Gills Of Tilapia Research Articles

Differential expression patterns and localization of glucocorticoid and mineralocorticoid receptor transcripts in the osmoregulatory organs of tilapia during salinity stress

The glucocorticoid receptor (GR) plays an essential role during seawater (SW) acclimation. However, the regulation of GR isoforms 1 and 2 (GR1 and GR2) and the mineralocorticoid receptor (MR) during SW acclimation is poorly understood. To address this, we localized and examined the GR1, GR2 and MR transcripts in the tilapia gill, kidney and intestine. Our results indicated that the GR1, GR2 and MR levels were increased in the kidney and intestine on day 1 in seawater (SW) fish, which is in agreement with the recognized osmoregulatory role of the corticosteroid receptors. The SW transfer increased the GR2 and MR transcripts in the gill on day 1 and 4, respectively. Surprisingly, no significant difference was obtained for the GR1 mRNA level. Analysis of the plasma parameters in freshwater (FW) and SW tilapia showed that the plasma cortisol levels were significantly increased at day 1 in the SW fish compared to the FW fish. This is the first study that focused on the spatial distribution of GR1, GR2 and MR in the osmoregulatory organs of freshwater (FW)- and SW-acclimated tilapia by in situ hybridization. Consistent with the Q-PCR results, the expression levels of the GR1, GR2 and MR transcripts were increased or decreased in the SW-acclimated tilapia’s gill, kidney and intestine compared to the FW fish. We observed that GR1, GR2 and MR were localized in the branchial epithelial cells and chloride cells of the gill, proximal tubules of the kidney and columnar cells of the intestine. Together, these results indicate that the mobilization of corticosteroid receptors is dependent on the target tissue, salinity and exposure time.

Cloning and functional characterization of three novel antimicrobial peptides from tilapia (Oreochromis niloticus)

Antimicrobial peptides constitute an important component of the innate immune system. Teleost fish represent a potentially fruitful resource for novel antimicrobial peptide discovery since these organisms rely significantly on their innate immune systems to combat the constant threat of infections in the aquatic environment. In the present study, we isolated three antimicrobial peptides-like transcripts from tilapia (Oreochromis niloticus) gills based on EST reported sequences. These peptides were named oreochromicins (Oreoch-1, Oreoch-2 and Oreoch-3). The cDNA sequences for these putative AMPs encode three pre-pro-peptides with the highest similarity with the members of the piscidin family from teleost fish. The predicted three pre-pro-peptides consist of a signal peptide, a highly cationic mature peptide of 23, 25, and 32 amino acids, respectively and a carboxy terminal pro-domain. The synthetic peptides displayed a broad-spectrum of antimicrobial activity against Gram-negative, Gram-positive bacteria and fungi. These peptides are constitutively expressed in the brain, heart, head kidney, spleen and gut. Additionally, their binding properties to lipopolysaccharide and cytotoxic activity in mammalian and fish cells were assayed.

MiR-429 regulation of osmotic stress transcription factor 1 (OSTF1) in tilapia during osmotic stress

The Nile tilapia represents an excellent model for osmoregulation study. Osmotic stress transcription factor 1 (OSTF1) identified in tilapia gill epithelium is a critical element of osmosensory signal transduction by means of transcriptional regulation. Thus, tight regulation of OSTF1 level is necessary for tilapia osmotic adaptation. microRNAs (miRNAs), have emerged as a crucial regulator of gene expression at post-transcriptional level. We reasoned that OSTF1 expression could be regulated by miRNAs. By bioinformatics analysis, we identified a putative miR-429 binding site in the OSTF1 mRNA. Interestingly, miR-429 is down-regulated in tilapia upon osmotic stress, consistent with OSTF1 protein up-regulation. miR-429 directly regulates OSTF1 expression by targeting its 3′-UTR, and inhibition of miR-429 substantially increases OSTF1 level in vivo. Moreover, miR-429 loss of function could influence the regulation of plasma osmolality and ion concentration responding to osmotic stress. Taken together, miR-429 is an endogenous regulator of OSTF1 expression, which participates in a regulatory circuit that allows rapid gene program transitions in response to osmotic stress.

Gill Oxidative Stress and Histopathological Biomarkers of Pollution Impacts in Nile Tilapia from Lake Mariut and Lake Edku, Egypt

Various oxidative stress and histopathological biomarkers in gill tissues of Nile tilapia Oreochromis niloticus were investigated. Fish were collected from four sites that differ in their extent of pollution load, including heavy metals: the southeast basin (SEB), main basin (MB), and northwest basin (NWB) of Lake Mariut; and Boughaz El-Maadiya, a channel in Lake Edku. The oxidative stress biomarkers that were analyzed included lipid peroxidation (LPO), superoxide dismutase (SOD), catalase (CAT), and glutathione redox cycle enzymes (glutathione peroxidase [GPx] and glutathione reductase [GR]). Levels of reduced glutathione (GSH) were also evaluated. Gill morphology was analyzed by light microscopy and scanning electron microscopy (SEM). Gill LPO was significantly higher in gill tissues of fish collected from the more heavily contaminated MB (40.0%) and NWB (51.4%) sites than in gill samples from the less-contaminated (reference) site, the SEB. Gill LPO in fish from Lake Edku was intermediate but was not significantly higher (17.1%) than the reference. The activities of antioxidant enzymes and the redox-sensitive thiol compound GSH were significantly lower in gill samples from the disturbed sites than in samples from the reference site. Specifically, SOD in MB, NWB, and Lake Edku samples; CAT and GPx in NWB samples; and GR activity and GSH content in MB and NWB samples were lower than those in SEB samples. In most cases, gill tissues from Lake Edku fish had intermediate levels of antioxidants. The main histopathological alterations observed in gills were epithelial lifting, hyperplasia and hypertrophy of the respiratory epithelium, lamellar fusion, and aneurysms. In addition, SEM results demonstrated transformation of the surface structure of epithelial pavement cells. Pathological reactions in the gills of Nile tilapia were most severe at the MB and NWB sites. Our findings suggest that Nile tilapia responded differently according to the environmental stress index in each sampling area. This study is the first to report gill oxidative stress and histopathologies in Nile tilapia from Egyptian aquatic environments.

Involvement of Corticotrophin‐Releasing Hormone and Corticosteroid Receptors in the Brain–Pituitary–Gill of Tilapia During the Course of Seawater Acclimation

The mRNA expression of genes for corticotrophin-releasing hormone (CRH) and the hormone receptors CRH-receptor/CRH-R, glucocorticoid receptor 1/2 (GR1/2) and mineralocorticoid receptor (MR) was studied in the brain, pituitary and gill of tilapia (Oreochromis mossambibus) during salinity and handling stress by real-time quantitative-polymerase chain reaction analysis. The results indicated that the transcripts of CRH and CRH-R were increased in the forebrain, midbrain and gill, whereas elevated hypothalamic CRH mRNA suppressed the CRH-R mRNA in the pituitary in seawater (SW) fish. The levels of plasma osmolality and cortisol were significantly increased in SW compared to freshwater fish. The up-regulation of GR1, GR2, MR and α-NKA (Na(+) /K(+) -ATPase) transcripts in SW fish provided evidence that cortisol responds to stress and involves ion-base regulation via the GR1, GR2 and MR receptors in the gill. These data suggest that GR1, GR2 and MR have a pivotal role in the brain and gill. GR1, GR2 and MR expression may be dependent on CRH and cortisol expression in the brain and gill. In addition, we performed in situ hybridisation analysis to localise and differentiate the CRH, CRH-R, GR1, GR2 and MR transcripts in the brain of FW- and SW-acute acclimated tilapia during salinity stress. In almost all transcripts, the hybridisation signal was significantly abundant in the SW-acute acclimated tilapia brain, especially in the dorsal ventral cephalon, dorsal nucleus preopticus pars magnocellularis and dorsal nucleus preopticus pars parvocellularis. Salinity stress induced differential and specific responses in the gill and brain compared to handling stress.

Hyperosmotic stress induces the myo‐inositol pathway by several orders of magnitude in tilapia (Oreochromis mossambicus) gill epithelium

Myo‐inositol (MI) biosynthesis from glucose is one mechanism by which organisms can accumulate compatible organic osmolytes to counteract hyperosmotic stress. Here we show that the entire MI pathway is strongly induced by hyperosmotic stress in tilapia gill epithelium. We found that the second enzyme of this two‐step pathway, inositol monophosphatase (IMPA), is strongly up‐regulated by hyperosmotic stress at the protein level as shown by online LCMS. Using quantitative real‐time PCR we have investigated the level of induction of the MI biosynthesis pathway in gill epithelium after acclimating tilapia acutely and gradually from fresh water to either 34, 70 or 90 ppt salinity. Two distinct myo‐inositol‐phosphate synthase (MIPS) transcripts of the same gene showed similarly high levels of mRNA up‐regulation during all types of hyperosmotic stress. While only a single MIPS gene was found we detected at least two distinct IMPA genes in the tilapia genome. The IMPA1 gene that was highly up‐regulated after hyperosmotic stress at the protein level was also found highly up‐regulated at the mRNA level during all types of hyperosmotic stress. In contrast, IMPA2 was not up‐regulated suggesting that it lacks osmoresponsive enhancers. We conclude that the MI biosynthesis pathway represents a major hyperosmotic stress coping mechanism for euryhaline fish such as tilapia. Supported by NSF grant IOS‐1049780.

Excretion of cesium and rubidium via the branchial potassium-transporting pathway in Mozambique tilapia

Using an insolubilization technique in combination with element analysis, we examined the possible excretion of Cs+ and Rb+, both known to be biochemical analogs of K+, through the K+-transporting pathway in the gills of seawater-adapted Mozambique tilapia. To detect ion excretion from gills infused with Rb+ or Cs+, the isolated gills were treated with sodium tetraphenylborate, which reacts not only with K+ but also with Rb+ and Cs+ to form insoluble precipitates. The precipitates were formed specifically at the apical openings of mitochondrion-rich (MR) cells, which are responsible for K+ excretion in marine teleosts. Elemental analysis showed that Cs and Rb were distributed at the area of precipitates on the gill surface, and that these elements were colocalized with K. Our findings indicate that the gills eliminate unnecessary Cs+ and Rb+ in the body fluid, presumably through the same pathway as the K+ excretion in MR cells.

Responses of gill mitochondria-rich cells in Mozambique tilapia exposed to acidic environments (pH 4.0) in combination with different salinities

On exposure to hyposmotic acidic water, teleost fish suffer from decreases in blood osmolality and pH, and consequently activate osmoregulatory and acid–base regulatory mechanisms to restore disturbed ion and acid–base balances. In Mozambique tilapia Oreochromis mossambicus exposed to acidic (pH 4.0) or neutral (pH 7.4–7.7) freshwater in combination with 0mM or 50mM NaCl, we examined functional and morphological changes in gill mitochondria-rich (MR) cells. We assessed gene expression of Na+/H+ exchanger-3 (NHE3), Na+/Cl− cotransporter (NCC), vacuolar-type H+-ATPase (V-ATPase) and Na+/HCO3− cotransporter-1 (NBC1) in the gills. The mRNA expression of NHE3 and NCC in tilapia gills were higher in acidic freshwater than in that supplemented with 50mM NaCl, while there was no significant difference in mRNA levels of V-ATPase and NBC1. In addition, immunocytochemical observations showed that apical-NHE3 MR cells were enlarged, and frequently formed multicellular complexes with developed deep apical openings in acidic freshwater with 0mM and 50mM NaCl. These findings suggest that gill MR cells respond to external salinity and pH treatments, by parallel manipulation of osmoregulatory and acid–base regulatory mechanisms.

Dynamic gene expression of GH/PRL-family hormone receptors in gill and kidney during freshwater-acclimation of Mozambique tilapia

In teleosts, prolactin (PRL) and growth hormone (GH) act at key osmoregulatory tissues to regulate hydromineral balance. This study was aimed at characterizing patterns of expression for genes encoding receptors for the GH/PRL-family of hormones in the gill and kidney of Mozambique tilapia ( Oreochromis mossambicus) during freshwater (FW)-acclimation. Transfer of seawater (SW)-acclimated tilapia to FW elicited rapid and sustained increases in plasma levels and pituitary gene expression of PRL 177 and PRL 188; plasma hormone and pituitary mRNA levels of GH were unchanged. In the gill, PRL receptor 1 (PRLR1) mRNA increased markedly after transfer to FW by 6 h, while increases in GH receptor (GHR) mRNA were observed 48 h and 14 d after the transfer. By contrast, neither PRLR2 nor the somatolactin receptor (SLR) was responsive to FW transfer. Paralleling these endocrine responses were marked increases in branchial gene expression of a Na +/Cl − cotransporter and a Na +/H + exchanger, indicators of FW-type mitochondrion-rich cells (MRCs), at 24 and 48 h after FW transfer, respectively. Expression of Na +/K +/2Cl − cotransporter, an indicator of SW-type MRCs, was sharply down-regulated by 6 h after transfer to FW. In kidney, PRLR1, PRLR2 and SLR mRNA levels were unchanged, while GHR mRNA was up-regulated from 6 h after FW transfer to all points thereafter. Collectively, these results suggest that the modulation of the gene expression for PRL and GH receptors in osmoregulatory tissues represents an important aspect of FW-acclimation of tilapia.

Acclimation Induced Responses of SDH Activity of Tilapia (Oreochromis mossambicus) Following Introduction in a New Pond Habitat

Responses of the major mitochondrial respiratory enzyme succinate dehydrogenase (SDH) activity in gill and muscle tissue of tilapia (Oreochromis mossambicus) were investigated upon their transfer to a new pond habitat. Sixty healthy adult fish were procured from each of the three ponds used and were distributed in three cages in equal numbers; the cages were placed in each of the other two ponds as well as into original rearing pond. Four fish were removed from each cage every week and were sacrificed for the assay of SDH activity in gills and muscles. Transfer of fish from a stress condition to a benign environment and vice versa resulted in an increase and decrease in SDH activity of fish, respectively. The intensity of increase upon transfer was again dependent upon the amount of stress in the new habitat. In general, the SDH activity of the test fish strongly correlated with the ammonia concentration (P < 0.05) of water regardless of habitats. Time required for the introduced fish to acclimatize with new environmental conditions was dependent upon the environmental milieu of both its initial and final place of rearing and hence their physiological states. Differences in water quality, especially ammonia concentration, between its original place of rearing and the place of transfer were found to be responsible for the differences in acclimation period of two or three weeks. Relatively less difference in ammonia (2.68 for gills and 3.20 for muscles) between the initial place of rearing and new habitat resulted in acclimation of the fish one week earlier (second week) than the relatively wide difference (4.46 for gills and 5.62 for muscles) for third week. It may be reasonable to conclude that the varied responses of the mitochondrial respiratory enzyme of exogenously introduced fishes with the differences in the water quality—especially the ammonia concentration of ambient water between the original fish holding pond and growout pond—can be used to predict the time that will be required for the exogenously introduced fish to fully acclimatize with the new habitat.

Effect of montmorillonite on dietary lead (Pb) accumulation in tissues of tilapia ( Oreochromis niloticus)

The effect of montmorillonite (MMT) on dietary lead (Pb) accumulation in tissues of tilapia ( Oreochromis niloticus) was investigated. Two hundred forty tilapia were randomly divided into four groups and fed with a basal diet, a basal diet supplemented with 0.5% MMT, Pb-contaminated basal diet (100 mg Pb/kg dry mass) and Pb-contaminated basal diet supplemented with 0.5% MMT, respectively. After 60 days, tilapia were sacrificed and sampled to determine Pb accumulation, zinc and iron concentration in the tissues of tilapia. MMT significantly reduced Pb accumulation in kidney, intestine, bone, stomach, gill, liver, spleen, muscle, spermary and brain of tilapia( P < 0.05). Concentration of zinc (Zn) and iron (Fe) in the sampled tissues (kidney, bone, liver, spleen and spermary) of tilapia were not affected by MMT ( P > 0.05). Addition of MMT in diet could protect tilapia from dietary Pb accumulation in tissues.

Changing expression patterns: focus on “The transcription factor, glial cell missing 2, is involved in differentiation and functional regulation of H+-ATPase-rich cells in zebrafish (Danio rerio)”

euryhaline species of fish have a remarkable osmo- and ionoregulatory capacity. Some euryhaline species like the Mozambique tilapia can directly be transferred from freshwater to seawater and vice versa, i.e., osmolarity of the external fluid changes by ∼1,000 mOsm. Many others can tolerate this

Differential responses in gills of euryhaline tilapia, Oreochromis mossambicus, to various hyperosmotic shocks

Euryhaline tilapia ( Oreochromis mossambicus) survived in brackish water (BW; 20‰) but died in seawater (SW; 35‰) within 6 h when transferred directly from fresh water (FW). The purpose of this study was to clarify responses in gills of FW tilapia to various hyperosmotic shocks induced by BW or SW. In FW-acclimated tilapia, scanning electron micrographs of gills revealed three subtypes of MR cell apical surfaces: wavy-convex (subtype I), shallow-basin (subtype II), and deep-hole (subtype III). Density of apical surfaces of mitochondrion-rich (MR) cell in gills of the BW-transfer tilapia decreased significantly within 3 h post-transfer due to disappearance of subtype I cells, but increased from 48 h post-transfer because of increasing density of subtype III cells. SW-transfer individuals, however, showed decreased density of MR cell openings after 1 h post-transfer because subtype I MR cell disappeared. On the other hand, relative branchial Na +/K +-ATPase (NKA) α1-subunit mRNA levels, protein abundance, and NKA activity of the BW-transfer group increased significantly at 6, 12, and 12 h post-transfer, respectively. In the SW-transfer group, relative mRNA and protein abundance of gill NKA α1-subunit did not change while NKA activity declined before dying in 5 h. Upon SW transfer, dramatic increases (nearly 2-fold) of plasma osmolality, [Na +], and [Cl −] were found prior to death. For the BW-transfer group, plasma osmolality was eventually controlled by 96 h post-transfer by enhancement of NKA expression and subtype III MR cell. The success or failure of NKA activation from gene to functional protein as well as the development of specific SW subtype in gills were crucial for the survival of euryhaline tilapia to various hyperosmotic shocks.

Evidence for an apical Na–Cl cotransporter involved in ion uptake in a teleost fish

Cation-chloride cotransporters, such as the Na(+)/K(+)/2Cl(-) cotransporter (NKCC) and Na(+)/Cl(-) cotransporter (NCC), are localized to the apical or basolateral plasma membranes of epithelial cells and are involved in active ion absorption or secretion. The objectives of this study were to clone and identify ;freshwater-type' and ;seawater-type' cation-chloride cotransporters of euryhaline Mozambique tilapia (Oreochromis mossambicus) and to determine their intracellular localization patterns within mitochondria-rich cells (MRCs). From tilapia gills, we cloned four full-length cDNAs homologous to human cation-chloride cotransporters and designated them as tilapia NKCC1a, NKCC1b, NKCC2 and NCC. Out of the four candidates, the mRNA encoding NKCC1a was highly expressed in the yolk-sac membrane and gills (sites of the MRC localization) of seawater-acclimatized fish, whereas the mRNA encoding NCC was exclusively expressed in the yolk-sac membrane and gills of freshwater-acclimatized fish. We then generated antibodies specific for tilapia NKCC1a and NCC and conducted whole-mount immunofluorescence staining for NKCC1a and NCC, together with Na(+)/K(+)-ATPase, cystic fibrosis transmembrane conductance regulator (CFTR) and Na(+)/H(+) exchanger 3 (NHE3), on the yolk-sac membrane of tilapia embryos acclimatized to freshwater or seawater. The simultaneous quintuple-color immunofluorescence staining allowed us to classify MRCs clearly into four types: types I, II, III and IV. The NKCC1a immunoreactivity was localized to the basolateral membrane of seawater-specific type-IV MRCs, whereas the NCC immunoreactivity was restricted to the apical membrane of freshwater-specific type-II MRCs. Taking account of these data at the level of both mRNA and protein, we deduce that NKCC1a is the seawater-type cotransporter involved in ion secretion by type-IV MRCs and that NCC is the freshwater-type cotransporter involved in ion absorption by type-II MRCs. We propose a novel ion-uptake model by MRCs in freshwater that incorporates apically located NCC. We also reevaluate a traditional ion-uptake model incorporating NHE3; the mRNA was highly expressed in freshwater, and the immunoreactivity was found at the apical membrane of other freshwater-specific MRCs.

Behavior and Gill profile of Nile Tilapia (Oreochromis niloticus) Induced by Density stress

The aim of this research was to observe behavior and gill profile of nile tilaphia (Oreochromis niloticus) induced by density stress. A total of 50 nile tilapia fish with the age of 3-8 months and 80-100 bwwere divided into 4 groups. Group I was control group contained 5 fish, group II,III, and IV contained 10, 15, and 20 fish, respectively. Treatment was performed for 24 hours, and fish behavior was observed every 3 hours. Gillsample was examined by anatomical pathology then tissue samples were collected and fixed in 10% Davidson solution, routinely processed,embedded in paraffin, sectioned at 5 microns, stained with hematoxylin and eosin (HE), and examined by light microscopy. The data wasanalyzed descriptively. Behavior changessuch as swim up to water surface and rapid movement of operculum occur earlier than passivemovement and decreased reflex of fish on group II, III, and IV. The anatomical pathology of nile tilapia gills observed were darker colour ofgills, gill rott, and over mucus.Histopathological result showed that haematoma, necrosis, hyperplasia of primary and secondary lamella, andfusion lamella were observed in gills of nile tilapia induced by density stress.____________________________________________________________________________________________________________________Key words: histopathology, nile tilapia, gill, density stress

Phenotypic Changes in Mitochondrion-Rich Cells and Responses of Na+/K+-ATPase in Gills of Tilapia Exposed to Deionized Water

The aim of this study was to illustrate the phenotypic modification of mitochondrion-rich (MR) cells and Na(+)/K(+)-ATPase (NKA) responses, including relative protein abundance, specific activity, and immunolocalization in gills of euryhaline tilapia exposed to deionized water (DW) for one week. The plasma osmolality was not significantly different between tilapia of the local fresh water (LFW) group and DW group. Remodeling of MR cells occurred in DW-exposed fish. After transfer to DW for one week, the relative percentage of subtype-I (wavy-convex) MR cells with apical size ranging from 3 to 9 microm increased and eventually became the dominant MR cell subtype. In DW tilapia gills, relative percentages of lamellar NKA immunoreactive (NKIR) cells among total NKIR cells increased to 29% and led to significant increases in the number of NKIR cells. In addition, the relative protein abundance and specific activity of NKA were significantly higher in gills of the DW-exposed fish. Our study concluded that tilapia require the development of subtype-I MR cells, the presence of lamellar NKIR cells, and enhancement of NKA protein abundance and activity in gills to deal with the challenge of an ion-deficient environment.

Salinity regulates claudin mRNA and protein expression in the teleost gill

The teleost gill carries out NaCl uptake in freshwater (FW) and NaCl excretion in seawater (SW). This transformation with salinity requires close regulation of ion transporter capacity and epithelial permeability. This study investigates the regulation of tight-junctional claudins during salinity acclimation in fish. We identified claudin 3- and claudin 4-like immunoreactive proteins and examined their expression and that of select ion transporters by performing Western blot in tilapia (Oreochromis mossambicus) gill during FW and SW acclimation. Transfer of FW tilapia to SW increased plasma osmolality, which was corrected after 4 days, coinciding with increased gill Na+-K+-ATPase and Na+-K+-2Cl(-) cotransporter expression. Gill claudin 3- and claudin 4-like proteins were reduced with exposure to SW. Transfer to FW increased both claudin-like proteins. Immunohistochemistry shows that claudin 3-like protein was localized deep in the FW gill filament, whereas staining was found apically in SW gill. Claudin 4-like proteins are localized predominantly in the filament outer epithelial layer, and staining appears more intense in the gill of FW versus SW fish. In addition, tilapia claudin 28a and 30 genes were characterized, and mRNA expression was found to increase during FW acclimation. These studies are the first to detect putative claudin proteins in teleosts and show their localization and regulation with salinity in gill epithelium. The data indicate that claudins may be important in permeability changes associated with salinity acclimation and possibly the formation of deeper tight junctions in FW gill. This may reduce ion permeability, which is a critical facet of FW osmoregulation.

Regulation of glycogen metabolism in gills and liver of the euryhaline tilapia (Oreochromis mossambicus) during acclimation to seawater

Glucose, which plays a central role in providing energy for metabolism, is primarily stored as glycogen. The synthesis and degradation of glycogen are mainly initialized by glycogen synthase (GS) and glycogen phosphorylase (GP), respectively. The present study aimed to examine the glycogen metabolism in fish liver and gills during acute exposure to seawater. In tilapia (Oreochromis mossambicus) gill, GP, GS and glycogen were immunocytochemically colocalized in a specific group of glycogen-rich (GR) cells, which are adjacent to the gill's main ionocytes, mitochondrion-rich (MR) cells. Na+/K+-ATPase activity in the gills, protein expression and/or activity of GP and GS and the glycogen content of the gills and liver were examined in tilapia after their acute transfer from freshwater (FW) to 25 per thousand seawater (SW). Gill Na+/K+-ATPase activity rapidly increased immediately after SW transfer. Glycogen content in both the gills and liver were significantly depleted after SW transfer, but the depletion occurred earlier in gills than in the liver. Gill GP activity and protein expression were upregulated 1-3 h post-transfer and eventually recovered to the normal level as determined in the control group. At the same time, GS protein expression was downregulated. Similar changes in liver GP and GS protein expression were also observed but they occurred later at 6-12 h post-transfer. In conclusion, GR cells are initially stimulated to provide prompt energy for neighboring MR cells that trigger ion-secretion mechanisms. Several hours later, the liver begins to degrade its glycogen stores for the subsequent energy supply.

Juvenile Tilapia (Oreochromis mossambicus) Strive to Maintain Physiological Functions After Waterborne Copper Exposure

Juvenile tilapia were acutely exposed to 0.2 and 2 mg/L Cu(2+) for up to 144 h. The Na(+)-K(+)-ATPase (NKA)-specific activity in the gills of tilapia exposed to 0.2 mg/L Cu(2+) significantly decreased over 48-72 h and was restored to the control level after 96 h, but was again depressed during 120-144 h. The whole-body Cl(-) levels significantly decreased after 48 h, but recovered shortly afterwards and continued to do so until 144 h with 0.2 mg/L Cu exposure. During 48-72 h, the numbers of the wavy-convex type of mitochondria-rich (MR) cells appeared to significantly increase and the cortisol content also significantly increased. Changes in MR cell morphology might be necessary in order to enhance Cl(-) uptake, and this might be related to changes in cortisol levels. Whole-body Na(+) concentrations had significantly decreased by 72 h, but recovered during 96-144 h. Whole-body Cu(2+) concentrations also significantly increased compared to the initial concentration during 72-144 h of Cu exposure. All measured parameters (NKA activity, Na(+) concentration, and MR cell numbers) significantly decreased in fish exposed to 2 mg/L Cu, and no recovery was observed. These data demonstrate that juvenile tilapia strived to maintain physiological functions after exposure to sub-lethal concentrations of Cu.

Seasonal Trends in Gill Bacterial Flora of Hybrid Tilapia, Oreochromis niloticus × O. aureus

ABSTRACT Seasonal bacterial flora associated with the gills of hybrid tilapia, Oreochromis niloticus × O. aureus, cultured in earthen ponds were studied quantitatively and qualitatively for the first time in Saudi Arabia at quarterly intervals for one year. The recovered isolates were identified to species level where possible. Total viable counts (TVC) of bacteria in the gills ranged from 9.8±0.9 × 105 to 4.2±3.1× 106 colony forming units (cfu)/g of gills in spring, 3.9±1.7 × 106 to 1.1±2.4 × 107 cfu/g in summer, 6.5±2.3 × 106 to 4.2±2.6 × 107cfu/g in autumn, and 1.9±2.0 × 105 to 1.2±2.9 × 106 cfu/g in winter. In total, 15 bacterial genera were identified from the gills of tilapia and less diversification of bacterial genera (7) was observed in summer. The bacterial population was dominated by Gram-negative rods (77%). In all the seasons, Aeromonas hydrophila, Shewanella putrefaciens, Escherichia coli, and Corynebacterium sp. were the most abundant species with a prevalence of >10%. Aeromonas hydrophila was 26%, significantly higher (P < 0.005) in the population. Pseudomonas fluorescens was present in considerable number only during winter. Pseudomonas sp., Pasteurella sp., and Bacillus sp. were observed in most of the seasons. The variation of ambient seasonal temperature could account for some of the variation in the bacterial population.