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Pansteatitis is the leading cause for the decline in Nile crocodile populations and the sporadic mortality of fish in the Olifants River System, South Africa. To determine the prevalence of this disease in lentic systems, Mozambique tilapia, Oreochromis mossambicus, were collected from Lake Loskop, Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi. The former three impoundments are located within the main stem of the Olifants River, while the latter, which is geographically isolated and situated in the Limpopo River System, served as a reference site. Mesenteric adipose, liver, serosa of the swim bladder, gill and the skeletal muscle of fish sampled were examined for gross and microscopic evidence of pansteatitis. Microscopically observed changes were used to statistically compare pansteatitis prevalence between samples and sites. Based on histopathological evaluation, the adipose tissue in the liver, swim bladder serosa and coelom from severely debilitated individuals showed the most significant pathological changes. Lesions indicative of steatitis were observed in fish collected from Lake Loskop (75%), Lake Flag Boshielo (22%) and Lake Luphephe-Nwanedi (15%). Further investigation is warranted to understand the pervasiveness and mechanisms driving pathological changes of pansteatitis at Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi.

The opioid peptides are involved in the regulation of neuroendocrine functions in vertebrates. Nonetheless, the influence of an opioid peptide, dynorphin A (DYN), on reproduction in fish is understudied. The aim of this work was to study the influence of DYN on the pituitary-ovary axis in Oreochromis mossambicus. Daily injections (ip) of 250 μg DYN kg-1 body weight for 22 days during the ovarian cycle caused a reduction in the intensity and the per cent area of luteinizing hormone (LH) immunoreactive content in the proximal pars distalis region of the pituitary gland compared with an intense immunostaining in time-matched controls. In the ovary, DYN treatment caused a decrease in the number of stage I (previtellogenic) follicles compared with time-matched controls. No difference was observed in the number of stage IV (vitellogenic) follicles among different experimental groups, whereas the numbers of stage II and stage III follicles (previtellogenic) were higher in DYN-treated fish than in time-matched controls. Nonetheless, there was a reduction in the number of stage V (preovulatory) follicles in DYN-treated fish compared with time-matched controls. Taken together, these results indicate that DYN exerts an inhibitory effect on follicular recruitment at the late vitellogenic stage, through the suppression of LH secretion in fish.

The transfer of the toxic heavy metal Cd from duckweed (Lemna minor L.) to the freshwater fish tilapia (Oreochromis mossambicus) was investigated. Concentrations of Cd in different chemical forms in duckweed and in different tissues (gut, edible muscle, and remnants or residual) of tilapia (i.e., ethanol-extractable fraction [FE ], HCl-extractable fraction [FHCl ], and residual fraction [FR ]) were quantified, and the bioaccumulation factors (BAFs) of Cd in the tilapia body were calculated. Simple linear regression analysis was used to unravel the correlation and accumulation mechanisms of Cd along the short food chain. Our results showed that with increasing exposure concentrations of Cd (0-50 μM for duckweed and 0-10 μM for tilapia), the total, FE (Fe,d )-, FHCl (Fh,d )-, and FR (Fr,d )-Cd concentrations in duckweed and different tissues of tilapia increased progressively. The Cd sources (aqueous or dietary) influenced the BAF for Cd accumulation in the whole body of tilapia. Furthermore, regression analyses yielded significant positive correlations (R2 > 0.96) between the Cd concentration in duckweed and in both the 3 parts and the whole body of tilapia. This finding suggests that Cd transfer from duckweed to tilapia can be quantitatively evaluated when tilapia is exposed only to duckweed. In addition, the linear regression between Cd accumulation in whole tilapia and Fe,d -, Fh,d -, and Fr,d -Cd showed that particularly the correlation with Fe,d -Cd is statistically significant (p < 0.001). The accumulated Cd concentrations and chemical forms in tilapia tissues also positively correlated with Cd sources (solution or duckweed). Compared with waterborne exposure only, duckweed especially increased the accumulation of Cd in the gut of tilapia. Taken together, our findings support a strong dependence of Cd accumulation and transfer from duckweed to tilapia on its chemical forms, especially on Fe,d -Cd. This knowledge may expedite more accurate risk assessment of heavy metals through aquatic food chain ecosystems. Environ Toxicol Chem 2018;37:1367-1377. © 2018 SETAC.

Small reservoirs are characterised by extreme fluctuations in water levels, but how this affects fish communities is not well understood. The aim of the study was to investigate fish communities in two small reservoirs which experience large water level fluctuations over two study years, wet and dry. Six fish species were caught in both reservoirs during the sampling period. The numerically dominant fish species was Enteromius paludinosus in both reservoirs, with Clarias gariepinus contributing the high overall fish biomass. The cyprinids Enteromius lineomaculatus and Enteromius trimaculatus occurred in small numbers, as well as the cichlids Oreochromis mossambicus and Tilapia sparrmanii. Using GLMM, the abundance of both C. gariepinus and E. paludinosus across the two reservoirs was found to be significantly associated with total nitrogen and inorganic nitrogen. C. gariepinus abundances were also associated with water transparency and reactive phosphorus whilst E. paludinosus abundances were associated with ammonia, alkalinity, total dissolved solutes and water depth. E. paludinosus bred mostly during the rainy year. Fish migrations and spawning events were largely triggered by rainfall. Differences between the fish populations in the two reservoirs were small based on fisheries metrics due to the biological attributes of the dominant species, E. paludinosus and C. gariepinus. The shallowness and frequent water level fluctuations in small reservoirs possibly do not allow for specialised habitats to develop, which could lead to high fish species diversity. Their suitability for small-scale fisheries has to be reconsidered as the demand for water for irrigation far outweighs that of the fishery.

Mozambique tilapia have been shown to be incredibly stress tolerant with respect to environmental salinity, hypoxia, and ammonia concentrations. Temperature challenges to this species have shown that they have difficulty with cold acclimation. The purpose of this study was to measure the effects of acclimation temperature and salinity on the thermal tolerance of Mozambique tilapia as assessed by critical thermal maxima (CTMax) and critical thermal minima (CTMin). We also monitored fish behavior and quantified ventilation rate. To our knowledge, this study was the first to investigate upper and lower thermal tolerances, and the effect of environmental salinity in this physiologically impressive species. Using predictive regression analyses of the thermal limits, thermal tolerance polygons were constructed and total areas were calculated 678.9°C2 for freshwater (FW)-acclimated tilapia, and 739.4°C2 seawater (SW)-acclimated tilapia. During the thermal challenges, we observed two novel behaviors in response to thermal challenge, ventilation cessation behavior (VCB) and aquatic surface respiration (ASR), and we conclude that the use of these behaviors extended the thermal limits of these fish in both FW and two-thirds SW by limiting the exposure of the gill epithelium to the changing environment.

This study compares the aetiology of pansteatitis in Lake Loskop, relative to two other impoundments along the Olifants River. Macroscopic and microscopic pathology, age determination and analysis of stomach content, fatty acids and stable isotopes explain the high prevalence of pansteatitis in Oreochromis mossambicus (Peters) and several other species in Lake Loskop. All the dietary indicator comparisons between pansteatitis-affected and healthy fish fail to support a systemic cause. Pansteatitis in Lake Loskop was linked to size and weight of O. mossambicus, but not to ontogenic age. Fish in Lake Loskop showed abnormally high omega-3 to omega-6 fatty acid ratios normally only found in marine fish with no significant difference in degree of assimilation of these fatty acids between pansteatitis-affected and healthy fish. This explains the vulnerability to, but not the occurrence of, pansteatitis. As a cause for the pansteatitis, these results point towards sporadic vitamin E-depleting trigger events, known sporadic fish die-off occurrences that provide surviving fish with a rich source of rancid fats on which to scavenge. The mechanism ties pansteatitis to eutrophication and trophic cascade effects, the intrinsic drivers of the disease and suggests an adaptive management strategy that might be applied by relevant conservation authorities.

Knowledge regarding the potential impacts of crude oil on endocrine signalling in freshwater aquatic vertebrates is limited. In this study, the expression of selected genes as biomarkers for altered endocrine signalling were studied in African clawed frog, Xenopus laevis tadpoles, and juvenile Mozambique tilapia, Oreochromis mossambicus exposed to weathered bunker and un-weathered refinery crude oil water accommodated fractions (WAFs). In addition, the expression of the aforementioned genes was quantified in X. laevis tadpoles exposed to surface water collected from the proximity of an underground oil bunker. The (anti)estrogenicity and (anti)androgenicity of crude oil, crude oil WAFs and surface water were furthermore evaluated using recombinant yeast. Thyroid hormone receptor beta expression was significantly downregulated in X. laevis in response to both oil WAF types, whereas, a further thyroid linked gene, type 2 deiodinase was upregulated in O. mossambicus exposed to a high concentration of bunker oil WAF. In addition, both WAFs altered the expression of the adipogenesis-linked peroxisome proliferator-activated receptor gamma in X. laevis. The crude oil and WAFs exhibited anti-estrogenic and anti-androgenic activity in vitro. However, O. mossambicus androgen receptor 2 was the only gene, representing the reproductive system, significantly affected by WAF exposure. Estrogenicity, anti-estrogenicity and anti-androgenicity were detected in surface water samples; however, no significant changes were observed in the expression of any of the genes evaluated in X. laevis exposed to surface water. The responses varied among the two model organisms used, as well as among the two types of crude oil. Nonetheless, our data provide evidence that crude oil pollution may lead to adverse health effects in freshwater fish and amphibians due to altered endocrine signalling. This article is protected by copyright. All rights reserved

The tilapia (Oreochromis mossambicus) is a euryhaline fish exhibiting adaptive changes in cell size, phenotype, and ionoregulatory functions upon salinity challenge. Na(+) /Cl(-) cotransporter (NCC) and Na(+) /K(+) /2Cl(-) cotransporter (NKCC) are localized in the apical and basolateral membranes of mitochondria-rich (MR) cells of the gills. These cells are responsible for chloride absorption (NCC) and secretion (NKCC), respectively, thus, the switch of gill NCC and NKCC expression is a crucial regulatory mechanism for salinity adaptation in tilapia. However, little is known about the interaction of cytoskeleton and these adaptive changes. In this study, we examined the time-course of changes in the localization of NKCC/NCC in the gills of tilapia transferred from fresh water (FW) to brackish water (20‰) and from seawater (SW; 35‰) to FW. The results showed that basolateral NKCC disappeared and NCC was expressed in the apical membrane of MR cells. To further clarify the process of these adaptive changes, colchicine, a specific inhibitor of microtubule-dependent cellular regulating processes was used. SW-acclimated tilapia were transferred to SW, FW, and FW with colchicine (colchicine-FW) for 96 h. Compared with the FW-treatment group, in the MR cells of colchicine-FW-treatment group, (1) the average size was significantly larger, (2) only wavy-convex-subtype apical surfaces were found, and (3) the basolateral (cytoplasmic) NKCC signals were still exhibited. Taken together, our results suggest that changes in size, phenotype, as well as the expression of NCC and NKCC cotransporters of MR cells in the tilapia are microtubule-dependent. J. Morphol. 277:1113-1122, 2016. © 2016 Wiley Periodicals, Inc.

A 25-week immersion challenge was conducted exposing Oreochromis mossambicus, Oreochromis aureus and Oreochromis urolepis hornorum to Francisella noatunensis subsp. orientalis (Fno). Two populations were compared for each fish species; 'resident fish' were defined as fish maintained in tanks since week 0 of challenge, whereas 'naïve fish' were defined as fish added to tanks once temperature in water reached26 °C at 21 weeks post-challenge. Fno genome equivalents (GEs) in water were similar in all treatments 1 h post-challenge; however, significantly lower Fno GEs were detected 2 weeks post-challenge in all tanks, and the only treatment with detectable Fno GE after 4 weeks of challenge were the O. mossambicus tanks. Twenty-one weeks post-challenge, naïve fish were stocked with 'resident' cohorts. Over a 4-week period, mortalities occurred consistently only in O. mossambicus naïve cohorts. Overall presence of granulomas in spleen of survivors was similar (55%) in all resident populations; however, in naïve populations, only O. mossambicus presented granulomas. Similarly, only O. mossambicus presented viable Fno in the spleen of survivors, and Fno GEs were only detected in O. mossambicus, and in resident O. aureus. In conclusion, the results of this study suggest different susceptibility of tilapia species to piscine francisellosis.

The fish ear stones (otoliths) consist mainly of calcium carbonate and have lower amounts of a proteinous matrix. This matrix consists of macromolecules, which directly control the biomineralization process. We analyzed the composition of this proteinous matrix by mass spectrometry in a shotgun approach. For this purpose, an enhanced protein purification technique was developed that excludes any potential contamination of proteins from body fluids. Using this method we identified eight proteins in the inner ear of Oreochromis mossambicus. These include the common otolith matrix proteins (OMP-1, otolin-1, neuroserpin, SPARC and otoconin), and three proteins (alpha tectorin, otogelin and transferrin) not previously localized to the otoliths. Moreover, we were able to exclude the occurrence of two matrix proteins (starmaker and pre-cerebellin-like protein) known from other fish species. In further analyses, we show that the absence of the OMP starmaker corresponds to calcitic otoliths and that pre-cerebellin-like protein is not present at any stage during the development of the otoliths of the inner ear. This study shows O. mossambicus does not have all of the known otolith proteins indicating that the matrix proteins in the inner ear of fish are not the same across species. Further functional studies of the novel proteins we identified during otolith development are required.

The myo-inositol biosynthesis (MIB) pathway converts glucose-6-phosphate to the compatible osmolyte myo-inositol, which protects cells from salinity stress. We exposed tilapia larvae just after yolk sac resorption to various hypersaline environments and recorded robust induction of the enzymes that constitute the MIB pathway, myo-inositol-phosphate synthase (MIPS), and inositol monophosphatase 1 (IMPA1). Strong up-regulation of these enzymes is evident at both mRNA (quantitative real-time PCR) and protein (densitometric analysis of Western blots) levels. The highest level of induction of these enzymes occurs at the highest salinity that larvae were exposed to (90 ppt). Less severe salinity stress causes a proportionately reduced induction of the MIB pathway. Two distinct MIPS mRNA variants are present in tilapia larvae and both are induced at comparable levels for all the salinity challenges tested (34, 70, and 90 ppt). Immunohistochemical localization of IMPA1 protein in sagittal sections of salinity stressed and control larvae identified tissues that are particularly potent in inducing the MIB pathway. These tissues include the skin (epidermis), gills, eye (ciliary epithelium) and heart. In particular, the epidermis directly facing the external milieu showed a very strong induction of IMPA1 immunoreactivity. IMPA1 induction in response to salinity stress was not observed in other tissues suggesting that tilapia larvae may also utilize compatible organic osmolytes other than solely myo-inositol for osmoprotection. We conclude that the MIB pathway plays an important role in protecting multiple (but not all) tissues of tilapia larvae from hyperosmotic salinity stress. J. Exp. Zool. 321A: 457–466, 2014. © 2014 Wiley Periodicals, Inc.

Allspice Pimenta dioica as a feed additive was studied for its effects on growth performance and disease resistance in Mozambique Tilapia Oreochromis mossambicus. Five isonitrogenous (36% crude protein) and isocaloric (18.5 kJ/g) diets were formulated to contain 0 (control), 5, 10, 15, or 20 g of allspice/kg of fish feed. In a 50-d feeding trial, 15 plastic tanks (21 L) were stocked with 35 fish fry (0.012 g) each. After the feeding trial, fish were exposed to Streptococcus iniae and mortalities were recorded. The second-order polynomial regression indicated that the dietary allspice level of 10 g/kg provided the best growth performance and feed utilization. The greatest survival after pathogen challenge was also obtained from the diet supplemented with allspice at 10 g/kg. Therefore, allspice acts as a growth promoter to improve feed utilization and weight gain in Mozambique Tilapia fry and acts an antimicrobial agent to enhance disease resistance during first feeding of fry. These results suggest that allspice can be used as an alternative to antibiotics in controlling streptococcal disease in tilapia culture. Received October 19, 2012; accepted January 20, 2014.

Tilapia have relatively rapid osmoregulatory abilities, but the combined stress due to extreme temperature and salinity can negatively affect the survival of the fish. This study compared the tolerance of the California Mozambique Tilapia hybrid (Mozambique Tilapia Oreochromis mossambicus × Wami Tilapia O. urolepis; CA hybrid) from aquaculture and three species of tilapia that currently live in the Salton Sea area: Blue Tilapia O. aureus, Redbelly Tilapia Tilapia zillii, and CA hybrid collected from the sea. The CA hybrid tilapia (both cultured and feral) was the most resistant species across all treatments and could survive salinities up to 60 g/L (‰). The CA hybrid from aquaculture was the most tolerant to higher temperatures (33–38°C), while the one from the Salton Sea was the most tolerant to colder temperatures (11–16°C). In terms of salinity regimes, the aquaculture CA hybrid and Blue Tilapia survived better at 20‰, while the CA hybrid from the sea did best at 45‰. The different stocks of ti...

Summary Pansteatitis (yellow fat disease) is ubiquitous in the free-ranging population of Oreochromis mossambicus from Loskop Reservoir (LR), South Africa. The disease is nutritionally mediated and associated with a diet high in polyunsaturated or rancid fats, frequently of fish origin. While piscivory has never been reported in dietary studies of O. mossambicus in their native range, their opportunistic and omnivorous feeding habits mean that piscivory cannot be ruled out as a cause of the disease. The diet of O. mossambicus from LR (n = 91) was compared with a population from Flag Boshielo Reservoir (FBR; n = 81) located

We showed previously that exposure to mild acute stressors leads to inhibition of follicular development and luteinizing hormone (LH) secretion in tilapia. In this study, we examined whether the hypothalamo–pituitary–interrenal axis was involved in such inhibition. Administration (i.p.) of corticotropin-releasing hormone (CRH) to stripped Oreochromis mossambicus (eggs manually removed from mouth brooder) during the ovarian cycle for 22 days resulted in a significant increase in the serum levels of cortisol, and significantly lower gonadosomatic and hepatosomatic indices concomitant with complete absence of stage V (vitellogenic) follicles in the ovary compared to controls. Furthermore, the LH secreting cells at the proximal pars distalis (PPD) in the pituitary gland showed weak immunostaining in contrast to the intensely stained immunoreactive cells in controls during prespawning phase. On the other hand, while exposure of fish to aquacultural stressors produced effects similar to that of CRH treatment, treatment of glucocorticoid synthesis inhibitor metyrapone to stressed fish during the ovarian cycle did not show significant serum cortisol response. The LH secreting cells in these fish showed intense immunostaining at the PPD in the pituitary gland, and the ovary contained stage V follicles similar to that of controls prior to spawning phase. These results suggest that the inhibitory effects of CRH treatment on LH secretion and recruitment of follicles for vitellogenic growth are mediated through the stress hormone cortisol in O. mossambicus.

SummaryBackground Tilapia is among the most common fresh water fish species raised by fish farms and can cause allergic reactions upon ingestion. Objective To investigate important allergens in Tilapia (Oreochromis mossambicus). Methods Allergens were detected using immunoblotting. An important allergen was purified to homogeneity by reversed-phase High Pressure Liquid Chromatography and characterized by enzyme linked immunosorbent assay (ELISA), competitive ELISA, Mass spectrometry (MS), circular dichroism measurements and differential scanning calorimetry. Results By immunoblotting using sera from 10 patients with confirmed tilapia allergy, we identified a number of allergens with apparent molecular weights 114 to 17 kD. All patients produced IgE against a 32 kD allergen, Ore m 4, which was identified by MS as tropomyosin (TM). IgE binding of the pure protein was confirmed by immunoblotting, ELISA and ELISA inhibition. cDNA from tilapia tropomyosin (TM) was sequenced and compared with TMs from other species. The tilapia TM showed 53.5% homology to TM from shrimp. Homology was much higher to human TM isoform 5 (87.7%). Conclusion and Clinical Relevance TMs are the major allergens in allergy to crustaceans. Auto-antibodies against human TM isoform 5 have been implicated as a causative agent in inflammatory bowel disease (IBD). Intriguingly, six of the 10 tilapia allergic patients had also been diagnosed with IBD, corroborating a connection between allergy and IBD. To our knowledge, this is the first report of tropomyosin from vertebrates as an allergen.

The opioid peptide β-endorphin (β-EP) is known to play modulatory role in vertebrate reproduction. The objective of the present study was to determine the influence of β-EP and the opioid receptor antagonist naltrexone (NALT) on follicular development in normal, and stressed female tilapia Oreochromis mossambicus. Administration of 4 µg β-EP, but not 0.5 or 1.5 µg β-EP daily for 22 days caused a significant reduction in the mean GSI, HSI, and number of Stage IV (vitellogenic) follicles compared to experimental controls during the prespawning phase of the ovarian cycle. Furthermore, the Stage V (vitellogenic) follicles were completely absent during the prespawning phase concomitant with the significantly lower serum levels of estradiol and cortisol in 4 µg β-EP treated fish compared to experimental controls. On the other hand, exposure of the fish to mild acute stressors for 22 days caused changes in the ovary similar to that of high dose of β-EP, whereas administration of NALT attenuated these effects. The results reveal that β-EP exerts inhibitory effect on the vitellogenic follicular growth through the suppression of ovarian steroidogenesis. The study provides evidence for the opioidergic mediation of the ovarian stress response for the first time in fish. J. Exp. Zool. 319A:156–165, 2013. © 2013 Wiley Periodicals, Inc.

Acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were extracted from the muscles of selected cultured catfish (hybrid of Clarias gariepinus x Clarias macrocephalus), red tilapia (Oreochromis niloticus), black tilapia (Oreochromis mossambicus), pangasius catfish (Pangasius sutchi), sultan fish (Leptobarbus hoevenii) and labyrinth fish (Trichogaster trichopterus), freshwater fishes that are widely consumed in Malaysia. The extracted yields for the tested species were higher for PSC as compared with ASC. The catfish contained the highest amount of collagen (PSC) at 368.36 ± 12.05 mg collagen/g muscles. A mathematical description of the principle kinetics involved in collagen extraction was attained using four two-parametric models, namely the power law, parabolic diffusion, Peleg's and Elovich's models. The power law model was found to be the best model capable of predicting the extraction data with R2 = 0.993, P value = 0.033% and root mean square deviation = 2.605%, respectively. PRACTICAL APPLICATIONS Utilization of fish collagen has been favorable over that of mammalian sources, mainly in making more effective use of underutilized resources. The application of acid-extraction technology to recover and isolate collagen from Malaysian freshwater fish muscles would be able to boost up the commercial values of these cheap and underutilized protein sources while assisting in conservation of these natural resources in Malaysia. Mathematic models proposed in this study were also proven to be successful in governing and describing the kinetics of collagen extraction process.

The objective of this study was to evaluate the particulate matter uptake, survival, condition index (CI), and proximate composition of Crassostrea gigas, cocultured in seawater with tilapia. We used three densities of oysters (two, four, and eight) and one control (no oysters) per 150 g of tilapia biomass. Water quality parameters were measured daily, whereas NH4–N, NO2–N, NO3–N, PO4, total Kjeldahl nitrogen (TKN), chlorophyll a (Chl a), total suspended solids (TSS) proximate composition and CI of C. gigas were determined at the beginning and at the end of the study. No significant differences in nutrient content were observed between treatments. Significant differences were observed in TKN, Chl a, and TSS between the control and the oyster tanks. Maximum removal percentages were 43.16 for TKN (two oyster treatment), 80.23 for Chl a, and 73.55 for TSS (both in eight oyster treatment). Survival of C. gigas was 100% in all treatments. Significantly higher growth was only observed in two oyster treatment. Protein and carbohydrate content in the oyster tissues diminished in all treatments, whereas lipid increased in treatments with two and four oysters. These results indicate that TSS produced from tilapia can be used as a source of food for C. gigas.

This study characterized endocrine and ionoregulatory responses accompanying seawater (SW) acclimation in Mozambique tilapia (Oreochromis mossambicus). Changes in plasma hormones and gene expression of hormone receptors, putative osmosensors, and ion transporters in the gill were measured. Transfer of freshwater (FW)-acclimated tilapia to SW resulted in a marked elevation in plasma osmolality and a significant rise in plasma growth hormone (GH) levels at 12 hr and 14 days after transfer. Significant reductions in plasma prolactin (PRL(177) and PRL(188)) levels also occurred in SW-transferred fish; no effect of transfer upon plasma cortisol or insulin-like growth factor I was observed. Gene expression of GH receptor increased strongly 6 hr after transfer, whereas PRL receptor was lower than controls at 12 hr. By contrast, mRNA levels of somatolactin and glucocorticoid receptors were unaffected by SW transfer. Osmotic stress transcription factor 1 mRNA levels rose significantly between 3 and 12 hr, whereas the calcium-sensing receptor was unaffected. Aquaporin-3 gene expression was strongly down-regulated during SW acclimation from 12 hr until the conclusion of the experiment. Na(+)/K(+)/2Cl(-) cotransporter gene expression increased significantly 3 hr after transfer, whereas expression of Na(+)/Cl(-) cotransporter, specific to FW-type chloride cells, declined by 6 hr into SW acclimation. The response of Na(+)/H(+) exchanger was less pronounced, but showed a similar pattern to that of the Na(+)/Cl(-) cotransporter. These results suggest that acquisition of hyposmoregulatory mechanisms in Mozambique tilapia entails the coordinated interaction of systemic hormones with local factors in the gill, including hormone receptors, ion transporters, and osmosensors.

Stomach residence time was tested over 24 h in three size classes of Oreochromis mossambicus using juvenile Lates calcarifer. In all 63 observations, the fish prey was digested within 24 h of consumption and most probably within 1 h, suggesting a need to re-evaluate the trophic status and potential effects of this highly invasive species.

This study describes experimental herbivory and detritivory of three common native aquatic macrophyte species by the introduced Mozambique tilapia Oreochromis mossambicus (Peters) (Pisces: Cichlidae), and its physiological response to their consumption. There was a highly significant effect of fish herbivory on plant weight for each of the macrophyte species, but this effect was not influenced by any preference for periphyton. Despite the herbivory, there was a highly significant loss of fish body weight across all plant species and weight could only be maintained by supplementary feeding of a high protein fish flake. These results suggest that despite eating these plants, an alternative food resource may be needed for survival and may trigger trophic plasticity in O. mossambicus.

The age, growth and reproductive biology of Marcusenius pongolensis, Oreochromis mossambicus and Schilbe intermedius were investigated in the Mnjoli Dam, Swaziland. Otolith annulus formation occurred in winter for M. pongolensis, and in spring/summer for O. mossambicus and S. intermedius. Maximum ages of 8, 6 and 8 years were recorded for M. pongolensis, O. mossambicus and S. intermedius, respectively. Growth was described by the von Bertalanffy growth model as Lt = 238.73(1 − exp−0.27(t+2.27) mm fork length (FL) for M. pongolensis, Lt = 226.83(1 − exp−0.45(t+2.02)) mm total length (TL) for O. mossambicus, and Lt = 214.59(1 − exp−0.60(t+1.20)) mm FL for S. intermedius. Sexual maturity was estimated for male and female M. pongolensis at 134 mm FL and 119 mm FL, respectively. Marcusenius pongolensis matured within their first year. Female O. mossambicus and S. intermedius matured at 239 mm TL and 205 mm FL, corresponding to 2 and 4 years of age, respectively. Extended spawning periods, with two spawning peaks was observed for M. pongolensis, one in spring (September) and the second in autumn (March) and one peak over late-summer for S. intermedius. Resume L’âge, la croissance et la biologie reproductive de Marcusenius pongolensis, Oreochromis mossambicus et Schilbe intermedius ont eteetudies dans le barrage de Mnjoli, au Swaziland. La formation des anneaux des otolithes se passe en hiver pour M. pongolensis et au printemps/ete pour O. mossambicus et S. intermedius. On a enregistre les âges maximum de 8, 6 et 8 ans respectivement pour Marcusenius pongolensis, Oreochromis mossambicus et Schilbe intermedius. La croissance a ete decrite selon le modele de croissance de von Bertalanffy selon la formule suivante: Lt = 238.73(1 − exp−0.27(t+2.27) mm LF pour M. pongolensis, Lt = 226.83(1 − exp−0.45(t+2.02)) mm LT pour O. mossambicus, et Lt = 214.59(1 − exp−0.60(t+1.20)) mm LF pour S. intermedius. On a estime que la maturite sexuelle etait atteinte a 134 LF et a 119 LF respectivement pour le mâle et la femelle de M. pongolensis, qui arrivaient a maturite au cours de leur premiere annee. Les femelles d’O. mossambicus et de S. intermedius devenaient matures a 239 mm LT et 205 mm LF, ce qui correspond a l’âge de 2 et de 4 ans, respectivement. On a observe des periodes de frai prolongees, avec deux periodes de frai pour M. pongolensis, une au printemps (septembre) et la seconde en automne (mars), et un pic en fin d’ete pour S. intermedius.

Experimental tanks were used to observe predatory effects in three different size classes of Mozambique tilapia Oreochromis mossambicus (one of the world's most widespread exotic species and generally regarded to be a herbivore or both herbivore and detritivore) when tested against 10 juvenile Australian freshwater fish species, and significant levels of predation against all were recorded. There was a general trend for larger O. mossambicus to kill more prey and this was also reflected in a separate series of experiments using juvenile barramundi Lates calcarifer over a range of size classes. Predatory effects by O. mossambicus broadly reflected the accepted models of predator-prey interactions, being that mortality (and survival) was closely related to relative body size and mouth gape limitation. Experimental evidence for piscivory in O. mossambicus was supported by field sampling that detected prey fish remains in 16% of all fish surveyed (n = 176). The recognition of active piscivory by O. mossambicus in laboratory and field situations is the first such evidence, and suggests a need to re-evaluate the nature of their effects in introduced environments.

The effects of supplementing diets with acetone extract (1% w/w) from four medicinal plants (Bermuda grass Cynodon dactylon, H(1), beal Aegle marmelos, H(2), winter cherry Withania somnifera, H(3) and ginger Zingiber officinale, H(4)) on growth, the non-specific immune response and ability to resist pathogen infection in tilapia Oreochromis mossambicus were assessed. In addition, the antimicrobial properties of the extract were assessed against Vibrio alginolyticus, Vibrioparahaemolyticus, Vibrio mimicus, Vibrio campbelli, Vibrio vulnificus, Vibrio harveyi and Photobacterium damselae. Oreochromis mossambicus were fed 5% of their body mass per day for 45 days, and those fed the experimental diets showed a greater increase in mass (111-139%) over the 45 days compared to those that received the control diet (98%). The specific growth rate of O. mossambicus fed the four diets was also significantly greater (1.66-1.93%) than control (1.52%) diet-fed fish. The blood plasma chemistry analysis revealed that protein, albumin, globulin, cholesterol, glucose and triglyceride levels of experimental fish were significantly higher than that of control fish. Packed cell volume of the blood samples of experimental diet-fed fish was also significantly higher (34.16-37.95%) than control fish (33.0%). Leucocrit value, phagocytic index and lysozyme activity were enhanced in fish fed the plant extract-supplemented diets. The acetone extract of the plants inhibited growth of Vibrio spp. and P. damselae with extracts from W. somnifera showing maximum growth inhibition. A challenge test with V. vulnificus showed 100% mortality in O. mossambicus fed the control diet by day 15, whereas the fish fed the experimental diets registered only 63-80% mortality at the end of challenge experiment (30 days). The cumulative mortality index for the control group was 12,000, which was equated to 1.0% mortality, and accordingly, the lowest mortality of 0.35% was registered in H(4)-diet-fed group.

We have developed a technique for immunocytochemistry of fish gill cells that we used to quantify tilapia (Oreochromis mossambicus) mitochondria-rich cells (MRC) and other gill cells (non-MRC) within different cell cycle phases by laser scanning cytometry. Gill cells fixed on coverslips were triple stained with propidium iodide to distinguish G1 vs. G2 phases, Ser10- phosphorylated histone H3 antibody to label mitotic cells, and Na + /K + ATPase antibody to label MRC. These parameters were measured at 0 (control), 4, 8, 16, 24, 48, 72, and 168 hr (1 week) following exposure of freshwater (FW) acclimated fish to 2/3 seawater (SW). MRC increased mitotic activity very rapidly peaking at 8 hr following SW exposure. This change in mitotic MRC is indicative of epithelial reorganization during SW acclimation. In contrast to MRC, the proportion of non-MRC (likely pavement cells (PVC)) in mitosis did not change significantly in response to SW exposure. Moreover, twice as many MRC were in mitosis compared with non-MRC, suggesting that MRC turn over faster than other cell types during SW acclimation. Following the mitosis peak, MRC accumulated in G2 phase over a period of 16-72 hr post-SW exposure. We also observed G2 arrest with similar kinetics following SW exposure in tilapia non-MRC (likely PVC). We interpret the G2 arrest that occurs after an initial wave of transient increase in MRC mitosis as a means for conserving energy for dealing with the osmotic stress imposed during the exposure of FW fish to SW. J. Exp. Zool. 311A:80-90, 2009. r 2008 Wiley-Liss, Inc.

Proteins from Oreochromis mossambicus, a freshwater fish, were hydrolysed, using alkalase 0.61, to produce a soluble, spray-dried hydrolysate. The hydrolysis was carried out at 50°C, using a ratio of one part water and one part fish mince, an enzyme:substrate ratio of 1:50 at pH 8.0. Reaction was terminated by heating to 90°C for 20min. After neutralization, the soluble fraction obtained after centrifugation was spray dried in a mini spray-drier, at an air inlet temperature of 170°C and a feed rate of 41−1. The spray-dried hydrolysate was incorporated into crackers which are fried before eating. Ten per cent hydrolysate was found to give maximum linear expansion. Sensory evaluation with 20 experienced assessors showed that in terms of appearance, crispiness and colour, crackers with hydrolysate had the highest scores, compared to crackers made with O. mossambicus and Sciaena sp. (Jewfish). There were no significant differences in overall acceptability in all three samples. Crackers with hydrolysate also had the highest nitrogen content.

The gene expression of parvalbumin (Pvalb), a high-affinity calcium-binding protein and the major fish allergen, was significantly increased in the tilapia fry treated with methyltestosterone (MT) as examined using a subtractive hybridization assay. Using the real-time quantitative PCR, we further confirmed the increased Pvalb expression in the MT-treated tilapia fry. The 568 base pairs (bp) tilapia Pvalb (tPvalb) cDNA clone was fully sequenced and found to contain a coding region of 330 bp, which encodes a 108 amino acids protein with a molecular weight of 11,370.5 and an calculated isoelectric point of 4.56. The predicted secondary structure of tPvalb is comprised of seven α helices. It contains two characteristic EF-hand calcium-binding motifs, one PKC and five casein kinase II consensus phosphorylation sites. The tPvalb is highly homologous to the selected fish Pvalbs at a similarity ranging from 53% to 80%. The phylogenetic tree analysis showed that the tPvalb is closest to the Scomber japonicus Pvalb. The tPvalb was found to express in the heart, muscle, gill, kidney, brain and ovary of adult fish by RT-PCR analysis. In situ hybridization also revealed that the tPvalb was highly expressed in the hypothalamus and sarcoplasmic reticulum. A tPvalb glutathione S-transferase (GST) fusion protein was generated and digested by thrombin to remove the GST moiety. Further Western analysis showed that the tPvalb protein was cross-reacted to an anti-rat Pvalb antibody. Those results suggest that Pvalb is evolutionally conserved in tilapia. J. Exp. Zool. 305A:51–61, 2007. © 2006 Wiley-Liss, Inc.

We studied the organization of the neuropeptide Y (NPY)-immunoreactive system in the forebrain of adult male cichlid fish Oreochromis mossambicus and its response to castration and testosterone replacement by using morphometric methods. Immunoreactivity for NPY was widely distributed in the forebrain, and the pattern generally resembled that in other teleosts. Whereas immunoreactivity was conspicuous in the ganglia of nervus terminalis (NT; or nucleus olfactoretinalis), a weak reaction was detected in some granule cells in the olfactory bulb and in the cells of area ventralis telencephali pars lateralis (Vl). Moderately to intensely immunoreactive cells were distinctly seen in the nucleus entopeduncularis (NE), nucleus preopticus (NPO), nucleus lateralis tuberis (NLT), paraventricular organ (PVO), and midbrain tegmentum (MT). NPY fibers were widely distributed in the forebrain. Castration for 10/15 days resulted in a drastic loss of immunoreactivity in the cells of NE (P

Regeneration of partially amputated caudal fin was studied in freshwater fish Oreochromis mossambicus exposed to sublethal concentrations of zinc (5.0 mg L—1 and 10.0 mg L—1) under ambient laboratory conditions over a period of 20 days. Caudal fin regeneration was measured on 5th, 10th, 15th and 20th day of exposure and after amputation. Significant ( p < 0.05) retardation in fin regeneration was observed on day 5th and 10th in fish exposed to the nominal concentration of 5.0 mg L—1 Zn, while retardation was found highly significant ( p < 0.01) at all the observations in 10.0 mg L—1. The maximum inhibition in caudal fin regeneration (20.8 % and 24.3 %) was found during the initial observation at both of the concentrations (5.0 mg L—1 and 10.0 mg L—1) of zinc exposure. Later on the regeneration rate was almost as good as in the control group. Thus in this study fin regeneration was significantly inhibited at all time points following Zn exposure as a detrimental effect of Zn to fish. This study demonstrates that fish caudal fin regeneration is a simple assay, sensitive and easy to perform, and can serve as a model to determine the toxicity of pollutants in aquatic environment. Hemmung der Flossen-Regeneration beim Suswasserfisch Oreochromis mossambicus durch Zink Untersucht wird die Regeneration der partiell amputierten Schwanzflosse des Suswasserfisches Oreochromis mossambicus bei Exposition gegen subletale Zink-Konzentrationen (5 mg L—1 und 10 mg L—1) im Laborversuch uber 20 Tage. Die Messung erfolgte am 5., 10., 15. und 20. Tag nach Amputation. Eine signifikante Hemmung ( p < 0.05) der Regeneration wurde bei 5 mg L—1 am 5. und 10. Tag beobachtet, eine hochsignifikante Hemmung ( p < 0.01) trat bei 10 mg L—1 uber die gesamte Versuchsdauer auf. Die maximale Hemmung trat jeweils zu Versuchsbeginn ein, spater entsprach die Regenerationsrate jener der Kontrolle. Insgesamt zeigt die Verzogerung der Regeneration einen signifikanten Einfluss von Zink auf Wachstumsprozesse. Die Regeneration der Schwanzflosse ist folglich ein einfaches und sensitives Prufungsverfahren fur toxische Wirkungen von Wasserinhaltsstoffen.

Two studies were conducted to test the relationship between androgens and routine metabolism in the Mozambique tilapia Oreochromis mossambicus. In the first study, endogenous levels of plasma levels of androgens and oxygen consumption rate were measured. In accordance with expectations routine metabolism corrected for metabolic body mass, was positively correlated with the behaviourally active metabolite of testosterone, 11-ketotestosterone, but not with testosterone itself. In the second study levels of 11-ketotestosterone were experimentally elevated, which increased the lowest values of (corrected) routine metabolism, indicating a positive relationship with standard metabolism. These results show the importance of measuring reproductive hormones, and are supportive of the hypothesis that elevated levels of androgens are a costly trait.

Sensitivity of skeletal ontogenesis to temperature was assessed in Mozambican tilapia Oreochromis mossambicus and culture temperature manipulations (22, 27 and 32° C) were used to establish if age or length gave the most suitable metric for standardization. Oreochromis mossambicus larval growth was composed of two growth stanzas: an initial period of rapid growth, followed by a slower growth phase. Irrespective of culture temperature chondrogenesis occurred during the first rapid growth phase and ossification was initiated during the second slower growth phase. The sequence of events and rate at which ossification occurred was much more sensitive to temperature than chondrogenesis. Cumulative counts provide a useful developmental index for skeletal ontogenesis; overall, age (effective days-degrees) gave the best estimation of developmental status during chondrogenesis and the initiation of ossification, although standard length (as log10LS) was a better metric for completion of ossification. The timing of development of functionally important structures, such as Meckel's cartilage, the branchial arches, the centra and the cleithrum important for breathing, feeding and swimming, was well conserved at all temperatures and may be a good index of teleost developmental stages.

Previous investigations revealed that fish inner ear otolith growth depends on the amplitude and the direction of gravity. Both otolith total size, otolith bilateral size-asymmetry and the total and bilateral calcium-incorporation are also affected by gravity. Hypergravity, e.g., slows down otolith growth and diminishes bilateral otolith asymmetry as compared to 1 g control specimens raised in parallel. Since the enzyme carbonic anhydrase (CA) plays a prominent role in otolithic calcification, the reactivity of inner ear CA during otolith growth under hypergravity was investigated. CA-reactivity was demonstrated histochemically and densitometrically on sections of inner ear maculae of larval cichlid fish (Oreochromis mossambicus), that were kept for 6 hrs in a 3 g hypergravity centrifuge. The total unilateral macular CA-reactivity and the bilateral difference in CA between the left and the right maculae were significantly lower in 3 g animals than in 1g controls. The result is in complete agreement with previous studies indicating that a regulatory mechanism, which adjusts otolith size and asymmetry towards the gravity vector, acts via activation/deactivation of macular CA.

Although hypothalamic corticotropin-releasing hormone (CRH) is involved in the stress response in all vertebrate groups, only a limited number of studies on this neuroendocrine peptide deals with non-mammalian neuroendocrine systems. We determined the cDNA sequence of the CRH precursor of the teleost Oreochromis mossambicus (tilapia) and studied the biological potency of the CRH peptide in a homologous teleost bioassay. Polymerase chain reaction (PCR) with degenerate and specific primers yielded fragments of tilapia CRH cDNA. Full-length CRH cDNA (988 nucleotides) was obtained by screening a tilapia hypothalamus cDNA library with the tilapia CRH PCR products. The precursor sequence (167 amino acids) contains a signal peptide, the CRH peptide and a motif conserved among all vertebrate CRH precursors. Tilapia CRH (41 aa) displays between 63% and 80% amino acid sequence identity to CRH from other vertebrates, whereas the degree of identity to members of the urotensin I/urocortin lineage is considerably lower. In a phylogenetic tree, based on alignment of all full CRH peptide precursors presently known, the three teleost CRH precursors (tilapia; sockeye salmon, Oncorhynchus nerka; white sucker, Catostomus commersoni) form a monophyletic group distinct from amphibian and mammalian precursors. Despite the differences between the primary structures of tilapia and rat CRH, maximally effective concentrations of tilapia and rat CRH were equally potent in stimulating adrenocorticotropic hormone (ACTH) and alpha-MSH release by tilapia pituitaries in vitro. The tilapia and salmon CRH sequences show that more variation exists between orthologous vertebrate CRH structures, and teleost CRHs in particular than previously recognized. Whether the structural differences reflect different mechanisms of action of this peptide in the stress response remains to be investigated.

Nitrogenous waste control in aquaculture systems is necessary to maintain healthy animals and to meet effluent standards. Decreased ammonia production has been attained in traditional livestock production systems by adding extracts of Yucca shidigera to the feed or storage lagoon system. An extract of Yucca shidigera was fed to post yolk-sac and juvenile channel catfish Ictalurus punctatus and hybrid tilapia Oreochrornis mossambicus × O. niloticus to determine the effects on growth, nitrogen retention, ammonia excretion, and toxicity. Post yolk-sac channel catfish fry fed the 1.0-g yucca extract/kg as an agar coating were the only group of experimental organisms that had significantly greater weight gains compared to the control and 0.5-g yucca extract/kg diet groups after 12 wk. Significantly lower fecal nitrogen concentrations were obtained from catfish fed diets containing yucca extract compared to the control groups, although no differences between fecal nitrogen concentrations for catfish fed diets with either 0.5-g or 1.0-g yucca extract/kg diet occurred. Ammonia excretion rates were significantly lower for catfish fed diets containing yucca extract compared to the control group. Accordingly, fish fed diets containing the yucca extract had significantly greater whole-body protein composition, while lipid levels were significantly lower. No significant differences in proximate composition occurred for fish fed any of the diets containing yucca extract, though growth rates were significantly higher than the controls. This study demonstrated that a yucca extract can be used in the diet of channel catfish, and increased growth and decreased ammonia concentrations can be obtained in rearing systems.

The role of so and production of the Mozambique tilapia Oreochromis mossambicus in agonistic and mating interactions observed during hierarchy formation and in established groups was examined. Only territorial males produced sounds, during male-female and male-male courtship interactions and during pit-related activities (e.g. dig, hover and still in the nest). Sound production rate was positively correlated with courting rate. Although sounds in other cichlids are typically emitted in early stages of courtship, O. mossambicus produced sounds in all phases, but especially during late stages of courtship, including spanking. It is suggested that the acoustic emissions in this species may play a role in advertising the presence and spawning readiness of males and in synchronizing gamete release.

Lysenin is a 33-kDa protein found in the coelomic fluid (CF) of the earthworm Eisenia foetida. Purified lysenin binds specifically to sphingomyelin (SM). In the present studies, we found that the white cloud mountain minnow Tanichthys albonubes and the Mozambique tilapia Oreochromis mossambicus died in solutions of lysenin (at concentrations above 2.5 microg/ml) and CF (0.6%, v/v) within 2 h. The gills of both species of fish were damaged similarly by lysenin and by CF. Most gill lamellae became irregularly bent or curled, with swelling of the epithelial cells of the lamellae. Red blood cells in the lamellar vascular sinuses, in the central venous sinuses, and in the blood vessels of the entire body became swollen and lysed, choking the sinuses. Epithelial cells in the skin were also damaged. When fish of both species were treated with lysenin or CF that had been incubated with SM-liposomes, they did not die. Their behavior remained normal and there was no damage to any cells or tissues. These findings suggest that SM might be involved in the lethal effects of lysenin and CF. It is likely that purified lysenin and lysenin in CF bound to SM in the cell membranes of the tissues mentioned above, damaging the cells. The presence of SM in the gills and skin was confirmed, supporting this hypothesis. The damage to gills and hemolysis might have resulted in lethal respiratory problems. Damage to the skin might disturb the exchange of ions through the skin, hastening death. Damage by lysenin and CF to epithelial cells of the cornea and the wall of the oral cavity was also recognized, but there was no such damage to the intestine.

Changes in expression of Na, K-ATPase (NKA) and morphometry of mitochon- drion-rich (MR) cells in gills of tilapia were investigated on a 96-hr time course following transfer from seawater (SW) to fresh water (FW). A transient decline in plasma osmolality and Na þ ,C l � concentrations occurred from 3 hrs onward. Gills responded to FW transfer by decreasing NKA activity as early as 3 hrs from transfer. This response was followed by a significant decrease in the NKA isoform a1-mRNA abundance, which was detected by real-time PCR at 6 hrs post transfer. Next, a decrease of a1-protein amounts were observed from 6 hrs until 24 hrs post transfer. Additionally, during the time course of FW transfer, modifications in number and size of subtypes of gill MR cells were observed although no significant difference was found in densities of all subtypes of MR cells. These modifications were found as early as 3 hrs, evident at 6 hrs (exhibition of 3 subtypes of MR cells), and mostly completed by 24 hrs post transfer. Such rapid responses (in 3 hrs) as concurrent changes in branchial NKA expression and modifications of MR cell subtypes are thought to improve the osmoregulatory capacity of tilapia in acclimation from hypertonic SW to hypotonic FW. J. Exp. Zool. 301A:85-96, 2004. r 2004 Wiley-Liss, Inc.

Electro-olfactogram (EOG) recordings from female Mozambique tilapia Oreochromis mossambicus gave large responses (up to 45 mV) to water previously occupied by sexually active males. Male body-fluids also elicited very strong olfactory responses with thresholds of detection of c. 1 : 10 6.9 (bile), 1: 10 5.2 (urine) and 1: 10 4.9 (faeces). Considering the likely rates of release of these fluids, it is the urine that provides the strongest olfactory stimulus for females. Crude fractionation of the male water and body-fluids implicated: (a) sulphated compounds, possibly steroids, as the most potent odorant in the urine (and water previously occupied by males), and (b) bile acids in the faeces and bile. Although the olfactory system of Mozambique tilapia was found to be sensitive to a range of amino acids and bile acids, steroids present in Mozambique tilapia plasma and steroids known to act as pheromones in other species elicited negligible responses. Although the present study clearly suggests that chemical communication might be important in Mozambique tilapia, the exact chemical identity of the compounds involved, and their biological functions, remain to be elucidated.

The role of hypothalamic neurotransmitter systems in behavioral thermoregulation was investigated in the prespawning female tilapia, Oreochromis mossambicus. Intrahypothalamic microinjection with serotonin (5-HT, 3 µl of 1.0×10−6 M) resulted in a significant increase in the selected temperature. This effect was mimicked by the agonist of 5-HT1A, 1B, and 2C receptors, N-3-trifluoromethylphenyl piperazine. Intrahypothalamic microinjection of tilapia with γ-aminobutyric acid (GABA) resulted in a biphasic effect of the temperature selection, whereas microinjection with muscimol, an agonist of GABAA receptor, had no effect on temperature selection. Both agonist and antagonist of glutamate (Glu), N-methyl-D-aspartate (NMDA), and MK-801 (1.0×10−6 M), a noncompetitive blocker of NMDA receptor, significantly decreased the preferred temperature. These results indicate that the hypothalamic 5-HT, GABA, and Glu systems play a role in the temperature selection of prespawning female tilapia. J. Exp. Zool. 293:443–449, 2002. © 2002 Wiley-Liss, Inc.

An examination of the occurrence and distribution of phthalate esters in the alimentary canal of a polyhybrid of Tilapia gave evidence of different and selective patterns of distribution in the organ tissues: the phthalate esters were shown to be concentrated in the stomach and anterior intestine. The restricted distribution of phthalate esters can have implications for the physiology of the digestive system. The phthalates, stored in the oxyntic cells of the gastric tubular glands, probably interfere with the digestive process. The strategic location of the enterocytes in the anterior intestine implies that they can hamper the reabsorption of digestion products. The endocrine disrupting effects known for these chemicals are probably related to the absorption of them via the alimentary canal.

The myo-inositol biosynthesis (MIB) pathway converts glucose-6-phosphate to the compatible osmolyte myo-inositol (MI), which protects cells from osmotic stress. We exposed tilapia larvae just after yolk sac resorption to various hypersaline environments and recorded robust induction of the enzymes that constitute the MIB pathway, myo-inositol-phosphate synthase (MIPS) and inositol monophosphatase 1 (IMPA1). Strong up-regulation of these enzymes is evident at both mRNA (quantitative real-time PCR) and protein (densitometric analysis of Western Blots) levels. The highest level of induction of MIB enzymes occurs at the highest salinity that larvae were exposed to (90ppt). Less severe osmotic stress causes proportionally lesser induction of the MIB pathway. Two distinct MIPS mRNA variants are present in tilapia larvae and both are induced at comparable levels for all the salinity challenges (34, 70 and 90ppt). Immunohistochemical localization of IMPA1 protein in sagittal sections of salinity stressed and cont...

Label-free quantitative (LFQ) proteomics was employed to analyze effects of salinity stress on the molecular phenotype, i.e. proteome, of gill epithelium in Mozambique tilapia (Oreochromis mossambicus). Fresh water (FW) acclimated tilapia were acclimated to 34 ppt, 70 ppt, and 90 ppt salinity and gill proteins extracted and trypsin-digested for analysis by LFQ LC-MS/MS. More than 600 proteins were identified with high identification scores (>85% represented by >5 MS/MS peptides, FDR < 2%). The overall effect of salinity acclimation on protein regulation ratios in gill epithelium (salinity exposed gill epithelia compared to FW handling controls) was found to be proportional to the degree of salinity stress. Salinity-induced changes in tilapia gill epithelial proteome directly reflected known salinity effects on gills of euryhaline fish, including an increase in the size and number of mitochondria-rich ionocytes, activities of specific ion transporters, and induction of specific molecular chaperones. Confir...

The effects of gonadal steroids on brain serotonin (5-HT) and aromatase activity during the critical period of sexual differentiation were investigated in tilapia, Oreochromis mossambicus. Treatment of tilapia with 17beta-oestradiol (E2) between days 7 and 10 posthatching resulted in a significant increase in the female : male ratio as determined at day 90, and a significant reduction in brain 5-HT content. Treatment between days 10 and 20, or between days 20 and 30, had no significant effect. Since the 5-HT system may influence sexual differentiation, we examined the effects of para-chlorophenylalanine (p-CPA), a 5-HT synthesis inhibitor. As with E2, treatment of tilapia with p-CPA between days 7 and 10 posthatching resulted in a significant increase in the female : male ratio. Again, treatment between days 10 and 20, or between days 20 and 30, had no significant effect. Both p-CPA and E2 significantly depressed brain aromatase activity when administrated between days 7 and 10, but not subsequently. In tilapia treated between days 7 and 10, the brain 5-HT content was lowered by E2 to an extent similar to that seen with p-CPA, which is consistent with the suggestion that the effect of E2 on sexual differentiation may be mediated by the 5-HT system. Treatment of tilapia with 17alpha-methyltestosterone (MT), by contrast, resulted in a reduction in the female : male ratio, and treatment was most effective when given between days 10 and 20. The period of maximal effect of MT upon sex ratio appears to coincide with the ability of MT to induce an increase in brain aromatase activity.