Tilapia Oreochromis Mossambicus Research Articles

Comparison of bioconcentration and kinetics of GenX in tilapia Oreochromis mossambicus in fresh and brackish water

Contaminants of emerging concern (CEC) are a broad suite of chemicals commonly found in the environment, aquatic organisms and even drinking water. They include pharmaceuticals, personal care products, industrial chemicals and compounds added to consumer products. The CEC ammonium 2,3,3,3-tetrafluoro-2-heptafluoropropoxy propanoic acid, which is more commonly known as generic name GenX, is a replacement of common processing aid longer chain perfluorinated compounds (PFAS) due to a manufacturing shift in 2002 following the EPA stewardship program of 2015/16 in USA (USEPA, 2006). However, recently reported in North Carolina drinking water, GenX raising concerns about its accumulation in aquatic organisms, both wild and cultured, which could be a pathway for human exposure. To examine GenX accumulation and potential for human exposure, tilapia (Oreochromis mossambicus) fingerlings were dosed with GenX for up to 96 h in fresh (0 ppt) or brackish (16 ppt) water to determine uptake and bioconcentration. Depuration values were also determined after a 96 h exposure followed by 96 h without exposure. Bioconcentration was in decreasing order of plasma > liver > carcass > muscle, with higher distribution to liver followed by carcass and muscle. Muscle was found to have the highest half-life (1278 h) followed by carcass (532 h), plasma (106 h), and liver (152 h). The rate of uptake and depuration was positively affected by the salinity. As bioconcentration in all tissues increased with increasing salinity, this may raise concern for marine organisms and human exposure.

Changes in an Exotic Fish Community Assemblage of a Thermal Spring in Central Idaho

Barney Hot Springs is a thermal spring in the headwaters of the Little Lost River drainage in central Idaho. Tropical fish have been released into Barney Hot Springs, and several species have established self-sustaining populations. The objectives of this study were to determine the current community assemblage of tropical fish in Barney Hot Springs and to assess species composition and extent of downstream distribution of tropical fish in Barney Creek. The composition in 2017 consisted of Amelanic Convict Cichlids Amatitlania nigrofasciata, Mozambique Tilapia Oreochromis mossambicus, Zebra Mbuna Maylandia zebra, and Green Swordtails Xiphophorus hellerii. Total abundance of all fish species was estimated at 12,043 fish (95% CI 9807–15,600), with Green Swordtails making up 68% of the population, Zebra Mbuna 20%, Convict Cichlids 9%, and Mozambique Tilapia 3%. In Barney Creek, fish were collected within 800 m of Barney Hot Springs. In March 2018, a rain-on-snow event occurred that resulted in a fish kill. In fall 2018 after this event, Convict Cichlids, Green Swordtails, and Goldfish Carassius auratus were collected. Overall abundance was estimated at 1972 fish (95% CI 1757–2227), with Green Swordtails and Goldfish each composing 50% of the population; no Convict Cichlids were recaptured, so abundance could not be estimated. In Barney Creek, fish were collected within 400 m of Barney Hot Springs. We documented current changes to the fish community assemblage of Barney Hot Springs and Barney Creek that were driven by colonization (i.e., introduction of aquarium fish) and by local extinction through species interactions and stochastic events. Currently, we do not know the impact that the introduced fish fauna of Barney Hot Springs may have on native species or ecosystem function.

Habitat structure differentially mitigates predation impact of juvenile largemouth bass and Florida bass

Habitat complexity plays an important role in structuring species diversity, behaviour and distribution. Furthermore, habitat complexity can mediate the strength of predator-prey interactions through the provision of prey refugia or through enhancing ambush predation. In this study, we use functional responses (FRs) to compare the effect of habitat complexity on resource utilisation between Largemouth Bass Micropterus salmoides and Florida Bass Micropterus floridanus predating upon Mozambique Tilapia Oreochromis mossambicus fry. Treatments for this study were zero and high habitat complexities, with the latter being artificially constructed using plastic strips. Both predator species exhibited a Type II FR in both habitat complexities, with Florida Bass exhibiting significantly higher FR magnitudes, compared with Largemouth Bass under both habitat complexities. Both species experienced dampening of FR magnitudes under high habitat complexity. Florida Bass had persistently lower handling parameters than Largemouth Bass regardless of habitat complexity. While higher habitat complexity may offer prey refugia from Florida Bass, changes in complexity had a negligible effect upon Largemouth Bass predatory efficiency. Measures to enhance natural complexity through system restoration may be a useful conservation measure for endemic fish in rivers invaded by Florida Bass, however, the same mitigation measures may not be as effective for Largemouth Bass.

Organic acid composition and consumer acceptability of fermented fish produced from black tilapia (Oreochromis mossambicus) and Javanese carp (Puntius gonionotus) using natural and acid-assisted fermentation

Ikan pekasam is an example of traditional fermented food products in Malaysia, prepared from freshwater fish such as black tilapia (Oreochromis mossambicus) and Javanese carp (Puntius gonionotus), salt and ground roasted rice, which is added as the only source of carbohydrate. However, some producers add tamarind (Tamarindus indica) pulp and/or dried slices of Garcinia atroviridis to assist the fermentation process. In this study, there was no correlation detected between pH value, titratable acidity (% lactic acid), salt concentration, organic acid composition and the consumer acceptability of ikan pekasam commercial samples made of black tilapia as well as Javanese carp. The organic acid composition in both natural and acid-assisted fermented ikan pekasam from black tilapia and Javanese carp were compared. The results obtained showed that lactic acid was the major organic acid detected, followed by succinic acid and acetic acid. The addition of tartaric and/or garcinia acids was proven to reduce the fermentation time. Therefore, the addition of acid has assisted the fermentation process by increasing the total organic acid content, mainly lactic acid. Moreover, the 9-point hedonic scale showed that ikan pekasam made of Javanese carp had higher overall acceptability due to tender flesh/muscle texture compared to black tilapia regardless of the fermentation process and organic acid content

Predictor complexity and feature selection affect Maxent model transferability: Evidence from global freshwater invasive species

AbstractAimEcological niche models (ENMs) are widely used to address urgent real‐world problems such as climate change effects or invasive species; however, the generality of models when projected through space and/or time, that is transferability, remains a key challenge. Here, we explored the effects of complex predictors and feature selection on ENM transferability in a widely employed algorithm, Maxent, using five globally invasive freshwater species as case studies.LocationGlobal.MethodsWe modelled the global distributions of five notorious freshwater invasive species (African sharptooth catfish Clarias gariepinus, Mozambique tilapia Oreochromis mossambicus, American bullfrog Lithobates catesbeianus, red swamp crayfish Procambarus clarkii, and Australian redclaw crayfish Cherax quadricarinatus), using three predictor datasets of varying complexities derived from two commonly used climatic data sources (WorldClim and IPCC) and three methods of model tuning that differentially incorporated feature selection. Spatially explicit transferability assessments were then conducted using a suite of evaluation metrics previously used to quantify Maxent model performance.ResultsWe show that in the absence of detailed biological knowledge of focal species, simpler predictor datasets produce models that are more accurate than those calibrated using comprehensive “bioclimatic” datasets. Additionally, we find that tuning models for both optimal regularization parameters as well as feature‐class combinations led to the greatest increases in transferability and geographic niche conservatism. Results indicate a tenuous link between model transferability and Akaike's information criterion corrected for small sample sizes (AICc), suggesting that the indiscriminate use of AICc as an estimate of model parsimony may lead to erratic model performance.Main conclusionsOur findings demonstrate that methodological considerations can drastically affect the reliability of spatial and possibly temporal projections, which has severe implications when ENMs are used to infer species’ niches, and quantify ecological or evolutionary change across impacted landscapes.

Assessment of interspecific interactions between the invasive red-claw crayfish (Cherax quadricarinatus) and the Mozambique tilapia (Oreochromis mossambicus).

The Australian red-claw crayfish, Cherax quadricarinatus, has been introduced for aquaculture purposes worldwide and consequently colonized natural environments, where it might cause ecosystem services losses or adversely affect native species and the local environment. This species was first found in Pequenos Libombos Reservoir in Maputo Province, Southern Mozambique in the late 2009 and is linked to reduction in tilapia fisheries. This study, conducted in 2015 under controlled conditions, aimed to assess the interspecific relationships between the Mozambique tilapia (Oreochromis mossambicus) and the alien crayfish. For both species, no significant differences in growth and survival rates were found between animals reared in the presence versus the absence of heterospecifics, indicating no direct deleterious interspecific effects. Behavioural observations revealed that fish and crayfish competed for shelter and food. Both species reduced the foraging in the presence of heterospecifics during feeding period, in the daytime. Crayfish seemed to have an advantage in competition for shelter, suggesting that they may interfere with tilapia sheltering activity and make tilapia vulnerable to predators in natural habitats.

Exploring source differences on diet-tissue discrimination factors in the analysis of stable isotope mixing models

Stable isotope mixing models are regularly used to provide probabilistic estimates of source contributions to dietary mixtures. Whilst Bayesian implementations of isotope mixing models have become prominent, the use of appropriate diet-tissue discrimination factors (DTDFs) remains as the least resolved aspect. The DTDFs are critical in providing accurate inferences from these models. Using both simulated and laboratory-based experimental data, this study provides conceptual and practical applications of isotope mixing models by exploring the role of DTDFs. The experimental study used Mozambique Tilapia Oreochromis mossambicus, a freshwater fish, to explore multi-tissue variations in isotopic incorporation patterns, and to evaluate isotope mixing model outputs based on the experiment- and literature-based DTDFs. Isotope incorporation patterns were variable for both muscle and fin tissues among the consumer groups that fed diet sources with different stable isotope values. Application of literature-based DTDFs in isotope mixing models consistently underestimated the dietary proportions of all single-source consumer groups. In contrast, application of diet-specific DTDFs provided better dietary estimates for single-source consumer groups. Variations in the proportional contributions of the individual sources were, nevertheless, observed for the mixed-source consumer group, which suggests that isotope assimilation of the individual food sources may have been influenced by other underlying physiological processes. This study provides evidence that stable isotope values from different diet sources exhibit large variations as they become incorporated into consumer tissues. This suggests that the application of isotope mixing models requires consideration of several aspects such as diet type and the associated biological processes that may influence DTDFs.

Methionine-enkephalin-treatment suppresses the pituitary-ovary axis in the cichlid fish Oreochromis mossambicus

The involvement of endogenous opioid peptides in regulation of reproductive activity is implicated in a majority of vertebrates. Methionine-enkephalin (M-ENK) is an endogenous opioid peptide neurotransmitter produced in the central nervous system. Although a role for M-ENK in antinociception (pain suppression) and mediation of stress has been suggested, its influence on fish reproduction is not clearly understood. The aim of the present investigation was to determine the role of M-ENK on the reproductive-axis of the female tilapia Oreochromis mossambicus. Treatment of stripped O. mossambicus with 300 μg M-ENK during the ovarian cycle resulted in suppression of luteinizing hormone (LH) secretory activity. This was evidenced by a significant reduction in the area and the intensity of LH immunoreactivity in the proximal pars distalis of the pituitary gland as compared to controls during the prespawning phase. At the ovarian level, the treatment of M-ENK caused a significant increase in the mean number of follicles with chromatin nucleolar (stage I), perinucleolar (stage II) and cortical alveolar stages (Stage III). Although the mean number of early vitellogenic follicles (stage IV) did not significantly differ from that of initial controls and controls, the mean number of late vitellogenic follicles (stage V, preovulatory) and the serum levels of estradiol were significantly lower in M-ENK treated fish compared to those of controls. However, there was a significant increase in the serum levels of cortisol in M-ENK treated fish compared to controls. Together, these results suggest that treatment of M-ENK inhibits the recruitment of follicles at late vitellogenic stage through the suppression of steroidogenesis in the ovary and LH secretory activity at the level of the pituitary gland in fish. Besides, the ability of M-ENK to stimulate serum cortisol levels indicates a role for this peptide in regulation of the hypothalamo-pituitary-interrenal axis in fish.

Determination of Iron (Fe) and Copper (Cu) on Pellets from Fermentation of Mozambique Tilapia (Oreochromis mossambicus) using Goat Dirt Adhesives

Tilapia fish waste and livestock manure are an environmental problem, besides being smelly pollution will also cause disease disorders for humans. The purpose of this study was to determine the levels of micronutrients of iron (Fe) and copper (Cu) on pellets from the fermentation of waste tilapia (oreochromis mossambicus) using adhesive goat manure. Fish waste was fermented for 15 days and mixed with adhesive goat manure and then was processed in a pellet making machine. The Fe and Cu levels were determined using Atomic Absorption Spectrophotometer (AAS). The results of the determination of levels Fe was 137 ppm and for Cu was 4.1 ppm.

Quality evaluation of fish burger from tilapia (Oreochromis mossambicus) during frozen storage (-18°c)

Quality evaluation of fish burger from tilapia (Oreochromis mossambicus) during frozen storage (-18°c)

Evaluation of genotoxicity, enzymatic alterations and cadmium accumulation in Mozambique tilapia Oreochromis mossambicus exposed to sub lethal concentrations of cadmium chloride

Abstract Cadmium (Cd), a heavy metal, is widely used in modern industries including in metal and mining industries as well as in the manufacture of Ni Cd batteries. Its bioaccumulation is reported to induce hazardous effects in aquatic organisms including fish. Hence, the present study was undertaken to evaluate the toxic potential of cadmium in Tilapia (Oreochromis mossambicus Peters). Fish were exposed to 3 sub-lethal concentrations of CdCl2: 7.4 μg/l (high), 3.7 μg/l (medium) and 1.85 μg/l (low) for a period of 21 days. Ten fish were used for each group and each exposure was done in triplicates. A group of 10 fish without exposure to CdCl2 was used as control. Genotoxic effects of Cd were assessed employing micronucleus assay and the comet assay. Along with these tests, alterations in the amount of the enzymes acetylcholine esterase (AChE) and catalase (CAT), as well as, the quantum of Cd accumulated in different tissues of the organism were also studied. A significant increase in DNA damage as % tail DNA and micronuclei were observed in the fish exposed to CdCl2. CdCl2 also induced a significant increase in the activity of CAT whereas a decrease in the activity of AChE was observed. A significant association was also observed between DNA damage parameters and catalase activity as well as Cd concentration in the gills. Cd may thus induce genotoxicity in O. mossambicus via oxidative stress and tissue accumulation. The combined use of these biomarkers in O. mossambicus could be used to monitor Cd contamination in the aquatic environment.

Influence of endomorphins along the pituitary-ovary axis in the Mozambique Tilapia Oreochromis mossambicus.

Endomorphins (EM-1 and EM-2) are the tetrapeptides involved in pain and neuroendocrine responses with a high affinity for μ-opioid receptors in vertebrates. However, their role in fish reproduction is not clear. The aim of this study was to investigate the influence of EM-1 and EM-2 on the pituitary-ovary axis in the Mozambique tilapia Oreochromis mossambicus. The experimental set-up consisted of four groups, namely, initial controls, controls, EM-1- and EM-2-treated groups (n = 10 in each group consisting of two replicates). Although the number of stage IV (vitellogenic) follicles was significantly lower (P < 0.05) in controls compared to initial controls, the stage V (preovulatory) follicles were present in controls in contrast to their absence in initial controls. Treatment of 40 μg EM-1/0.1 ml saline/fish/day for 22 days resulted in significant increase (P < 0.05) in the number of stage I follicles compared to controls. While similar treatment of EM-2 did not significantly alter the number of stage I follicles compared to controls, the number of stage II follicles was significantly lower (P < 0.05) in this group compared to those of controls and EM-1 treated fish. The number of stage III and IV follicles did not significantly differ among controls, EM-1- and EM-2-treated groups. However, a significant reduction (P < 0.05) in the mean number of stage V follicles was observed in EM-1- and EM-2-treated fish compared to controls. These changes were concomitant with significant reduction (P < 0.05) in the intensity and the percent area of immunoreactivity of luteinizing hormone (LH) secreting cells in the proximal pars distalis (PPD) of the pituitary gland and significantly higher (P < 0.05) percent occurrence of follicular atresia in EM-1- and EM-2-treated fish compared to those of controls. Taken together, these results suggest an inhibitory effect for endomorphins along the pituitary-ovary axis, for the first time in fish.

Exposure to hypoxia inhibits pituitary-testicular activity in the fish Oreochromis mossambicus

Fishes are exposed to natural hypoxic conditions during aquacultural practices. Although negative effects of hypoxia are documented on fish reproduction, the mechanism of hypoxia-induced alteration in spermatogenic process is not well understood in continuously breeding fishes. The aim of this investigation was to determine the influence of hypoxia on pituitary-testicular activity in the tilapia Oreochromis mossambicus, a cichlid fish that breeds throughout the year. The fish were exposed to moderate hypoxia (MH, Dissolved oxygen (DO) level, 3.24 ± 0.22 mg/L) and severe hypoxia (SH, DO level, 1.64 ± 0.38 mg/L) for 21 days. No significant differences were noticed in the mean numbers of spermatogonia (Sg), primary spermatocytes (Ps), secondary spermatocytes (Ss), early spermatids (Est) and late spermatids (Lst) between controls and fish subjected to MH, whereas the numbers of these cells were significantly lower in fish exposed to SH. Furthermore, weakly immunoreactive luteinizing hormone (LH) secreting cells in the proximal pars distalis (PPD) of the pituitary gland were concomitant with significant reduction in mean serum levels of LH and testosterone as well as androgen receptor immunoreactivity in the Sertoli cells in the testis of fish exposed to SH compared to other groups. On the other hand, the serum cortisol levels were significantly higher in fish exposed to SH compared with other experimental groups. Taken together, these results indicate that the tilapia is able to withstand the moderate hypoxic condition, whereas exposure to severe hypoxic condition suppresses the process of spermatogenesis through the inhibition of LH secretion, which in turn might suppress the testicular steroidogenesis and androgen receptor expression in the Sertoli cells. The results also suggest a possibility that this inhibition might be mediated through the activation of stress-axis in O. mossambicus.

Effect of food deprivation on neuropeptide Y immunoreactivity and concurrent biochemical and gonadal responses in tilapia Oreochromis mossambicus (Peters, 1852)

The effect of short- and long-term fasting on neuropeptide Y (NPY) secreting neurons in the brain and concurrent biochemical and gonadal responses were determined in the cichlid fish Oreochromis mossambicus (Peters, 1852). Exposure of fish to fasting for 6 or 12 days resulted in intensely stained NPY-immunoreactive neurons in the nucleus entopeduncularis and the nucleus preopticus regions of the brain in contrast to moderately stained neurons in control fishes, whereas food supplementation after 6 days starvation restored NPY-immunoreactive profile to the same state as in control groups in both male and female fish. The gonadosomatic index remained significantly lower in female fishes subjected to fasting alone as well as fasting followed by refeedings compared to controls. While the hepatosomatic index (HSI) also showed a significant decrease in fasting male and female fish compared to controls, it increased subsequently in fishes exposed to refeeding after starvation. In addition, a significant decrease in the serum levels of glucose and triglycerides as well as the hepatic tissue protein content in fasting fish compared to those of controls in both sexes suggested gluconeogenesis. Although the serum levels of glucose and triglycerides were reinstated in both males and female fishes subjected to starvation and refeeding, the hepatic tissue protein levels were not completely restored in females. Collectively, these results suggest that food-deprivation, either for short or long term duration, significantly increases the secretory activity of NPY neurons in the brain concomitant with a significant decrease in the serum levels of glucose and triglycerides, the hepatic tissue protein content and the GSI in both sexes. Although males recovered from the effects of starvation following refeeding, females appeared to be more vulnerable to the effects of fasting.

Rapid In Situ Action of Estradiol 17β on Ion Transporter Function in Brain Segments of Female Mozambique Tilapia ( Oreochromis mossambicus Peters)

Being the principal estrogen, estradiol 17I² (E 2 ) is essential for normal ovarian function in the vertebrates including fishes. Besides its primary role in reproduction, E 2 is also known for its role in many other physiological processes including water and mineral balance. However, it is uncertain, how E 2Â regulates ion-specific ATPases that drive Na + , K + , H + , Ca 2+ and Mg 2+ transport in fish brain. We, therefore, examined the short-term in situ action of E 2 on ion transporter function in the brain segments of freshwater female Mozambique tilapia Oreochromis mossambicus . Tilapia were perfused with increasing doses of E 2 (10 -9 , 10 -8 and 10 -7 M) for 20 min and sampled for determining Na + /K + -ATPase, H + -ATPase, Ca 2+ -ATPase, and Mg 2+ -ATPase activities in the prosencephalon (PC), mesencephalon (MC) and metencephalon (MeC) segments of brain. Dose-dependent increase in Na + /K + - and Ca 2+ -dependent transporter activities after E 2 perfusion were found in PC. In MC, E 2 treatment, however, produced significant increase in Mg 2+ , Ca 2+ and H + transport activities in mitochondria but decreased Na + /K + - and I½H + transporter activities. On the contrary, in MeC, E 2 administration while producing increase in Na + /K + -, mitochondrial- and I½H + -transport, lowered cytosolic and mitochondrial Ca 2+ transport. Taken together, the data indicate that E 2 has rapid and direct action on ion transporter function that corresponds to the differential activation/inactivation of neuronal clusters in the brain segments of female freshwater tilapia.

SAT-LB069 Differential Regulation of Hypothalamic and Hepatic Reproductive Signals by Leptin and Sex Steroids in the Mozambique Tilapia Oreochromis mossambicus

Reproduction is a physiologically demanding process that relies on energy sufficiency, the lack of which can result in delayed puberty and suppression of reproductive function. The pleiotropic peptide hormone leptin is a key signal in energy homeostasis that relays information on peripheral energy availability to central circuits. In mammals, leptin has been found to serve as a critical permissive signal in the activation of the gonadotropic axis and onset of puberty. Although leptin effects on reproduction have been explored extensively in mammals, its actions and regulatory properties on reproduction in fishes remain unclear. The current study assesses (i) the effect of in vivo leptin treatment on hypothalamic kisspeptin (kiss2) and gonadotropin-releasing hormone (gnrh1), (ii) the effect of leptin treatment on major egg-yolk precursors, vitellogenins (vtga, vtgb, vtgc), and insulin-like growth factor (igf1) in primary tilapia hepatocytes, and (iii) the effect of sex steroid treatment on leptin (lep) and insulin-like growth factor in primary tilapia hepatocytes. Gene expression of lep in the liver, the primary source of circulating hormone, increased with gonadosomatic index and sexual maturation of male and female tilapia, suggesting the hormone may regulate reproductive function. Intraperitoneal injection and 6-hour treatment with recombinant tilapia leptin (rtLep) in adult male tilapia resulted in increased hypothalamic kiss2 and gnrh1 transcript levels versus saline control (P < 0.01). In primary hepatocyte culture, rtLep suppressed vtgb and vtgc transcript levels (P < 0.01), while it stimulated igf1 (P < 0.0001). Testosterone and estradiol reduced lep levels (P < 0.001), but disparately regulated ­igf1 whereby testosterone increased igf1 and estradiol decreased igf1 at 10 and 100 nM (P < 0.001). The non-aromatizable 11-ketotestosterone increased lep and igf1 transcript levels at 100 nM (P < 0.05). Our findings suggest that leptin expression rises with sexual maturation and the hormone exerts stimulatory effects on hypothalamic gonadotropic factors. By contrast, leptin reduces estrogen-sensitive vitellogenesis while promoting elements of the somatotropic axis (e.g., igf1), suggesting the hormone may have dual roles in regulating reproductive and somatic growth processes. We speculate that this latter effect may be associated with limiting energy partitioning to reproduction in instances of negative energy balance. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. s presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

Hormonal Profile and Reproductive Parameters of Pre-vitellogenic Mozambique tilapia (Oreochromis mossambicus) on Pawpaw (Carica papaya) Seed Meal

The use of phytochemicals to control precocious maturation and indiscriminate spawning among tilapia species is an important issue in aquaculture. This study investigated the influence of pawpaw (Carica papaya) seed meal on the reproductive performance, and the sex hormone profile of sexually immature Mozambique tilapia (Oreochromis mossambicus). Pawpaw seed meal (PSM) were included in a tilapia commercial diet (basal diet) at an inclusion level of 0 PSM, 10 PSM and 30 PSM g/kg of the basal diet (BD), respectively, and fed to immature O. mossambicus for a period of 30 and 60 days, respectively. Enzyme-linked immune-sorbent assay (ELISA) procedures were used to quantify the plasma levels of 17&amp;beta;-estradiol and 11-ketotestosterone. The inclusion of PSM did not affect the growth and survival rate of the O. mossambicus. The plasma levels of 11-ketotestosterone did not differ among the treatment groups. The 17&amp;beta;-estradiol levels of female fish that received 30 PSM g/kg BD for 60 days were significantly lower (p &amp;lt; 0.05) than the levels reported for females that were not fed the PSM. In females, the PSM reduced the gonad weight, GSI, fecundity and egg diameter of fish. The study concludes that pawpaw seed meal affected the reproductive function of the female O. mossambicus though the changes were reversible.

Food habits of three non-native cichlid fishes in the lowermost Chao Phraya River basin, Thailand

The food habits of three non-native cichlid fishes, Mayan cichlid (Mayaheros urophthalmus), Mozambique tilapia (Oreochromis mossambicus) and Nile tilapia (O. niloticus), in the lowermost Chao Phraya River basin, Thailand, was examined by stomach contents analysis. The index of preponderance, an index of the importance of prey items, was calculated from two relative metrics of prey quantity: percent frequency and percent volume. The index of niche breadth and the overlap coefficient were calculated to compare the breadth of food habits among the size classes and species groups. The M. urophthalmus mainly preyed on fish scales, detritus and aquatic invertebrates (molluscs and crustaceans). The O. mossambicus and O. niloticus fed mostly on detritus. The diets of the latter two species overlapped almost completely; however, green filamentous algae mixed with detritus was observed in the diet of the O. niloticus only. The observation that fish scales were a predominant food source in the stomach of M. urophthalmus (high importance value 45.48%) was specific to this study area.

Parasites of the invasive tilapia Oreochromis mossambicus: evidence for co-introduction

Reduced parasite species diversity and infection intensity on invasive populations can facilitate establishment and spread of invasive species. We investigated the parasite diversity of invasive populations of tilapia Oreochromis mossambicus from published literature and necropsies conducted on 72 fish captured in the Ross River, north Queensland, Australia. The parasite diversity of invasive O. mossambicus from 13 countries was compared to published reports on endemic populations in African river systems and tributaries to determine parasite species that had likely been co-introduced. In total, four parasite species were shared between native and invasive tilapia. We propose that these parasites (three monogeneans, Cichlidogyrus tilapiae Paperna, 1960, Cichlidogyrus sclerosus Paperna and Thurston, 1969, Cichlidogyrus halli (Price and Kirk, 1967) and one trichodinid Trichodina heterodentata Duncan, 1977) have likely been co-introduced with invasive Oreochromis mossambicus populations. Invasive Australian O. mossambicus had substantially reduced parasite diversity (five species) compared to cumulative parasite species diversity documented from the native region (23 species). Australian O. mossambicus were infected by two co-introduced parasites and three additional parasite species that have not been recorded previously on this species in Africa indicating possible parasite spillback from Australian natives or alternatively, acquisition from other introduced fauna. The substantially reduced parasite diversity on invasive Australian O. mossambicus could contribute to the ability of this species to become a serious fish pest.

Growth performance, digestive enzyme activities and serum nonspecific immunity of the red tilapia ( Oreochromis mossambicus × Oreochromis niloticus ) fed diets supplemented with ultrafine powder of Enteromopha prolifera

The present study evaluated effects of ultrafine powder of the green macroalgae Enteromopha prolifera as dietary supplement on growth performance, digestive enzyme activities and serum nonspecific immune responses of the red tilapia ( Oreochromis mossambicus × Oreochromis niloticus ). The red tilapia were fed five diets supplemented with different levels of E. prolifera ultrafine powder as well as a control diet containing no E. prolifera for seven weeks (Diets 0–6 contained 0 (control), 10, 20, 30, 40 and 50 g/kg of E. prolifera ultrafine powder, respectively). The results showed that diets supplemented with E. prolifera ultrafine powder generally improved growth, immunity and digestive enzyme activities of the red tilapia. In particular, the fish fed the diet incorporated 50 g/kg (5%) E. prolifera ultrafine powder (Diet 5) achieved the highest percentage weight gain, specific growth rate and the condition factor (increased by 15.4%, 8.0% and 5.7%, respectively when compared to the control). Feeding the diet also led to significantly increases ( P <0.05) in serum nonspecific immune responses, including total superoxide dismutase, acid phosphatase, alkaline phosphatase, lysozyme activities and serum total protein (increased by 19.4%, 48.1%, 29.5%, 30.3% and 8.7%, respectively) as well as digestive enzyme activities of erepsin, gastric amylase, gastric lipase, pepsin, intestinal amylase and gastric lipase (increased by 15.7%, 33.3%, 16.3%, 21.3%, 52.3% and 28.2%, respectively) than those of the control. Based on these results, it is recommended that the inclusion level of E. prolifera ultrafine powder in the diet of the red tilapia should be 50 g/kg (or 5%).