Cl- uptake mechanism in freshwater-adapted tilapia (Oreochromis mossambicus)

In this study, the correlation between Cl(-) influx in freshwater tilapia and various transporters or enzymes, the Cl(-)/HCO(3)(-) exchanger, Na(+),K(+)-ATPase, V-type H(+)-ATPase, and carbonic anhydrase were examined. The inhibitors 2x10(-4) M ouabain (a Na(+),K(+)-ATPase inhibitor), 10(-5) M NEM (a V-type H(+)-ATPase inhibitor), 10(-2) M ACTZ (acetazolamide, a carbonic anhydrase inhibitor), and 6x10(-4) M DIDS (a Cl(-)/HCO(3)(-) exchanger inhibitor) caused 40%, 60%-80%, 40%-60%, and 40%-60% reduction in Cl(-) influx of freshwater tilapia, respectively. The inhibitor 2x10(-4) M ouabain also caused 50%-65% inhibition in gill Na(+),K(+)-ATPase activity. Western blot results showed that protein levels of gill Na(+),K(+)-ATPase, V-type H(+)-ATPase, and carbonic anhydrase in tilapia acclimated in low-Cl(-) freshwater were significantly higher than those acclimated to high-Cl(-) freshwater. Based on these data, we conclude that Na(+),K(+)-ATPase, V-H(+)-ATPase, the Cl(-)/HCO(3)(-) exchanger, and carbonic anhydrase may be involved in the active Cl(-) uptake mechanism in gills of freshwater-adapted tilapia.     

Effects of cortisol and salinity challenge on water balance in developing larvae of tilapia (Oreochromis mossambicus)

Effects of exogenous cortisol on drinking rate and water content in developing larvae of tilapia (Oreochromis mossambicus) were examined. Both freshwater- and seawater-adapted larvae showed increases in drinking rates with development. Drinking rates of seawater-adapted larvae were about four- to ninefold higher than those of freshwater-adapted larvae from day 2 to day 5 after hatching. Seawater-adapted larvae showed declines in drinking rate and water content at 4 and 14 h, respectively, after immersion in 10 mg L(-1) cortisol. In the case of freshwater-adapted larvae, the drinking rate decreased after 8 h of cortisol immersion, while the water content did not show a significant change even after 32 h of cortisol immersion. In a subsequent experiment of transfer from freshwater to 20 ppt (parts per thousand, salinity) seawater, immersion in 10 mg L(-1) cortisol for 8-24 h enhanced the drinking rate in larvae at 4 h after transfer, but no significant difference was found in water contents between cortisol-treated and control groups following transfer. These results suggest that cortisol is involved in the regulation of drinking activity in developing tilapia larvae.     

Effects of cortisol on ion regulation in developing tilapia (Oreochromis mossambicus) larvae on seawater adaptation.

The yolk diameter of cortisol-treated tilapia (Oreochromis mossambicus) larvae, immersed in freshwater (FW) containing 10 mg L-1 cortisol from 48 h postfertilization to 12 d posthatching, was significantly larger than that of control larvae after 8 d of treatment, suggesting that inhibition on larval growth occurred only after a long-term treatment with cortisol. Tilapia embryos or larvae treated with 1-10 mg L-1 cortisol for 1-2 d and then transferred to 20-30 g L-1 seawater (SW) showed reduced cumulative larval mortality in SW compared with controls. Moreover, 4-5 d of cortisol treatments significantly diminished the degree of increase in larval body Na content after the transfer to SW. Significant effect of cortisol on body Na content of larvae occurred as early as 4-8 h after the transfer to SW, while no significant difference was found in the ouabain binding of yolk-sac epithelia between control and cortisol-treated larvae even 12 h after the transfer. Cortisol may be involved in the early phase of SW adaptation in developing larvae, and this mechanism may be achieved by other means than increasing the Na-K-ATPase of yolk-sac epithelia.     

Metallothionein induction in early larval stages of tilapia (Oreochromis mossambicus)

Amounts of whole-body metallothionein (MT) in tilapia (Oreochromis mossambicus) larvae increased to a peak (1,500 ng mg(-1) protein) 1 d after hatching (H1), decreased rapidly thereafter, and was maintained at a constant level (700 ng mg(-1)) 3 d after hatching (H3). Waterborne Cd(2+) could stimulate MT expression in newly hatched (H0) larvae in dose-dependent and time-dependent patterns. H0 larvae, which were treated with 35 microg L(-1) Cd(2+) for 24 h, showed a 1.7-fold increase in the MT amount (174.0+/-64.7) and a 6. 5-fold increase in accumulated Cd(2+) but no significant change in Ca(2+) content, compared with the H0 control (MT, 102.6+/-48.1). H3 larvae with the same treatment revealed about a 10-fold increase in accumulated Cd(2+), a 10% decrease in Ca(2+) content, but no change in MT (261.2+/-120.0), compared with the H3 control (MT, 330+/-74.0). H0 larvae could synthesize more MT to bind Cd(2+) for detoxification in 35 microg L(-1) Cd(2+), a dose that would not affect normal physiology or survival of H0 larvae. On the other hand, 35 microg L(-1) Cd(2+) caused H3 larvae to experience hypocalcemia, an abnormal physiological condition, in which H3 larvae could not synthesize sufficient MT, thus causing greater than 25% mortality. These results indicate for the first time that the inducibility of MT by waterborne Cd(2+) is development dependent, being correlated with inconsistent sensitivities to Cd(2+) during larval development.     

Near-infrared orientation of Mozambique tilapia Oreochromis mossambicus

Light plays a pivotal role in animal orientation. Aquatic animals face the problem that penetration of light in water is restricted through high attenuation which limits the use of visual cues. In pure water, blue and green light penetrates considerably deeper than red and infrared spectral components. Submicroscopic particles and coloured dissolved organic matter, however, may cause increased scattering and absorption of short-wave components of the solar spectrum, resulting in a relative increase of red and infrared illumination. Here we investigated the potential of near-infrared (NIR) light as a cue for swimming orientation of the African cichlid fish (Cichlidae) Oreochromis mossambicus. A high-throughput semi-automated video tracking assay was used to analyse innate behavioural NIR-sensitivity. Fish revealed a strong preference to swim in the direction of NIR light of a spectral range of 850-950nm at an irradiance similar to values typical of natural surface waters. Our study demonstrates the ability of teleost fish to sense NIR and use it for phototactic swimming orientation.     

Innate-immune responses of tilapia (Oreochromis mossambicus) exposure to acute cold stress

In this present study, Oreochromis mossambicus tilapia were transferred to cold water at 12°C for various time intervals (1, 4, 8, 24, and 48 hr) and its innate immune response was analyzed by studying cellular and humoral parameters. In vivo, alternative complement pathway activity in blood plasma was rapidly increased at 1 hr of cold water (12°C) exposure. Lysozyme activity and cortisol levels of plasma were increased at 4 and 1 hr, respectively. Surprisingly, only plasma cortisol levels remained unchanged through 24 hr of cold water transfer. Phagocytic ability, phagocytic capacity, and respiratory burst (RB) activity of head kidney (HK) leukocytes and splenocytes showed no any significant changes. In peripheral blood leukocytes, phagocytic capacity, and RB activity were increased at 24 hr of cold water exposure. The expressions of genes involved innate immunity in splenocytes and HK leukocytes of tilapia cold water exposure were analyzed, messenger RNA (mRNA) expressions of HSP70, HSP90, and immunoglobulin M failed to change upon exposure to cold stress. Major histocompatibility complex-I and II mRNAs were significantly increased in tilapia splenocytes at 1 hr of cold water transferred. Whereas myxovirus (Mx) expression was increased in splenocytes and HK leukocytes of tilapia after 1 hr of cold water exposed. Our result reveals that the exposure of tilapia to acute cold stress condition significantly enhances plasma acid phosphatase activity and both phagocytic capacity and RB activity. Furthermore, cold stress significantly stimulates Mx gene expression in splenocytes and HK leukocytes.     

Cellular distributions of creatine kinase in branchia of euryhaline tilapia (Oreochromis mossambicus)

Although euryhalineteleosts can adapt to environmental fluctuation of salinity, theirenergy source for responding to changes in salinity and osmolarityremains unclear. This study examines the cellular localization ofcreatine kinase (CK) expression in branchia of tilapia(Oreochromis mossambicus). Western blot analysis ofmuscle-type CK (MM form) revealed a high association with salinity changes, but BB and MB forms of CK in the gills of fish adapted toseawater did not change. With the use of immunocytochemistry, three CKisoforms (MM, MB, and BB) were localized in mitochondria-rich (MR)cells and other epithelial cells of tilapia gills. In addition, staining intensity of MM-form CK in MR cells increased after seawater transfer, whereas BB and MB forms did not significantly change. To ourknowledge, this work presents the first evidence of CK expression in MRcells of tilapia gills, highlighting the potential role of CK inproviding energy for ion transport.

     

Changes of glycogen metabolism in the gills and hepatic tissue of tilapia (Oreochromis mossambicus) during short-term Cd exposure

The aim of the study was to test the hypothesis that the mechanism of glycogen metabolism has taken place in gills rather than in liver during Cd exposure. Male tilapia were exposed to 44.45 μM ambient Cd for 12 h, and we found blood glucose significantly increased, however, lactate levels showed no significant changes. The glycogen phosphorylase (GP) activity increased immediately after 0.75 to 3 h of Cd exposure in the gills, and after 1 to 6 h in the liver, respectively. In addition, the glycogen level depleted faster in the gills than in the liver. Plasma cortisol level increased from 0.25 to 1 h and recovered after 3 h, while the glucagon did not significantly change during Cd exposure. Glucocorticoid receptor (GR) mRNA expression decreased after 0.75 h in the gills, while it significantly increased after 6 h in the liver. Ca²⁺, Na⁺, Cl⁻, and K⁺ significantly decreased upon Cd exposure within 6 h following Cd-induced toxic stress. We suggested that the cortisol is the spontaneous stimulation of glycogen metabolism in the gills, and it triggers a subsequent energy supply later in the liver. Taken together, the profile of glycogen metabolism between gills and liver during Cd-exposure stress provide good support to our hypothesis.     

Toxicological impact of Zinc Nano Particles on tilapia fish (Oreochromis mossambicus)

In this study we investigated the acute toxicity of Zinc Nano Particles (ZnO NPs) and bulk ZnO on tilapia fish (Oreochromis mossambicus). Oreochromis mossambicus was exposed to the different concentration of ZnO NPs, ZnO and mixed solution of both ZnO NPs and ZnO (20 ppb, 20 ppb, 20 ppb) respectively for 96 h. A very high impact was recorded in hematological parameters which shows significant increased (p < 0.05) in count of white WBCs and platelets in all the experimental groups compared tocontrol group. The count of RBCs, Hb, hematocrit and MCHC were significantly decreased. The remarkable changes which were recorded during this study were histopathological lesions in the gills of exposed fish including, disorganization of gill lamella, cartilaginous core disruption, lifting of epithelium, loss of secondary gill lamellae, blood congestion, fusion of secondary gills lamellae, shortening of secondary gills lamellae, atrophy and curling. Disassembly were seen in plasma membrane of liver along with blood congestion, pyknosis, necrosis, hyperplasia and formation of vacuoles. Intestinal alterations which were observed include shortening of villi, necrosis, detachment and fusion of villi and extreme goblet cells formation. It is concluded from the present study that high level of ZnO NPs, ZnO and mixed solution has a strong tendency to alter hematological parameters, histological architecture, therefore, the indiscriminate use of ZnO NPs and ZnO can subsidize in reducing the population of Oreochromis mossambicus in natural water bodies.     

Diurnal changes in the territorial behaviour of the tilapia Oreochromis mossambicus (Peters)

The numbers of black, territorial, male tilapia in large tanks undergoes a clear diurnal cyclicity, with peak numbers seen in the afternoon. It is suggested that this cyclicity is functionally related to an observed spawning cyclicity.     

Scanning electron microscopic evaluation of effect of cortisol on chloride cells of tilapia, Oreochromis mossambicus

The effect of exogenous administration of cortisol (0.2 microg/g body weight) for 24, 48 and 72 hr on the gill epithelium of Tilapia has been studied. The results clearly revealed that out of the three sub-types of chloride cells viz., shallow basin, wavy convex and deep hole, the shallow basin ones are the most abundant in number. In vivo administration of cortisol conspicuously increased the number of the shallow basin chloride cells and caused noticeable changes in the microridges of pavement cells right from 24 hr treatment onwards. The present study confirms heterogeneity of chloride cells in teleosts.     

The effect of elevated salinity on 'California' Mozambique tilapia (Oreochromis mossambicus x O. urolepis hornorum) metabolism

California Mozambique tilapia (Oreochromis mossambicus x O. urolepis hornorum) are extremely saline tolerant and have been previously shown to reduce whole-animal oxygen consumption rate (MO(2)) upon exposures to salinities greater than that of seawater (SW). In this study tilapia were acclimated to 15, 30, 45, 60 and 75 g/L salinity for 1, 5, 14, or 28 days. There was little change in plasma osmolality or muscle water content in salinities below 60 g/L, and branchial Na(+), K(+)-ATPase (NKA) activity was low in 15 and 30 g/L relative to 60 and 75 g/L. When tilapia were exposed to 75 g/L, plasma osmolality and NKA activity were significantly increased within 5 days of exposure relative to those in 15 and 30 g/L, and remained elevated over the entire 28 days acclimation, indicating that short term salinity challenges (i.e., 5 days) are predictive of longer exposure durations in this species. MO(2) following transfer to 15 and 30 g/L was elevated, reflecting the high energy demand required for switching from a hyper- to a hypo-osmoregulatory strategy. The MO(2) of 60 g/L-exposed fish was significantly reduced at 1, 5, and 14 days, relative to 30 g/L-exposed fish; however by 28 days there were no significant differences. We investigated the potential for a metabolic basis for the salinity-induced MO(2) reduction, using forward stepwise linear regression to correlate enzyme activities of brain, liver, and kidney with MO(2). Brain NKA was correlated with MO(2) after 5 days (p<0.01, r(2)=0.944) and both brain NKA and hepatic total ATPase were correlated with the reduced MO(2) at 14 days (p=0.027, r(2)=0.980 and p=0.025, r(2)=0.780, respectively). These results may indicate a tissue-level metabolic suppression, which has not been previously described as a response to hypersaline exposure in fishes.     

Regulation of drinking rate in euryhaline tilapia larvae (Oreochromis mossambicus) during salinity challenges

Euryhaline tilapia larvae are capable of adapting to environmental salinity changes even when transferred from freshwater (FW) to seawater (SW) or vice versa. In this study, the water balance of developing tilapia larvae (Oreochromis mossambicus) adapted to FW or SW was compared, and the short-term regulation of drinking rate of the larvae during salinity adaptation was also examined. Following development, wet weight and water content of both SW- and FW-adapted larvae increased gradually, while the dry weight of both group larvae showed a slow but significant decline. On the other hand, the drinking rate of SW-adapted larvae was four- to ninefold higher than that of FW-adapted larvae from day 2 to day 5 after hatching. During acute salinity challenges, tilapia larvae reacted profoundly in drinking rate, that is, increased or decreased drinking rate within several hours while facing hypertonic or hypotonic challenges, to maintain their constancy of body fluid. This rapid regulation in water balance upon salinity challenges may be critical for the development and survival of developing larvae.     

Molecular and functional studies of tilapia (Oreochromis mossambicus) NMDA receptor NR1 subunits

The Pin-tailed Manakin (Ilicura militaris) is a small, sexually dimorphic, frugivorous suboscine songbird (Pipridae; Passeriformes; Aves) endemic to the Atlantic Forest of Brazil. A variant individual of this species was recently described in which the red patches that characterise the male's Definitive plumage were replaced by orange-yellow ones. We show here that the pigments in the feathers of the colour variant are common dietary carotenoids (zeaxanthin, beta-cryptoxanthin), not carotenoids synthesised by birds, lending support to the suggestion that the individual is a colour mutant lacking the capability to transform yellow dietary pigments into the red pigments normally present in these feathers. By comparison, the yellow crown feathers of a close relative, the Golden-winged Manakin (Masius chrysopterus), contained predominantly endogenously produced epsilon-caroten-3'-ones. Surprisingly, the normal-coloured feathers of the male Pin-tailed Manakin owe their red hue to rhodoxanthin, an unusual carotenoid more commonly found in plants, rather than 4-keto-carotenoids typically found in red plumages and found lacking in previously characterised bird colour variants. The implication is that birds, like the tilapia fish, may be able to synthesise this unusual pigment endogenously from dietary precursors. A newly described carotenoid, 6-hydroxy-epsilon,epsilon-carotene-3,3'-dione, here named piprixanthin, present in the red feathers of the Pin-tailed Manakin, provides a plausible intermediate between epsilon,epsilon-carotene-3,3'-dione (canary-xanthophyll B), a bright yellow pigment found in this and other songbirds, and rhodoxanthin. It is apparent that pigeons (Columbidae, Columbiformes) also have the capability to produce rhodoxanthin, and a structurally related pigment, endogenously. The ability to synthesise rhodoxanthin might have arisen at least twice in birds.     

Evaluating the toxic potential of agrochemicals on the hypothalamic-pituitary-thyroid axis in tilapia (Oreochromis mossambicus)

Agrochemicals are a major cause of concern for the aquatic environment because of their toxicity, persistence, and tendency to accumulate in the organisms. The impact of these chemicals on aquatic organisms is due to their movement from various diffuse or point sources, which poses a great threat to aquatic fauna especially fishes, which constitute one of the major sources of protein-rich food for mankind. The present study is a first of its kind, where the toxic potential of two sublethal concentration (LC_1/10th and LC_1/25th) of four different classes of agrochemicals have been tested (Insecticide- Imidacloprid-0.074 ppm, 0.02 ppm, Fungicide-Curzate- 4.9 ppm, 1.96 ppm, Herbicide- Pyrazosulphuron ethyl-50 ppm, 20 ppm and Fertilizer-Micronutrient mixture 500 ppm, 200 ppm) on candidate markers of hypothalamus pituitary-thyroid axis (TSH, T₃, T₄, TSHβr) in Oreochromis mossambicus (tilapia) by validating hormonal level and mRNA expression. The results reveal that exposure to agrochemicals resulted in a broad range of alterations with maximum damage being caused by insecticide followed by herbicide and fungicide in that order on the thyroid axis. The results of the present study highlight the need for more detailed studies on the effects of agrochemicals that accumulate in organisms and propose that there should be a check on the rampant use of agrochemicals.