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Several studies have been conducted in the last 3 years to evaluate tilapia's parasitic and bacterial infection in cultures in Mexico. The present work evaluates the severity, prevalence, and health condition through the histopathological index based on the damage in the organs and tissues of tilapia cultured in ponds and cages during 2018 and 2019. Seven hundred and eight fish were collected from ponds and cages of tilapia farms in Chiapas, Oaxaca, and Guerrero and preserved and processed for histological observations. The prevalence of histopathological alterations found in each biological system was calculated and expressed in percentage. The histopathological index of each fish (HIfish) was calculated based on two different semi-quantitative methods. Histologically, the tilapia showed alterations as inflammation, melanomacrophage centers, hyperplasia, telangiectasias, and epitheliocystis unrelated to specific infectious pathogenic agents in both years but suggest effects associated with diverse factors in different biological systems. The prevalence was higher in all the parameters evaluated in 2018. The pathological manifestations in both years show that the health condition of the fish was affected regardless of the type of culture (cages and ponds), with the respiratory and digestive systems the most affected. These results show a baseline of the health condition of the tilapias cultured in southeast Mexico. The observed damages were not lethal but reflected a constant exposition to stressful conditions to trigger chronic inflammatory responses in the fish and make them susceptible to pathogens present in the environment. [ABSTRACT FROM AUTHOR]

The present study investigates molecular‐based PCR techniques to estimate the prevalence of fish pathogens in southwest Mexico where recurrent mortality in the tilapia cultures has been observed. Sample of internal organs and lesions of Nile tilapia were taken and analysed in 2018, 2019, 2020 and 2022 to detect bacterial pathogens using PCR. No samples were taken in 2021 due to the COVID‐19 pandemic. The real‐time PCR conditions were optimized to allow a qualitative reliable detection of the bacteria from fixed fish tissue. A total of 599 pond‐ and cage‐cultured tilapia from the southwestern Mexican Pacific (Guerrero, Oaxaca and Chiapas states) were analysed. In this tropical region, during 2018 and 2019 water temperatures of the tilapia cultures were generally with the optimal range to grow Nile tilapia, although extreme values were recorded on some farms. Most of the tilapia sampled were apparently healthy. No Francisella sp. was detected in any sample, and Staphylococcus sp. was the most prevalent (from 0% to 64%) bacteria from the three states over time. Low prevalence of Aeromonas sp. was found, from 0% to 4.3%, although the fish pathogen Aeromonas dhakensis was not detected. Sterptococcus iniae was only detected in Chiapas in 2019 at a low prevalence (1.4%), while the major tilapia pathogen S. agalactiae was detected at a high prevalence (from 0% to 59%) in the three Mexican states. This is the first detection of these pathogenic bacteria in rural farms using real‐time PCR and constitutes a great risk for tilapia aquaculture in Mexico, as well as a potential dispersion of these pathogens to other aquaculture areas. [ABSTRACT FROM AUTHOR]

Simple Summary: The development of the production of freshwater species such as Nile tilapia has favored the increase in larger-scale infectious outbreaks and new diseases in this industry. This work aimed to determine the presence of bacterial diseases in Nile tilapia cultured in Chiapas, Mexico. Blood and viscera samples were taken from healthy and sick animals from several commercial farms. The isolated bacteria were identified and characterized by different laboratory tests. The isolation, identification and characterization of two pathogens involved in an infectious process were achieved: Staphylococcus haemolyticus and Providencia vermicola. Both bacteria were cataloged as causal agents of diseases in tilapia farming in Mexico. This is the first report of bacterial diseases in tilapia farms caused by two rare but potentially emerging pathogens for the species. These results make it possible to know the health situation of the region, estimate economic losses, know the behavior of pathogens and propose effective prevention and control measures. This work aimed to determine the presence of bacterial pathogens in fish with a clinical picture suggestive of infectious disease in Nile tilapia reared in Chiapas, Mexico. Blood and viscera samples were taken from healthy and diseased animals from commercial farms. Clinical and pathological examinations of each individual were performed and samples were collected for bacteriological studies. The bacterial isolates were identified and characterized by culture, biochemical tests, antibiogram, challenge tests and 16S rRNA sequencing. Staphylococcus haemolyticus and Providencia vermicola were isolated from various diseased organisms. The clinical picture caused by Staphylococcus haemolyticus was characterized by appetite disorders, neurological signs, nodulation or ulceration in different areas and congestion or enlargement of internal organs. Providenciosis in juvenile specimens caused a characteristic picture of hemorrhagic septicemia. Challenge tests performed in healthy organisms revealed that both infections caused higher mortality rates in fish (p < 0.05) compared with non-infected specimens, with 100% survival. There was 100% mortality for animals infected with P. vermicola after three days post infection and 45% for those infected with S. haemolyticus. The isolation and identification of two pathogens involved in an infection process were achieved and cataloged as potential causal agents of disease outbreaks in tilapia farming in Mexico. This is the first report of possible bacterial infection caused by S. haemolyticus and P. vermicola in tilapia farms, which are two uncommon but potentially emerging pathogens for the species. [ABSTRACT FROM AUTHOR]

Objective: Propose alternatives to strengthen national food security from the production of Nile tilapia Oreochromis niloticus. Methodology: An analysis of tilapia production in Mexico from 1994 to 2020; the production of tilapia fingerlings from 1985 to 2021; the trade balance of imports and exports of tilapia from 2006 to 2020 is analyzed and the national per capita consumption of fishery products from 1970 to 2020 is analyzed. Results: The national aquaculture production of tilapia from 1994 to 2020 presented an upward trend, with an annual average of 86,135 t, whose production oscillated between 61,516 t in 2003 and 152,840 t in 2016. In 2020, 96,977 t were produced, of which 56.6 % came from controlled systems and 43.3 % from fisheries based in cultivation in reservoirs. Production of tilapia fingerlings from 1994 to 2020 was moderately related to aquaculture production in controlled systems (r=0.50459040, p < 0.05). Limitations: As of 2000, the federal government significantly reduced the operation of the aquaculture centers under its responsibility, dedicated to the production of tilapia fingerlings, while as of 2006 the private sector joined this productive activity. Conclusions: The Nile tilapia O. niloticus constitutes a key fishing resource to strengthen national food security. [ABSTRACT FROM AUTHOR]

Backyard aquaculture is gaining importance as a source of food and economic input for rural families in Mexico. The profitability of this system needs to be determined. Bioeconomic tools allow for making profit projections of any production system. A bioeconomic model composed of biological, production, and economic sub-models was developed to evaluate a low-cost backyard aquaculture system (BAS) appropriate for rural communities, considering theoretical productive parameters at certain environmental conditions. The BAS consisted of a 2800 L water reservoir stocked with 168 masculinized 1 g fingerlings of tilapia (Oreochromis niloticus) at 60 ind m-3 density and aerated with two ventury-type submerged pumps of 0.046 hp at a rate of 1400 L h-1 each. Two culture cycles of 25 weeks each were analysed. The initial investment was USD 1200 (USD 775 equipment + USD 425 operation cost yr-1). Results from the model indicate the production of 303 fishes of 614 g, equivalent to 186 kg yr-1, considering 10% mortality. Selling at USD 3.62 kg-1, net profits varied from USD 184 to 16 at 0 and 25% self-consumption. The payback period was three and four years at 0 and 10% self-consumption but was longer than five years at 25%. A response surface plot of profitability indicators (costbenefit, net present value, and internal rate of return) was constructed at different self-consumption percentages, sale prices, and temperatures. In conclusion, BAS is a viable self-sustainable alternative for tilapia production at a low scale in rural areas of Mexico and other Latin American countries. [ABSTRACT FROM AUTHOR]

Aquatic ecosystems have been suffering deleterious effects due to the development of different economic activities. Metal(loid)s are one of the most persistent chemicals in environmental reservoirs, and may produce adverse effects on different organisms. Since fishes have been largely used in studies of metal(loid)s exposure, tilapia and largemouth bass were collected in three ecosystems from the Yaqui River Basin to measure the concentrations of metal(loid)s (chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), zinc (Zn) arsenic (As), mercury (Hg), and selenium (Se)) and some biomarkers (somatic indices, metallothionein expression and histopathological analysis) in tissues of both species. Metal(loid) concentrations varied seasonally among ecosystems in tissues of both species. The elements varied seasonally and spatially in tissues of both species, with a general distribution of liver > gills > gonads. Also, biomarkers showed variations indicative that the fish species were exposed to different environmental stressor conditions. The highest values of some biomarkers were in largemouth bass, possibly due to differences in their biological characteristics, mainly feeding habits. The multivariate analysis showed positive associations between metal(loid)s and biomarkers, which are usually associated to the use of these elements in metabolic and/or regulatory physiological processes. Both fish species presented histological damage at different levels, from SI types (changes that are reversible for organ structure) to SII types (changes that are more severe but may be repairable). Taken together, the results from this study suggest that the Yaqui River Basin is moderately impacted by metals and metalloids. [ABSTRACT FROM AUTHOR]

"Cacti" are rich sources of phytochemicals with antioxidant activity, and their use is mainly focused on infusions in traditional medicine in Mexico. This study characterizes the chemical compounds found in Cylindropuntia cholla root by gas chromatography coupled to mass spectrometry (GC-MS) and determines the total content of polyphenols and flavonoids, as well as their antioxidant capacity. The immunostimulatory effect of aqueous C. cholla root extract (ACcr) was evaluated at concentrations of 50, 250, 500, and 1000 μg/mL in Tilapia peripheral blood leukocytes. The results obtained by the GC-MS analysis revealed the presence of phenolic acids, flavonoid and phytosterol derivatives as β-sitosterol and campesterol. The determination of the total polyphenol and flavonoid contents indicated that ACcr is abundant in polyphenols, showing an anti-radical capacity of scavenging free radicals, such as those of hydroxyl and superoxide, as well as an increase in lipid peroxidation inhibition capacity. Stimulation of tilapia leukocytes resulted in the increase of its phagocytic activity, respiratory burst, nitric oxide production, and superoxide dismutase activity. Finally, the results obtained for the first time allowed establishing the chemical profile of ACcr and its antimicrobial activity against three important pathogenic bacteria. The potential of this root is indicated as an additive in formulating antioxidant and immunostimulant supplements for the aquaculture and pharmaceutical industry. [Display omitted] • GC-MS chemical compounds are reported for the first time for C. cholla root. • Aqueous C. cholla root is rich in phytosterols and polyphenols and flavonoids. • Aqueous C. cholla root showing an anti-radical capacity of scavenging free radicals. • C. cholla root have a strong antimicrobial activity against pathogenic bacteria. • Aqueous C. cholla root enhanced cellular immune parameters in leukocytes. [ABSTRACT FROM AUTHOR]

Epitheliocystis is an emergent infectious disease affecting fish gills and skin worldwide. Few studies document their distribution in wild and cultured fish in Latin America. This study reports the epitheliocystis distribution and prevalence, histopathological index (HI), and its possible relation with other observed pathologies in the gills of cultured tilapias Oreochromis niloticus in ponds and cages of three states of southwestern Mexico. In Guerrero, the number of affected fishes was less (29.2%) compared to Oaxaca (39.8%) and Chiapas (49.1%), with significant difference (Gadj = 13.39, df = 2, P = 0.01). The size of the cysts was between 5.37 to 52.96 µm, and most of the analyzed fish showed a low number of cysts per gill arch. The prevalence by regions was varied (0 to 75%) and no correlation (r = -0.002, P = 0.659, n = 474) between epitheliocystis prevalence and type culture. The fish had a low infestation of Trichodina sp. and monogeneans plus different pathologies such as inflammation, eosinophilic cells, rodlet cells, telangiectasia, edema, and thrombosis. The correlation analyses show a low inverse correlation (r = -0.281, P = 0.000, n = 474) between epitheliocystis prevalence and fish weight; and a low correlation (r = 0.372, P = 0.000, n = 474) between epitheliocystis prevalence vs. HI. The presence of the pathologies registered in this study seems to be possibly associated with other conditions like water quality or toxicants. This research is the first scientific study documenting the presence and distribution of epitheliocystis in Mexico. [ABSTRACT FROM AUTHOR]

Invasive species cause substantial changes to the biodiversity of freshwater systems. The African Nile tilapia (Oreochromis niloticus) is now widely distributed in tropical freshwaters globally. Despite indications that feral populations can influence native species through competitive effects, direct evidence of competition between Nile tilapia and native species is rare. Moreover, it is not clear if environmental variables such as temperature and oxygen concentration modulate competition. Here, interactions between Nile tilapia and the native Mayan cichlid (Mayaheros urophthalmus) were studied in experimental mesocosms in south-eastern Mexico. We found that Nile tilapia was the more active and aggressive of the two species, and their movement was only weakly influenced by temperature and oxygen concentration. By contrast, movement of the Mayan cichlid was strongly predicted by the movement and aggression of Nile tilapia, and the Mayan cichlid showed a steep decline in behaviours with increased water temperature and reduced oxygen. Our results suggest that broad environmental tolerance of the intrinsically aggressive Nile tilapia provides it with an advantage over native species. Collectively these traits may help to exacerbate its invasive success as those environmental conditions become more commonplace in a changing world. [ABSTRACT FROM AUTHOR]

Activities like agriculture contribute to the pollution of aquatic systems by fungicides, such as benomyl/carbendazim. This chemical inhibits the activity of acetylcholinesterase (AChE), having teratogenic, oncogenic, reproductive, and hepatic effects on aquatic and soil organisms. This paper presents the results of a study conducted in the Tenango dam, Mexico, aimed at detecting and determining the spatial and temporal variability of benomyl/carbendazim fungicide in the dam's water and its possible impact on Nile tilapia (Oreochromis niloticus), farmed and commercialized in the site. Five site visits were made during 2015. Benomyl/carbendazim was quantified at 34 georeferenced stations. Thirty O. niloticus specimens were collected per visit. The quality of water and O. niloticus specimens was evaluated according to the Mexican standards. The fungicide concentrations in the O. niloticus muscle and the AChE activity were measured. Seasonal and spatial variations of benomyl/carbendazim were determined using geostatistical methods (ordinary kriging [OK] and universal kriging [UK]). Geostatistical analyses demonstrated that agriculture contributes to the increased amounts of the chemical in specific areas. Even though the fungicide levels in water varied over time, they did not represent a risk to O. niloticus according to the current standards. The specimens met the quality criteria for their commercialization; however, they had low weights and small sizes. The benomyl/carbendazim concentration in the muscle increased with the size and exhibited a negative correlation with the AChE activity, thus indicating a potential harmful effect. [ABSTRACT FROM AUTHOR]

The Mayan cichlid (Cichlasoma urophthalmus), is a freshwater fish of the Cichlidae family, native to the south east of Mexico, it has potential for extensive cultivation due to its excellent meat quality and local demand. However, the nutrigenomic aspects and molecular expression of genes involved in its digestion that could contribute to its growth during the larval stage are unknown. Some enzymes such as Pepsin (PEP), pancreatic such as trypsin (TRY), Chymotrypsin [CHY] and intestinal enzymes such as Leucine aminopeptidase [ANPEP], function during larval ontogenesis and activity patterns of the key factors involved in the digestive system. For this study, 30–50 larvae were collected, which were processed with mRNA extraction techniques and cDNA synthesis by RT‐PCR using qPCR oligos designed from Oreochromis niloticus, measuring molecular expression during the initial ontogeny of C. urophthalmus. The results obtained show the molecular expression of these enzymes occurs through epigenetic factors such as changes from endogenous to exogenous feeding, presenting the activation of genes for the formation of organs of the digestive tract that allow the secretion of specific enzymes for processing and digestion of food, that can activate these genes to increase the digestion efficiency and the optimal use of nutrients. [ABSTRACT FROM AUTHOR]

Urbanization, livestock activities, and rainfall are factors that contribute to the contamination of inland water. This study aimed to determine the spatial and temporal variability of total coliforms (TCs) and fecal coliforms (FCs) in the surface water of San Pedro Lake as well as the gills and skin of Nile tilapia (Oreochromis niloticus) cultivated in the lake. The study consisted of seasonal sampling during an annual cycle. Using the multiple‐tube fermentation technique, we quantified the microbial load of TCs in the lake and fish. The median of the TC and FC groups in surface water showed differences during the seasonal cycle, in which a significant correlation was observed between rainfall and bacterial load in the lake surface water. There was a significant seasonal difference between FCs and TCs in the gills as well as in skin FCs. Anthropogenic activities in the watershed combined with rainfall influence the bacterial load of San Pedro Lake. However, the water quality is still classified as excellent and uncontaminated according to Mexican regulations with lower FC values acceptable for higher FC values. In addition, the bacterial load in tilapia from San Pedro Lake does not pose a risk to human health. Practitioner points: Watershed livestock activities combined with rainfall increase fecal matter pollution in specific areas of the lake.San Pedro Lake displays satisfactory quality for aquatic life.The median fecal coliform population in lake fish (gills and skin) differs by season. [ABSTRACT FROM AUTHOR]

In Mexico, bullfrog (Lithobates catesbeianus) production is carried out in only 35 animal production units, and improvements in its commercialization are necessary to increase demand. Faced with these challenges, innovative technological options such as Biofloc are emerging, which improve production efficiency in favor of environmental, economic and social sustainability. Thus, this study measured the effect of using reused water from a Biofloc system for tilapia (Oreochromis niloticus) culture in the intensive production of bullfrogs (Lithobates catesbeianus). With a biological material of 4,000 organisms (Lithobates catesbeianus), treatments were evaluated: T1 (drinking water), T2 (30% Biofloc reuse water), T3 (60% Biofloc reuse water) and T4 (90% Biofloc reuse water); the variables Weight Gain (WG), Specific Growth Rate (SGR), Survival Percentage (%S), Survival Rate (SR) and Feed Conversion (FC) were measured. The results were analyzed in SPSS Statistic version 27.0.0 with an ANOVA and Mauchly's test of sphericity. The results showed that intensive production of bullfrogs (Lithobates catesbeianus) with reused water from a Biofloc system of tilapia (Oreochromis niloticus) culture is feasible. [ABSTRACT FROM AUTHOR]

The production of Nile tilapia (Oreochromis niloticus) has good technological development; however, today, it is still necessary to make it more efficient. One way to increase efficiency is to prevent disease and improve the food conversion factor. Since previous investigations of tilapia microbiota detected a high proportion of organisms belonging to the order Actinomycetes, this study was to isolate, identify, and describe the species of bacteria microbiota belonging to the cultured Nile tilapia. These were done with Nile tilapia grown in a warm sub-humid climate during spring and summer seasons. The biopsy of different organs was performed for bacteriological culture and 16S rRNA sequencing analysis. From the 180 tissue samples, 49 isolates of the order Actinomycetes were obtained, representing ten species from seven genera: Microbacterium, Brevibacterium, Cellulomonas, Corynebacterium, Kocuria, Actinomyces, and Micrococcus. In spring, Microbacterium dominated, accounting for 74% of the total population. In the summer, lower diversity was observed, with 39% represented by Microbacterium. 16S rRNA sequencing analysis enabled the classification of Actinomyces neuii and Microbacterium lacticum as Kocuria varians and Agromyces indicus; the classification of Microbacterium imperiale as Rhodococcus and Micrococcus luteus was confirmed. No sequences of K. varians have been reported in fish. Microbacterium dextranoliticum showed high similarity to environmental samples. Here is the first study that analyzes the bacteria population in tilapia at the genetic level with an ecosystem approach, present in healthy cultured tilapia, indicating their beneficial associations with the host, making them candidates as probiotics, among other possible functions, applicable in tilapia cultivation. [ABSTRACT FROM AUTHOR]

Brucellosis is a zoonosis caused by bacteria of the Brucella genus. Any source of contamination that could be infectious must be monitored to reduce the risk of exposure to brucellosis, so the purpose of this work was to determine the presence of Brucella spp. on surface water and tilapia (Oreochromis niloticus) skin from a volcanic lake in Mexico. A seasonal sampling during 2016–2017 was carried out at fifteen specific sites for water sampling and five sites for the collection of tilapia fish. From all water and fish samples tested, we found only three isolates of Brucella species. We isolated and identified B. abortus from surface water through bacteriological and molecular techniques, and B. abortus and B. suis from the same tilapia skin sample. The isolated strains likely came from breeding animals that are common to the region, such as infected pigs or cattle with Brucella abortus or B. suis, respectively. A similar finding has not been reported in a water from volcanic lake or tilapia fish in Mexico. We concluded that B. abortus and B. suis are present on the surface water of the volcanic lake and tilapia skin as possible contaminants derived from biological material from cows and pigs carrying this bacterium. [ABSTRACT FROM AUTHOR]

Objective: Analyze the productive development performed by two aquatic species of recent introduction in our country, the giant freshwater prawn (Macrobrachium rosenbergii) and tilapia (Oreochromis niloticus), arguing their potential under mono and polyculture systems. Design/methodology/approximation: The bibliographic meta-analysis was developed searching information on the internet, and is presented in a chronological manner with the analysis of the technological, social and political dimensions, visualizing the benefits and advantages of applying the polyculture production system. Results: A data base on the development of the tilapia-freshwater prawn polyculture in our country was obtained. Mexico presents the required physical characteristics for both species production. Thus, polyculture allows the use of the same infrastructure, resulting in a better productivity and income. Limitations of the study/implications: Polyculture information registered on electronic media was scarce. Findings/conclusions: The polyculture production of the Malaysian prawn and tilapia is a profitable option for the aquaculture producer in tropical areas of Mexico. [ABSTRACT FROM AUTHOR]

The present study was carried out to determine the effect of tilapia Oreochromis niloticus on the physical and chemical sediment parameters on an earthen pond in monoculture (shrimp Penaeus vannamei) and co-culture (tilapia-shrimp) during the dry and wet seasons in a commercial farm during the period from mid- September to end-December 2017 and February to mid-May 2018. Chemical and physical analyses were realized on sediment samples from brackish water ponds representing shrimp farms in San Blas Nayarit, Mexico. Concentrations of organic carbon, nitrogen, potassium, magnesium and calcium were higher in co-culture ponds, and there was a tendency to a higher concentration of phosphorus and sodium in the sediment of monoculture ponds. The texture of the ponds showed a tendency in the dry season to increase the percentage of clay in coculture due to the effect of bioturbation caused by tilapia. There was no evidence of poor development of sediment quality in any treatment. It was found that tilapia was a factor that affected sediment quality, differences in growth between shrimp monoculture and tilapia-shrimp co-culture can be explained, at least in part, by differences in their sediment. [ABSTRACT FROM AUTHOR]

We tested the effects of turbidity on the prey consumption by larvae of an endemic predator (Ambystoma mexicanum) and an introduced predator (Oreochromis niloticus). Prey visibility is influenced by turbidity due to organic (algae, detritus) or inorganic (sediment) matter. We hypothesized that the axolotl would be more adversely influenced by high turbidity as compared to Tilapia, resulting in a decrease in the population of the former under natural conditions. In order to test this, we conducted prey preference experiments and tested the reactive distance of both predators at different turbidity levels. Prey species used were the cladocerans Alona glabra, Moina macrocopa, Macrothrix triserialis and Simocephalus vetulus and the ostracod Heterocypris incongruens. In both, clear and turbid waters, the fish consumed about 17.5% and 2.5%, respectively, more prey. The axolotl had a greater preference for H. incongruens and M. triserialis , and the fish for S. vetulus and M. triserialis. These results indicate that turbidity decreases the visual ability during the larval stages of A. mexicanum which in turn influences its capacity to compete against the invasive fish. Implications of these results on conservation efforts for the highly endangered Ambystoma mexicanum are discussed. [ABSTRACT FROM AUTHOR]

Monogenean parasites associated to cultured Nile tilapia Oreochromis niloticus have been co-introduced globally. In this survey, we assessed how prevalent these ectoparasites are in both rustic fish farms in Oaxaca, Mexico and in feral tilapia in the vicinity of these farms. We provide molecular data (D2 + D3 domains of the large subunit of the 28S rDNA gene and the Internal Transcribed Spacers, ITS1 + 5.8S + ITS2 rDNA) to confirm the taxonomic identity of the parasites and —eventually— to trace their anthropogenic introductions and assess their ecological impact. We demonstrate that four African monogeneans infect farmed and feral tilapia in Oaxaca. The dactylogyrids Cichlidogyrus sclerosus and C. tilapiae were recorded on farmed tilapia, and C. sclerosus on feral fish in the vicinity of farms. The gyrodactylids Gyrodactylus cichlidarum and G. yacatli infected feral tilapia, both near and further away from farms. The present survey suggests that the deficient biosafety protocols in rustic tilapia farms enable parasites to escape from fish farms and potentially spill-over to native fishes. Considering monogeneans associated to tilapia are known pathogens and very successful invaders, an effort should be made to assess their impact on native fishes — particularly in very biodiverse regions, like Oaxaca. • Monogenean parasites associated to cultured tilapia have been co-introduced globally. • We studied prevalence of these ectoparasites in both farmed and feral fish in Mexico. • African dactylogyrids and gyrodactylids infect cultured and feral tilapia. • These pathogens may spill-over to native fishes, becoming a conservation risk. [ABSTRACT FROM AUTHOR]

This study compared survival, growth, feed conversion rate (FCR) and harvested biomass of two commercial strains of tilapia (Oreochromis niloticus) cultivated in Mexico: Spring Genetic-Benchmark Holding® originated from the Genetically Improved Farmed Tilapia GIFT (Genebank: GIFT GU477624.1) and strain B from different line-breeding (Genebank: Philippines GU477626.1, Guangdong GU477627.1, and America GU477628.1). The study was performed in six geomembrane ponds (2,520 m³; 30 x 40 x 1.5 m) with supplementary aeration, in Los Pozos farm, El Rosario, Sinaloa, Mexico. In July 2016, 26,762 ± 170 fries of each strain (2.9 ± 0.1 g and 5.4 ± 0.2 cm) were cultivated in the nursery under similar conditions in triplicate at 11 ind m-3 for 34 days; then, they were transferred to the grow-out ponds and fed with 30% crude protein balanced feed (Purina®) at a rate of 12% live weight day-1 in three rations (07:00, 12:00 and 17:00 h) for 123 days. The results showed that Spring had a lower variation coefficient (VC) and higher survival, growth rate in weight, initial and final size, and harvested biomass. Survival was 30.7% greater in Spring and doubled harvested biomass (Spring 10 ± 0.8 t ha-1 vs. B strain 5 ± 4.7 t ha-1). Sixty percent of the Spring population reached a commercial weight of 500 g in day 123th of cultivation compared with 20% of B population in the same period. Except for FCR, VC was lower in the Spring strain. Differences in productive parameters were probably due to the genetic selection programs at which both strains were subjected. [ABSTRACT FROM AUTHOR]

Nile tilapia Oreochromis niloticus is one of the most economically important freshwater fish cultivated worldwide. Despite its importance and being one of the cichlid fish most studied from a parasitological point of view in Mexico, there are few studies about the ectoparasite protozoa that infect them. In this study, a total of 240 juvenile individuals of O. niloticus from an experimental culture (in Tabasco, Mexico) were examined to detect the presence of trichodinid parasites. Trichodinid parasites were impregnated with silver nitrate and stained with Harris´ hematoxylin solution for taxonomic evaluation. A disc-shaped trichodinid with a body diameter of 38 ± 3.3 μm adhesive disc diameter of 34 ± 3.3 μm and a denticulate ring diameter of 19 ± 2.1 μm was found. Trichodina centrostrigeata has been previously reported having specificity for cypriniform species, but in the present study, the Nile tilapia was reported as a new fish host and southeastern Mexico as a new geographical distribution for this parasite. [ABSTRACT FROM AUTHOR]

Cyanotoxins from toxic blooms in lakes or eutrophic reservoirs are harmful to several organisms including zooplankton, which often act as vectors of these secondary metabolites, because they consume cyanobacteria, bioaccumulate the cyanotoxins and pass them on along the food chain. Microcystins are among the most commonly found cyanotoxins and often cause zooplankton mortality. Although cyanobacterial blooms are common and persistent in Mexican water bodies, information on the bioaccumulation of cyanotoxins is scarce. In this study we present data on the bioaccumulation of cyanotoxins from Planktothrix agardhii , Microcystis sp., Cylindrospermopsis raciborskii and Dolichospermum planctonicum blooms in the seston (suspended particulate matter more than 1.2 μm) by zooplankton and fish (tilapia (Oreochromis niloticus) and mesa silverside (Chirostoma jordani) samples from Lake Zumpango (Mexico City). The cyanotoxins were extracted from the seston, zooplankton and fish tissue by disintegration using mechanical homogenization and 75% methanol. After extraction, microcystins were measured using an ELISA kit (Envirologix). Concentration of microcystins expressed as equivalents, reached a maximum value of 117 μg g−1 on sestonic samples; in zooplankton they were in the range of 0.0070–0.29 μg g−1. The dominant zooplankton taxa included Acanthocyclops americanus copepodites, Daphnia laevis and Bosmina longirostris. Our results indicate twice the permissible limits of microcystins (0.04 μg kg−1 d−1) for consumption of cyanobacterial products in whole fish tissue of Chirostoma jordani. The data have been discussed with emphasis on the importance of regular monitoring of water bodies in Mexico to test the ecotoxicological impacts of cyanobacterial blooms and the risk that consumption of products with microcystins could promote. Image 10330 • Cyanobacterial blooms result in high levels of microcystins in water, zooplankton and fish. • We observed bioaccumulation of microcystins in the primary and secondary consumers. • This is a risk to those who consume small species of fish such as Chirostoma whole and raw (dried). • Larger species, especially tilapia was not much affected and is probably a better dietary option. • Regular risk assessment of aquaculture produce, an important protein source, is recommended. [ABSTRACT FROM AUTHOR]

Trichodiniasis is one of the major diseases found in fish aquaculture worldwide causing massive fish mortality and costly effects. In this study, fresh smears of gills and skin were prepared and analyzed for the presence of trichodinids under light microscopy, revealing the presence of Trichodina pediculus Ehrenberg, 1831, T. compacta Van As & Basson, 1989, and T. nigra Lom, 1960 and T. centrostrigeata (Basson, Van As & Paperna, 1983). The effectiveness of treatment with sodium chloride and formaldehyde was evaluated for controlling infection caused by these parasites in tilapia Oreochromis niloticus Linnaeus, 1758 in aquaculture facilities in southeastern Mexico. A total of 240 fish were examined. The results showed that all doses using sodium were effective for controlling trichodinids and eliminated the parasites (100%) however, fish exposed to doses of formalin showed a higher level of stress than those exposed to sodium chloride. Bathing in formalin 0.250 mL L-1 for 10 min and 30 g L-1 of sodium chloride for 10 min, significantly reduced parasitic infection in tilapia under captive conditions (P < 0.05). This is the first record of a trichodinids species for native wild freshwater fish in a culture environment in southeastern Mexico since all previous records were from exotic cultured fish. The species found were Trichodina pediculus, T. compacta, T. nigra and T. centrostrigeata are new records of host and geographic location. [ABSTRACT FROM AUTHOR]

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The current study aimed to describe the massive mortality of farmed Nile tilapia Oreochromis niloticus associated with the monogenean Gyrodactylus cichlidarum from the northwestern Mexican Pacific coast. The ectoparasite was identified using measurements of the hard parts and compared with previous literature. Approximately 20,000 tilapias were subjected to subsequent losses over a three day period, a total of 2% of the initial seed stocked died due to the presence of this gyrodactylid parasite. The presence of the monogenean was the principal cause for chemical treatments. There is no doubt that infections by parasites have major consequences for species of small fish in culture and must consequently be considered as a fundamental factor within any system of aquaculture. A histo-pathological examination of the gills of fish showed the presence of the monogenean attached to the filaments was causing hyperplasia. The fish showed no signs of bacteria or virus infection. This study reports for the first time the occurrence of massive mortality caused by this monogenean in a tilapia fish farm in the Mexican Pacific and also extends their known geographical distribution. [ABSTRACT FROM AUTHOR]

Nile tilapia is the most commercially important fish in Chiapas as well as in other parts of the world. An understanding of parasite infection dynamics in tilapia may assist in applying proper prophylactic measures for reducing the loss of fish caused by parasitic diseases. Different environments and culture systems may imply different infection dynamics; therefore, the present study identified and compared the infection parameters (prevalence, mean abundance, and intensity) of parasites of Oreochromis niloticus cultured in floating cages and ponds. A total of 18 metazoan parasite taxa were recovered from gills, skin, fins and intestines of 310 specimens from floating cages and ponds. Fourteen species of parasites were found in floating cages: 8 monogenean species, 1 nematode, 1 digenea, 1 crustacea, 3 protozoans. In ponds, 16 parasite taxa were reported: 11 were monogeneans species, 4 protozoans and 1 crustacean. In both systems, monogeneans (Cichlidogyrus sclerosus, C. tilapiae, Gyrodactylus cichlidarum) and protozoans (Trichodina compacta) were most prevalent. Tilapia in ponds sustained higher parasitic infections than those in floating cages (p < 0.05). The Canonical Correspondence Analysis showed two groups: the first grouped the ponds, associated with high values of nitrite, nitrate, ammonia, conductivity, temperature, and the abundance of the ectoparasites C. halli, C. dossoui, Scutogyrus longicornis, C. sclerosus and T. compacta. The second group grouped the cages, associated with Clinostomum marginatum, Apiosoma piscicola, Lernea sp., and Contracaecum sp. and a high dissolved oxygen concentration. Our findings suggest that monitoring programs are required to improve the sanitary conditions of tilapia cultures in Chiapas., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Aims To identify bacterial pathogens of diseased NiIe tilapia Oreochromis niloticus and determine their virulence. Methods and Results Sixteen bacterial isolates were recovered from diseased Nile tilapias ( O. niloticus) reared in floating cages in Adolfo Lopez Mateos (ALM), Sanalona and Dique IV dams in Sinaloa, Mexico, from February to May 2009. The bacterial isolates were identified by phenotypic and molecular (rep-PCR and 16S rRNA sequencing) methods and were mostly isolated from the kidneys and the brain of tilapias. Bacterial cells and extracellular products (ECPs) of strains were characterized and used in experimental infections with sole Solea vulgaris and Mozambican tilapia Oreochromis mossambicus. The fish challenged with Aeromonas dhakensis sp. nov. comb nov , Pseudomonas mosselii and Microbacterium paraoxydans (3·1 × 106 CFU g−1) exhibited mortality between 40 and 100% starting at 6 h postinoculation. The ECPs displayed gelatinase, haemolytic and cytotoxic activity, causing the total destruction of the HeLa cell lines. Conclusions Aeromonas dhakensis and Ps. mosselii were virulent to O. mossambicus, whereas Mic. paraoxydans displayed virulence to S. vulgaris. Significance and Impact of the Study This the first time that Aeromonas dhakensis and Ps. mosselii are reported as pathogens to tilapia and Mic. paraoxydans was isolated from fish; then, these fish pathogens could be a threat to farmed Nile tilapia in Mexico. [ABSTRACT FROM AUTHOR]

Objective. Determine the presence and prevalence of Mycobacterium spp., at tilapia (Oreochromis niloticus) farms in the municipality of Champotón, Campeche, Mexico. Materials and methods. The collection of organisms was conducted in three farms of Nile tilapia at Champotón township, Campeche, Mexico. The organisms were examined externally and internally and a kidney sample was inoculated in different growth media: Löwestein-Jensen, TCBS, KF and TSA. The plates were incubated at 35°C for 24 to 48 hours, the organs were fixed in 10% buffered formalin to be processed for routine histology for further analysis. Likewise, bacterial culture samples and tissue were stained through the Ziel-Neelsen technique to observe the presence of acid-fast bacilli. Results. The results suggest that the presence of Mycobacterium spp., is constant and its high prevalence and could be an undermining issue in the profitability of this culture. Conclusions. The presence of Mycobacterium spp., represents a risk for tilapia culture in the municipality of Champotón, it is a very persistent and difficult to eradicate disease once an outbreak has occurred, reason for which it is important to bring more detailed studies of the presence of this bacterial genus, as well as prevention and spread of this pathogen in adjacent cultures. [ABSTRACT FROM AUTHOR]

Studies on age and growth in fishes are essential to establish models on population dynamics. The previous issues were determined in this study by scale growth analyses. Between September 2003 and May 2004, 382 organisms were captured using gill and atarraya nets. Eight samples were developed every month a long this study. Standard length in centimeters (Le), total weight in grams (Pt), scale length in centimeters (Lesc) and growth rings were determined. The size and weight ranged from 38 to 232mm (Le) and 8.7 to 311.9g (Pt), respectively. The growth rings analyses reveal four age groups, being the second group the most representative with 34.3% of the total sampled. The scale ring analyses showed two growth rings, one develops between November-January and the other between April-May, in good correlation with low temperature and gonad development, respectively. The growth parameters were established as: L∞=281.1mm, W∞=877.1g, K=0.33 and T0=0.88year-1. The growth curves based on length and weight were described by using the von Bertalanffy model: Le =28.11[1-e-0.33(t+0.88)] and Pt=877.17[1-e-0.33(t+0.88)]³. Finally, it is concluded that commercial catches in this dam are between a year and year and half-old when exploited. Rev. Biol. Trop. 59 (2): 761-770. Epub 2011 June 01. [ABSTRACT FROM AUTHOR]

Abstract: Local communities in Mexico consume Jatropha platyphylla seeds after roasting. The kernels of J. platyphylla contained ca. 60% oil and were free of phorbol esters. The kernel meal of this Jatropha species contained trypsin inhibitor, lectins and phytate. However, trypsin inhibitor and lectins are heat labile so this explains why the local people can eat roasted seeds without ill effects. Heat-treated J. platyphylla kernel meal (JPKM) was free of trypsin inhibitor and lectin activities. Crude protein content of JPKM was 75%. Heated JPKM and soybean meal were included in a standard diet (crude protein 36%) for Nile tilapia (Oreochromis niloticus) to replace 50% of the fish meal protein. The growth of fish in all the three groups was statistically similar and the blood biochemical parameters that serve as biomarkers for toxicity were within the normal ranges. This is the first study that confirms the non-toxic nature of J. platyphylla. [ABSTRACT FROM AUTHOR]

Abstract  Several tilapia species in Mexican reservoirs have been used as food source for more than 40 years but little effort has been devoted to the conservation and genetic selection of those species. Our objective was to evaluate genetic variability in feral (n = 59) and hatchery-produced (n = 58) Oreochromis niloticus stocked in the Benito Juarez dam. Allozyme analyses for 13 enzymatic systems and general proteins yielded 27 genetic loci. Seventeen loci were polymorphic in at least one sample. The observed heterozygosity was lower than expected and the imbalance in the Hardy–Weinberg equilibrium in almost all loci was caused by heterozygote deficiency. The inbreeding coefficient was 84%. Although the evidence suggests moderate genetic differentiation, it is probable that a great proportion of the source of hatchery organisms is from feral organisms. According to our results, management of the hatchery strain is inadequate, therefore other breeding strategies are needed to increase the genetic variability of O. niloticus from Oaxaca. [ABSTRACT FROM AUTHOR]

Vitellogenin (Vtg), 17β-estradiol (E2) and testosterone (T) were used as biomarkers of endocrine disruption in mature male nile tilapia ( Oreochromis niloticus) from three lakes (Rio, Enmedio and Limon) in Chiapas, Mexico. Vitellogenesis induction was found in tilapias from Rio and Limon, moderately high E2 levels in Rio and Limon tilapias, compared with controls (cultured tilapias). Significant correlations between benzo( a)pyrene (BaP) metabolites and hexachlorobenzene (HCB) with Vtg and E2 were found. The results of this study indicate that endocrine disruption exists in tilapias from Rio and Limon lakes, and that exposure to HCB and B aP could be causing these alterations. [ABSTRACT FROM AUTHOR]

Age and growth of Nile tilapia (Oreochromis niloticus) were determined using 1 039 specimens collected in a tropical shallow lake of Mexico, from January to December 1993. Standard length of females ranged from 9.0 to 16.5 cm and males from 8.9 to 14.8 cm. The standard length-weight relationships for all individuals was BW=0.1207 SL2.469. The age data, derived from opercular bone readings, were used to estimate the growth parameters of the von Bertalanffy equation: L∞=17.88 cm, K=0.3409, to=-1.543, and W∞=149.21 g. The oldest male and female were 2.5 years old. The sex ratio (female:male) was of 1:1 (χ²=0.02, p>0.05). [ABSTRACT FROM AUTHOR]

Species that invade a new environment often may lead to population declines of endemic species. Here I document the invasions of an African cichlid (genus Oreochromis) in 1988 and the Mexican Astyanax fasciatus (Characidae) in 1996 into Laguna Chichancanab (Yucatan, Mexico), and the impact on an endemic Cyprinodon species flock and the poeciliid Gambusia sexradiata. After the invasion of Astyanax fasciatus, their relative abundances decreased enormously, most likely caused by predation on the fry. One species, Cyprinodon simus, might have even gone extinct or just occurs in extremely reduced numbers. Furthermore, it was observed that the percentage abundance of the detritivorous Cyprinodon beltrani increased significantly, in contrast to all other Cyprinodon species. This study also revealed that infestation by metacercaria (black spots) of an ectoparasitic trematode and of an endoparasitic nematode increased in the Cyprinodon spp. following the introduction of Oreochromis. Whereas the infestation by trematodes decreased after a period of 6 years, the prevalence and intensity of infestation by nematodes stayed at a high level. In contrast, in G. sexradiata the parasite load remained always very low. [ABSTRACT FROM AUTHOR]

The effects of the oil industry and environmental pollutants present in four lakes from Reforma, Chiapas, Mexico, were assessed via ethoxyresorufin O-deethylase activity (EROD), PAH metabolites, and butyrylcholinesterase activity (BChE) in Nile Tilapia, Oreochrornis niloticus. Fish were collected during two seasons (the rainy season in September 2000 and the dry season in May 2002) from the lakes Caracol, Rio, Enmedio, and Limón. Fish were sacrificed and EROD activities, hydrocarbons, organochlorine pesticide and heavy metal concentrations were determined in the liver, while PAH metabolites and cholinesterase activity were measured in bile and muscle, respectively. Hydrocarbon concentrations in fish liver were moderately high, as compared with results reported for the other species in different coastal ecosystems in Mexico. The highest concentrations of total hydrocarbons were found in fish captured in Lake Limón, and the lowest in Lake Caracol. The highest EROD and PAH metabolites were found in fish collected from Limón and Enmedio lakes. A Spearman test showed significant negative correlations between EROD and BChE activity with fish weight. EROD correlated with total hydrocarbons, the metabolites of pyrene and benzo[a]pyrene, and negatively with polychlorinated biphenyls (PCBs), endosulphan, hexachlorobenzene (HCB), and pentachloroanisol. BChE activity in the four lakes was lower than the activity measured in laboratory cultured tilapias, indicating the presence of anti-cholinergic pollutants in the area; Caracol was the lake with the lowest enzyme activity. This study demonstrated that high concentrations of contaminants can cause effects on fish metabolism, and that tilapia can be used as a test organism in tropical ecosystems. [ABSTRACT FROM AUTHOR]

• The ectoparasitic burden have negative effect on condition factor of the Nile tilapia. • The fish with low K values (K ≤ 0.25) were associated with a high ectoparasitic burden (295 ± 191). • Cichlidogyrus genus, Trichodina sp. and G. cichlidarum showed a negative effect in K values. • Ectoparasites can be responsible of loss up to 12–15 % in profit margin per ton of fish. Nile tilapia (Oreochromis niloticus Linnaeus, 1758) is one of the most important aquaculture species in the world, and, when introduced, the ectoparasites of Nile tilapia have followed. Currently, farmers worldwide consider these ectoparasites harmless, but intensities can reach up to 1000 individuals per fish in tropical regions. In this cross-sectional study, we used the condition factor to estimate the potential effects of low (45 ± 31 ectoparasites per fish) and high (295 ± 191) ectoparasitic burdens across 28 tilapia farms and included the analysis of the effects of 44 management and environmental variable from the farms. A stepwise procedure in a multiple linear regression analysis retained the variables that explained the most variance, which was the ectoparasitic burden (57 %). We found significantly higher values of the condition factor in Nile tilapia with low ectoparasitic burden than in those with high ectoparasitic burden. Additionally, Nile tilapia with a high ectoparasitic burden weighed less than half than those with a low burden (102 ± 105 g versus 230 ± 128 g, respectively). We also found a significant non-linear, negative relationship between the ectoparasitic burden and the relative condition factor values per fish, which was most likely due to an increase in gill mucus caused by the ectoparasitic burden that depleted energy in the Nile tilapia. The economic consequence of the ectoparasitic burden translated roughly into a loss up to 12–15 % in profit margin per ton of fish, based on the price of Nile tilapia in the Mexican market. [ABSTRACT FROM AUTHOR]

In the present study, microplastics (MPs) and metal concentrations were studied in the widely consumed tilapia (Oreochromis niloticus) fishes (n = 15) collected from a metropolitan reservoir of the Atoyac River basin, Mexico. Nearly 139 fibers were extracted from the gastrointestinal tracts and assessed using optical microscopy to evaluate their physical characteristics. The colour distribution of the fibers was mainly black (40%), blue (19%), red and white (14%). SEM images represented the surface morphology, while the elemental composition of the fibers was studied using EDX spectra. Polymer characterization using μFTIR aided in confirming the fibers as plastics (polyamide, polyester, and synthetic cellulose) and non-plastics (natural cellulose). Henceforth, ∼33% of the fibers, provisionally thought to be plastics, were natural fibers. The total metal concentrations were higher in the liver (259.24 mg kg−1) than the muscle (122.56 mg kg−1) due to diverse metabolic functions in the hepatic tissues. Human health risk assessment in terms of Hazard Index (HI) presented Pb and Zn values above unity in both adults and children, prompting regulatory measures. Statistical tests between MPs and fish biometry did not present any substantial correlations. The present study also affirmed that the presence of MPs and metals in fishes of a highly contaminated region is not only governed by their bioavailabilities, but also on the physiological characteristics of the individual organism. Image 1 • Microplastic prevalence of 53.67% was found in Freshwater Tilapia from a metropolitan reservoir. • HI values > 1 for Pb and Zn in adults and children prompt remedial actions. • No significant correlations between MPs and fish biometry/metal levels. [ABSTRACT FROM AUTHOR]