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.     

Respiratory responses of Oreochromis niloticus (Pisces, Cichlidae) to environmental hypoxia under different thermal conditions

The oxygen uptake ( V O₂), breathing frequency ( f _R), breath volume ( V _S.R), gill ventilation ( V G) and oxygen extraction (%) from the ventilatory current of four groups of Oreochromis niloticus during graded hypoxia were measured under the following acclimation temperatures: 20. 25. 30 and 35°C. The critical oxygen tensions ( P O₂), determined from V O₂ v. P O₂ of inspired water at each experimental temperature were, respectively. 19±1±3±1. 18±0±4±9, 29±7± 4±1 and 30±2± 0.6 mmHg. The f _R remained nearly constant during the reductions of O₂ at all the temperatures studied. V G increased discretely from normoxic levels until the P O₂ was reached, below which it assumed extremely high values (17-fold higher or more). The increases observed in V G resulted, at all the acclimation temperatures, in an elevation in V _S.R rather than in f _R. The extraction of O₂ decreased gradually from normoxia until the P O₂ was reached, below which an abrupt reduction of extraction was recorded, except at 35°C when fish showed a gradual reduction in extraction just below the tension of 80 mmHg.     

Evidence of cylindrospermopsin uptake and clearance in fish (Oreochromis niloticus) under laboratory conditions

Cylindrospermopsin (CYN) is a cyanotoxin that has raised serious concerns about public health in many parts of the world. It can bioaccumulate and affect the health of aquatic organisms, but despite this, few studies have been conducted on CYN uptake and clearance in fish. In this paper, the authors evaluate the uptake and clearance of CYN in the muscle tissue and viscera of juvenile tilapia (Oreochromis niloticus) after exposure to aqueous extracts and whole cells of Cylindrospermopsis raciborskii (CYN-producer). CYN blended with commercial fish food, and three experiments were conducted. In the first trial, fish food, and aqueous extracts containing 0.31 μg CYN g⁻¹ of food per day, was administered to tilapia for 15 days. In the second trial, fish were provided food and intact cells (5.4 μg CYN g⁻¹ of food per day) for 15 days. In the last trial, they were provided fish food and aqueous extracts (0.8 μg CYN g⁻¹ of food per day) for 12 days, and for the next 10 days, the animals were fed food without toxic cell extracts (to simulate a clearance period). The concentration of CYN in muscle tissue and viscera was analysed using ELISA. In the case of juvenile tilapia, the presence of CYN was higher in viscera than in muscle tissue, and the toxin remained in the tissues even after 10 days without the addition of contaminated food. The results suggest that tilapia represents a potential source of CYN transfer through the food web, and this shows the need for a continuous monitoring of this compound in organisms that are used for human and animal consumption.     

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.     

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.     

Relationship of saccular ultrastructure to otolith growth in the teleost Oreochromis niloticus

The sacculus of Oreochromis niloticus is anatomically separated from the utriculus and semicircular canals. The saccular wall is composed of the sensory epithelium, transitional epithelia, and squamous epithelium. Cellular granules are abundant in the sensory and transitional epithelia but scarce in the squamous epithelium. Over the dorsal side of the dorsal transitional epithelium there exists an oval patch of cells with distinctive microvilli. New finding is a shallow groove which extends from the anterior end of the sensory epithelium approximately halfway down along the ventral perimacular transitional epithelium. Small vesicles, which appear “empty” under transmission electron microscopy (TEM), are aggregated in the posterior region of the groove. These small vesicles are also present in both the sensory and transitional epithelia. A second kind of vesicle is comparatively large and appears filled with stainable contents. These vesicles are restricted to the sensory region. Both kinds of vesicles appear to be involved in apical secretion and possibly provide the otolithic membrane with fibers. The otolithic membrane is composed of a gelatinuous layer and subcupular meshwork. The meshwork appears to contribute to the formation of the otolith. The small empty vesicles appear to originate in sensory and transitional epithelial cells and may form the subcupular meshwork. The larger filled vesicles are derived predominantly from sensory cells in the sensory epithelium and appear to contribute to the gelatinuous layer of otoliths. © 1992 Wiley-Liss, Inc.     

Mhc class I genes of the cichlid fish Oreochromis niloticus

In terms of number of species, perciform (perch-like) fishes are one of the most diversified groups of modern vertebrates. Within this group, the family Cichlidae is best known for its spectacular adaptive radiation in the great lakes of East Africa. The molecular tool kit used in the study of this radiation includes the major histocompatibility complex (Mhc) genes. To refine this tool, information about the organization of the Mhc regions is badly needed. In this study, the first step was taken toward providing such information for the Mhc class one regions of Oreochromis niloticus, a representative species of the tilapiine branch of the Cichlidae, for which good bacterial artificial chromosome library is available. Screening of the library with class I gene probes led to the identification and isolation of 31 class-I-positive clones. Sequencing of one of these clones and partial characterization of the remaining clones for the presence of class I exons resulted in the construction of two contigs representing the class I region of this species as well as identification of seven additional class-I-positive singleton clones. The O. niloticus genome was shown to contain at least 28 class I genes or gene fragments. The shorter of the two contigs was approximately 330 kb long and contained eight class I genes/gene fragments; the longer contig encompassed 1,200 kb of sequence and contained minimally 17 class I genes/gene fragments; three additional class I genes were found to be borne by a clone that might be part of the shorter contig. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. This work had been carried out in part at the Max-Planck-Institut für Biologie, Abteilung Immungenetik, Tübingen, Germany (A.S., R.D., N.T., S.S., and J.K.). The sequences reported in this paper have been deposited in the GenBank database (accession nos. AB270803–AB270897).     

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.

     

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.     

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.     

Expressed sequence tags derived from brain tissue of Oreochromis niloticus

Expressed sequence tags (ESTs) were obtained from complementary DNA libraries derived from the brain of the cichlid fish, Oreochromis niloticus. Single-pass sequencing of 183 cDNA clones generated 294 ESTs; 57 of these clones (31%) were identified based on their similarity to sequences in GenBank.     

Growth requires bone resorption at particular skeletal elements in a teleost fish with acellular bone (Oreochromis niloticus, Teleostei: Cichlidae)

To date, little is known about bone resorption during skeletal development in teleostean fish with acellular bone. We report here about bone resorption with regard to growth in the tilapia Oreochromis niloticus. Nine skeletal elements obtained from growing juveniles were examined using histological and histochemical methods, and transmission electron microscopy (TEM). Tartrate-resistant acid phosphatase (TRAP) served as a marker for bone resorbing cells (osteoclasts), alkaline phosphatase (ALP) was used to identify osteoblasts, and alizarin staining indicated sites of bone formation. TRAP-activity was located at those skeletal elements where growth requires bone resorption, and at sites of cartilage degeneration. No TRAP-activity was found at those skeletal elements where resorption was not required for growth. The examination of the praeopercular shaft leads to a model of bone enlargement, including bone resorption by TRAP-positive cells located at the endosteal bone surface and bone formation by ALP-positive cells located at the periosteal bone surface. TRAP-positive cells were mononucleated and lacked a ruffled border. They appeared either as cell aggregates (resembling the shape of multinucleated giant cells) or as flat cells (resembling bone lining cells). Problems of osteoclast identification in bony fish are discussed.     

A novel cold-adapted imidase from fish Oreochromis niloticus that catalyzes hydrolysis of maleimide

In this paper we report the first comparative study of cold-adapted imidase (EC 3.5.2.2) from the fish (Oreochromis niloticus) liver and its thermophilic counterparts taken from pig liver and Escherichia coli (overexpressed recombinant hydantoinase from Agrobacterium radiobacter NRRL B1). Approximately 6000-fold purification and a 40% yield of fish imidase activity were obtained through ammonium sulfate precipitation, octyl, chelating, DEAE, and hydroxyapatite chromatography. This cold-adapted imidase was characterized by a specific activity 10- to a 100-fold higher than those of its thermophilic counterparts below room temperature (25 degrees C or lower) conditions but less stable at elevated temperatures (40 degrees C or higher). A less organized helical structure (compared to those of pig liver and bacterial imidases) was observed by circular dichroism. Furthermore, maleimide was first identified as a novel substrate of all imidases examined, and confirmed by HPLC and NMR analysis. These results constituted a first study to discover a novel cold-adapted imidase with surprising high activity. These findings might be also helpful for industrial application of imidase.     

A genetic linkage map of a cichlid fish,the tilapia (Oreochromis niloticus).

We have constructed a genetic map for a tilapia, Oreochromis niloticus, using DNA markers. The segregation of 62 microsatellite and 112 anonymous fragment length polymorphisms (AFLPs) was studied in 41 haploid embryos derived from a single female. We have identified linkages among 162 (93.1%) of these markers. 95% of the microsatellites and 92% of the AFLPs were linked in the final map. The map spans 704 Kosambi cM in 30 linkage groups covering the 22 chromosomes of this species. Twenty-four of these linkage groups contain at least one microsatellite polymorphism. From the number of markers 15 or fewer cM apart, we estimate a total map length of approximately 1000-1200 cM. High levels of interference are observed, consistent with measurements in other fish species. This map is a starting point for the mapping of single loci and quantitative traits in cichlid fishes.     

Observations on limnological conditions associated with a fish kill of Oreochromis niloticus in Lake Chivero following collapse of an algal bloom

Possible causes of deaths of Oreochromis niloticus in Lake Chivero were examined in relation to changes in limnological conditions monitored over a 25‐month period. The fish deaths coincided with the collapse of an algal bloom that had developed and builtup in the lake for 8 months. Chlorophyll a and dissolved oxygen increased to average concentrations of 42.4 μg l^?1 and 10.9 mg l^?1 respectively prior to the collapse of the bloom. Dissolved oxygen decreased when the bloom started to die off and coincided with the fish deaths when the average surface dissolved oxygen concentration in the lake was 3.9 mg l^?1 and was at a depth of 5 m <2 mg l^?1. Mortality probably resulted from depressed oxygen levels caused by the high oxygen demand from the massive algal die‐off and released algal toxins. This is the first time that die‐off of algae has been linked to fish‐kills in Lake Chivero as occurs in other hypereutrophic systems.     

Effects of calcium and phosphate on the corpuscles of Stannius of the teleost fish,Oreochromis mossambicus

Summary Removal of the corpuscles of Stannius (CS) in Oreochromis mossambicus leads to hypercalcemia and hypophosphatemia. The effects on CS size and ultrastructure of different calcium and phosphate concentrations of the ambient water and of the food were investigated. A six-fold increase of the calcium concentration of the water leads to a four-fold increase in CS volume; this is mainly caused by an increase in the size and number of the type-1 cells. The effect of external calcium is most probably mediated by the calcium concentration of the blood plasma. Plasma ionic calcium may be the relevant factor. Changes in the calcium concentration of the food had no effect on the CS. Similarly, hyperphosphatemia or hypophosphatemia induced by high phosphate concentrations of the water or the food, or by a phosphate-deficient diet, had no noticeable effect on the CS. The results support the hypothesis that the type-1 cells produce the hypocalcemic factor of the CS. There is no evidence for the production by the CS of an endocrine factor involved in the control of phosphate metabolism.