A case of complete loss of gill parasites in the invasive cichlid Oreochromis mossambicus
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Keywords:
Cichlid
Oreochromis mossambicus
Three species of tilapia viz; Oreochromis mossambicus, Oreochromis niloticus and Tilapia rendalli, are well established in Sri Lanka and significant in fresh water fishery. Introgressive hybridisation is common between certain tilapia species producing hybrids that can obscure the morphological boundaries between species and also have numerous negative effects on long-term fishery. Therefore an easy index for identification of tilapia species and their hybrids in the field, which is based on morphometry of tilapia fish is essential. However, such a morphological index substantiated by DNA based study is not available. The present investigation reports the most important morphometric characters for the identification of tilapia species in Sri Lanka. The maternal origin of selected individuals of such groups was determined using heteroduplex formation of PCR products of a part of control region of mitochondrial DNA (mtDNA) with the PCR product of the same region of an authentic O. mossambicus. The majority of individuals tested had maternal origin conforming to the present morphologically defined species, whereas a few (03) O. niloticus individuals had mossambicus maternal origin indicating hybridisation.
Oreochromis mossambicus
Sri lanka
Aquaculture of tilapia
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Abstract.— Densities of 9 tilapia (hybrid Oreochromis mossambicus × O. urolepis hornorum)/m 3 gave the highest production among five densities (1, 3, 6, 9, and 12 fish/m 3 ) tested in a pulsed‐flow culture system. Culture of fish in irrigation ditches may have great potential for integrating fish farming with irrigated agriculture. Each 1,000 meters of ditch could potentially produce up to 1,400 kg of tilapia during a 112‐d growing season.
Oreochromis mossambicus
Ditch
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Feeding habits and environmental tolerances are presented for the major co-cultured tilapia, including Oreochromis niloticus, Oreochromis aureus, and Oreochromis mossambicus. In general, cultured tilapia consume plankton. Depending upon species and age, there may be a preference for zooplankton or phytoplankton. Tilapia also take readily to prepared feeds. Tilapia generally have high tolerance to low levels of dissolved oxygen but develop diseases at temperatures below about 20 °C, and mortality will occur as temperature decreases. Salinity tolerance varies among species, with O. mossambicus and some red hybrids tolerating full seawater salinity or higher.
Oreochromis mossambicus
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Kelana Jaya Ponds are typical aquatic ecosystems of great importance with regard to biodiversity and aesthetic value in urban areas of Peninsular Malaysia. Concentrations of Cd, Cu and Zn were determined in the edible flesh (muscles), scales and gills of the fish tilapia Oreochromis mossambicus caught at one of the ponds in Kelana Jaya. The ranges of mean concentrations of metals (μg/g dry weight) in the fish were Cd: 2.42, 3.95 and 4.48; Cu: 1.98, 3.78 and 2.89 and Zn: 58.4, 71.1 and 80.5, in the muscles, scales and gills, respectively. Generally, scales and gills showed higher metal concentrations than muscles. Although the lake is thought to receive semi-untreated domestic wastes and dumping, the results of these metals (especially in the edible part of the fish) did not exceed the permissible limits for human consumption for fish product. Therefore, this should not pose health problems for consumers of the tilapia species but further intensive studies are warranted.
Oreochromis mossambicus
Aquaculture of tilapia
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Su-Mei Wu, Yi-Ying Chou and Am-Ni Deng (2002) Effects of exogenous cortisol and progesterone on metallothionein expression and tolerance to waterborne cadmium in tilapia (Oreochromis mossambicus). Zoological Studies 41(1): 111-118. The object of the present study was to test the hypothesis that glucocorticoids can induce the expression of metallothionein (MT) which consequently enhances the tolerance to metal toxicity in tilapia (Oreochromis mossambicus). Adult tilapia (4-5 cm in total length and 5.0-6.0 g in body weight) and larval tilapia (0.5-0.7 cm in total length and 0.012-0.017 g in body weight) were reared with artificial feed containing 0 (control), 50 (low dose), 125 (medium dose), or 250 mg/kg (high dose) of cortisol or progesterone for 10 d. Liver and whole-body contents of MT and mortality in tilapia upon Cd 2 + exposure were examined after the steroid-rearing experiments. Both cortisol and progesterone significantly increased survival rates in adult fish after Cd 2 + challenge. Treatment with middle and high doses of progesterone significantly stimulated the expression of MT in adult fish, but stimulation by cortisol showed no significant effect on MT expression. More MT was expressed after Cd 2 + challenge in both cortisol- and progesterone-treated groups. However, exogenous steroids caused no significant effect on MT contents or survival upon Cd 2 + challenge in tilapia larvae. This suggests that cortisol and progesterone are involved in metal-detoxification mechanisms in adult tilapia via regulating the expression of MT, but the occurrence of this pathway in developing fish is unclear.
Oreochromis mossambicus
Metallothionein
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Studies were undertaken to determine whether several indicators of growth hormone (GH) cell activity, namely GH content, fine structure, and volume of the GH region, differ in the pituitaries of freshwater (FW) and seawater (SW) tilapia, Oreochromis mossambicus. Tilapia raised from the stage of yolk-sac absorption for 7 months in SW contain significantly more GH in their pituitaries than in those of fish reared in FW. Pituitary growth hormone content in tilapia raised in FW for 7 months and transferred to SW for 49 days is greater than that in sibling tilapia retained in FW. Conversely, GH content is significantly lower in the pituitaries of SW-reared tilapia transferred to FW for 49 days than that in the pituitaries from fish retained in SW. Likewise, the volume of the GH region and activity of the GH cells are enhanced in pituitaries from SW-reared tilapia over that seen in pituitaries from FW fish. Taken together, all data indicate heightened GH cell activity in SW-raised tilapia and suggest that GH may play a causal role in the greater growth rates observed in SW tilapia compared to FW fish and/or that GH may be involved in SW osmoregulation. The latter suggestion is supported, in part, by our observation that in vivo oGH treatment (2 μg/g body wt) stimulated gill Na+,K+-ATPase activity.
Oreochromis mossambicus
Euryhaline
Osmoregulation
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Oreochromis mossambicus
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Oreochromis mossambicus
Aquaculture of tilapia
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