration (MCHC) reduced significantly. Contrarily, the counts of total leukocytes (TLCs), thrombocytes (TCs), lymphocytes (LCs) and neutrophils (NCs) increased significantly within 7 days of EB-dosing (ED) in both groups. The TECs, Hb, TCs and MCs normalized on day 35 post-EB-dosing (PED), while Ht, MCH, LCs, and MCs recuperated on day 14 PED. Both groups experienced a significant increase in serum glucose, alkaline phosphatase, alanine transaminase, aspartate transaminase and creatinine levels as well as a decrease in calcium, chloride ions and acetylcholinesterase levels during the ED period. The alkaline phosphatase and creatinine levels of the 1× group recovered on day 14 and 28 PED, respectively but not in the 3× group. The dosed fish documented reduced erythrocyte cellular and nuclear morphometry like larger axis, minor axis, volume, and surface area, which recovered during the PED period, except for the nuclear volume. The results suggested the tolerability of O. niloticus juveniles and their ability to mount adaptive responses to the effect of EB to recuperate with the suspension of dosing.

AQUACULTURE IN TURKEY

The world's resources dedicated to fisheries and aquaculture are predicted to remain stable at their maximum utilization rate. Many intensive fish farms with recirculation production systems are needed in order to achieve sustainable output. Combined or integrated production projects are needed for sustainable production and to meet the high demand for food supplies. However, due to a substantial migration problem from rural areas to metropolitan centers, labor may be a concern in the aquaculture business. Turkey is still improving technology in order to maximize resource utilization while minimizing disruption to aquatic systems. With the growth of aquaculture, some environmental issues have been identified. Based on the present study, it was predicted that Tukey will produce 700,000 tons of fish by 2050. The purpose of this paper is to provide an overview of the current situation, as well as studies on sustainability and future developments in the field.

Antibiotic resistance and polymyxin B resistance mechanism of Aeromonas spp. isolated from yellow catfish, hybrid snakeheads and associated water from intensive fish farms in Southern China

Aeromonas are often found in aquatic environments, in which they may cause disease in marine fish and are associated with seafood-related outbreaks worldwide. The objective of this study was to determine the antibiotic resistance and polymyxin B resistance mechanism of 200 isolates of Aeromonas spp. obtained from apparently healthy yellow catfish, hybrid snakehead and associated water, respectively, in seven intensive aquatic farms in Guangdong, China. Six Aeromonas species were identified, of which A. veronii was the most prevailing species. The susceptibility to 16 antimicrobial agents was evaluated by the broth microdilution method. All isolates were resistant to at least one antibiotic, with the highest resistance percentage to ampicillin (99.0%), and relative lower resistance rates to tetracycline (49.0%) and trimethoprim-sulfamethoxazole (43.0%). More than half of the strains were multi-drug resistant (MDR). Seven strains were resistant to polymyxin B with minimum inhibitory concentration (MIC) values of 4–512 mg/L, which were mediated by novel variable mcr-3-like and mcr-7-like genes. The results of this study indicated that yellow catfish, hybrid snakeheads and associated environments in intensive fish farms are reservoir of antibiotic resistant Aeromonas which may contaminate associated fish products and spread through food chain to human, representing a potential public health risk.

Experimental Biology in Conflict Resolutions: The Case of Pelicans and Cormorants in Israel

In Israel, which is a bottleneck for some six hundred million migrating birds, the drainage of the Hula Lake in the north resulted in serious conflicts between fish-eating birds and the intensive fish farming and agriculture that became established on the reclaimed land. Implementation of various deterrence methods, including lethal control, failed to solve these conflicts. We followed the concept that only by understanding the biology of the organism in question could the tools (indications) for effective and sustainable management be devised that would solve such conflicts while helping the preservation of natural assets such as wetlands and their inhabitants. We demonstrated this concept in the solutions reached in the case studies of pelicans and cormorants and their interactions with intensive commercial fish ponds. We studied the physiological condition, food preference and energy demands, and ecological constraints of Great White Pelican Pelecanus onocrotalus, Great Cormorant Phalacrocorax carbo and Pygmy Cormorant Microcarbo pygmeus. As a result, we suggested different management solutions that are currently implemented with the full cooperation of the fishermen and the nature preservation authorities. Based on assessment of visual acuity to detect and catch fish under water Great Cormorants were effectively pushed towards Lake Kinneret where they could hunt more profitable fish than in the turbid fish ponds. The established roosts there were not controlled such as to lead the birds away from the fishponds. In case of the pelicans, part of the drained Hula valley was reflooded and extra fish was provided. Both measures effectively reduced the damage at the fish farms. We have shown that such solutions are economically helpful for fishermen and enable the preservation of the wetland habitat.

Membrane aerated biofilm reactor in recirculating aquaculture system for effluent treatment

ABSTRACT The implementation of fish farming has been increasing worldwide over the last decades, as well the search for alternative production systems and the treatment of their generated effluent. Recirculating Aquaculture System (RAS) is a compact solution for future intensive fish farming. However, few configurations of treatment technologies were tested in RAS, such as systems with a Membrane Aerated Biofilm Reactor (MABR). In this scene, this study aimed to evaluate the RAS effluent treatment efficiency device for intensive Nile tilapia (Oreochromis niloticus) production, the fish species most cultivated worldwide. The novel RAS configuration was composed of a cultivation tank (CT), a Column Settler, and a MABR. The RAS performance was evaluated by pH, temperature, turbidity, dissolved oxygen (DO), total nitrogen (TN), ammonia, nitrite, nitrate, total solids (TS), and chemical oxygen demand (COD). The obtained results in average values for temperature, pH, and DO inside the CT were 25.22 ± 1.88°C, 7.61 ± 0.33, and 3.80 ± 1.30 mg L−1, respectively, as ideal for tilapias survival. Average removal efficiencies found in the RAS for turbidity, COD, TN, nitrite, nitrate, ammonia, and TS were 50.0, 40.5, 11.7, 40.2, 13.1, 35.0, and 11.4%, respectively. Overall, we observed removals for all parameters studied, with good results, particularly, for COD, turbidity, nitrite, and ammonia. The evaluated system proved an effective alternative for water reuse in RAS capable of maintaining water quality characteristics within the recommended values for fish farming.

Ultrasonic monitoring of early larval development of fish in tanks. Case study: Gilthead seabream (Sparus aurata)

Swimbladder inflation is a significant matter in intensive fish farming, since it is related to larval survival rate and the morphological quality of individuals. In this work, we propose a non-invasive acoustic technique using ultrasound to monitor the swimbladder development of gilthead seabream (Sparus aurata) in tanks. The fundamental hypothesis is that, due to the high acoustic contrast of gas, the swimbladder’s inflation process can be detected by measuring the larvae’s target strength during their early development. Backscatter numerical models using the finite element method, developed from biological measurement data, were applied to evaluate the feasibility of the proposed method. The acoustic measurements were obtained using an EK60 Simrad echosounder working at 200 kHz. The target strength values were evidenced with and without the presence of a developed swimbladder, showing a statistically significant relationship with the swimbladder’s standard length, area and the percentage of larvae with a swimbladder. The experiments were carried out in the Spanish Institute of Oceanography (IEO)’s marine aquaculture plant at Mazarrón (Murcia, Spain).

Genes and elements involved in the regulation of the nervous system and growth affect the development of spinal deformity in Cyprinus carpio.

Spinal deformity is a serious economic and animal welfare problem in intensive fish farming systems, which will be a significant unsolved problem for the fish sector. The aim of this study was to determine the relative expression of genes (Akt1 substrate 1, Calreticulin, Collagen type I alpha 2 chain, Corticotropin-releasing hormone, Chromodomain-Helicase DNA-binding, Growth hormone, Insulin like growth factor 1, Myostatin, Sine oculis-related homeobox 3, Toll-like receptor 2) in different tissues associated with spinal deformity and to determine the macroelement (calcium, magnesium, phosphorus, potassium, sodium, sulfur) and microelement (barium, copper, iron, manganese, strontium, zinc) content of spine in healthy and deformed common carps (Cyprinus carpio) in Hungary. The mRNA levels of the genes were measured in 7 different tissues (abdominal fat, blood, brain, dorsal muscle, genitals, heart, liver) by qRT-PCR. Correlations between gene expression and element content were analyzed by using linear regression and Spearman rank correlation. In a total of 15 cases, we found a statistically significant connection between gene expression in a tissue and the macro- or microelement content of the spine. In these contexts, the genes Akt1 substrate 1 (3), Collagen type I alpha 2 chain (2), Corticotropin-releasing hormone (4), Insulin-like growth factor 1 (4), and Myostatin (2), the tissue’s blood (3), brain (6), heart (5), and liver (1), the macroelements sodium (4), magnesium (4), phosphorus (1) and sulfur (2) as well as the microelement iron (4) were involved. We also found statistically significant mRNA level differences between healthy and deformed common carps in tissues that were not directly affected by the deformation. Based on our results, genes regulating the nervous system and growth, elements, and tissues are the most associated components in the phenomenon of spinal deformity. With our study, we wish to give direction to and momentum for the exploration of these complex processes.

Multi-scale variation in coral reef metrics on four Philippine reef systems

Multi-scale studies were conducted to examine variations in hard coral cover and generic richness in four reef systems in the Philippines in relation to different stressors. The study sites included Bolinao, where sedimentation and eutrophication due to intensive fish farming are causing seawater acidification, and reefs inside and outside embayments in Lian, which experience different levels of sedimentation. The other two reef systems are those of Mabini and Tubbataha, which are popular sites for dive tourism and are thus better managed. Mabini experiences periodic upwelling while the offshore Tubbataha sites are generally well-flushed by currents which might mitigate thermal stress in these areas. We tested differences in hard coral cover and generic richness between locations, sites in a location, and stations between sites to capture scales at which differences attributable to such factors might be observed. Statistically significant variation was detected at all scales (station, site, and location) examined. Hard coral cover was found to have the largest variance at the site level (scales of hundreds to thousands of meters), while generic richness varied most at the location level (scales of tens to hundreds of kilometers). The coral metrics were shown to be related to factors such as thermal stress, nutrient enrichment and eutrophication, and water motion relative to the degree of embayment. Understanding the nature of the dynamics between coral metrics and environmental factors can aid managers in maintaining reef quality and projecting future trajectories of reef states. This work provides specific hypotheses on the factors affecting coral reefs (coral bleaching, eutrophication and acidification from fish farming, embayment, and associated processes), particularly coral cover and generic richness at the location and biogeographic region (sub-national) scales. It also provides a framework by which the relative importance of these factors may be recognized at different spatial scales. This framework is potentially valuable in developing countries with significant reef areas, especially where a more ecosystem-based approach to the management of coastal waters is applicable.

Chloramine-T application for Trichodina sp. in Arapaima gigas juveniles: Acute toxicity, histopathology, efficacy, and physiological effects

Trichodinids are problematic ectoparasites for intensive arapaima fish farming, which can make their breeding costly and unprofitable. The search for effective and safe therapeutic molecules is constant, and chloramine-T has stood out as an effective biocide to treat various pathogens in aquaculture. Here we investigated the acute toxicity (LC50-4h) of chloramine-T and its behavioural, morphological, histological, physiological, and antiparasitic effects on the control of trichodinids in arapaima juveniles. Initially arapaima were exposed to chloramine-T (0, 10, 20, 40, 50, 60, 80, 100 mg L−1) for 4 h. During this period, behavioural, morphological, and mortality changes were recorded. Immediately after a toxicity test, gills were collected for the histological analysis. The LC50-4h was calculated at 23.8 mg L−1 of chloramine-T. Behavioural changes like erratic swimming, loss of balance, gasping at the water surface, excessive mucus, jumping at the water surface, lethargy and gill hyperventilation, and morphological changes like loss of scales, ocular opacity, and skin darkening, were considered mild in arapaima exposed to 10 and 20 mg L−1 of chloramine-T for 4 h. The arapaima gills exposed to 10, 20 and, 40 mg L−1 of chloramine-T presented epithelial hyperplasia, dilated venous sinus and eosinophilic infiltrate, but they were reversible and of a low pathological degree. Based on the acute toxicity test (LC50-4h) results, concentrations were defined for the in vivo efficacy test, during which arapaima were exposed to 0, 10, 15, and 20 mg L−1 of chloramine-T for 1 h. After a therapeutic bath, physiological and parasitological analyses were performed. The use of 20 mg L−1 of chloramine-T significantly reduced (p < 0.05) parasitism by Trichodina sp. with an efficacy of 50.27 % and 53.23 % in gills and on the body surface, respectively. Chloramine-T did not change haematological parameters (erythrogram and thrombogram) or the biochemical parameters of arapaima after 1 h of exposure. However, monocytosis and neutrophilia were noted at slightly higher concentrations (15 and 20 mg L−1), but changes in fish homeostasis were not characterised. Thus, we demonstrate that the application of a therapeutic bath with 20 mg L−1 of chloramine-T for 1 h reduces parasitism by trichodinids and does not affect general arapaima juvenile health.

Sarcodia suiae Water Extract Promotes the Expression of Proinflammatory and Th1-Type Cytokines and Delay the Onset of Mortality in Cobia (Rachycentron canadum) During Photobacterium damselae subsp. damselae Infection.

Cobia (Rachycentron canadum) is a marine fish of high economic value that grows at a fast rate. However, intensive fish farming has led to disease outbreaks in cobia cultures, which is highly costly to the industry. The impact of infectious diseases on cobia production has led to the inappropriate and increased use of chemicals and antibiotics, which negatively affects the environment and human health and promotes the spread of drug-resistant pathogens. Hence, prophylactic measurements, such as the use of immunomodulators, are required to improve the health of cultured animals against pathogens. In this study, we examined the effects of Sarcodia suiae water extract (SSWE) in cobia in vitro and in vivo. We found that treatment with SSWE could significantly increase the expression of cytokines (e.g., IL-1β, IL-6, IL-10, IL-12, and TNF-α) and chemokines (e.g., IL-8) in primary cultured head kidney leukocytes. Intraperitoneal injection of SSWE (20 μg/g body weight) promoted higher expression of IL-6, IL-8, IL-10, IL-12, chemokines (e.g., CC1), and antibodies (e.g., IgT) in head kidney and spleen tissues of the fish compared with other dose levels. Additionally, we describe for the second time (only after India) of the isolation of Photobacterium damselae subsp. damselae (Phdd) from a deadly epizootic in cage-farmed cobia. An intraperitoneal inoculation of SSWE before Phdd challenge showed that SSWE treatment could delay the onset of mortality of cobia. Finally, fish that received SSWE intraperitoneally before infection with Phdd exhibited elevated expression of Th1-type cytokines, namely, IL-8, IL-12, TNF-α, and IFN-γ. At the same time, the expression of Th2-related factors (such as IL-10 in the head kidney, and IgM and IgT in the spleen) were lower for the fish that received SSWE instead of PBS before the Phdd challenge. The results indicate that SSWE treatment facilitates the induction of Th1-type cytokines in cobia to fight against Phdd infection and has the potential to be used as an immunostimulant and vaccine adjuvant for fish.

Prevalence and Antimicrobial Resistance of Escherichia coli, Salmonella and Vibrio Derived from Farm-Raised Red Hybrid Tilapia (Oreochromis spp.) and Asian Sea Bass (Lates calcarifer, Bloch 1970) on the West Coast of Peninsular Malaysia.

Antibiotics are widely used in intensive fish farming, which in turn increases the emergence of antimicrobial-resistant (AMR) bacteria in the aquatic environment. The current study investigates the prevalence and determines the antimicrobial susceptibility of E. coli, Salmonella, and Vibrio in farmed fishes on the west coast of Peninsular Malaysia. Over a period of 12 months, 32 aquaculture farms from the Malaysian states of Selangor, Negeri Sembilan, Melaka, and Perak were sampled. Both E. coli and Salmonella were highly resistant to erythromycin, ampicillin, tetracycline, and trimethoprim, while Vibrio was highly resistant to ampicillin and streptomycin. Resistance to the antibiotics listed as the highest priority and critically important for human therapy, such as colistin in E. coli (18.1%) and Salmonella (20%) in fish, is a growing public health concern. The multi-drug resistance (MDR) levels of E. coli and Salmonella in tilapia were 46.5% and 77.8%, respectively. Meanwhile, the MDR levels of E. coli, Salmonella, V. parahaemolyticus, V. vulnificus and V. cholerae in Asian seabass were 34%, 100%, 21.6%, 8.3% and 16.7%, respectively. Our findings provide much-needed information on AMR in aquaculture settings that can be used to tailor better strategies for the use of antibiotics in aquaculture production at the local and regional levels.

Lunar Cycle Influences Production of Tilapia (Oreochromis spp) Eggs in an Intensive Outdoor Production System in the Tropics

A robust body of evidence has demonstrated that the lunar cycle plays an important role in the reproduction of fish living in natural environments. However, little is known about the influence of the moon on tilapia reproductive activity in intensive fish farming systems. This study aims to evaluate the influence of the lunar cycle on the reproductive performance of tilapias in an intensive outdoor tropical production system in Latin America. Records of two tilapia strains (Nile tilapia [Oreochromis niloticus; n = 75] and Red tilapia [Oreochromis spp.; n = 1335]) reared in concrete tanks in a commercial fish farm were analyzed. Over a 3-year period, 60,136 captures were made in intervals of 12 to 14 days and 6,600 females were manually spawned. The number of females spawned and the volume of eggs collected from each tank (n = 9) were recorded. Data was analyzed by the general linear model and means were compared by least squares means method. A very slight or no variation was observed when the lunar cycle was split into two halves (crescent and waning). The proportions of females spawned and the volume of eggs per spawned female and per female in the tank varied considerably across the eight periods of the lunar cycle, with greater values in the waning than in the crescent phase. A significantly greater proportion of tilapia spawned and yielded more eggs around the full moon than around the new moon and remaining days of the lunar cycle. The moon cycle affected the reproductive activity of tilapia, which were more reproductively active around the full moon and most of the waning phase.

Effect of an amalgamated antibiotic and its connection to cyto-genotoxicity and histo-architectural malformations in stinging catfish

Intensive fish farming has an excessive prevalence of infection and is typically controlled by the administration of antibiotics. Although amalgamated antibiotics are a relatively novel therapeutic idea and more effective than traditional antibiotic monotherapy, they can also have a toxic effect on the fish body when it is administered abruptly. This study investigated the cyto-genotoxic effects on erythrocytes and histo-architectural malformations in the liver and kidneys of stinging catfish (Heteropneustes fossilis) in relation to Enrocip plus use as an amalgamated antibiotic agent. The experimental fish with an initial average weight of 17.38 ± 1.94 g were divided into four treatment groups with antibiotic doses: according to the recommendation of the manufacturer 0.167 mg/ml Enrocip plus was used as a standard dose (x) and it was treated as T3, while 0% of the standard dose (0× mg/ml), 1/2× (0.083 mg/ml), and 2× (0.333 mg/ml) were treated as T1, T2 and T4, respectively for a period of 30 days. The observed erythrocyte cellular deformities (ECD) were twin, tear-drop, serrated, tail budded and de-membranated cells, whereas the erythrocyte nuclear deformities (END) were a nuclear bridge, bi-nucleus, nuclear termination, karyopyknosis, and micronucleus at different concentrations of Enrocip plus. Both ECD and END percentages experienced the interaction of antibiotic dose and exposure time, and were significantly different (P < 0.01). Significant changes in hepatocytes, mild to severe necrosis, vacuole formation, and hepatopancreas damage were also observed in the liver of the treated fish whereas highly degraded renal tubules and hematopoietic tissue, glomerular occlusion, and vacuolation were evident in the kidneys. The current investigation fully emphasizes the adverse effects of amalgamated antibiotics on the cyto-genotoxicity and the histomorphology of the kidneys and liver of fish. Thus, the use of an amalgamated antibiotic in aquaculture must be carefully evaluated.

Four decades of nitrous oxide emission from Chinese aquaculture underscores the urgency and opportunity for climate change mitigation

As the fastest growing food production sector in the world, aquaculture may become an important source of nitrous oxide (N2O)—a potent greenhouse gas and the dominant source of ozone-depleting substances in the stratosphere. China is the largest aquaculture producer globally; however, the magnitude of N2O emission from Chinese aquaculture systems (CASs) has not yet been extensively investigated. Here, we quantified N2O emission from the CASs since the Reform and Opening-up (1979–2019) at the species-, provincial-, and national-levels using annual aquaculture production data, based on nitrogen (N) levels in feed type, feed amount, feed conversion ratio, and emission factor (EF). Our estimate indicates that over the past 41 years, N2O emission from CASs has increased approximately 25 times from 0.67 ± 0.04 GgN in 1979 to 16.69 ± 0.31 GgN in 2019. Freshwater fish farming, primarily in two provinces, namely, Guangdong and Hubei, where intensive freshwater fish farming has been adopted in the past decades, accounted for approximately 89% of this emission increase. We also calculated the EF for each species, ranging from 0.79 ± 0.23 g N2O kg−1 animal to 2.41 ± 0.14 g N2O kg−1 animal. The results of this study suggest that selecting low-EF species and improving feed use efficiency can help reduce aquaculture N2O emission for building a climate-resilient sustainable aquaculture.

Assessment of heavy metals in wild and farmed tilapia (Oreochromis niloticus) on Lake Kariba, Zambia: implications for human and fish health

ABSTRACT The aim of this study was to assess the levels of heavy metals in both wild and farmed tilapia on Lake Kariba in Zambia and to evaluate the impact of intensive fish farming on wild tilapia. Three sites for wild fish (2 distant and 1 proximal to fish farms) and two fish farms were selected. One hundred fish (52 from distant sites; 20 near fish farms; 28 farmed fish) were sampled and muscle tissues excised for analysis of heavy metals (Mg, Fe, Zn, Al, Cu, Se, Co, Mo, As, Cr, V, Ni, Hg, Pb, Li, Cd, and Ag) by acid (HNO3) digestion and ICP-MS. All metals were found to be below the maximum limits (MLs) set by WHO/EU. Essential metals were higher in farmed tilapia, whereas non-essential metals were higher in wild tilapia. Significantly higher levels of essential metals were found in wild fish near the fish farms than those distant from the farms. Estimated weekly intake (EWI) for all metals were less than the provisional tolerable weekly intakes (PTWI). Target hazard quotients (THQ) and Hazard Indices (HI) were <1, indicating no health risks from a lifetime of fish consumption. Selenium Health Benefit Value (HBVSe) was positive for all locations, indicating protective effects of selenium against mercury in fish. Total cancer risk (CR) due to As, Cr, Cd, Ni and Pb was less than 1 × 10−4, indicating less than 1 in 10,000 carcinogenic risk from a lifetime consumption of tilapia from Lake Kariba. Hg levels (0.021 mg/kg) in wild tilapia at site 1 were higher than the Environmental quality standard (EQS = 0.020 mg/kg) set by EU, indicating possible risk of adverse effects to fish. Except for Hg, levels of metals in fish were safe for human consumption and had no adverse effects on fish.