Observations on metal concentrations in commercial landings of two species of tilapia (Oreochromis mossambicus and Oreochromis niloticus) from reservoirs in six river basins in Sri Lanka

Samples of the muscle of two species of tilapia (Oreochromis mossambicus and O. niloticus; 17-20 cm length) were obtained from at least one reservoir in each of the six river basins (Aruvi Aru, Kala Oya, Kirindi Oya, Ma Oya, Mahaweli, and Walawe Ganga catchments) in Sri Lanka. The metals Ca, Cu, Fe, K, Mg, Mn, Na, and Zn were consistently detected in the muscle tissue. Overall, there were few differences in the concentration of metals between the two species of fish, although there were also some statistically significant differences (p < 0.05) in the concentrations of some metals in fish obtained from some of the reservoirs. Aruvi Aru stands out as a river basin in which the two fish species have significantly lower concentration of metals when compared to other river basins. The concentration of the metals studied were below WHO and FSANZ guideline values for fish, suggesting that the consumption of the metals found in tilapia from these reservoirs poses little risk to human health.

Genetic changes, intra- and inter-specific introgression in farmed Nile tilapia (Oreochromis niloticus) in Thailand

Fourteen microsatellite loci were used to examine genetic changes of four strains in Nile tilapia (Oreochromis niloticus) derived from genetically improved farmed tilapia (GIFT) and two strains derived from a local Chitralada strain of Nile tilapia in Thailand. Reference populations, including the ninth generation of GIFT strain, the original Chitralada strain, two conspecific reference populations from Ivory Coast and Uganda, and one population each of Oreochromis mossambicus and Oreochromis aureus, were also examined. Despite minor genetic changes, three of the four GIFT-derived populations retained their purity as GIFT while genetic variation did not decline. One of the GIFT-derived populations showed high levels of introgression from the Chitralada strain. Likewise, introgression from GIFT to the Chitralada-derived populations was seen. Inter-specific introgression from O. mossambicus was observed in the GIFT reference population and one of the Chitralada-derived strains. Introgression from O. aureus was detected in one of the GIFT-derived populations with a history of intensive inter-strain crossing. However, the introgression resulted in elevated genetic variation relative to the Chitralada original strains.

Sex reversal in Nile tilapia (Oreochromis niloticus Linnaeus) by androgen immersion

Two experiments were conducted to investigate the efficacy of three androgens applied through immersion treatments on the sex ratio of Nile tilapia (Oreochromis niloticus L.) fry. In experiment 1, 14 days post-hatching (DPH) larvae were exposed to a single immersion treatment in 17α-methyltestosterone (MT), 17α-methyldihydrotestosterone (MDHT) or 17α-ethynyltestosterone (ET) at 200, 600 and 1800 μg L⁻¹ over 4 h (130 larvae per treatment). In experiment 2, Nile tilapia larvae were exposed to the higher androgen concentration (1800 μg L⁻¹) applied as either a single immersion (14 DPH) or double immersion (10 and 14 DPH) over 4 h (125 larvae per treatment). Change in sex proportion within each experiment as well as between experiments was analysed by the chi-square test. In experiment 1, MT, MDHT and ET were equally effective in significantly increasing the proportion of males when applied at 1800 μg L⁻¹ (86.0%, 90.0% and 86.7% respectively). At 200 μg L⁻¹ none of the androgens altered sex ratio. At 600 μg L⁻¹, only MDHT slightly, but significantly skewed the sex ratio towards males (73.0%). In experiment 2, a single immersion treatment at 14 DPH (1800 μg L⁻¹) significantly increased the proportion of males, but at this time the response was significantly hormone dependent (MDHT, 100.0%; MT, 91.6%; ET, 76.9%). When compared with a single immersion, two-immersion treatments significantly increased the proportion of males in the MT-treated group (from 91.6% to 98.3%), decreased the proportion of males in the MDHT group (from 100.0% to 93.4%) and had no significant effect the ET-treated group (change from 76.9% to 82.5%). The overall comparison of the sex ratio among same treatments from different experiments (a single immersion in 1800 μg L⁻¹) was not significantly different.

Tecnica simples de marcacao externa de reprodutores de tilapia nilotica (Oreochromis niloticus)

With the goal of organizing a control program of Nile tilapia (Oreochromis niloticus) reproduction in laboratory, a tecnique with ceramic pearls held on dorsal musculature by transfixion with flexible sintetic string was developed. Sixty fishes with 12g average weight and 60 with 19g average weight were used. Marking was done on three positions: frontal (F), median (M), and caudal (C). Different combinations of three collored pearls were fixed on the right side (defining number), and were linked to only one pearl in the left side (defining sex), with a slack of about 1.5cm to prevent growth damage. The animals were individually identified and weigthed at 30, 60 and 130 days after surgery. Results showed that both F and M positions allowed normal growth and reproductive behavior, whereas the C position induced mortality and loss of marker in some specimens. The M position is recomended as the best, or the intermediate between F and M positions.

Tecnica simples para identificacao de femeas de tilapia nilotica (Oreochromis niloticus) realizando incubacao oral dos ovos

In aquaculture laboratories which work with Nile tilapia (Oreochromis niloticus) reproduction and use crystalline water, is frequently necessary to verify whether the females are incubating orally the eggs. The identification of the females when there is not know-how is difficult and slow, and in most cases is stressful and damage the eggs. This study describes a simple technique, using a mirror, to identify Nile tilapia incubating eggs orally in crystalline water. The results showed that is possible to identify the females which are incubating orally with 100% efficiency.

Validation of the aceto-carmine technique for evaluating phenotypic sex in Nile tilapia (Oreochromis niloticus) fry

In this study a method for evaluating phenotypic sex in Nile tilapia was validated. A technique that uses aceto-carmine squash mounts to stain the entire gonadal tissue for microscopic examination (Method 2- squash mounts) was compared with a technique based on traditional histology. Approximately 2600 Nile tilapia fry weighing and measuring, respectively, between 0.25-2.50g and 26-53mm, aged 35 to 60 days after hatch (DAH), were sexed using this methodology. In situ microscopic examination on the gonads was also performed. A reliable sexing using squash mount was possible with fish weighing more than 0.500g, 45-47 DAH. Results from microscopic observation using the aceto-carmine stain coincided 100% with the histological examination. Male gonadal tissue was characterized by the presence of cysts containing spermatogonia and spermatocytes, while females were easily identified by the presence of oocytes at the perinucleolar stage. The technique proved to be efficient not only in terms of evaluating sex proportion in fish but also because it allows immediate evaluation of gonadal sex and demands less time and labour.

Efeitos da tilápia do Nilo (Oreochromis niloticus) e do enriquecimento por nutrientes sobre a comunidade planctônica em um lago artificial no semi-árido brasileiro

The major aim of this study was to test the hypothesis that the introduction of the Nile tilapia (Oreochromis niloticus) and the enrichment with nutrients (N and P) interact synergistically to change the structure of plankton communities, increase phytoplankton biomass and decrease water transparency of a semi-arid tropical reservoir. One field experiment was performed during five weeks in twenty enclosures (8m3) to where four treatments were randomly allocated: with tilapia addition (T), with nutrients addition (NP), with tilapia and nutrients addition (T+NP) and a control treatment with no tilapia or nutrients addition (C). A two-way repeated measures ANOVA was done to test for time (t), tilapia (T) and nutrient (NP) effects and their interaction on water transparency, total phosphorus, total nitrogen, phytoplankton and zooplankton. The results show that there was no effect of nutrient addition on these variables but significant fish effects on the biomass of total zooplankton, nauplii, rotifers, cladocerans and calanoid copepods, on the biovolume of Bacillariophyta, Zygnemaphyceae and large algae (GALD ≥ 50 μm) and on Secchi depth. In addition, we found significant interaction effects between tilapia and nutrients on Secchi depth and rotifers. Overall, tilapia decreased the biomass of most zooplankton taxa and large algae (diatoms) and decreased the water transparency while nutrient enrichment increased the biomass of zooplankton (rotifers) but only in the absence of tilapia. In conclusion, the influence of fish on the reservoir plankton community and water transparency was greater than that of nutrient loading. This finding suggests that biomanipulation should be a greater priority in the restoration of eutrophic reservoirs in tropical semi-arid regions

Ecologia do fitoplâncton impactado por cultivo de tilápia do Nilo, oreochromis niloticus, em tanques-rede no açude Ministro João Alves, Parelhas, Rio Grande do Norte

The dams are limnic ecosystems of great importance for its multiple uses, among them, water supply for the public and to culture of artisanal fish are most relevant. The aim of the present study is to evaluate the physical-chemical characteristics and the phytoplankton community in two chosen sites (Point 1 littoral zone of point source; Point 2 pelagic zone of non-point source) of the Minister João Alves dam, which is also known as Boqueirão de Parelhas/RN. This represents the spatial distribution of the phytoplankton species in order to understand any possible alterations of the water quality and the phytoplankton composition in relation to the water quality originating from the impact of the tilapia, Oreochromis niloticus, culture. The study period also encompasses temporal variations exhibited in two seasons of an annual cycle, one during the dry season (Oct, Nov and Dec of 2008 and Jan of 2009), and the other rainy season (Mar, Apr, May and June of 2008) to extend the observation. The physicalchemical parameters, such as pH, temperature, electrical conductivity, concentration of dissolved oxygen were measured in situ and the values of the inorganic nutrients (nitrate, ammonium and orto-phosfato) and chlorophyll in the laboratory. The quali-quantitative analyses of the phytoplankton had been carried through sedimentation technique and the enumeration of the random of 400 cells, colonies and filaments counted using Sedgwick-Rafter counting chamber. The results of pH varied widely from the acidic to alkaline range with the minimum of 5.8 (± 0.8) and the maximum of 9.2 (± 0.7-0.8), at point 1 and 2. The dissolved oxygen content was higher in the rainy period than that in the dry period. The maximum electrical conductivity was of 1409 μScm-1 in point 1 and 431 minim of μScm-1, in point 2. There was a considerable alteration in the levels of inorganic nutrients such as nitrate-nitrogen, ammoniacal nitrogen and orthophosphate during the two cycles of study period. Phytoplankton assemblages presented a picture of alternate dominance among species Cyanobacteria, Bacillariophyceae and Chlorophyceae. The trophic state index diagnosed to the category of mesotrophic, which is based on the values of chlorophyll, total phosphorus and Secchi-disc measurements. The wind driven turbulence of the water column and the fresh inflow of water (flushing and dilution) during rainy season acted as constraint and did-not allow an exaggerated growth of the species of cyanobacteria. On the basis of the present we conclude that the culture of tilapias in cage-culture fails to produce pollution load that could compromise the quality of the water of the dam, probably be due to small dimension of the culture in relation to the size, volume of the water and the reservoir capacity support its own environment

Influência do método de filetagem e categorias de peso sobre rendimento de carcaça, filé e pele da tilápia do Nilo (Oreochromis niloticus)

The objective of this study was to evaluate the processing methods (F-1 = to remove skin with pliers and then to cut in fillets; F-2 = cut in fillet and then to remove skin with knife and pliers help) and weight categories (W-1=250-300 g; W-2=301-350 g; W-3 = 351-400 g and W-4 = 401-450 g), on the carcass (CY), fillet (FY) and skin yield of Nile tilapia. Forty-eight fishes were used in a completely randomized design. There was effect for the processing method, being the F-1 mean (56.43 and 36.67 %) higher to the F-2 (53.46 and 32.89%) for CY and FY respectively. For the weight categories, W-1 (56.49 and 37.34%) and W-2 (56.34 and 36.40%) were superior as compared to W-3 (53.27 and 31.98%) and W-4 (53.71 and 33.42%), respectively for CY and FY. Crude skin percentage, clean and of fleshed were higher for F-2, but there was no effect for weight categories. The F-1 processing method promoted the best yield and skin results, and for the weight categories W-1 and W-2 higher yields.

Sexagem histológica e desempenho de Oreochromis niloticus testando diâmetros de ração de acordo com o aparato bucal

Estudou-se o tamanho da boca de larvas de tilápia-do-nilo e testou-se o efeito de diferentes granulometrias da ração sobre o ganho de peso, comprimento e sobrevivência das larvas aos 30 e 60 dias de arraçoamento. Avaliou-se também o método de sexagem por meio de microscopia de luz aos 35 dias de idade. A medida da boca das larvas apresentou valores médios de 918,2±152,9μm aos cinco dias de idade. de acordo com esse dado, testaram-se três granulometrias: 0,25, 0,35 e 0,50mm. Aos 30 e aos 60 dias de arraçoamento, 10% das larvas foram medidas, pesadas e contadas para cálculo da taxa de sobrevivência. O tamanho dos grânulos testados não afetou o desempenho das larvas de tilápia nilótica com alimentação iniciada aos cinco dias pós-eclosão. Quanto à sexagem histológica aos 35 dias de idade, as gônadas apresentaram-se, em sua maioria, indiferenciadas. Recomenda-se que essa análise deva ser realizada de acordo com o tamanho dos animais e não com a idade.

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

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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.

Conservação de filés de tilápia-do-nilo (Oreochromis niloticus) em salga seca e salga úmida

Acompanhou-se o desenvolvimento dos processos da salga em salmoura saturada (salga úmida) e salga seca de filés de tilápia-do-nilo (Oreochromis niloticus) e avaliaram-se algumas características indicativas de qualidade do produto durante a estocagem. Os processos foram acompanhados por 156 horas na salga úmida e por 96 horas na salga seca, e os filés salgados foram estocados, respectivamente, por 60 e 45 dias à temperatura ambiente. Os teores máximos de cloreto nos filés (14%) foram atingidos com 72 horas na salga úmida e com 36 horas na salga seca. Os filés de tilápia salgados em salmoura mantiveram as características próprias do produto por um período de 45 dias, e os submetidos à salga seca apresentaram baixo teor de umidade (6%) e alta concentração de extrato etéreo (4,6%). Recomenda-se somente o processo de salga em salmoura saturada como forma de conservação dos filés de tilápia-do-nilo.