Ultrastructure of otolith increments and checks in the teleost fish Oreochromis niloticus

An otolith increment is composed of an incremental zone and a discontinous zone. Observation of the otoliths of Oreochromis niloticus with transmission and scanning electron microscopy reveals that organic fibers are concentrated in the discontinuous zone and are relatively scarce in the incremental zone. On the other hand, calcium carbonate crystals are chiefly packed in the incremental zone and are less dense in the discontinuous zone. Both fibers and crystals are oriented perpendicular to the growth increments. Otolith checks, or discontinuities, contain even denser fibers and fewer fine crystals than does the discontinuous zone. A higher proportion of individual fibers is prominently stained in the discontinuous zone and check than in the incremental zone. Other features of individual fibers appear to be the same among the three zones. The crystals on either side of a check or a discontinuous zone resemble each other both in size and orientation. Zonation of protein and mineral components of otoliths can be understood in terms of both incremental growth and the daily cycle of deposition.     

Fine structure of the branchial epithelium in the teleost Oreochromis niloticus

We have studied the gill epithelium of Oreochromis niloticus using transmission electron microscopy with the particular interested relationship between cell morphology and osmotic, immunoregulatory, or other non‐regulatory functions of the gill. Pavement cells covered the filament epithelium and lamellae of gills, with filament pavement cells showing distinct features from lamellar pavement cells. The superficial layer of the filament epithelium was formed by osmoregulatory elements, the columnar mitochondria‐rich, mucous and support cells, as well as by their precursors. Light mitochondria‐rich cells were located next to lamellae. They exhibited an apical crypt with microvilli and horizontal small dense rod‐like vesicles, sealed by tight junctions to pavement cells. Dark mitochondria‐rich cells had long dense rod‐like vesicles and a small apical opening sealed by tight junctions to pavement cells. The deep layer of the filament epithelium was formed by a network of undifferentiated cells, containing neuroepithelial and myoepithelial cells, macrophage and eosinophil‐like cells and their precursors, as well as precursors of mucous cells. The lateral‐basal surface was coated by myoepithelial cells and a basal lamina. The lamellar blood lacunae was lined by pillar cells and surrounded by a basal lamina and pericytes. The data presented here support the existence of two distinct types of pavement cells, mitochondria‐rich cells, and mitochondria‐rich cells precursors, a structural role for support cells, a common origin for pavement cells and support cells, a paracrine function for neuroepithelial cells in the superficial layer, and the control of the lamellar capillary base by endocrine and contractile cells. Data further suggest that the filament superficial layer is involved in gill osmoregulation, that may interact, through pale mitochondria‐rich cells, with the deep layer and lamellae, whereas the deep layer, through immune and neuroendocrine systems, acts in the regeneration and defense of the tissue. J. Morphol. 2010. © 2010 Wiley‐Liss, Inc.     

Effect of the hydrostatic pressure on otolith growth of early juveniles of Nile tilapia Oreochromis niloticus

Nile tilapia Oreochromis niloticus early juveniles were maintained for 2 weeks in a pressurized system under a controlled photoperiod, at constant salinity and temperature. Groups of fish were exposed to one of three absolute hydrostatic pressure (HP) regimes: (1) a constant normal atmospheric pressure (100 kPa), (2) a constant 40 m pressure (500 kPa) or (3) a semi-diurnal cyclic vertical migration (100-500 kPa). No significant differences were detected in otolith size and incremental periodicity among the three HP treatments, suggesting that HP does not affect otolith growth of early juveniles O. niloticus.     

Initial development of Oreochromis niloticus (Teleostei: Cichlidae) otolith

Otoliths of Oreochromis niloricus initiate as separate protein granules, surrounded by numerous dark particles. These granules merge to form the sub-primordium, after a layer of calcium and a layer of protein has been added to each one. Large amounts of protein are accreted on to the subprimordium to form the primordium. Calcification takes place shortly afterwards. In the otocyst lumen filaments and vesicles are abundant and associated. They seem to contribute to the proteins of the primordium and the calcified otolith. Mitochondria, Golgi complexes and intracellular granules are abundant in the epithelium, from which vesicles extrude.     

Cardiac tissue function of the teleost fish Oreochromis niloticus under different thermal conditions

The cardiac responses of Oreochromis niloticus acclimated to 25 degrees C were assessed using ventricle strips mounted for isometric force recording (Fc) and in vivo heart rate (f(H)). f(H) increased progressively from 25 to 40 degrees C. At extracellular Ca(2+) concentrations of 1.25 and 9.25 mM, a transition from 25 to 40 degrees C resulted in a decreased Fc. At both 25 and 40 degrees C, Fc rose when [Ca(2+)] was increased from 1.25 to 9.25 mM. Fc remained constant at 72 and 120 contractions.min(-1) at 25 and 40 degrees C, respectively, and declined thereafter. The post-rest potentiation was not influenced by ryanodine, indicating that the sarcoplasmic reticulum is not important to the excitation-contraction coupling.     

Enhancement of growth of tilapia Oreochromis niloticus in iso-osmotic medium

Tilapia ( Oreochromis niloticus ) kept in 15 ppt sea water (roughly iso-osmotic salinity) had higher growth rates than fish kept in 0 ppt (freshwater) or 30 ppt seawater, but circulating level of growth hormone was highest in fish exhibiting the poorest growth rate (30 ppt seawater). Serum thyroxine concentration was highest in 15 ppt seawater. Intestinal trypsin may play a role in promoting growth in iso-osmotic salinity since its activity was highest in fish cultured in 15 ppt seawater. The results indicate that changes in the digestive power, coupled with changes in thyroxine secretion, may account for the variations in growth rate in tilapia reared under different salinities.     

Relationship of respiration to body weight in the tilapia Oreochromis niloticus under resting and normoxic conditions

• 1.1. The relationships of oxygen consumption (V_o2, ml/min/fish), ventilation volume (V_g, ml/min/fish), stroke volume (V_s, ml/stroke/fish), respiration frequency (RF, stroke/min) and oxygen utilization (U, %) to body weight (W, g) in the tilapia under resting and normoxic conditions were V_o2 = 0.002835W^0.754193, V_g = 0.688965W^0.722786, V_s = 0.002790W^1.017188, RF = 248.58210W^−0.296139, U = 0.000935W + 87.394288, respectively.

     

Mechanism of biosynthesis of trimethylamine oxide from choline in the teleost tilapia, Oreochromis niloticus, under freshwater conditions

The mechanism of biosynthesis of trimethylamine oxide (TMAO) from dietary precursors in the teleost tilapia (Oreochromis niloticus) was investigated. Diets supplemented with quaternary ammonium choline, glycine betaine, carnitine or phosphatidylcholine were administered and significant increases in TMAO levels in the muscle were only observed with choline. [Methyl-14C] and [1,2-14C] cholines were given through dietary and intraperitoneal injection routes, but 14C-TMAO was detected only in fish with dietary administration of [methyl-14C] choline. Dietary treatment with [15N] choline resulted in the formation of [15N] TMAO in the muscle. The incorporation of radioactivity into TMAO was also observed both following dietary administration and intraperitoneal injection of [14C] trimethylamine (TMA). When choline was introduced into the isolated intestine, marked increases in TMA levels occurred. These increases were significantly suppressed in the presence of penicillin. [14C]-TMA derived from [methyl-14C] choline was detected in the cavity of the isolated intestine. The introduction of [15N] choline into the intestinal cavity resulted in the formation of [15N] TMA. TMA mono-oxygenase activities were detected in the liver and kidney. We conclude that tilapia possess the ability to produce TMAO from choline, which is related to intestinal microorganisms and tissue mono-oxygenase under freshwater conditions.     

Effect of sublethal concentrations of copper on the growth performance of Oreochromis niloticus

The study evaluated the effect of different sublethal concentrations of copper in water (0, 0.15, 0.3 and 0.5 p.p.m.) on the behavioural response, growth performance, and whole body and liver composition of Oreochromis niloticus. Hyperactivity and reduced exploratory behaviour were observed when fishes were subjected to different levels of copper in water as compared with the control. Fish refused to accept the feed immediately after exposure and only began taking it up after about 4–5 h as compared with the control. Weight gain, specific growth rate and condition factor (k) decreased significantly (P < 0.05) as compared with the control; this decrease was linearly correlated with the increase of copper concentration in water. Exposure of the fish to different copper concentrations in water significantly (P < 0.05) reduced their feed consumption as compared with the control. Values for the feed conversion ratio increased (P < 0.05) whereas the protein efficiency ratio and net protein retention values decreased (P < 0.05) with the copper level increase in water. The hepatosomatic index increased with the copper concentration increase in water. Body moisture and ash contents were the highest (P < 0.05) whereas the fat and gross energy contents were the lowest (P < 0.05) in fish reared in water containing 0.5 p.p.m. of copper as compared with others. No significant (P < 0.05) differences were observed in the whole body crude protein content of fish exposed to different concentrations of copper as compared with the control. Liver moisture and ash contents increased (P < 0.05) whereas the crude protein, fat, nitrogen free extract and gross energy contents decreased (P < 0.05) when the fish were exposed to different concentrations of copper as compared with the control. The liver glycogen level decreased whereas the copper level in the whole body and liver increased significantly (P < 0.05) with the copper concentration increase in water.     

Innate sound production in the cichlid Oreochromis niloticus

The mouthbrooding cichlid Oreochromis niloticus is one of the world's best-studied fish and is raised extensively for aquaculture. Although it is a common behavioural model, its acoustic communication has been neglected. Because of extensive parental care, the species is a good candidate for vocal learning. In male O. niloticus , we investigated for the first time sound production in agonistic interactions during nest construction. Males produce short-duration (250–400 ms), often double-pulse sounds. Most energy is below 200 Hz and includes three main low-frequency peaks although energy extends beyond 1 kHz. Males (separated as eggs and raised in isolation) produce similar sounds in the same context as parental fish, indicating that the ability to produce sounds and the basic properties of the sounds are innate.     

A high molecular weight glycoprotein in seminal plasma is a sperm immobilizing factor in the teleost Nile tilapia, Oreochromis niloticus

Sperm that have acquired potential for motility are kept immotile in seminal plasma in the teleost, Nile tilapia. In order to investigate the mechanism of immobilization, several experiments were performed using a previously characterized monoclonal antibody (TAT-30) against a molecular weight (Mr) = 120,000 protein that is secreted by Sertoli cells and epithelial cells of the sperm duct, and is also bound to the head of the spermatozoon. First, we assessed sperm motility in the seminal plasma protein fraction (SPP), and demonstrated that the sperm motility is inhibited by SPP in a concentration-dependent manner. Furthermore, sperm motility was recovered if SPP was pretreated with TAT-30, suggesting that the TAT-30 antigen is one of the components of the sperm immobilizing factor. Calibration by gel filtration followed by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting with TAT-30 demonstrated that the sperm immobilizing factor was more than Mr = 1,000,000 in seminal plasma, suggesting that it is a homopolymer of the Mr = 120,000-TAT-30 positive protein. Additionally, lectin blot analysis showed that the TAT-30 antigen was reactive with Lens culinarin agglutinin (LCA) and Conavalia ensiformis agglutinin (ConA), indicating that it is a glycoprotein. Immunohistochemical studies showed that the TAT-30 antigen was localized specifically on the heads of spermatozoa and on the apical surface, lysosomes and rough endoplasmic reticulum of Sertoli cells.     

Molecular cloning and immunohistochemical localization of ubiquitin C-Terminal hydrolase expressed in testis of a teleost,the Nile Tilapia,Oreochromis niloticus

We previously produced four monoclonal antibodies to testicular proteins of a teleost, the Nile tilapia. One of the monoclonal antibodies, TAT(Testicular Antigen of Tilapia)-10, recognizes a Mr=27,000 protein (27 kD protein), which is present in A and early B type spermatogonia, spermatids, and spermatozoa in testis. In order to clarify the function of this protein, molecular cloning was conducted. The cDNA for the 27 kD protein contains a complete open reading frame encoding 220 amino acid residues. The predicted amino acid sequence of the 27 kD protein was homologous to those of the ubiquitin carboxy-terminal hydrolases (UCH) reported in mammals. The measurement of the ubiquitin-releasing activity of the recombinant 27 kD protein revealed that the protein is the active form of UCH. Northern blot analysis showed that the UCH mRNA was expressed in ovary and brain in addition to the testis. Immunohistochemical study showed that, in brain, UCH was localized especially on the olfactory organ including the olfactory bulb and olfactory epithelium in olfactory rosetta, suggesting the involvement of the protein in chemoreceptive function. In the Tilapia ovary, UCH localized especially in pre-vitellogenic oocytes, suggesting that the enzyme activity could be important in oocyte growth. This is the first report for the cDNA cloning and cellular localization of UCH in fish. J. Exp. Zool. 293:368-383, 2002.     

Enzymatic responses to metal exposures in a freshwater fish Oreochromis niloticus

Freshwater fish Oreochromis niloticus were exposed to 5, 10 and 20 microM concentrations of Cd, Cu, Zn and Pb for 14 days and responses of several enzymes were determined subsequently. Liver catalase (CAT) activity was influenced by Cd and Pb exposures, while it was inhibited by Zn exposure. Copper, on the other hand, did not cause significant changes in CAT activity. Liver alkaline phosphatase (AP) activity was first stimulated at lowest (5 microM) exposure concentration, while there were significant inhibitions at higher (10 microM) exposure concentration. At the highest (20 microM) exposure concentration, AP activity was compensated coming to the control level, except Pb exposure. Intestine and serum AP activities were stimulated by all Zn exposures and 10 microM Cu exposure, while other exposures did not cause significant changes on AP activity. Na,K-ATPase activity in the gill and intestine was inhibited by all the metal exposures, except 20 microM Pb exposure that resulted in an increase in the activity in the gill. Similarly, muscle Ca-ATPase activity was inhibited by all the metal exposures, except Cu exposures. This study indicated that enzymatic systems may be used as a sensitive bioindicator of metal contamination in aquatic systems. Nevertheless, the results also stress the importance of addressing the sensitivity of these enzymes when they are used as a bioindicator for metal contamination, because the responses of the enzymes varied considerably according to metal types and concentrations.     

The first mitochondrial 5-methylcytosine map in a non-model teleost (Oreochromis niloticus) reveals extensive strand-specific and non-CpG methylation

DNA methylation is one of the main epigenetic mechanisms that regulate gene expression in a manner that depends on the genomic context and varies considerably across taxa. This DNA modification was first found in nuclear genomes of eukaryote several decades ago and it has also been described in mitochondrial DNA. It has recently been shown that mitochondrial DNA is extensively methylated in mammals and other vertebrates. Our current knowledge of mitochondrial DNA methylation in fish is very limited, especially in non-model teleosts. In this study, using whole-genome bisulfite sequencing, we determined methylation patterns within non-CpG (CH) and CpG (CG) contexts in the mitochondrial genome of Nile tilapia, a non-model teleost of high economic importance. Our results demonstrate the presence of mitochondrial DNA methylation in this species predominantly within a non-CpG context, similarly to mammals. We found a strand-specific distribution of methylation, in which highly methylated cytosines were located on the minus strand. The D-loop region had the highest mean methylation level among all mitochondrial loci. Our data provide new insights into the potential role of epigenetic mechanisms in regulating metabolic flexibility of mitochondria in fish, with implications in various biological processes, such as growth and development.     

Effects of sodium chloride on water quality and growth of Oreochromis niloticus in earthen ponds

A 2 × 2 factorial experiment was conducted between April and August 2001 to evaluate the effects of NaCl on Oreochromis niloticus growth and water quality in twelve 0.015 ha limed ponds. The design involved fertilizer and salt as factors with two treatments for each factor. Each salt‐fertilizer combination was replicated three times and fish were not offered external food during the 98 days culture. Growth of O. niloticus was significantly enhanced by salt at higher fertilizer level but not at the lower fertilization level. Although salt had no direct effect on fish growth, a significant salt‐fertilizer interaction was demonstrated. Water quality variables, with a few exceptions, were similar among the salted treatments. Total ammonia increased significantly with fertilization level, but the values were similar in salted and unsalted treatments at the same fertilizer level. Total nitrogen was higher in the salted than unsalted treatments while the organic matter content was lower in the salted treatments. The reasons for the better growth of O. niloticus, are discussed with respect to water quality variables. The present results suggest that fertilization rates of 20 kg N ha^?1 may have negative effects on fish growth. However, presence of sodium chloride seems to reduce these negative effects.     

Differential expression of vasa homologue gene in the germ cells during oogenesis and spermatogenesis in a teleost fish, tilapia, Oreochromis niloticus

Vas (a Drosophila vasa homologue) gene expression pattern in germ cells during oogenesis and spermatogenesis was examined using all genetic females and males of a teleost fish, tilapia. Primordial germ cells (PGC) reach the gonadal anlagen 3 days after hatching (7 days after fertilization), the time when the gonadal anlagen was first formed. Prior to meiosis, no differences in vas RNA are observed in male and female germ cells. In the ovary, vas is expressed strongly in oogonia to diplotene oocytes and becomes localized as patches in auxocytes and then strong signals are uniformly distributed in the cytoplasm of previtellogenic oocytes, followed by a decrease from vitellogenic to postvitellogenic oocytes. In the testis, vas signals are strong in spermatogonia and decrease in early primary spermatocytes. No vas RNA expression is evident in either diplotene primary spermatocytes, secondary spermatocytes, spermatids or spermatozoa. The observed differences in vas RNA expression suggest a differential function of vas in the regulation of meiotic progression of female and male germ cells.     

Immunohistochemical identification of a vacuolar proton pump (V-ATPase) in bone-resorbing cells of an advanced teleost species, Oreochromis niloticus

Poly-and monoclonal antibodies, raised against mammalian membrane-bound proton pump (V-ATPase) were applied to the bone-resorbing cells of Oreochromis niloticus to clarify if osteoclasts of an advanced teleost species display V-ATPase, a key enzyme in the process of bone resorption. All antibodies labelled cells at known sites of bone resorption, the endosteal bone surfaces surrounding the tooth anlagen. The best results were achieved with a monoclonal antibody (E11). Although the majority of labelled cells were flat and mononucleated, the occurrence of V-ATPase in these cells indicates that they function as active bone-resorbing cells. The monoclonal antibody E11 was also applied successfully to monocytes, cells that are believed to be related most closely to osteoclasts. The assignment of V-ATPase to boneresorbing cells of O. niloticus was confirmed by application of the additional osteoclast markers, tartrate-resistant acid phosphatase (TRAP) and tartrate-resistant ATPase (TraATPase). Co-expression of V-ATPase, TRAP and TraATPase in fish osteoclasts is demonstrated for the first time.