Fine tuning for the tropics: application of eDNA technology for invasive fish detection in tropical freshwater ecosystems

Invasive species pose a major threat to aquatic ecosystems. Their impact can be particularly severe in tropical regions, like those in northern Australia, where >20 invasive fish species are recorded. In temperate regions, environmental DNA (eDNA) technology is gaining momentum as a tool to detect aquatic pests, but the technology's effectiveness has not been fully explored in tropical systems with their unique climatic challenges (i.e. high turbidity, temperatures and ultraviolet light). In this study, we modified conventional eDNA protocols for use in tropical environments using the invasive fish, Mozambique tilapia (Oreochromis mossambicus) as a detection model. We evaluated the effects of high water temperatures and fish density on the detection of tilapia eDNA, using filters with larger pores to facilitate filtration. Large-pore filters (20 μm) were effective in filtering turbid waters and retaining sufficient eDNA, whilst achieving filtration times of 2-3 min per 2-L sample. High water temperatures, often experienced in the tropics (23, 29, 35 °C), did not affect eDNA degradation rates, although high temperatures (35 °C) did significantly increase fish eDNA shedding rates. We established a minimum detection limit for tilapia (1 fish/0.4 megalitres/after 4 days) and found that low water flow (3.17 L/s) into ponds with high fish density (>16 fish/0.4 megalitres) did not affect eDNA detection. These results demonstrate that eDNA technology can be effectively used in tropical ecosystems to detect invasive fish species. © 2016 John Wiley & Sons Ltd.

Cage culture of Nile Tilapia

Nile tilapia (oreochromis niloticus) a fish introduced into Lake Victoria to boost the fishery industry after the Nile perch lates niloticus fed on the native tilapiine oreochromis esculentus and Oreochromis viabillis to almost extinction has been proposed to be cultured in the Lake Victoria. The fact sheet explains the culture of Nile tilapia in cages in Lake Victoria, Uganda.

The state and known impacts of fish species transferred to or within continental Africa

Fish introductions have been made from small fish ponds to the largest lakes in Africa. The primary intent of these introductions has been to sustain or increase fish production, although some introductions have been made to develop sport fisheries and to control unwanted organisms. Some of these introductions have fulfilled their objective in the short term, but several of these "successful" introductions have created uncertainties about their long term sustainability. Lates niloticus, Oreochromis niloticus, O. leucostictus, Tilapia melanopleura and T. zilli were introduced into lakes Victoria and Kyoga in 1950s and early 1960s. By the 1980s O. niloticus and O. niloticus dominated the fisheries of these lakes, virtually eliminating a number of endemic fish species. The loss of genetic diversity of the fish in the worlds second largest lake has also been accompanied by a loss of trophic diversity. The transformation of the fish community has, in Lake Victoria coincided with a profound eutrophication (algal blooms, fish kills, hypolimnetic anoxia) which might be related to alterations of the lake's food-web structure. In contrast, the introduction of a planktivore, Limnothrissa miodon into Lake Kivu and the Kariba reservoir has established highly successful fisheries with little documented effect on the pre-existing fish community or trophic ecology of the lakes. The highly endemised species-rich African Great lakes may be particularly sensitive to species introductions and require special consideration and caution when introductions are contemplated because species extinctions, introgressive hybridization and ecosystem alterations may occur following fish introductions.

A multi-component pheromone in the urine of dominant male tilapia (Oreochromis mossambicus) reduces aggression in rivals

Males often use scent to communicate their domi- nance, and to mediate aggressive and breeding behaviors. In teleost fish, however, the chemical composition of male pher- omones is poorly understood. Male Mozambique tilapia, Oreochromis mossambicus, use urine that signals social status and primes females to spawn. The urinary sex pheromone di- rected at females consists of 5β-pregnane-3α,17α,20β-triol 3- glucuronate and its 20α-epimer. The concentration of these is positively correlated with male social rank. This study tested whether dominant male urine reduces aggression in receiver males, and whether the pregnanetriol 3-glucuronates also re- duce male-male aggression. Males were allowed to fight their mirror image when exposed to either: i) water control or a chemical stimulus; ii) dominant male urine (DMU); iii) C18- solid phase (C18-SPE) DMU eluate; iv) C18-SPE DMU eluate plus filtrate; v) the two pregnanetriol 3-glucuronates (P3Gs); or vi) P3Gs plus DMU filtrate. Control males mounted an increas- ingly aggressive fight against their image over time. However, DMU significantly reduced this aggressive response. The two urinary P3Gs did not replicate the effect of whole DMU. Neither did the C18-SPE DMU eluate, containing the P3Gs, alone, nor the C18-SPE DMU filtrate to which the two P3Gs were added. Only exposure to reconstituted DMU (C18-SPE eluate plus filtrate) restored the aggression-reducing effect of whole DMU. Olfactory activity was present in the eluate and the polar filtrate in electro-olfactogram studies. We conclude that P3Gs alone have no reducing effect on aggression and that the urinary signal driving off male competition is likely to be a multi-component pheromone, with components present in both the polar and non-polar urine fractions.

Fishing effort and fish yield over a 15 year period on Lake Victoria, Uganda: management implications

The National Fisheries Resources Research Institute (NaFIRRI), the Directorate of Fisheries Resources (DiFR), the Local Government fisheries staff and those from the Beach Management Units (BMUs) of the riparian districts to Lake Victoria regularly and jointly conduct Frame and Catch Assessment Surveys. The information obtained is used to guide fisheries management and development. We reveal the trends in the commercial fish catch landings and fishing effort on the Uganda side of Lake Victoria, over a 15 year period (2000-2015) and provide the underlying factors to the observed changes. The contribution of the high value large size species (Nile perch and Tilapia) to the commercial catch of Lake Victoria has significantly reduced while that of the low value small size species, Mukene has increased over a ten year (2005-2015)period. The information is intended to update and sensitize the key stakeholders on the status of the Lake Victoria fisheries. In addition, the information provided is expected to guide policy formulation and management planning by the fisheries managers at all levels including the BMUs and Landing Site Management Committees (LSMCs), the Local government fisheries staff and the Directorate of Fisheries Resources. The information is anticipated to create awareness among the lakeside fisher communities to reverse the current trend in fish declines.

Amino acid composition of processed fish silage using different raw materials

The objective was to evaluate amino acid composition of silages produced from three raw materials. Commercial marine fish waste, commercial freshwater fish waste, and tilapia filleting residue were used to produce fish silage by acid digestion (20 ml/kg formic acid and 20 ml/kg sulfuric acid) and anaerobic fermentation (50 g/kg Lactobacillus plantarum, 150 g/kg sugar cane molasses). Protein content and amino acid composition were determined for raw materials and silage. Marine fish waste had higher crude protein content (776.7 g/kg) compared to freshwater fish waste (496.2 g/kg) and tilapia filleting residue (429.9 g/kg). All silages lacked up to three amino acids for each product according to FAO standards for essential amino acids. However, considering as the limiting factor only the amino acids below the 30% minimum requirement for fish in general, all products were satisfactory with respect to essential amino acids. Therefore, the results suggest that all products investigated are appropriate for use in balanced fish diets. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Characterization and evaluation of the impact of feed management on the effluents of Nile tilapia (Oreochromis niloticus) culture

O objetivo deste trabalho foi avaliar o efeito da utilização de diferentes manejos alimentares: alimento natural, ração peletizada, extrusada ou farelada, sobre a qualidade da água dos efluentes gerados em uma criação de tilápia do Nilo (Oreochromis niloticus). O experimento foi desenvolvido durante 19 semanas em doze viveiros de 300 m², com renovação contínua de água, povoados com juvenis machos de tilápia do Nilo na densidade de 1,7 peixes m-2. As rações isoproteícas (30% de proteína bruta) e isoenergéticas (3.000kcal de energia digestível) foram fornecidas duas vezes ao dia. Quanto ao tratamento alimento natural, foi utilizado esterco de galinha poedeira. Semanalmente, foram aferidos na água de abastecimento e nos efluentes, temperatura, oxigênio dissolvido, pH, fósforo total, nitrogênio total, clorofila a e material em suspensão. de maneira geral, houve piora na qualidade da água dos efluentes de todos os tratamentos estudados, em comparação a água de abastecimento, evidenciando o impacto ambiental desta atividade produtiva, podendo levar a eutrofização dos corpos d'água receptores.

Hematology and productive performance of nile tilapia (Oreochromis niloticus) naturally infected with Flavobacterium columnare

Columnaris disease is one of the main causes of mortality in tilapia rearing and is responsible for large economic losses worldwide. Hematology is a tool that makes it possible to study organisms' physiological responses to pathogens. It may assist in making diagnoses and prognoses on diseases in fish populations. The hematological variables of nile tilapia were studied in specimens with a clinical diagnosis of columnaris disease and in specimens that were disease-free. The total erythrocyte count, hemoglobin rate, hematocrit percentage, mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular volume (MCV), organic defense blood cell percentages (leukocytes and thrombocytes) and hepatosomatic and splenosomatic index were determined. The results showed that there were changes in the erythrocytic series and in organic defense blood cells, in the fish infected with the bacterium, with reductions in erythrocytic variables and significant increases in the numbers of circulating lymphocytes and neutrophils.

ACUTE TOXICITY of SODIUM SELENITE and SODIUM SELENATE TO TILAPIA, Oreochromis niloticus, FINGERLINGS

Selenium is an essential nutrient for many organisms, including fish. It can be released in the water by natural processes of dissolving rocks and minerals, and by the wastewater from industries and agricultural activities, which can increase its concentration in the environment, leading to toxic effects to the aquatic biota. Median Lethal Concentrations (LC(50-96h)) of two forms of selenium were estimated to fingerlings of Nile tilapia Oreochromis niloticus, focusing on estimating indicators for future environmental risk assessments in aquatic ecosystems contaminated with those elements, particularly for evaluate sources of water quality suitable for rearing tilapia. The results were: LC(50-96h) of sodium selenite (Na(2)SeO(3)) = 4.42 mg Se(4+) L(-1), and LC(50-96h) of sodium selenate (Na(2)SeO(4)) = 14,67 mg Se(6+) L(-1). According to those data, it was possible to classify sodium selenite as highly toxic and sodium selenate as moderately toxic to fingerlings of tilapia.

Selenite and Selenate Effects on Mercury (Hg2+) Uptake and Distribution in Tilapia, Oreochromis niloticus L., Assessed by Chronic Bioassay

Aquatic organisms are considered excellent biomarkers of mercury (Hg) occurrence in the environment. Selenium (Se) acts in antagonism to this metal, stimulating its elimination, and reducing its toxicity. In this paper, tilapia (Oreochromis niloticus) were chronically acclimated in sub-lethal Hg2+, Hg2+ + Se4+ and Hg2+ + Se6+ concentrations. Distribution and bioaccumulation of both elements were evaluated in fish tissues. The kidney was the main target of the Hg and Se uptake, and the presence of Hg induced the Se hepatic elimination. The Hg bioaccumulation in the gill, spleen and heart were higher in the presence of Se6+ than in the presence of Se4+.

Toxicity of the therapeutic potassium permanganate to tilapia Oreochromis niloticus and to non-target organisms Ceriodaphnia dubia (microcrustacean cladocera) and Pseudokirchneriella subcapitata (green microalgae)

Potassium permanganate is a chemical compound widely used in aquaculture for the control and removal of parasites, and in the prevention of diseases caused by bacteria and fungi. However, this compound can be toxic to fish, being a strong oxidant. Moreover, there is no consistent information in the literature about its toxicity to non-target organisms. The purpose of this study was to evaluate the acute toxicity (LC50;96h) of potassium permanganate for tilapia, Oreochromis niloticus, and to determine its toxic effects on nontarget organisms using ecotoxicological assays performed with the microcrustacean Ceriodaphnia dubia and with the green microalgae Pseudokirchneriella subcapitata. The results showed that the concentration of 1.81 mg L-1 of potassium permanganate caused acute toxic effect in tilapia fingerlings. The ecotoxicological assays demonstrated that concentrations above 0.12 mg L-1 can cause chronic toxic effects on non-target organisms, indicating possible deleterious effects on the food chain of the aquatic ecosystem that may receive the discharge of effluents released by fish cultures treated with this chemotherapy. All toxic concentrations determined in this study were below those recommended in the literature for the use of this chemotherapy in fish cultures, demonstrating that this type of therapy should be more carefully considered in order to avoid damage to the treated fish and to the environment. (C) 2011 Elsevier B.V. All rights reserved.

Eutrophization process in a system used for rearing the nile tilapia (Oreochromis niloticus), São Paulo State, Brazil

Dos vários aspectos inerentes à aquicultura, a eutrofização devido ao manejo alimentar tem efeitos diretos no viveiro e no sistema aquático no qual ele está inserido. Neste contexto, o presente estudo objetivou analisar a qualidade da água do sistema aquático de um viveiro. em uma criação de tilápia do Nilo (Oreochromis niloticus), foram realizadas coletas de água em seis pontos do sistema aquático, durante um ciclo de engorda (seis meses), compreendendo a água de abastecimento, o viveiro, o efluente e sua mistura com as águas do sistema. Das variáveis ambientais analisadas nas amostras, a aplicação de uma análise de componentes principais revelou que as concentrações de clorofila-a, nitrogênio e fósforo total e o teor de matéria orgânica foram responsáveis pelas variações observadas no sistema durante o cultivo. Variações extrínsecas ao viveiro de cultivo deixaram evidente que o manejo deve ser aplicado a todo o sistema aquático, minimizando efeitos ambientais negativos.

The effect of increased light intensity on the aggressive behavior of the Nile tilapia, Oreochromis niloticus (Teleostei: Cichlidae)

Animals show behavioral and physiological changes that emerge in response to environmental perturbations (i.e., emergency life-history stages). In this study, we investigate the effects of light intensity on aggressive encounters and social stability in groups of adult male Nile tilapia, Oreochromis niloticus (Linnaeus, 1758). The study compared the behavior observed under low (280.75 ± 50.60 lx) and high (1394.14 ± 520.32 lx) light intensities, with 12 replicates for each treatment. Adult fish were isolated in 36-L aquaria for 96 hours, and three males were grouped for 11 days in 140-L aquaria. Agonistic behavior was video-recorded (10 min/day) on the 3rd, 5th, 7th, and 9th day to quantify aggressive interactions and social stability. There was an effect of light intensity and day of observation on the total number of agonistic behaviors performed by the fish group. Besides, increased frequency of aggressive interactions (the sum of the four sessions) by the alpha, beta and gamma fish occurred at the higher light intensity. The dominance ranks of the fish remained unchanged across the observation sessions under both the low and high light intensities. We concluded that enhanced light intensity has a cumulative effect that increases the aggressiveness of the Nile tilapia but that this effect is not sufficiently strong to destabilize the social hierarchy.

Influence of levels and forms of selenium associated with levels of vitamins C and E on the performance, yield and composition of tilapia fillet

Objetivou-se avaliar a influência da vitamina C (VC), vitamina E (VE) e de duas formas de selênio sobre o desempenho, rendimento e qualidade do filé de tilápia Nilótica. O experimento foi realizado num delineamento inteiramente casualizado composto por seis tratamentos, os quais foram constituídos pela adição de 100, 200 e 400 mg kg-1 das vitaminas C e E, associados com 0,1, 0,2 e 0,4 mg kg-1 de duas formas de selênio. Cada tratamento foi constituído por cinco repetições de 30 peixes cada. A dieta com 200 mg kg-1 de VC e VE + 0,2 mg kg-1 de selênio orgânico proporcionou ganho de peso, comprimento corporal e fator de conversão alimentar semelhantes aos tratamentos com 400 mg kg-1 de VC e VE + 0,4 mg kg-1 de selênio orgânico ou inorgânico. A adição de selênio orgânico à dieta melhorou o ganho de peso e o fator de conversão alimentar em comparação com o selênio inorgânico. A dieta com 0,2 mg kg-1 de selênio orgânico apresentou nível de glutationa peroxidase igual ao da dieta com 0,4 mg kg-1 de selênio inorgânico. Os rendimentos de carcaça e filé não foram influenciados pelos tratamentos, entretanto houve efeito dos tratamentos na composição química do filé.

Anaerobic bio-digestion of concentrate obtained in the process of ultra filtration of effluents from tilapia processing unit

The objective of the present study was to evaluate the efficiency of the process of biodigestion of the protein concentrate resulting from the ultrafiltration of the effluent from a slaughterhouse freezer of Nile tilapia. Bench digesters were used with excrements and water (control) in comparison with a mixture of cattle manure and effluent from the stages of filleting and bleeding of tilapias. The effluent obtained in the continuous process (bleeding + filleting) was the one with highest accumulated population from the 37th day, as well as greatest daily production. Gases composition did not differ between the protein concentrates, but the gas obtained with the use of the effluent from the filleting stage presented highest methane gas average (78.05%) in comparison with those obtained in the bleeding stage (69.95%) and in the continuous process (70.02%) or by the control method (68.59%).