Gonad pathology and intersex severity in pelagic (Tilapia zilli) and benthic (Neochanna diversus and Clarias gariepinus) species from a pesticide-impacted agrarian catchment, south-south Nigeria

Pesticides are distributed to different degrees in surface water and sediment, thus, risks of toxicity and adverse impacts to physiology of resident species could be determined by their microhabitat (sub-habitat) associations, either water column or sediment. River Owan receives pesticide input from diffuse sources from adjacent farmlands. Surface water, sediment and fish samples [(Pelagic: Tilapia zilli (n = 92) and benthic: Neochanna diversus (n = 59), Clarias gariepinus (n = 68) were collected within the catchment area across seasons for 18-months (August 2016-January 2018) and measured for pesticide levels. Testicular and Ovarian tissue samples across the three species were also examined for pathological alterations. Individual pesticide concentrations in surface water and sediment exceeded international allowable limits, while concentration of pesticide residues in tissues of benthic species was higher compared to pelagic fish. Histopathological assessment revealed a higher incidence of ovarian disruption including atretic follicles, intersex and disorganization of ovarian structure in benthic (bottom-dwelling) fish (C. gariepinus and N. diversus) compared to pelagic (water-column) fish (T. zilli). Males benthic fish species also recorded more severe anomalies, compared to pelagic fish. The damages and anomalies observed in ovarian and testicular tissue indicate chronic responses to pollutant exposure, and implicates the elevation of pesticide concentrations in surface water and sediment above permissible limits. The higher incidence of anomalies recorded for benthic species compared to pelagic species, indicates greater risks of reproductive disruption and could be associated with the microhabitat preferences (water-column or sediment).

A Method for Mass Harvesting Islets (Brockmann Bodies) from Teleost Fish

In certain species of fish, the insulin-producing tissue is uniquely located in separate structures called Brockmann bodies (BBs). Tilapia BBs have been shown to be a simple and inexpensive source of islet cells for xenotransplantation research. Each donor tilapia contains roughly 12-15 BBs, measuring from 0.3 to 5.0 mm in maximum dimension, in a triangular region of adipose tissue bounded by the liver, stomach, and spleen/gallbladder. At present, the larger BBs (usually 2-4) are harvested by microdissecting these “BB regions” using jeweler's forceps and microvascular scissors while being visualized with the aid of a dissecting microscope. It is a simple but time-consuming task that would not be applicable for harvesting massive amounts of BB tissue for large animal studies. Therefore, we have developed an easier and more efficient method of harvesting BBs based on a standard enzymatic method for isolating human adipocytes. BB regions are harvested from donor fish and pooled into a 50 mL plastic tube containing collagenase Type II (3 mg/mL) in Hank's balanced salt solution (HBSS); the tube is then placed in a 37°C waterbath/shaker for roughly 15 min. The exact length of the digestion interval is determined by visual inspection of the tube to determine whether the BBs have been liberated. The digestion is then stopped by adding excess cold HBSS. The adipocytes float while the BBs and residual connective tissue (i.e., a few blood vessels, nerves, and bile ducts) form a pellet. The pellet is washed several times in HBSS and then placed in a culture dish. The BBs are easily handpicked with a siliconized pipette. Based on functional data and DNA content, this new method roughly doubles or triples our yield of BB tissue per donor fish. To determine whether BBs harvested in this manner functioned in a manner similar to those harvested by microdissection, we performed a series of transplants using mass-harvested BBs. Long-term normoglycemia was achieved in streptozotocin-diabetic nude mice and mean graft survival time was not altered in streptozotocin-diabetic euthymic balb/c mice. However, the total weight of donor fish required per recipient was decreased by 50% in both strains.

Histopathological analysis of tilapia gills (Oreochromis niloticus Linnaeus, 1758) exposed to sugarcane vinasse

Sugarcane vinasse is one of the main residues generated by the transformation of cane into ethanol. Because of the high organic content (COD), high biochemical oxygen demand (BOD), low pH, the large amount that this residue is generated (15l for every liter of ethanol produced) and their use as fertilizer on the sugarcane crop, this residue is potentially polluting to the soil ecossystem and by percolation to water ecossystem too. Thus, this study aimed to assess the toxicity of vinasse by analyzing Oreochromis niloticus gills exposed to different dilutions (1%, 2.5%, 5% and 10%) in two bioassays. The gills were collected, fixed and analyzed using ultra morphological, histological, and histochemical techniques. After exposure to the vinasse, a statistically significant reduction of the ridges present on the surface of pavimentous cells was observed in one of the bioassays; such structures are responsible for mucus retention, which helps to protect the tissue. In addition, an intumescence of the cells was observed in the treatments with vinasse as well as an increase in the amount of chloridric cells. Some striking tissue changes detected in the treatments were epithelial detachment and loss of integrity of secondary lamellae, causing their rupture and consequent hemorrhage. In the first bioassay, the amount of these changes was statistically significant at the 5% dilution, and the focus of hemorrhage was significant at all dilution ratios. In the second bioassay, the epithelial disorganization was statistically significant only at the 2.5% dilution of vinasse. Moreover, for both bioassays performed, a significant increase in mucous cells was observed when compared with the control. Our results demonstrate the toxic action of sugarcane vinasse, which caused histopathological changes in the exposed animals at all four dilution tested. This highlights the need for caution in the disposal of sugarcane vinasse on the soil, especially due to its capacity for being leached or percolated into water resources, which could seriously damage aquatic fauna.

Endocrine-disruptor molecular responses, occurrence of intersex and gonado-histopathological changes in tilapia species from a tropical freshwater dam (Awba Dam) in Ibadan, Nigeria

In the present study, the occurrence of endocrine disruptive responses in Tilapia species from Awba Dam has been investigated, and compared to a reference site (Modete Dam). The Awba Dam is a recipient of effluents from University of Ibadan (Nigeria) and several other anthropogenic sources. A total of 132 Tilapia species (Sarotherodon malenotheron (n=57 and 32, males and females, respectively) and Tilapia guineensis (n=23 and 20, males and females, respectively)) were collected from June to September 2014. At the reference site, samples of adult male and female S. melanotheron (48 males and 47 females) and T. guineensis (84 males and 27 females) were collected. Gonads were morphologically and histologically examined and gonadosomatic index (GSI) was calculated. Hepatic mRNA transcriptions of vitellogenin (Vtg) and zona radiata protein (Zrp) genes were analyzed using validated RT-qPCR. Significant increase in Vtg and Zrp transcripts were observed in male tilapias from Awba Dam, compared to males from the reference site. In addition, male tilapias from Awba Dam produced significantly higher Vtg and Zrp mRNA, compared to females in June and July. However, at the natural peak spawning period in August and September, females produced, significantly higher Vtg and Zrp mRNA, compared to males. Fish gonads revealed varying incidence of intersex with a striking presence of two (2) pairs of testes and a pair of ovary in S. melanotheron from Awba Dam. The entire fish population examined at Awba Dam showed a high prevalence of intersex (34.8%), involving phenotypic males and females of both species. Analysis of sediment contaminant levels revealed that As, Cd, Pb, Hg and Ni (heavy metals), monobutyltin cation, 4-iso-nonyphenol and PCB congeners (138, 153 and 180) were significantly higher in Awba Dam, compared to the reference site. Principal component analysis (PCA) showed that fish variables were positively correlated with sediment contaminant burden at Awba Dam, indicating that the observed endocrine disruptive responses are associated with contaminant concentrations. Overall, the occurrence of intersex and elevated expressions of Vtg and Zrp in male fish, suggest that the measured contaminants were eliciting severe endocrine disruptive effects in Awba Dam biota, which is an important source of domestic water supply and fisheries for the University of Ibadan community.

Anatomical and functional gonadotrope networks in the teleost pituitary

Mammalian pituitaries exhibit a high degree of intercellular coordination; this enables them to mount large-scale coordinated responses to various physiological stimuli. This type of communication has not been adequately demonstrated in teleost pituitaries, which exhibit direct hypothalamic innervation and expression of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in distinct cell types. We found that in two fish species, namely tilapia and zebrafish, LH cells exhibit close cell-cell contacts and form a continuous network throughout the gland. FSH cells were more loosely distributed but maintained some degree of cell-cell contact by virtue of cytoplasmic processes. These anatomical differences also manifest themselves at the functional level as evidenced by the effect of gap-junction uncouplers on gonadotropin release. These substances abolished the LH response to gonadotropin-releasing hormone stimulation but did not affect the FSH response to the same stimuli. Dye transfer between neighboring LH cells provides further evidence for functional coupling. The two gonadotropins were also found to be differently packaged within their corresponding cell types. Our findings highlight the evolutionary origin of pituitary cell networks and demonstrate how the different levels of cell-cell coordination within the LH and FSH cell populations are reflected in their distinct secretion patterns.

The three-dimensional structure of anosteocytic lamellated bone of fish

Fish represent the most diverse and numerous of the vertebrate clades. In contrast to the bones of all tetrapods and evolutionarily primitive fish, many of the evolutionarily more advanced fish have bones that do not contain osteocytes. Here we use a variety of imaging techniques to show that anosteocytic fish bone is composed of a sequence of planar layers containing mainly aligned collagen fibrils, in which the prevailing principal orientation progressively spirals. When the sequence of fibril orientations completes a rotation of around 180°, a thin layer of poorly oriented fibrils is present between it and the next layer. The thick layer of aligned fibrils and the thin layer of non-aligned fibrils constitute a lamella. Although both basic components of mammalian lamellar bone are found here as well, the arrangement is unique, and we therefore call this structure lamellated bone. We further show that the lamellae of anosteocytic fish bone contain an array of dense, small-diameter (1-4 μm) bundles of hypomineralized collagen fibrils that are oriented mostly orthogonal to the lamellar plane. Results of mechanical tests conducted on beams from anosteocytic fish bone and human cortical bone show that the fish bones are less stiff but much tougher than the human bones. We propose that the unique lamellar structure and the orthogonal hypomineralized collagen bundles are responsible for the unusual mechanical properties and mineral distribution in anosteocytic fish bone.

Acute exposure to pure cylindrospermopsin results in oxidative stress and pathological alterations in tilapia (Oreochromis niloticus)

Cylindrospermopsin (CYN) is increasingly recognized as a potential threat to drinking water safety, due to its ubiquity. This cyanotoxin has been found to cause toxic effects in mammals, and although fish could be in contact with this toxin, acute toxicity studies on fish are nonexistent. This is the first study showing that single doses of CYN pure standard (200 or 400 μg CYN/kg fish bw) by oral route (gavage) generate histopathological effects in fish (Tilapia-Oreochromis niloticus) exposed to the toxin under laboratory condition. Among the morphological changes, disorganized parenchymal architecture in the liver, dilated Bowman's space in the kidney, fibrolysis in the heart, necrotic enteritis in the intestines, and hemorrhages in the gills, were observed. Moreover, some oxidative stress biomarkers in the liver and kidney of tilapias were altered. Thus, CYN exposure induced increased protein oxidation products in both organs, NADPH oxidase activity was significantly increased with the kidney being the most affected organ, and decreased GSH contents were also detected in both organs, at the higher dose assayed.

Air breathing in Magadi tilapia Alcolapia grahami, under normoxic and hyperoxic conditions, and the association with sunlight and reactive oxygen species

Observations of the Magadi tilapia Alcolapia grahami in hot, highly alkaline Lake Magadi revealed that they air breathe not only during hypoxia, as described previously, but also during normoxia and hyperoxia. Air breathing under these latter conditions occurred within distinct groupings of fish (pods) and involved only a small proportion of the population. Air breathing properties (duration and frequency) were quantified from video footage. Air breathing within the population followed a diel pattern with the maximum extent of pod formation occurring in early afternoon. High levels of reactive oxygen species (ROS) in the water may be an irritant that encourages the air-breathing behaviour. The diel pattern of air breathing in the field and in experiments followed the diel pattern of ROS concentrations in the water which are amongst the highest reported in the literature (maximum daytime values of 2.53 – 8.10 μM H₂O₂). Interlamellar cell masses (ILCM) occurred between the gill lamellae of fish from the lagoon with highest ROS and highest oxygen levels, while fish from a normoxic lagoon with one third the ROS had little or no ILCM. This is the first record of air breathing in a facultative air-breathing fish in hyperoxic conditions and the first record of an ILCM in a cichlid species.

Biomarker responses and morphological effects in juvenile tilapia Oreochromis mossambicus following sequential exposure to the organophosphate azinphos-methyl

Pesticides are contaminants of aquatic environments. Such ecosystems in the Western Cape, South Africa are at risk as most organophosphates are highly toxic to fish and other aquatic organisms. The objective of this experimental study was firstly to determine the acute toxicity of azinphos-methyl (AZP) to juvenile fish (Oreochromis mossambicus) and, secondly, to investigate the effects of repeated exposure of fish to an array of sublethal concentrations on morphological parameters such as growth, condition factor and organ-somatic indices. Food consumption and feeding response time were investigated as ecologically relevant behavioral endpoints which could affect growth, reproduction and survival and subsequently causes impacts at the population and/or community level. Finally, acetylcholinesterase (AChE) was used as biomarker to investigate effects at sub-organismal level following sequential exposure to AZP. The aim was to determine how sequential spraying procedures, using different exposure concentrations and intervals, affected fish as reflected by their responses at different organizational levels. A dose-dependent effect on feeding impairment was observed in the feeding response experiment. The correlation found between growth impairment, feeding activity and AChE inhibition therefore indicates that frequency of exposure can play an important role regarding the severity of impacts to non-target organisms. This study provides evidence that AZP has harmful effects on non-target aquatic organisms, such as fish which can be manifested in the early developmental stages. Sequential exposures showed that dosage and frequency of spraying and spraying interval could exacerbate harmful effects. AChE inhibition and organosomatic indices can be used effectively to measure effects.

Toxicity of melamine, an adulterant in fish feeds: experimental assessment of its effects on tilapia

Unscrupulous inclusion of melamine in fish feeds can be harmful to fish and may be hazardous to human health. An eight-week feeding trial examined the effects of melamine (inclusion levels; 5-30 g kg⁻¹ feed) on the growth performance, feed efficiency, histopathological changes and melamine residues in sex-reversed red tilapia, Oreochromis niloticus (L.) × O.mossambicus (Peters). Fish which received melamine-containing feeds grew less, utilized feeds less efficiently and performed poorly, besides exhibiting defects such as fin erosion, anorexia, sluggish swimming behaviour, paling/darkening of skin and low survival. Melamine concentration in the fish reflected its inclusion level in the feeds, and the content was higher in the viscera than in the fish fillet or whole fish. Histopathological alterations were evident in the kidney, liver and gills of fish subjected to melamine treatment - the severity of lesions corresponded to its dosage. Enlargement of renal tubules was observed in the kidney of fish fed with ≥10 g melamine kg⁻¹ feed, although, crystals were not deposited. Fish subjected to melamine insult had more prominent lesions in liver than in kidney. Toxic effects on the gills manifested as epithelial hyperplasia of the primary and secondary lamellae. The anomalies were severe at higher intake levels of melamine.

Early response of protein quality control in gills is associated with survival of hypertonic shock in Mozambique tilapia

The protein quality control (PQC) mechanism is essential for cell function and viability. PQC with proper biological function depends on molecular chaperones and proteases. The hypertonicity-induced protein damage and responses of PQC mechanism in aquatic organisms, however, are poorly understood. In this study, we examine the short-term effects of different hypertonic shocks on the levels of heat shock proteins (HSPs, e.g., HSP70 and HSP90), ubiquitin-conjugated proteins and protein aggregation in gills of the Mozambique tilapia (Oreochromis mossambicus). Following transfer from fresh water (FW) to 20‰ hypertonicity, all examined individuals survived to the end of experiment. Moreover, the levels of branchial HSPs and ubiquitin-conjugated proteins significantly increased at 3 and 24 h post-transfer, respectively. Up-regulation of HSPs and ubiquitin-conjugated proteins was sufficient to prevent the accumulation of aggregated proteins. However, the survival rate of tilapia dramatically declined at 5 h and all fish died within 7 h after direct transfer to 30‰ hypertonicity. We presumed that this result was due to the failed activation of gill PQC system, which resulted in elevating the levels of aggregated proteins at 3 and 4 h. Furthermore, in aggregated protein fractions, the amounts of gill Na⁺/K⁺-ATPase (NKA) remained relatively low when fish were transferred to 20‰ hypertonicity, whereas abundant NKA was found at 4 h post-transfer to 30‰ hypertonicity. This study demonstrated that the response of PQC in gills is earlier than observable changes in localization of ion-secreting transport proteins upon hypertonic challenge. To our knowledge, this is the first study to investigate the regulation of PQC mechanism in fish and characterize its important role in euryhaline teleost survival in response to hypertonic stress.

A three-dimensional stereotaxic MRI brain atlas of the cichlid fish Oreochromis mossambicus

The African cichlid Oreochromis mossambicus (Mozambique tilapia) has been used as a model system in a wide range of behavioural and neurobiological studies. The increasing number of genetic tools available for this species, together with the emerging interest in its use for neurobiological studies, increased the need for an accurate hodological mapping of the tilapia brain to supplement the available histological data. The goal of our study was to elaborate a three-dimensional, high-resolution digital atlas using magnetic resonance imaging, supported by Nissl staining. Resulting images were viewed and analysed in all orientations (transverse, sagittal, and horizontal) and manually labelled to reveal structures in the olfactory bulb, telencephalon, diencephalon, optic tectum, and cerebellum. This high resolution tilapia brain atlas is expected to become a very useful tool for neuroscientists using this fish model and will certainly expand their use in future studies regarding the central nervous system.

Comparative analysis of reproductive traits in black-chinned tilapia females from various coastal marine, estuarine and freshwater ecosystems

The black-chinned tilapia Sarotherodon melanotheron is a marine teleost characterised by an extreme euryhalinity. However, beyond a certain threshold at very high salinity, the species exhibits impaired growth and precocious reproduction. In this study, the relationships between reproductive parameters, environmental salinity and condition factor were investigated in wild populations of this species that were sampled in two consecutive years (2003 and 2004) from three locations in Senegal with different salinities: Guiers lake (freshwater, 0 psu), Hann bay (seawater, 37 psu) and Saloum estuary (hypersaline water, 66–127 psu). The highest absolute fecundity and spawning weight were recorded in seawater by comparison to either freshwater or hypersaline water whereas the poorest condition factors were observed in the most saline sampling site. These results reflect higher resource allocation to the reproduction due to the lowest costs of adaptation to salinity in seawater (the natural environment of this species) rather than differences in food resources at sites and/or efficiency at foraging and prey availability. Fecundities, oocyte size as well as spawning weight were consistent from year to year. However, the relative fecundity in the Saloum estuary varied significantly between the dry and rainy raisons with higher values in the wet season, which seems to reflect seasonal variations in environmental salinity. Such a reproductive tactic of producing large amounts of eggs in the rainy season when the salinity in the estuary was lower, would give the fry a better chance at survival and therefore assures a high larval recruitment. An inverse correlation was found between relative fecundity and oocyte size at the two extreme salinity locations, indicating that S. melanotheron has different reproductive strategies in these ecosystems. The adaptive significance of these two reproductive modes is discussed in regard to the heavy osmotic constraint imposed by extreme salinities and high inter-specific competition.

Ontogenetic changes in location and morphology of chloride cells during early life stages of the Nile tilapia Oreochromis niloticus adapted to fresh and brackish water

Ontogenetic changes in the location, size, density and morphology of chloride cells in the Nile tilapia Oreochromis niloticus adapted to fresh and brackish water are described using Na(+) /K(+) -ATPase immunohistochemistry, light microscopy (LM), scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM). The pattern of chloride cell distribution changed during development under both treatments, with chloride cell density decreasing significantly from hatch to 7 days post-hatch, but appearing on the inner opercular area at 3 days post-hatch and increasing significantly thereafter (P < 0·05). Chloride cells were always denser in fresh- than in brackish-water larvae. In both treatments, chloride cells located on the outer operculum and tail showed a marked increase in size with age, but cells located on the abdominal epithelium of the yolk sac and the inner operculum showed a significant decrease in size (P < 0·05). Chloride cells from brackish-water adapted larvae from 1 day post-hatch onwards were always significantly larger (P < 0·05) than those from freshwater-adapted larvae. SEM revealed structural differences in chloride cell apical morphology according to environmental conditions. There appears to be clearly defined temporal staging of the appearance of adaptive mechanisms that confer an ability to cope with varying environmental conditions during early development.

[Age and growth of the hybrid tilapia Oreochromis niloticus x Oreochromis aureus (Perciformes: Cichlidae) in the dam "Zimapan" Mexico]

Studies on age and growth in fishes are essential to establish models on population dynamics. The previous issues were determined in this study by scale growth analyses. Between September 2003 and May 2004, 382 organisms were captured using gill and atarraya nets. Eight samples were developed every month a long this study. Standard length in centimeters (L(e)), total weight in grams (P9t)), scale length in centimeters (L(esc)) and growth rings were determined. The size and weight ranged from 38 to 232 mm (L(e)) and 8.7 to 311.9 g (P(t)), respectively. The growth rings analyses reveal four age groups, being the second group the most representative with 34.3% of the total sampled. The scale ring analyses showed two growth rings, one develops between November-January and the other between April-May, in good correlation with low temperature and gonad development, respectively. The growth parameters were established as: L infinity = 281.1mm, W infinity = 877.1g, K = 0.33 and T(0) = 0.88 year(-1). The growth curves based on length and weight were described by using the von Bertalanffy model: L(e) = 28.11[1 -e (-0.33(t+0.88))] and P(t) = 877.17[1-e (-0.33(t+0.88))]3. Finally, it is concluded that commercial catches in this dam are between a year and year and half-old when exploited.

Microstructures and rheological properties of tilapia fish-scale collagen hydrogels with aligned fibrils fabricated under magnetic fields

Tilapia fish-scale type I atelocollagen hydrogels with aligned fibril structures were fabricated under a strong magnetic field of 6 or 12 T using two different methods. In the first method, a solution of acid-soluble collagen was neutralized with phosphate buffer saline and maintained in the magnetic field at 28°C for 3h. Under these conditions fibrogenesis occurs, and a hydrogel is formed. The hydrogel was subsequently crosslinked with ethyl-dimethylcarbodiimide (EDC). In the second method, the hydrogels were formed as described above, but in the absence of an applied magnetic field. Only after being crosslinked with EDC were these gels exposed to the magnetic field (28°C for 3h). Both methods led to alignment of the collagen fibrils perpendicular to the magnetic direction, the extent of which depended on the duration of magnetic treatment. Even after EDC treatment, collagen fibrils can align, indicating that crosslinking has taken place within fibrils. Both sorts of aligned hydrogels exhibited similar rheological properties with higher storage and loss moduli than were observed with unoriented gels. The hydrogels treated at 6 T had the best rheological properties. The decrease in tangent angle phase delta indicated that the ratio of elasticity to viscosity was greater in the crosslinked than in the non-crosslinked hydrogels. Atomic force microscopy images showed that magnetic treatment had no effect on the nanostructure of collagen fibrils. Differential scanning calorimetry measurements indicated that collagen hydrogels with and without magnetic treatment had the same denaturation temperature, 48°C, while EDC crosslinking increased the denaturation temperature to 62°C.

Effects of phenanthrene on hepatic enzymatic activities in tilapia (Oreochromis niloticus female x O. aureus male)

The effects of phenanthrene (Phe) on hepatosomatic index (HSI) and hepatic enzymatic activities in hybrid tilapia (Oreochromis niloticus female x O. aureus male) were investigated via the static freshwater exposure at dosage of 50, 100, and 400 microg/L for 4-14 d. Compared with the control group, HSI was significantly decreased (P < 0.05) at 400 microg/L at day 14. Increased enzymatic activities (P < 0.05) were observed for catalase (CAT), glutathione peroxidase (GPx) and superoxide dismutase (SOD) at either 100 or 400 microg/L at day 8 and 14, as well as for CAT at 50 microg/L at day 14, except for GPx at 400 microg/L at day 8. Ethoxyresorufin O-deethylase (EROD) activity was significantly increased (P < 0.05) at all dosage at day 4 as well as at 50 microg/L at day 8, but significantly decreased at either 100 or 400 microg/L at day 14 (P < 0.05). Glutathione-S-transferase (GST) activity was not affected. The results suggest that CAT, GPx, SOD and EROD, as well as HSI in tilapia may be used as the biomarkers or indexes for evaluating or monitoring the pollution of polycyclic aromatic hydrocarbons (PAHs) such as Phe.

Eyes of a lower vertebrate are susceptible to the visual environment

PURPOSE

Recently, it has been found that form deprivation myopia can be induced in fish (tilapia). This study examined the sensitivity of the tilapia eye to positive and negative lenses. It further investigated the sensitivity of the fish eye to form deprivation by examining the effect of fish weight.

METHODS

Twenty-five Nile tilapia (Oreochromis niloticus; group 1) were weighed (range, 26-101 g) and killed, and their eyes were measured to provide normative data regarding fish eye size, body weight, and refractive state. Goggles with lenses of refractive powers in water of either +15 D (group 2, n = 7) or -12 D (group 3, n = 7) were sutured over the right eye of for 2 weeks to induce hyperopia or myopia. The untreated contralateral eye served as a control. An additional six fish (group 4), each wearing a goggle with an open central area, were used to evaluate the effect of the goggle itself. Refractive measurements for these 20 fish were made before and after treatment, after which the fish were killed, the eyes were removed, and axial lengths were measured from frozen sections. Another 21 fish were treated with goggles with lenses for 2 weeks, after which the goggle was removed and the refractive states of both eyes were measured every day for 6 days (day 19) and then after 28 days. These fish were placed in one group (group 5) wearing negative (-12 D) lenses (n = 8; average weight, 25.5 g) and two groups (groups 6, 7) of different size (average weights, 13.9 g [n = 5] and 26.9 g [n = 8], respectively) wearing positive (+15 D) lenses during the treatment period. In addition, translucent goggles were applied for 2 weeks to induce form deprivation myopia in three groups of fish (groups 8, 9, 10) of different weights, averaging 16.0 g (n = 7), 57.4 g, (n = 8), and 98.4 g, (n = 7), to provide an evaluation of the effect of weight on the development of form deprivation myopia.

RESULTS

In untreated fish (group 1), the axial length of the eye, ranging from 5.86 mm to 7.16 mm, was proportional to weight (26.5-101 g), whereas refractive state shifted from hyperopia (+15D for 10-g fish) toward emmetropia. The +15D lens-treated fish (group 2) became hyperopic relative to the contralateral eye (+7.7 +/- 1.6 D; mean +/- SD), whereas the -12 D lenses (group 3) induced myopia relative to the control eye (-8.4 +/- 0.8 D) within 2 weeks. Hyperopic eyes were shorter (4.16 +/- 0.11 mm vs. 4.28 +/- 0.06 mm) and myopic were eyes longer (3.96 +/- 0.36 mm vs. 3.84 +/- 0.27 mm) than their contralateral control eyes. There were no significant differences in eye size or refractive state between treated and untreated eyes of fish wearing open goggles. In the groups that were allowed to recover (groups 5, 6, 7), the fish treated with minus lenses developed an average of -9.8 +/- 1.9 D myopia, whereas +15 D lenses induced average hyperopia amounts of +8.1 +/- 1.4 D (group 6) and +6.2 5 +/- 2.87 D (group 7). All these fish recovered completely within 2 weeks once the goggles with lenses were removed. Pretreatment and posttreatment refractive results indicated that the contralateral control eyes were affected by the positive and negative lens treatments, though to a lesser extent. Form deprivation myopia was induced in all three different weight groups, averaging -11.9 +/- 2.9 D for group 8, 6.3 +/- 2.5 D for group 9, and -2.3 +/- 1.0 D for group 10. All form-deprived eyes and those treated with positive and negative lenses recovered-i.e., little or no difference resulted in refractive state or dimensions between the treated and untreated eyes-to pretreatment levels within 1 week of goggle removal.

CONCLUSIONS

Tilapia, a lower vertebrate species, exhibits positive and negative lens-induced refractive change, as is the case for higher vertebrates. In addition, the level of sensitivity to form deprivation is weight dependent.

Insulin expression in the brain and pituitary cells of tilapia (Oreochromis niloticus)

While the presence of immunoreactive insulin in the central nervous system of many vertebrate species is well known, the origin of brain insulin is still debated. In this study, we applied RT-PCR, quantitative RT-PCR (qRT-PCR), and Northern hybridization to examine expression of the insulin gene in different tissues of an adult teleost fish, the Nile Tilapia (Oreochromis niloticus). We found that the insulin gene is transcribed at a high level in Brockmann bodies (pancreatic islet organs) and at a low level in the brain and pituitary gland. In the brain, insulin transcripts were detected in all areas by qRT-PCR and in situ hybridization. The highest level of insulin mRNA was found in the hypothalamus. The level of insulin transcription in the pituitary gland was 6-fold higher than that in the brain and 4.6-fold higher than that in the hypothalamus. Furthermore, insulin mRNA and immunoreactive insulin-like protein was detected in the pituitary gland using in situ hybridization, immunohistochemistry, and Western blot analysis. Our results indicate that in adult tilapia insulin expression is not restricted to the endocrine pancreatic cells, but also occurs in endocrine cells of the pituitary gland and in the neuronal cells of the brain, suggesting that the brain/pituitary gland might represent extrapancreatic origin of insulin production.

Fiber connections of the corpus glomerulosum pars rotunda, with special reference to efferent projection pattern to the inferior lobe in a percomorph teleost, tilapia (Oreochromis niloticus)

Fiber connections of the corpus glomerulosum pars rotunda (GR) in a teleost, tilapia Oreochromis niloticus, were studied by biotinylated dextran amine injections into the GR and inferior lobe. After tracer injections into the GR, major groups of labeled somata were found bilaterally in the cortical nucleus and ipsilaterally in the nucleus intermedius. Numerous labeled terminals were found ipsilaterally in the central nucleus, nucleus of lateral recess, and diffuse nucleus (NDLI) of the inferior lobe. Some other connections were also elucidated in the present study, although these were less abundant. Notably, efferent projections to the inferior lobe were not evenly distributed within each lobar nucleus. Labeled terminals were confined to the cell body zone of central nucleus and the outer cell-sparse layer of the nucleus of lateral recess. The rostrolateral portion of NDLI and ventrolateral portion of middle to caudal NDLI received few GR fibers, the rostromedial portion of NDLI a moderate density of fibers, and the rest of the nucleus numerous fibers. These different portions of the NDLI, to some extent, also differed in other afferent and efferent connections, suggesting regional specialization of the nucleus. Furthermore, restricted injections to the lobar nuclei suggest different efferent projections of the component cells of the GR: large and small cells. The large cells project only to the central nucleus, whereas the small cells project to the NDLI and nucleus of lateral recess. Therefore, the two types of GR cells appear to constitute parallel pathways from the pretectum to the inferior lobe.

Bioenergetics-based matrix population modeling enhances life-cycle toxicity assessment of tilapia Oreochromis mossambicus exposed to arsenic

The objective of this study was to integrate a bioenergetics-based modeling approach into a population stage structure to enhance life-cycle toxicity assessments of the effects of waterborne arsenic (As) on the population dynamics of the tilapia Oreochromis mossambicus. The proposed mathematical model links a Leslie matrix population model and a universal ontogenetic growth model embedding the population-level growth rate and stage-specific modes of toxic action. We present data analyses of key parameters and distributions and discuss the processes of data capture and analysis and the impact of acute/chronic As toxicity responses on population-level effects. We employed a three-parameter Hill equation model to describe the relationship between tilapia whole-body burden and mortality in order to estimate the probability of stage-specific vital rate of survival. Using the DEBtox theory, we distinguished three modes of toxic action (MOA): direct effects on growth and indirect effects via maintenance and food consumption on inhibition by arsenic of the growth of a tilapia population. The asymptotic population growth rate decreased from lambda = 1.0027 for the control group to lambda = 0.9935 for tilapia population exposed to 4 microg mL(-1) As, indicating a potential risk of population intrinsic growth rates for tilapia exposed to higher levels of waterborne As. Our results estimated that an As concentration of 1.02 microg mL(-1) would cause a 50% reduction in the tilapia population. We found that the interplay between external stressors of waterborne As concentration and internally generated modes of action decreasing feeding in the juvenile stage and increasing the maintenance cost in the adult stage had a pronounced influence on the population stage structure of tilapia.

Temperature and gender influences on the hepatic stroma (and associated pancreatic acini) of Nile tilapia,Oreochromis niloticus (Teleostei, Cichlidae): A stereological analysis by light microscopy

The normal organ morphology and function in fishes varies according to several natural factors, and such variability is found in liver. Knowledge about the normal liver microanatomy is fundamental to pathological evaluation. Even though gender and temperature are important factors for modulating morphophysiological processes in fishes, their influences on liver stroma are virtually unknown. Because temperature- and gender-related changes exist in liver parenchyma, we predict both factors should also influence the normal stromal structure. Using Nile tilapia as a model, we undertook a study to: 1) establish baseline quantitative structural data on the hepatic stroma (and intimately associated pancreatic acini); 2) compare data with those available from other species, namely, salmonids that do not have a liver with pancreatic acini; and 3) test our hypothesis that, within normal healthy limits, the stroma and its structural components may vary significantly with temperature and gender. We used 1-year-old male and female specimens acclimated to 17 degrees C (breeding noncompatible) and 27 degrees C (breeding compatible) for 45 days. Basic morphometric fish parameters were recorded. After estimation of liver volume, the organ was sliced and pieces systematically sampled for light microscopy. Stereology allowed estimation of the relative volumes of organ components. The total volumes were computed by combining the relative volumes with the total liver volumes. Nile tilapia of both genders, held at 17 vs. 27 degrees C, showed structural quantitative differences in the relative volumes of stroma and most of its components, and in the total volumes of certain stromal elements. The total volume of the stroma and of associated pancreatic acini did not differ. We first established that, in fishes, the total amount (volume) of liver biliary ducts and of eosinophilic granule cells might significantly change (increase and decrease, respectively) with a higher acclimation temperature. Indeed, virtually all the stereological changes were, essentially, temperature- and not gender-related. At 27 degrees C, parallel changes in the parenchyma caused a decreased liver volume and hepatic-somatic index (HSI). The relative volumetric proportion of stroma vs. parenchyma in tilapia is higher than in salmonids. The differences found in this study could not be detected with a qualitative approach, thus stressing the importance of using stereology for analyzing histological patterns and for establishing reliable baseline values in healthy conditions. It was also anticipated that in experimental settings with fish the baseline liver stromal architecture may be different according to temperature and breeding status; in consequence, the effects of the tested variable may also diverge. Our data do not fully explain the lower liver volume and HSI at 27 degrees C, thus justifying studies on the parenchyma, particularly on cell size and number.

Localization of the three GnRH types and GnRH receptors in the brain of a cichlid fish: Insights into their neuroendocrine and neuromodulator functions

The cognate receptor for any of the known gonadotropin-releasing hormones (GnRHs) has not been directly demonstrated. In order to establish this and shed light on the functions of GnRH types, we analyzed the neuroanatomical location and time of initial expression of three distinct GnRH receptors (GnRH-Rs) and the three endogenous GnRHs in the brain of developing and sexually mature tilapia Oreochromis niloticus using immunocytochemistry. In all age groups, including males and females, GnRH-RIA was seen specifically in gonadotropes (Parhar et al. [2002] J Neuroendocrinol 14:657-665) but was undetectable in the brain. On day 8 after fertilization, GnRH-RIB was first seen in the periventricular hypothalamus (lateral recess nucleus, posterior recess nucleus, posterior tuberal nucleus) and GnRH-RIII in the olfactory epithelium, olfactory bulb, telencephalon, preoptic region, mediobasal hypothalamus, thalamus, mesencephalon, and in the hindbrain. Double-label immunocytochemistry showed GnRH1 (Ser(8) GnRH)-immunoreactive neuronal processes projecting mainly to the proximal pars distalis of the pituitary, while GnRH2 (His(5), Trp(7), Tyr(8) GnRH) and GnRH3 (Trp(7), Leu(8) GnRH) fibers were observed in close association with cells containing GnRH-RIB and GnRH-RIII in the brain. These results suggest that GnRH-RIA might be hypophysiotropic in nature, whereas GnRH-RIB and GnRH-RIII could have additional neuromodulatory functions. Further, evidence of close proximity of GnRH-R-containing cells and neuronal processes of multiple GnRH types suggests complex cross-talk between several GnRH ligands and GnRH-Rs.

Morphological aspects of muscle regeneration in the Nile tilapia (Oreochromis niloticus)

The aim of our study was to analyze the morphological events in the skeletal muscle of the Nile tilapia (Oreochromis niloticus) after a traumatic lesion. Thirty-two fish were used, on which a small longitudinal incision was made in the muscle. The fish were sacrificed after 7, 14, 21, and 42 days and muscle samples were collected from the lesion and processed for morphological analysis. Muscle regeneration in the tilapia occurred gradually through the analyzed period, possibly due to the proliferation and differentiation of myosatellite cells, which were more morphologically evident 7 and 14 days after lesion.

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.

Fiber connections of the lateral valvular nucleus in a percomorph teleost, tilapia (Oreochromis niloticus)

Fiber connections of the lateral valvular nucleus were investigated in a percomorph teleost, the tilapia (Oreochromis niloticus), by tract-tracing methods. Following tracer injections into the lateral valvular nucleus, neurons were labeled in the ipsilateral dorsal part of dorsal telencephalic area, corpus glomerulosum pars anterior, dorsomedial thalamic nucleus, central nucleus of the inferior lobe, mammillary body, semicircular torus, valvular and cerebellar corpus, in the bilateral rostral regions of the central part of dorsal telencephalic area, dorsal region of the medial part of dorsal telencephalic area, habenula, anterior tuberal nucleus, posterior tuberal nucleus, and spinal cord, and in the contralateral lateral funicular nucleus. Labeled fibers and terminals were found in the ipsilateral cerebellar corpus and bilateral valvula of the cerebellum. Tracers were injected into portions of the telencephalon, pretectum, inferior lobe, and cerebellum to confirm reciprocally connections with the lateral valvular nucleus and to determine afferent terminal morphology in the lateral valvular nucleus. Telencephalic fibers terminated mainly in a dorsolateral portion of the lateral valvular nucleus. Terminals from the corpus glomerulosum pars anterior, central nucleus of the inferior lobe, and mammillary body showed more diffuse distributions and were not confined to particular portions of the lateral valvular nucleus. Labeled terminals in the lateral valvular nucleus were cup-shaped or of beaded morphology. These results indicate that the lateral valvular nucleus receives projections from various sources including the telencephalon, pretectum, and inferior lobe to relay information to the valvular and cerebellar corpus. In addition, the corpus glomerulosum pars anterior in tilapia is considered to be homologous to the magnocellular part of superficial pretectal nucleus in cyprinids.

Eye color as an indicator of social rank in the fish Nile tilapia

We investigated the association of eye color with the dominant-subordinate relationship in the fish Nile tilapia, Oreochromis niloticus. Eye color pattern was also examined in relation to the intensity of attacks. We paired 20 size-matched fish (intruder: 73.69 11.49 g; resident: 75.42 8.83 g) and evaluated eye color and fights. These fish were isolated in individual aquaria for 10 days and then their eye color was measured 5 min before pairing (basal values). Twenty minutes after pairing, eye color and fights were quantified for 10 min. Clear establishment of social hierarchy was observed in 7 of 10 pairs of fish. Number of attacks ranged from 1 to 168 among pairs. The quartile was calculated for these data and the pairs were then divided into two classes: low-attack (1 to 111 attacks - 2 lower quartiles) or high-attack (112 to 168 attacks - 2 higher quartiles). Dominance decreased the eye-darkening patterns of the fish after pairing, while subordinance increased darkening compared to dominance. Subordinate fish in low-attack confrontations presented a darker eye compared to dominant fish and to the basal condition. We also observed a paler eye pattern in dominants that shared low-attack interactions after pairing compared to the subordinates and within the group. However, we found no differences in the darkening pattern between dominants and subordinates from the high-attack groups. We conclude that eye color is associated with social rank in this species. Moreover, the association between eye color and social rank in the low-attack pairs may function to reduce aggression.

Biochemical and histopathological effects of glyphosate herbicide on Nile tilapia (Oreochromis niloticus)

In Oreochromis niloticus that had been exposed for 3 months to sublethal concentrations (5 and 15 ppm) of the commercial glyphosate herbicide (C(3)H(8)NO(5)P) Roundup, the organs exhibited varying degrees of histopathological change. In the gills filament cell proliferation, lamellar cell hyperplasia, lamellar fusion, epithelial lifting, and aneurysm were observed. In the liver there were vacuolation of hepatocytes and nuclear pyknosis. Kidney lesions consisted of dilation of Bowman's space and accumulation of hyaline droplets in the tubular epithelial cells. The structural damages could be correlated to the significant increase (p Collapse

Key Words Collapse

MESH Headings

• Alanine Transaminase/chemistry
• Alkaline Phosphatase/chemistry
• Animals
• Aquaculture
• Aspartate Aminotransferases/chemistry
• Gills/pathology
• Glycine/analogs & derivatives
• Glycine/toxicity
• Histological Techniques
• Kidney/pathology
• Liver/pathology
• Tilapia/anatomy & histology
• Tilapia/metabolism
• Glyphosate

Collapse

Grants Collapse

Affiliation(s)

W Jiraungkoorskul Department of Biology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
E S Upatham
M Kruatrachue
S Sahaphong
S Vichasri-Grams
P Pokethitiyook

Collapse

Stimulation of Cl- uptake and morphological changes in gill mitochondria-rich cells in freshwater tilapia (Oreochromis mossambicus)

The purpose of the present article is to examine the relationships between ion uptakes and morphologies of gill mitochondria-rich (MR) cells in freshwater tilapia. Tilapia were acclimated to three different artificial freshwaters (high Na [10 mM], high Cl [7.5 mM]; high Na, low Cl [0.02-0.07 mM], and low Na [0.5 mM], low Cl) for 1 wk, and then morphological measurements of gill MR cells were made and ion influxes were determined. The number and the apical size of wavy-convex MR cells positively associated with the level of Cl(-) influx. Conversely, Na(+) influx showed no positive correlation with the morphologies of MR cells. The dominant MR cell type in tilapia gills changed from deep-hole to wavy-convex within 6 h after acute transfer from a high-Cl(-) to a low-Cl(-) environment. Deep-hole MR cells became dominant 24-96 h after acute transfer from a low-Cl(-) to a high-Cl(-) environment. We conclude that wavy-convex MR cells associate with Cl(-) uptake but not Na(+) uptake, and the rapid formation of wavy-convex MR cells reflects the timely stimulation of Cl(-) uptake to recover the homeostasis of internal Cl(-) levels on acute challenge with low environmental Cl(-).

Culture conditions affect induction of vitellogenin synthesis by estradiol-17 beta in primary cultures of tilapia hepatocytes

In vitro synthesis of vitellogenin (VTG), a female-specific protein, after estradiol-17 beta (E(2)) treatment was compared among different culture conditions using the hepatocytes of tilapia, Oreochromis mossambicus. VTG was measured by enzyme-linked immunosorbent assay. Comparison of Leibovitz's L-15 medium (L-15), Williams' medium E (WE) and Medium 199 (M199), which have been used for hepatocyte cultures in certain teleost fishes, showed that monolayer formation of the hepatocytes on the plate in WE and M199 was faster than in L-15 at the beginning of the culture. Morphological differences in the hepatocytes among the culture media were not evident by 96 h after culture. VTG synthesis in L-15 after E(2) treatment was higher than in WE and M199. A concentration of NaHCO(3) at 5 mM in L-15 resulted in faster monolayer formation of the cells and higher VTG synthesis than at 0 and 23 mM. Primary culture of the tilapia hepatocytes at 28 degrees C showed higher synthesis of VTG than at 23 and 33 degrees C. These results suggest that nutritional requirements are vitally different among species, and there are optimal ranges in the pH and the temperature in cultured hepatocytes.

Muscle growth in Nile tilapia (Oreochromis niloticus): histochemical, ultrastructural and morphometric study

Muscle growth in Nile tilapia (Oreochromis niloticus) was studied focusing on histochemical, ultrastructural, and morphometric characteristics of muscle fibers. Based on body length (cm), we studied four groups: G1=1.36+/-0.09, G2=3.38+/-0.44, G3=8.90+/-1.47, and G4=28.30+/-3.29 (mean+/-S.D.). All groups showed intense reaction to NADH-TR in subdermal fibers and weak or no reaction in deep layer fibers. In G3 and G4, an intermediate layer was also observed with fibers presenting weak reaction; in G4, groups of fibers with intense reaction were observed in the subdermal region. The myosin ATPase (m-ATPase) activities were acid-stable and alkali-labile in subdermal fibers; most deep layer fibers were alkali-stable and acid-labile. Intermediate fibers were acid-labile and alkali-stable. Two fiber populations were observed near deep muscle layer: one large presenting weak acid- and alkali-stable and the other small alkali-stable. During growth, muscle fiber hypertrophy was more evident in intermediate and white fibers for G3 and G4. However, in these groups, the presence of fiber diameters < or =21 microm suggested that there is still substantial fiber recruitment, confirmed by ultrastructural study, but hypertrophy is the main mechanism contributing to increase in muscular mass.

Modification of morphology and function of integument mitochondria-rich cells in tilapia larvae (Oreochromis mossambicus) acclimated to ambient chloride levels

Similar to those of the gills of adults, three types of mitochondria-rich (MR) cells with different morphologies of apical surfaces (wavy convex, shallow basin, and deep hole) were identified on the integument of freshwater-acclimated tilapia larvae (Oreochromis mossambicus). The object of this study is to test the hypothesis that these subtype cells may represent MR cells equipped with variable efficiencies in Cl(-) uptake. Larvae acclimated to low-Cl(-) =0.001-0.007 mM) water developed higher densities of MR cells than those acclimated to high-Cl(-) =7.3-7.9 mM) water. The percentage of wavy-convex-type cells in total MR cells was higher in low-Cl(-)-acclimated larvae than in high-Cl(-)-acclimated larvae, which displayed only deep-hole type. In addition, Cl(-) influx rates of whole larva measured with (36)Cl(-) showed a coincident correlation with MR cell densities, that is, low-Cl(-) larvae displayed higher Cl(-) influx rates than did high-Cl(-) larva, suggesting that tilapia larvae develop a higher density of MR cells with larger apical surfaces (wavy-convex type) to boost Cl(-) uptake in Cl(-)-deficient water. The distinct types of apical surfaces may represent different phases of MR cells that possess different efficiencies of Cl(-) uptake. Increased apical membrane surface areas of MR cells may provide larvae with rapid regulation of Cl(-) before new MR cells differentiate.

Genetic and ecological divergence of a monophyletic cichlid species pair under fully sympatric conditions in Lake Ejagham, Cameroon

Although there is mounting evidence that speciation can occur under sympatric conditions, unambiguous examples from nature are rare and it is almost always possible to propose alternative allopatric or parapatric scenarios. To identify an unequivocal case of sympatric speciation it is, therefore, necessary to analyse natural settings where recent monophyletic species flocks have evolved within a small and confined spatial range. We have studied such a case with a cichlid species flock that comprises five Tilapia forms endemic to a tiny lake (Lake Ejagham with a surface area of approximately 0.49 km2) in Western Cameroon. Analysis of mitochondrial D-Loop sequences shows that the flock is very young (approximately 10(4) years) and has originated from an adjacent riverine founder population. We have focused our study on a particular pair of forms within the lake that currently appears to be in the process of speciation. This pair is characterized by an unique breeding colouration and specific morphological aspects, which can serve as synapomorphic characters to prove monophyly. It has differentiated into a large inshore and a small pelagic form, apparently as a response to differential utilization of food resources. Still, breeding and brood care occurs in overlapping areas, both in time and space. Analysis of nuclear gene flow on the basis of microsatellite polymorphisms shows a highly restricted gene flow between the forms, suggesting reproductive isolation between them. This reproductive isolation is apparently achieved by size assortative mating, although occasional mixed pairs can be observed. Our findings are congruent with recent theoretical models for sympatric speciation, which show that differential ecological adaptations in combination with assortative mating could easily lead to speciation in sympatry.

The development of NADPH-diaphorase and nitric oxide synthase in the visual system of the cichlid fish, Tilapia mariae

The pattern of NADPH-diaphorase expression was studied in the retina and optic tectum of the cichlid fish Tilapia mariae during the first developmental stages. NADPH-diaphorase activity was seen early, at hatching. In the retina a few cell bodies of the retinal inner nuclear layer showed a faint labeling. Scattered labeled cells were found in the stratum periventriculare of the optic tectum, while the optic nerve was unlabeled. Two days after hatching, the number of labeled neurons increased in the inner nuclear layer and a few stained cell bodies were also scattered in the ganglion cell layer. Both the inner and outer plexiform layers showed a diffuse staining and the optic nerve was devoid of labeling. In the optic tectum several positive cells in the periventricular layer, with their dendritic trees extending in the superficial fibrous layer, were found. In 1-month-old Tilapia, NADPH-diaphorase staining and nitric oxide synthase immunoreactivity were found to overlap in both the retina and optic tectum. The density of NADPH-diaphorase labeled neurons in the inner nuclear layer of the retina and in the stratum periventriculare of the optic tectum was largely reduced in comparison with 2 days posthatching embryos. These findings indicated an early and transient production of nitric oxide in the retina and optic tectum of Tilapia, suggesting a functional role for nitric oxide in the development of visual structures in aquatic vertebrates.

Vesicular bodies in fish maculae are artifacts not contributing to otolith growth

The presence, morphology and possible origin of vesicle-like bodies (VBs) within the inner ear macular otolithic membrane of developmental stages of cichlid fish Oreochromis mossambicus and neonate (i.e. functionally fully developed except the reproductive organs) swordtail fish Xiphophorus helleri were analyzed by means of transmission and scanning electron microscopy (TEM and SEM, respectively) employing various fixation procedures. Some authors believe that these VBs are involved in the formation of the organic phase of inner ear otoliths (or statoliths in birds and mammals). Decreasing the osmolarity of the fixation medium from a value rather close to that of native fresh water fish tissue (i.e. 250 mOsm and 290--300 mOsm, respectively) to a value of fixatives mostly employed in TEM studies (ca. 190 mOsm), the amount of VBs increased and the components of sensory inner ear tissue increasingly dilated. Whilst a conventional prefixation with aldehydes followed by osmium tetroxide postfixation yielded numerous VBs, only few of them were observed when the tissue was fixed with aldehydes and osmium tetroxide simultaneously. Therefore, the results demonstrate that inner ear sensory epithelia are extremely sensitive to altering fixation media. On this background it must be concluded that VBs are fixative (i.e. glutaraldehyde) induced artificial structures, so-called membrane blisters. Thus, the protein matrix of otoliths (and possibly that of statoliths in higher vertebrates) is rather provided by secretion processes than by the release of vesicles.

Histological study of the development of the embryo and early larva of Oreochromis niloticus (Pisces: Cichlidae)

The developmental stages of Oreochromis niloticus are similar to those described in other mouth-breeding tilapias except that, as in zebrafish, no cavity was found in the blastula. Variation in the rate of development of the embryo and larva of O. niloticus was found within a clutch of eggs as well as between clutches. Hatching glands are described for the first time in tilapias. They are widely distributed within the ectoderm covering the head, body, tail, and surface of the yolk sac near its attachment to the embryo. Timing of larval development is similar to that in other mouthbrooding tilapias, but is slower than that found in substrate-spawning tilapias. A pneumatic duct connects the swimbladder to the digestive tract and swimbladder inflation and initiation of feeding occurs at about the same time. The digestive tract of the larva 8 and 9 days after fertilization is similar to that found in the adult, except that there are no digestive glands. An endocrine pancreatic islet was first seen 76 h after fertilization. A prominent thymus gland is present at 100 h. Hematopoietic tissue develops in the vicinity of the pronephros during early larval development. A spleen develops later, 7 days after fertilization.

Physiological and molecular characterization of urea transport by the gills of the Lake Magadi tilapia (Alcolapia grahami)

The Lake Magadi tilapia (Alcolapia grahami) is an unusual fish, excreting all its nitrogenous waste as urea because of its highly alkaline and buffered aquatic habitat. Here, using both physiological and molecular studies, we describe the mechanism of branchial urea excretion in this species. In vivo, repeated short-interval sampling revealed that urea excretion is continuous. The computed urea permeability of A. grahami gill is 4.74×10(−)(5)+/−0.38×10(−)(5)cm s(−)(1) (mean +/− s.e.m., N=11), some 10 times higher than passive permeability through a lipid bilayer and some five times higher than that of even the most urea-permeable teleosts studied to date (e.g. the gulf toadfish). Transport of urea was bidirectional, as demonstrated by experiments in which external [urea] was elevated. Furthermore, urea transport was inhibited by classic inhibitors of mammalian and piscine urea transporters in the order thiourea&gt;N-methylurea&gt;acetamide. A 1700 base pair cDNA for a putative Magadi tilapia urea transporter (mtUT) was cloned, sequenced and found to display high homology with urea transporters from mammals, amphibians and other fishes. When cRNA transcribed from mtUT cDNA was injected into Xenopus laevis oocytes, phloretin-inhibitable urea uptake was enhanced 3.4-fold relative to water-injected controls. Northern analysis of gill, red blood cells, liver, muscle and brain using a portion of mtUT as a probe revealed that gill is the only tissue in which mtUT RNA is expressed. Magadi tilapia gill pavement cells exhibited a trafficking of dense-cored vesicles between the well-developed Golgi cisternae and the apical membrane. The absence of this trafficking and the poor development of the Golgi system in a non-ureotelic relative (Oreochromis niloticus) suggest that vesicle trafficking could be related to urea excretion in Alcolapia grahami. Taken together, the above findings suggest that the gills of this alkaline-lake-adapted species excrete urea constitutively via the specific facilitated urea transporter mtUT.

Altered gravitational forces affect the development of the static vestibuloocular reflex in fish (Oreochromis mossambicus)

Young fish (Oreochromis mossambicus) were exposed to microgravity (micro g) for 9 to 10 days during space missions STS-55 and STS-84, or to hypergravity (hg) for 9 days. Young animals (stages 11-12), which had not yet developed the roll-induced static vestibuloocular reflex (rVOR) at micro g- and hg-onset, and older ones (stages 14-16), which had already developed the rVOR, were used. For several weeks afterwards, the rVOR was recorded after termination of mug and hg. Here are the main results: (1) In the stage 11-12 fish, the rVOR gain (response angle/roll angle) measured for roll angles 15 degrees, 30 degrees, and 45 degrees was not affected by microgravity if animals were rolled from the horizontal to the inclined posture, but was increased significantly if animals were rolled in the opposite manner. The rVOR amplitude (maximal eye movement during a complete 360 degrees roll) of micro g animals increased significantly by 25% compared to 1g controls during the first postflight week, but decreased to the control level during the second postflight week. Microgravity had no effect in stage 14-16 fish on either rVOR gain or amplitude. (2) After 3g exposure, both rVOR gain and amplitude were significantly reduced for both stage 11-12 and stage 15 fish. One g readaptation was completed during the second post-3g week. Hypergravity at 2 or 2.5 g had no effect. (3) Hypergravity at all three levels tested (2g, 2.5g, and 3g) accelerated the morphological development as assessed by external morphological markers. Exposure to micro g- or 3g-periods during an early developmental period modifies the physiological properties of the neuronal network underlying the static rVOR; in susceptible developmental stages, these modifications include sensitization by microgravity and desensitization by hypergravity.

Afferent sources to the ganglion of the terminal nerve in teleosts

Afferent sources to the ganglion (ggl) of the terminal nerve (TN) were studied in percomorph teleosts the tilapia and dwarf gourami. After tracer applications to the TN-ggl and the surrounding bulbus olfactorius, retrogradely labeled neurons were present in the area dorsalis telencephali pars posterior (Dp), area ventralis telencephali pars ventralis et supracommissuralis (Vv and Vs), nucleus tegmento-olfactorius of Prasada Rao and Finger (1984), and locus coeruleus. In the contralateral bulbus olfactorius labeled cells were observed, and terminals were seen in the TN-ggl. Tracer injection experiments to the possible sources of origin to the TN-ggl were then performed. Tracer applications to the nucleus tegmento-olfactorius labeled abundant terminals in the TN-ggl but labeled very few in the bulbus olfactorius proper. Retrogradely labeled neurons were present in the nucleus ventromedialis thalami, nucleus commissurae posterioris, area pretectalis pars dorsalis et ventralis, nucleus sensorius nervi trigemini, and formatio reticularis pars superius et medius. Tracer applications to the Dp or Vs/Vv labeled terminals mainly in the bulbus olfactorius proper. However, terminals to the TN-ggl were supplied from labeled axons on their way to the bulbus olfactorius. Tracer injections to the locus coeruleus labeled only a few fibers around the TN-ggl. These results suggest that the TN-ggl receives somatosensory and visual inputs from the nucleus tegmento-olfactorius and olfactory inputs from the bulbus olfactorius and telencephalic subdivisions, which receive secondary olfactory projections. The locus coeruleus may also send fibers to the TN-ggl.

Cortisol increases Na(+)/K(+)-ATPase density in plasma membranes of gill chloride cells in the freshwater tilapia Oreochromis mossambicus

The effect of cortisol on Na(+)/K(+)-ATPase expression in the gill chloride cells of tilapia Oreochromis mossambicus was studied by immunocytochemistry at the light and electron microscope levels. One of three doses of cortisol (low, 125 mg kg(−1)food; middle, 375 mg kg(−1)food; high, 750 mg kg(−1) food) was administered via the food (at a ration of 1.5 % of body mass) and the fish were sampled after 5 days. Plasma osmolality and Na(+) levels were elevated in the middle- and high-dose groups, and plasma cortisol levels in the high-dose groups. Hematocrit values were not affected by the treatments. Opercular membrane chloride cell density increased by 94 % and 286 % in the middle- and high-dose fish, respectively, whereas the gill chloride cell frequency increased by up to 28 % maximally in the high-dose fish. Lamellar gill chloride cells were absent in the control and low-dose groups, but were observed in the middle- and high-dose groups. Cortisol increased the volume of the tubular membrane system in mature gill chloride cells. Quantification of immunogold-labelled Na(+)/K(+)-ATPase antigen (a 104 kDa protein species, as demonstrated by western blot) revealed that the high dose of cortisol increases the Na(+)/K(+)-ATPase density in the tubular system of chloride cells. This is the first direct evidence that cortisol not only increases chloride cell numbers but also Na(+)/K(+)-ATPase density in these cells.

NaCl uptake by the branchial epithelium in freshwater teleost fish: an immunological approach to ion-transport protein localization

Teleost fishes, living in fresh water, engage in active ion uptake to maintain ion homeostasis. Current models for NaCl uptake involve Na(+) uptake via an apical amiloride-sensitive epithelial Na(+) channel (ENaC), energized by an apical vacuolar-type proton pump (V-ATPase) or alternatively by an amiloride-sensitive Na(+)/H(+) exchange (NHE) protein, and apical Cl(−) uptake mediated by an electroneutral, SITS-sensitive Cl(−)/HCO(3-) anion-exchange protein. Using non-homologous antibodies, we have determined the cellular distributions of these ion-transport proteins to test the predicted models. Na(+)/K(+)-ATPase was used as a cellular marker for differentiating branchial epithelium mitochondria-rich (MR) cells from pavement cells. In both the freshwater tilapia (Oreochromis mossambicus) and rainbow trout (Oncorhynchus mykiss), V-ATPase and ENaC-like immunoreactivity co-localized to pavement cells, although apical labelling was also found in MR cells in the trout. In the freshwater tilapia, apical anion-exchanger-like immunoreactivity is found in the MR cells. Thus, a freshwater-type MR chloride cell exists in teleost fishes. The NHE-like immunoreactivity is associated with the accessory cell type and with a small population of pavement cells in tilapia.

Gross morphology and topography of the adult intestinal tract of the tilapian fish, Oreochromis niloticus L

The intestinal tract of the Nile tilapia, Oreochromis niloticus L., follows a complex course involving multiple loops and coils arranged in a previously undescribed form. From cranial to caudal, five principal regions were identified and designated as the hepatic loop (HL), proximal major coil (PMC), gastric loop (GL), distal major coil (DMC), and terminal segment (TS). The first four of these regions each possessed a reversal flexure and thus could be divided into proximal and distal limbs. Only the terminal segment was straight and undivided. The PMC and DMC were disposed in a spiral, cone-shaped mass (spiral intestine) - their proximal and distal limbs are thus designated as centripetal and centrifugal limbs. These spiral limbs were arranged with each successive limb nested internal to the previous one. Beginning from the stomach, the complete course of the gut including designations of the subdivisions of the major regions was as follows: proximal limb of the HL, distal limb of the HL, centripetal limb of the PMC, centrifugal limb of the PMC, proximal limb of the GL, distal limb of the GL, centripetal limb of the DMC, centrifugal limb of the DMC, and the TS. Though the topographical relations of the various gut loops permitted ready identification of each, external surface features were so similar among the segments that extirpated segments of gut could not be identified as to region of origin. The nesting of successive intestinal loops of the spiral intestine in this fish is novel among patterns previously described, and also among the more intricate of those that have been described.

Fiber connections of the corpus mamillare in a percomorph teleost, tilapia Oreochromis niloticus

The hypothalamus and perhaps its function appear to be similar among vertebrates. Thus, studying the teleostean hypothalamus could be a good model for understanding common neural circuits and mechanisms retained through the vertebrates. However, connections of the inferior lobe, which is considered the hypothalamus in teleosts, is poorly known. The corpus mamillare (CM) is a nucleus of the inferior lobe named after the mammalian mamillary body based on similarities in external morphology. Afferent connections of the CM have been reported only in cypriniform teleosts. These include projections from the nucleus pretectalis superficialis pars magnocellularis, a nucleus lacking in percomorph teleosts, and projections from the secondary gustatory nucleus. Efferent connections of the CM have not been reported in teleosts. In the present study, the CM and its subdivisions and the connections of these subnuclei were identified in isolated and maintained brains of tilapia Oreochromis niloticus by local DiI and biocytin injection. Afferent connections confirmed by reciprocal injections were from the nucleus diffusus lobi inferioris (NDLI) and the nucleus diffusus tori lateralis (NDTL). Efferent connections of each CM subnuclei were also reciprocally confirmed. These connections were to the area dorsalis pars medialis of the telencephalon, the nucleus ventromedialis (NVM) of the thalamus, the tectum opticum (TO), and the nucleus posterioris periventricularis. Because the NDLI is known to receive gustatory information in tilapia, the CM could relay gustatory inputs to multisensory areas, the TO and NVM, for which there are no current reports regarding gustatory inputs.

The effects of oral administration with 17 alpha-methyltestosterone on chromosomal synapsis in Oreochromis niloticus (Pisces, Cichlidae)

The pattern of chromosomal synapsis after treatment with 17 alpha-methyltestosterone (MT), a testosterone analogue routinely used for the reversal of phenotypic sex in aquaculture, was investigated using the Nile tilapia (Oreochromis niloticus) as a model teleost species. Progeny-tested, monosex diploid (2n = 44) individuals were orally administered with diets containing 50 mg/kg MT for 30 days after first feeding (XX(MT) neomales and XY(MT) males) and compared to controls (XY males). The formation and structure of the synaptonemal complex (SC) and the nature of chromosomal synapsis were investigated in control and treated groups by computer-assisted image analysis of transmission electron microscope (TEM) microphotographs taken from SC spreads. Nuclei at the pachytene stage were first observed in XX(MT) neomales, indicating an earlier commitment of genetically female spermatocytes to enter the first meiotic prophase. Administration of MT did not result in obvious SC lesions, breakage, asynapsis or formation of multivalents in genotypic females (XX(MT) neomales). Administration of MT resulted in a significant increase in the SC lengths in XY(MT) males, although it did not significantly alter the pattern of synapsis (SC structure and number and morphology of bivalents) in comparison to XY controls. The significance of the effects and the putative mode(s) of action of MT on chromosomal synapsis in teleosts is discussed.

Ultrastructure and distribution dynamics of chloride cells in tilapia larvae in fresh water and sea water

Integumental and branchial chloride cells of tilapia larvae (Oreochromis mossambicus) were studied at the light-microscopical and ultrastructural level. Total numbers and distribution of chloride cells were quantified after immunostaining of cross sections of the entire larvae with an antibody against the alpha-subunit of Na+/K+-ATPase. The majority (66%) of Na+/K+-ATPase-immunoreactive (ir) cells, i.e. chloride cells, of freshwater tilapia larvae were located extrabranchially up to 48 h after hatching. Five days after hatching, the majority (80%) of chloride cells were found in the buccal cavity. Transfer of 24-h-old larvae to 20% sea water speeded up this process; 24 h after transfer (i.e. 48 h after hatching), the majority (59%) of chloride cells were located in the buccal cavity. The branchial chloride cell population of 24-h- and 120-h-old larvae consisted of immature, mature, apoptotic and necrotic chloride cells. However, relatively more immature chloride cells were observed in freshwater larvae (42-63%) than in (previously studied) freshwater adults (21%), illustrating the developmental state of the gills. After transfer to sea water, the incidence of degenerative chloride cells did not change. Furthermore, the incidence of immature cells had decreased and a new subtype of chloride cells, the "mitochondria-poor" cells, appeared more frequently. These mitochondria-poor chloride cells were characterised by an abundant tubular system and relatively few mitochondria, which were aligned at the border or concentrated in one part of the cytoplasm. Most of these cells did not contact the water. The function of their enhanced appearance after seawater transfer is unknown.

Immunocytochemical characterization of the pancreatic islet cells of the Nile Tilapia (Oreochromis niloticus)

The cellular composition and topography of the pancreatic islet of Oreochromis niloticus, now known to be a donor source for islet xenotransplantation studies, were characterized. Whole tilapia islets were harvested using an enzymatic method and then further digested into single-cell preparations. Cell cytospin preparations of islet cells and paraffin sections of whole islets were stained using antisera against tilapia insulin, human glucagon, salmon somatostatin-25 (SST-25), human somatostatin-14 (SST-14), and salmon peptide tyrosine-tyrosine (PYY) using the immunoperoxidase method. Cell counts, performed on cytospin preparations using a Quantimet 570 computerized image analysis system, revealed that O. niloticus islets contained 78% endocrine cells and 22% immunonegative cells (i. e., mainly nucleated erythrocytes and rare tissue eosinophils). The proportions of immunopositive endocrine cell types were: 42.3% insulin immunopositive cells, 11.5% glucagon immunopositive cells, 23.1% SST-25 immunopositive cells, 21.8% SST-14 immunopositive cells, and 1.3% PYY immunopositive cells. Islet cell topography was evaluated using histologic sections of whole endocrine pancreata including large, medium, and small islets. Round to polygonal insulin immunopositive cells with round central nuclei were distributed in clusters throughout both the principal and the smaller islets. Elongate SST-14 immunopositive cells were closely associated with the clusters of insulin immunopositive cells; both were surrounded by SST-25 immunopositive cells, which were similar in shape to the insulin immunopositive cells. There were elongate glucagon immunopositive cells throughout the islets, whereas the PYY immunopositive cells were restricted to the periphery and to channels of fibrovascular connective tissue penetrating the islets.

On the influence of altered gravity on the growth of fish inner ear otoliths

Inner ear stones (otoliths) of developing cichlid fish (Oreochromis mossambicus) were marked with the calcium tracer alizarin-complexone (AC) at 1g-earth gravity before and after a longterm (20 days) stay of the animals at moderate hypergravity conditions (3g; centrifuge). AC deposition at the otoliths resulted in two fluorescence bands, which enclosed the area grown during exposure to altered gravity. This area was measured with regard to size and asymmetry (size difference between the left and the right stones). Both utricular and saccular otoliths (lapilli and sagittae, respectively) were significantly smaller after hyper-g exposure as compared to parallely raised 1 g-control specimens. The asymmetry concerning the lapilli was pronouncedly decreased in comparison to the 1g-controls. These findings suggest, that the growth and the development of bilateral asymmetry of otoliths is guided by the environmental gravity vector. Some of the hyper-g animals revealed a kinetotic behaviour at the transfer from hyper-g to normal 1g-earth gravity conditions, which was qualitatively similar to the behaviour observed in previous experiments at the transfer from 1 g to microgravity in the course of parabolic aircraft flights. The lapillar asymmetry of kinetotic samples was found to be significantly higher than that of normally behaving experimental specimens. This result supports an earlier theoretical concept, according to which human static space sickness might be based on asymmetric utricular otoliths

GnRH-systems in the forebrain of cichlid fish

The neuronal systems that contain gonadotropin-releasing hormone (GnRH) were quantitatively examined in the forebrain of two cichlid species (Oreochromis niloticus Lin. and Tilapia maria Boulenger) using tracing methods and immunostaining. In both species the nucleus olfacto-retinalis and a population of neurons in the basal preoptic region contained GnRH. The nucleus olfacto-retinalis was divided into several neuronal subpopulations which differed with respect to cytology, projection pattern, and peptide content. GnRH cell number increased with body size, the rates being different for the different subpopulations. A sexual dimorphism was found in the basal preoptic region of Tilapia; males had significantly fewer GnRH-containing cells than females. Selective staining of the basal preoptic region demonstrated that this cell group is the main source of GnRH-innervation of the pituitary gland and indicate that the molecular forms of GnRH expressed in the two cell populations studied may be different.

Morphometry of fish inner ear otoliths after development at 3g hypergravity

Size and asymmetry (size difference between the left and right sides) of inner ear otoliths of larval cichlid fish were determined after a long-term stay in moderate hypergravity conditions (3g; centrifuge), in the course of which the animals completed their ontogenetic development from hatch to freely swimming. Neither the normal morphogenetic development nor the timely onset and gain of performance of swimming behaviour were impaired by the experimental conditions. However, both utricular and saccular otoliths (lapilli and sagittae, respectively) were significantly smaller after hyper-g exposure compared to 1g control specimens raised in parallel. The asymmetry of sagittae was significantly increased in the experimental animals, whereas the respective asymmetry of lapilli was pronouncedly decreased compared with the 1g controls. These findings suggest that growth and development of bilateral asymmetry of otoliths are guided by the environmental gravity vector. Some of the hyper-g animals revealed a kinetotic behaviour on transfer to normal 1g earth conditions, which was similar to the behaviour observed in previous experiments on the transfer from 1g to microgravity (parabolic aircraft flights). The lapillar asymmetry of kinetotic samples was found to be significantly higher than that of normally behaving experimental specimens. No differences in asymmetry of sagittae were obtained between the two groups. This supports an earlier theoretical concept, according to which human static space sickness might be based on asymmetric utricular otoliths.

Benzo[a]pyrene-induced hypocellularity of the pronephros in tilapia (Oreochromis niloticus) is accompanied by alterations in stromal and parenchymal cells and by enhanced immune cell apoptosis

Numerous reports indicate that carcinogenic polycyclic aromatic hydrocarbons (PAH) are mammalian immunotoxicants. These environmental contaminants are widely distributed in both freshwater and costal marine ecosystems where they have been found to bioaccumulate in aquatic species, yet limited information exists regarding potential adverse effects of specific PAH on fish immune function. In the present report, Oreochromis niloticus fish (tilapia) were exposed by intraperitoneal injection to 5, 25, or 50 mg/kg of the PAH, benzo[a]pyrene (B[a]P). Histopathologic evaluation of the primary hematopoietic compartment of fish, the pronephros, demonstrated increased vacuolation of both stromal and parenchymal cells, reduction of lymphoid elements, and immune cell apoptosis. Total pronephros cell counts were diminished in a dose-dependent manner by the chemical exposure. The oxidative metabolic burst in phorbol myristate acetate (PMA)-simulated macrophages isolated from the pronephros was significantly inhibited by B[a]P, but only at the highest dose level employed. The phagocytic capacity of pronephros macrophages was not altered by the chemical treatment.