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During salinity stress, osmoregulatory processes in euryhaline fish need to modify for their survival, and glucose is the preferred mode of extra energy during such conditions. These organisms must have a proper mechanism to maintain glucose homeostasis during such modified osmoregulatory process across different body fluids. Hence, we studied high salinity effect on regulation of glucose homeostasis in Mozambique tilapia. The fish were induced to 15‰ salinity for 21 days. Glucose, glycogen, ion concentrations, Na+-K+-ATPase, pyruvate kinase, γ-amylase activities and GLUT mRNA expressions were investigated in liver, intestine, gill and white muscle tissues. At the end of experiment, Na+ ion concentrations, glucose content and activity of Na+-K+-ATPase especially in the gill and intestine were increased, while decrease in liver and gill glycogen content was seen. Lower concentration of glycogen decrease was observed in the intestine and white muscle of the treated group. High pyruvate kinase activity was noticed in liver and gill tissues that correlates with high Na+-K+-ATPase activity. Elevated γ-amylase activity was observed in the liver and intestine suggesting breakdown of glycogen; however, gill and white muscle did not show any increased activity. Increase in GLUT1 and GLUT4 mRNA expressions was observed especially in the gill and intestine, while increase in GLUT2 mRNA expressions was observed in the liver. Upregulations of GLUTs suggest higher influx of glucose into the cell for catabolism to provide energy and further to drive the enhanced osmoregulatory process. These findings suggest glucose homeostasis being regulated in Mozambique tilapia during salinity acclimation.

The aim of this investigation was to examine the influence of temperature on testicular activity in the continuously breeding fish Oreochromis mossambicus. The fish were subjected to natural temperature (controls; 21.95 ± 0.21 °C), and low water temperature (LT; 18.18 ± 0.17 °C) or high water temperature (HT; 34.66 ± 0.31 °C) for an experimental period of 21 days, following which they were euthanized and the testes examined. The mean number of spermatogonia was significantly higher in fish exposed to the HT treatment than in the controls and fish exposed to the LT treatment. However, a significant reduction in the mean number of primary spermatocytes, secondary spermatocytes, early spermatids and late spermatids was observed in fish subjected to the LT and HT treatments compared to the controls. In addition, the mean serum testosterone levels were significantly decreased in fish exposed to the LT and HT, whereas the serum cortisol levels were significantly higher in these fish groups compared with the control fish. Taken together, these results suggest that exposure of fish to LT or HT activates the neuroendocrine axis that regulates the stress respone, leading to the inhibition of the process of spermatogenesis, possibly through the suppression of testicular steroidogenesis in O. mossambicus.

In this investigation, we examined the influence of alpha-melanocyte stimulating hormone (α-MSH), a proopiomelanocortin-derived peptide, along the hypothalamic-pituitary-gonad axis in a cichlid fish Oreochromis mossambicus. Administration of α-MSH (40 µg/0.1 ml saline) for 22 days did not affect the number of stage I (previtellogenic) follicles but caused significant reduction in the mean numbers of previtellogenic (stages II and III), vitellogenic (stage IV) and preovulatory (stage V) follicles compared to those of controls. While the gonadosomatic index was significantly lower, the rate of follicular atresia in stages II, III and IV remained significantly higher in α-MSH-treated fish compared to the controls. Furthermore, the mean percent area of gonadotropin-releasing hormone-immunoreactive (GnRH-ir) fibres and luteinizing hormone-immunoreactive (LH-ir) cells were significantly reduced in the proximal pars distalis of the pituitary gland in α-MSH-treated fish compared with the controls. Together, our findings suggest for the first time that the treatment of α-MSH blocks the follicular developmental process during the ovarian cycle, possibly through the inhibition of GnRH-LH pathway in teleosts.

The effect of female body color on mate selection by male Mozambique Tilapia (Oreochromis mossambicus) was assessed. A single black or gold male was placed in each of nine spawning net cages along ...

The occurrence of fish diseases contributes to massive economic loss to the aquaculture industry. Edwardsiella tarda, a known pathogenic organism in Oreochromis mossambicus, infects several freshwater fishes. The present study attempts to find an effective treatment against E. tarda infection using natural plant-based bioproducts. Tamarindus indica seed extract was used to study its antibacterial activity against E. tarda. The study revealed that the petroleum ether extract and ethanolic extracts were effective in controlling the infection. It was found to be effective in both in vitro and in vivo. A maximum zone of inhibition, i.e., 9 and 24 mm, was recorded when 40μL of the petroleum ether extract and 40 μL of the ethanolic extract were loaded separately in the well against the test organism. Results showed that the petroleum ether and ethanol extract of T. indica seed were effective in treating the E. tarda infection.

Aquaculture in Mozambique was introduced in the late 1950s, and several strategies have since been put in place to develop the sector, especially in growing the Mozambique Tilapia (Oreochromis mossambicus). The study assessed aquaculture production in the Gaza Province of Mozambique. Data was obtained from semi-structured interviews and questionnaires in companies, community associations, and individuals focusing mainly on their adopted production systems, challenges, and opportunities. The study identified 15 fish farmers, with a total of 301 fish culture facilities in which 86% were ponds and 14% cages with cultivation structure varying from 120 m2 to 2000 m2 for ponds and 6 m3 to 13 m3 for cages. Two production systems were distinguished including extensive and semi-intensive with 61% and 39% respectively. Oreochromis niloticus was the main cultured species. These farmers get their feed from Livestock Feed Limited (LFL) and AquaPlus. The unavailability of quality feed, seed and inadequate extension workers were listed as the main challenges faced by the farmers leading to low fish production. Our findings clearly show that fish farming is an attractive activity for small and medium-scale farmers, and it can grow especially if necessary measures are taken to improve management, access to inputs, and extension services.

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.

Although photoperiod plays a critical role in seasonally breeding fish, effect of altered photoperiod on reproduction of continuously breeding fish is not well understood. The objective of this investigation is to determine the effect of continuous light exposure on testicular activity in Oreochromis mossambicus. The fish were exposed to simulated photoperiod and continuous light for 21 days. Although the mean numbers of spermatogonia and primary spermatocytes did not show significant difference, the mean numbers of secondary spermatocytes, early spermatids and late spermatids were significantly lower in fish exposed to continuous light compared to those of initial controls (fish euthanized on the day of commencement of experiment), controls (fish kept in natural photoperiod) and fish exposed to simulated photoperiod. Furthermore, diminished immunoreactivity of androgen receptors was observed in the Sertoli cells concomitant with significantly lower serum levels of testosterone in fish exposed to continuous light compared to other experimental groups. In addition, the mean serum cortisol levels were significantly higher in continuous light fish group compared to other experimental groups. Overall, these results indicate that exposure to continuous light inhibits advanced stages of spermatogenesis, possibly through the suppression of testicular steroidogenesis and that this effect might be mediated through the stress-axis in O. mossambicus.

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.

An experiment was conducted to replace soya bean meal (SBM) with cashew nut meal (CNM) in the diet of tilapia (Oreochromis mossambicus). Five isonitrogenous (30% CP) and isolipidic (6% CL) diets, CNM0 to CNM4, were prepared replacing SBM at 0%, 12.5%, 25%, 37.5% and 50% with CNM. The feeding trial was conducted in FRP digestibility tanks of 150 L capacity for 60 days. Twenty tilapia fry (20.56 ± 0.05 g) were stocked in each tank. The final weight, weight gain and weight gain% of tilapia that received the CNM4 diet were significantly higher (p .05) among the treatments. It can be concluded from the study that 50% replacement of SBM with CNM in the diet is suitable for the enhancement of growth, nutrient utilization and health status of tilapia.

To develop an alternative to conventional antibiotics used in the aquaculture and livestock industries, we employed Bacillus subtilis, considered a biosafe microorganism, to express the degradable antimicrobial peptide lactoferricin. An expression plasmid pP43-6LFBII-GFP, in which reporter GFP cDNA was fused downstream of lactoferricin cDNA driven by an endogenous constitutive P43 promoter was electroporated into B. subtilis, followed by regeneration and cultivation. The putative colonies harboring plasmids were primarily screened by PCR-amplification of lactoferricin cDNA. Four transformants which were stable inheritance of plasmid containing lactoferricin cDNA included strains T1, T4, T7 and T13. Based on Western blot and Southern blot analyses, we found that transgenic strains T1 and T13 not only highly expressed exogenous recombinant lactoferricin, but also exhibited more stable inheritance of plasmids with 931 and 647 copies per cell, respectively. In the antibacterial in vitro experiment, the bactericidal activity of each microliter of cell lysate from transgenic strains T1 and T13 (5 × 108 CFU) for Escherichia coli was equivalent to 56 and 53 ng of Ampicillin dosage, respectively, while for Staphylococcus epidermidis, the equivalency T1 and T13 was 154 and 130 ng of Ampicillin dosage, respectively. Equivalencies of bacterial activity for Vibrio parahaemolyticus and Edwardsiella tarda followed suit. In the antibacterial in vivo experiment, we oral-in-tube fed tilapia fry (Oreochromis mossambicus X O. niloticus) with cell lysate from transgenic strain T1 and T13 individually. After 1-h of incubation, we immersed these treated fish fry in a water tank containing E. tarda (5 × 1011 CFU) for a 5-hr bacterial challenge. After one month cultivation, an average survival rate of 63 and 67% was observed after having fed the fish fry with transgenic strains T1 and T13, respectively. However, the average survival rate of fish fry fed with B. subtilis WT strain and transgenic strain T19 without expressing recombinant lactoferricin reached only 5 and 9%, respectively. These data indicate that the survival of fish fry infected by the intestinal pathogen tested could be significantly enhanced by feeding transgenic B. subtilis containing antibacterial peptide. Therefore, we suggest that this strategy could be applied to both aquaculture and livestock industries to (i) reduce the dependency on conventional antibiotics during seasonal outbreaks and (ii) eliminate the problem of antibiotic resistance.

The present study evaluated the growth performance and whole-body composition of the hybrid red tilapia ( Oreochromis mossambicus × O. aureus ) raised in saltwater and fed three experimental diets containing different protein levels (25.6, 30.8 and 35.6% CP; crude protein). The hybrid red tilapia showed a high production performance across all dietary treatments: specific growth rate (SGR) = 3.12-3.51% body weight d -1 ; weight gain = 391-503%; feed conversion ratio (FCR) = 0.90-1.07; thermal growth coefficient (TGC) = 1.50-1.67; condition factor (CF) = 0.19-0.26. Dietary protein content significantly affected feed intake; fish fed the 30.8% CP diets displayed higher feed intake than those fed the 25.6% CP diet. Although the protein efficiency ratio (PER) was not significantly affected by dietary treatments, fish fed 25.6% CP diet demonstrated numerically higher values than those fed the other dietary treatments (4.34 vs . 3.06-3.35). The viscerosomatic index was significantly reduced in the 25.6% CP group compared to 30.8 and 35.6% CP groups. Regarding the whole-body composition, dietary protein affected all parameters, except lipid content. Fish fed the 30.8% CP diet exhibited significantly reduced relative protein content and elevated ash content in the whole-body in comparison to other dietary groups. The results of the present study indicated that juveniles of hybrid red tilapia accepted all dietary treatments. However, according to polynomial regression analyses based on PER and the high ash content in tilapias fed the 30.8% CP, it is suggested that the optimum dietary protein content for juvenile hybrid red tilapia was 25.6%.

Tilapias are important aquaculture species. Male-biased sexual size dimorphism is very common and males are preferred for aquaculture in tilapia. However, the mechanisms underlying sexual dimorphism remain to be elucidated. One hundred and thirty-six sex-biased genes, of which 23 were male-biased and 113 were female-biased, were identified via reanalysis of a muscle transcriptome data using the latest reference genome assembly. These genes were mapped to KEGG pathways that are related to somatic cell metabolism, growth and differentiations, such as MAPK, FoxO4 and metabolism pathways as well as developmental processes responsible for skeletal muscle development. Pathways related to cell growth and proliferations such as MAPK signaling pathways are upregulated in males while pathways regulating cell division such as FoxO4 are upregulated in females. Sex-biased genes in tilapia skeletal muscle have higher evolution rates (dN/dS) compared to unbiased genes. Female-biased and male-biased genes showed 17.4% and 13.5% higher dN/dS, respectively, compared to unbiased genes. Our results suggest that some of the male and female sex-biased genes were under selection pressures. Three SNPs located in the promoter region of one sex-biased gene RASGRF1 on LG1 were associated with bodyweight differences in the hybrid tilapia. These sex-biased genes identified in this study may serve as candidate genes for future functional analysis on sexual size dimorphism and for developing DNA markers for selecting fast-growing saline tilapia in aquaculture. Keywords: Sexual dimorphism, Body size, RNA-Seq, Tilapia, Aquaculture, Evolution

Comparative evaluation of mahua (Bassia latifolia) oil cake (MOC) and castor bean (Ricinus communis) seed (CBS) was tested as piscicides for tilapia (Oreochromis mossambicus) and panchax (Aplocheilus panchax), and residual toxicity test was done on Labeo bata. Delayed response of CBS compared with MOC was evident as first and total mortality of tilapia was encountered at 4th and 10th hour of application, against 26 hr and 42 hr in panchax respectively. Susceptibility of the test fish to the piscicides was highly variable as tilapia was more susceptible than panchax under both the piscicides tested especially in CBS. Residual toxicity decreased polynomialy over time (R² ≥ 0.99) and reduced to below 10% on day 13–14 in both MOC and CBS treatments. Both MOC and CBS contributed positively to the nutrient pool of water in which CBS provided more nitrogen compared with MOC. N: P ratio of water in CBS treatment increased exponentially to more than 18 indicating phosphorus limitation.

Nevirapine (NVP) is one of the HIV antiretrovirals detected recurrently in African surface waters. Liver side effects in humans were reported. Because the effects on fish are unknown, this study investigated the potential effects of NVP on selected biometric indices and liver histology of Oreochromis mossambicus (Mozambique tilapia) in a chronic exposure. Adult fish were exposed to two concentrations of NVP (1.48 and 3.74 µg l−1) in a static renewal system under controlled conditions for 30 days. At the end of the exposure, each fish was weighed, the total length recorded, and blood collected from the caudal vein. A standard necropsy was done, selected organs were sampled and weighed, and biometric indices calculated. Liver tissue was processed for histological assessment. Results showed significant differences (p < 0.001) in hepatosomatic indices between the exposed fish and the control, as well as in spleen indices of the fish exposed to the higher NVP concentration (p = 0.008). Liver tissue of exposed fish showed significant histological changes (p < 0.001), including hepatocyte apoptosis, vacuolation, and a mild fibrosis around some of the veins and bile ducts. Nevirapine in African surface waters could have long-term negative effects on the health of fish.Keywords: chronic effects, histology, histopathology, HIV antiretrovirals, liver toxicity, Mozambique tilapia

A recrystallized solvate of enrofloxacin in the form of hydrochloride dihydrate (enro-C) has shown a greater bioavailability in other species and a higher solubility in water compared to standard enrofloxacin. This led to define the pharmacokinetics (PK) of enro-C in tilapia (Oreochromis niloticus × Oreochromis mossambicus), when administered as in-feed medication, either by the addition of enro-C during food pelleting (T2) or by the coating of pre-manufactured pellets with a gelatin suspension containing enro-C (T1). T1 and T2 were both prepared with 3000 mg of enro-C/kg of feed, and a total dose of 10 mg/kg based on feed consumption. The trial was carried out in fresh water tanks, collecting blood samples twelve times during 70 h (three repetitions with five tilapias per sampling time). Maximum plasma concentrations (CMAX) for T1 and T2 were 1.35 ± 0.55 μg/mL and 1.92 ± 0.26 μg/mL, respectively. The time to achieve CMAX (TMAX) occurred almost simultaneously at 6.5 h. The area under the plasma vs time concentrations (AUC0-24) were 25.41 ± 24 μg/mL/h and 57.91 ± 30 μg/mL/h for T1 and T2, respectively. MIC data from available literature indicate that PK/PD ratios (CMAX/MIC90 and AUC0-24/MIC90) are higher in T2 compared to T1 in tilapia. Results indicate that the customary dose of enrofloxacin (10 mg/kg) using enro-C reaches, in particular, higher values of CMAX and AUC0-24. Thus, based on these results, it is feasible to propose enro-C for the treatment of bacterial diseases in tilapia, preferably as was done in T2. However, before this happens, toxicity and drug-residue studies, as well as environmental and public health issues, must be resolved.

Amoxicillin (AMX) is commonly used to treat Streptococcus spp. infection in hybrid red tilapia (Oreochromis mossambicus × Oreochromis niloticus), despite the lack of plasma pharmacokinetic data, and suitable edible tissue residue withdrawal time estimations. The aim of this study was therefore to investigate plasma pharmacokinetics and muscle tissue residues depletion of AMX in hybrid red tilapia raised in cages. Cage raised hybrid red tilapia (223 ± 11.5 g) from Southern Vietnam were treated with medicated feed containing AMX at a dose of 5000 mg/kg feed (equal to 50 mg/kg body weight fish) for five consecutive days. During administration of the medicated feed, fish muscle (including skin) samples were taken at days 1 and 5 (each time at 2 h, 12 h and 24 h after feeding) and at 3, 7 and 14 days after the cessation of medicated feed administration. Plasma was collected at 30 min, and at 1, 2, 6, 12 and 24 h after the first medication and at 2, 12 and 24 h after administration of medicated feed on day 2, 3, 4 and 5. AMX levels were determined by liquid chromatography coupled to tandem mass spectrometry. Results showed that AMX depleted rapidly in fish muscle and skin and was below the limit of quantification (5 μg/kg) within 24 h after five consecutive days of medication. Noncompartmental pharmacokinetic analysis of AMX revealed that maximum plasma concentration (Cmax) on day 1 was 2.75 ± 0.98 μg/mL (Tmax, 1 h), whereas it ranged from 0.81 to 0.97 μg/mL (day 2 to 4) and decreased to 0.27 ± 0.07 μg/mL (Tmax 2–12 h) on day five of medication. Also, the highest area under the plasma concentration-time curve from time 0 to 24 h (AUC0–24h; 28.06 ± 3.32 h·μg/mL) was found on the first day of treatment and decreased on the following days. The elimination rate constant (kel) was 0.17 h−1 and elimination half-life (T1/2el) was 4.1 h. Our results show that AMX is depleted from edible muscle tissue in a short time period, which suggests a low, if any, food safety hazard associated with common treatment regimes. However, further research is needed to define a well-suited therapeutic dose.

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.

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.

Streptococcosis and motile aeromonad septicemia (MAS) are well-known diseases in tilapia culture, which cause mass mortality with significant economic losses. The development of feed-based bivalent vaccines in controlling these diseases has been initiated, however, the mechanisms of immunities and cross-protection in fish remain unclear. This study was conducted to assess the immuno-protective as well as the cross-protective efficacy of a newly developed feed-based bivalent vaccine against Streptococcus and Aeromonas infections in red hybrid tilapia. A total of five groups of fish were vaccinated orally through two different techniques; bivalent vaccine (inactivated Streptococcus iniae and Aeromonas hydrophila) sprayed on feed pellets (BS group); bivalent vaccine (inactivated S. iniae and A. hydrophila) incorporated in feed (BI group); monovalent inactivated S. iniae and A. hydrophila vaccine separately incorporated into feed as monovalent S. iniae (MS group) and monovalent A. hydrophila (MA group); and control group (without vaccine). The feed-based vaccine was delivered orally at 5% of body weight for five consecutive days. The booster doses were given in the same manner on weeks 2 and 6. Serum and skin mucus samples were collected to assess the IgM responses using indirect ELISA. The first administration of the feed-based vaccine stimulated the IgM levels that lasted until week 3, while the second booster ensured that the IgM levels remained high for a period of 16 weeks in the BI, MS and MA groups. The BI group developed a strong and significantly (P

The current study focused on the immunostimulatory effects of intraperitoneal administration of the medicinal plant, Terminalia catappa leaf extract in red hybrid tilapia (Oreochromis mossambicus × O. niloticus). Fish were divided into four groups of 30 fish each. Group 1 served as the methanol control, administered 0.1 mL of methanol. Group 2 served as the negative control without any extract induced. Group 3 and 4 were administered intraperitoneally with 31.25 mg kg−1 and 62.5 mg kg−1 of Terminalia catappa methanol extract, respectively. The effect of the extract on some innate immune responses such as phagocytosis, respiratory burst activity, complement activity, lysozyme activity and resistance against Streptococcus agalactiae was determined after weeks 1, 2 and 4 post-injection respectively. Results indicated that the extract of 31.25 mg kg−1 and 62.5 mg kg−1 significantly enhanced the phagocytic, respiratory burst and lysozyme activities after two weeks. No significant difference was observed in the complement activity assay throughout the experimental period in the groups administered Terminalia catappa methanol leaf extract. However, a sequential decline in the innate immune response was observed in the methanol control group as the week progressed from week 1–4. Following the challenge with S. agalactiae, there was significantly lower percentage mortality in the group of fish administered 31.25 mg kg−1 and 62.5 mg kg−1 Terminalia catappa methanol leaf extract, thereby increasing the relative percentage survival of the fish. The highest dose of 62.5 mg kg−1 gave better protection than the 31.25 mg kg−1. The results indicated that the intraperitoneal injection of Terminalia catappa leaf extract enhanced the nonspecific immune responses and disease resistance of red hybrid tilapia against S. agalactiae.

Streptococcus iniae is a Gram-positive, opportunistically zoonotic bacterium infective to a wide variety of farmed and wild fish species worldwide. Outbreaks in wild fish can have detrimental environmental and cultural impacts, and mortality events in aquaculture can result in significant economic losses. As an emerging or re-emerging pathogen of global significance, understanding the coalescing factors contributing to piscine streptococcosis is crucial for developing strategies to control infections. Intraspecific antigenic and genetic variability of S. iniae has made development of autogenous vaccines a challenge, particularly where the diversity of locally endemic S. iniae strains is unknown. This study genetically and phenotypically characterized 11 S. iniae isolates from diseased wild and farmed fish from North America, Central America, and the Caribbean. A multilocus sequence analysis (MLSA) scheme was developed to phylogenetically compare these isolates to 84 other strains of Streptococcus spp. relevant to aquaculture. MLSA generated phylogenies comparable to established genotyping methods, and isolates formed distinct clades related to phenotype and host species. The endothelial Oreochromis mossambicus bulbus arteriosus cell line and whole blood from rainbow trout Oncorhynchus mykiss, Nile tilapia Oreochromis niloticus, and white sturgeon Acipenser transmontanus were used to investigate the persistence and virulence of the 11 isolates using in vitro assays. In vivo challenges using an O. niloticus model were used to evaluate virulence by the intragastric route of infection. Isolates showed significant differences (p < 0.05) in virulence and persistence, with some correlation to genogroup, establishing a basis for further work uncovering genetic factors leading to increased pathogenicity.

The “Molobicus” hybrid breeding programme was initiated to improve tilapia growth performance in brackish water. The base population was created by backcrossing F1 Oreochromis niloticus GIFT strains × feral O. mossambicus to O. mossambicus and selective breeding conducted for performance in brackish water with two lines selected in extensive or intensive rearing conditions. A panel of ten diagnostic SNP markers was applied to estimate the species composition at different stages in the Molobicus programme including parental stocks, F1 and seventh generation fish from the selective lines. The O. aureus-specific markers tested revealed zero or negligible contribution from O. aureus to all the groups analysed. Feral O. mossambicus possessed an estimated 0.98 frequency of O. mossambicus-specific alleles, while GIFT samples had an estimated mean frequency of 0.88 O. niloticus-specific alleles. Hybrid F1 GIFT × feral O. mossambicus samples demonstrated close to 50:50 allele frequencies from O. niloticus and O. mossambicus for seven of the eight SNP loci tested. Analysis of the combined seventh generation Molobicus samples revealed a significant excess of O. niloticus alleles in six out of the eight SNPs tested, with this trend being more pronounced in the line selected in intensive culture conditions and showing increased body weight. PCR-based SNP assays such as these can be used to inform on the individual species contribution of fish stocks and provide tools for the genetic management of the tilapia species and future breeding programmes.

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.

The effects of Azomite, a natural mineral of volcanic ash, on the sex steroid hormone (SSH) levels and milt quality indices (MQI); namely, the milt volume, motility of spermatozoa, its duration and sperm count, were evaluated in tilapia (Oreochromis mossambicus). Several reports have documented the positive effect of the Azomite supplementation on growth, survival, and immune response of aquatic organisms. In this study, a healthy brooder stock of male O. mossambicus was divided into four experimental groups, and fed with Azomite supplemented diets of varying concentrations: 0 g/kg body weight (Control), 2, 4, and 6 g/kg body weights. After the eight-week experimental trial feeding, the 4.0 g/kg Azomite supplemented diet presented greater SSH levels and MQI than the other diets and the control group. The quantity of milt enhanced with a significant (p < 0.01) increase in the 4 g/kg Azomite supplemented group compared to the control and other Azomite supplemented groups. Similarly, the maximum percentage of spermatocrit and sperm count was found in the 4 g/kg diet-fed group. Likewise, the highest percentage and duration of sperm motility, as well as sex-specific steroid hormones, such as testosterone (T), 11-ketotestosterone (11-KT) and 17β-estradiol (E₂) in the milt samples was found in 4 g/kg Azomite supplemented group. Dietary inclusion of 4 g/kg Azomite significant improved gonadal steroid hormone levels and milt quality indices in Oreochromis mossambicus.

Black scabbardfish, Aphanopus carbo, is a commercially important species that takes distant migrations throughout its life cycle. Sex steroids were measured by radioimmunoassay in the blood plasma of specimens caught off the Madeira Archipelago and mainland Portugal to link this species migratory path with its reproductive cycle. Furthermore, a pilot study using Mozambique tilapia (Oreochromis mossambicus) was designed to evaluate the effect of sample freshness on steroid levels because black scabbardfish blood was collected at separate times after specimens were caught. The changes in T and 11-KT concentrations between the time of blood extraction and the time after preservation did not statistically differ among the different methods applied. Therefore, measured black scabbardfish steroid concentrations were directly used in the subsequent data analyses. In females, E2 and in T concentrations peaked at a late stage of vitellogenesis. E2 concentration was significantly different between females caught off each area. Clustering E2 and T concentrations from all developing females resulted in the separation of two distinct groups, independently of their geographical area. In males, T and 11-KT were not significantly different between maturity stages. The hepatosomatic index of males caught off mainland Portugal was relatively high. This may reflect a mechanism for storing energy that will later be consumed during migration to the spawning grounds. The trend of sex steroids concentrations throughout the sexual maturation of the species is consistent with the morphological indicators and shows evidence of the reproductive and migratory pattern hypothesised for the black scabbardfish in NE Atlantic., This work was supported by the Portuguese Foundation for Science and Technology (FCT – Fundação para a Ciência e Tecnologia) under the PhD Grant SFRH/BD/64434/2009 to I. Fa. and the project UID/Multi/04326/2013 to A.V.M.C.; the Portuguese Government Development Investments and Expenses Program (PIDDAC – Programa de Investimentos e Despesas de Desenvolvimento da Administração Central) under the EU/DG Fisheries' Data Collection Framework (DCF); the Portuguese Fisheries Operational Program (2007–2013) (PROMAR – Programa Operacional Pescas), co-financed by the European Fisheries Fund (EFF) (2007–2013), under project CERTIFICA (2011–2015), MSC Certification in Portugal - Acquiring the knowledge and studying the viability for its application to coastal and artisanal fisheries.

Supplementation of red algae can act as potent immune stimulator and have the effectiveness to induce immune related genes which play an important role in host defense mechanism. The objective of the present study is to scrutinize the potentiality of Portieria hornemannii (pH) extract to improve the disease resistance and immune response in Tilapia (Oreochromis mossambicus). Fishes were fed with PH diet for 45 days prior to the experimental challenge with Vibrio parahaemolyticus. Expression of immune related genes and immune parameters were analyzed at 1, 7 and 14 day of post challenge period. Fishes fed with PH diet showed higher percentage of survival when compared to the control group 14 day post challenge. Significant increase in antiprotease, serum lysozyme and NBT activity were seen in tilapia fed with PH extract diet (15 mg/g). These results simplified that PH extract can elevate the survival rate restraining the immune response in O.mossambicus.

Light is an important factor for the successful reproduction of most fish. In this investigation, effect of different light intensities on pituitary-testis axis was studied for a period of 21 days, under normal photoperiodic regime in the tilapia Oreochromis mossambicus. The mean numbers of spermatogonia (Sg), primary spermatocytes (Ps), secondary spermatocytes (Ss), early spermatids (Est) and late spermatids (Lst) did not show significant difference between fish exposed to moderate light intensity (MLI) and initial controls or controls, whereas the mean numbers of Sg were significantly lower in fish exposed to low light intensity (LLI) compared to those of initial controls, controls and MLI groups. However, the mean numbers of Ps, Ss, Est and Lst were significantly lower in fish exposed to LLI and high light intensity (HLI) compared to those of other experimental groups. Furthermore, in the pituitary gland, weakly immunoreactive luteinizing hormone (LH) secreting cells were observed in the proximal pars distalis (PPD) region in fish exposed to LLI and HLI in contrast to the intense immunolabelling of these cells in initial controls, controls and MLI groups. The androgen receptors showed diminished immunoreactivity in the Sertoli cells along the seminiferous lobules of the testis in fish exposed to LLI and HLI, whereas the strongly immunoreactive androgen receptors were observed in the Sertoli cells in initial controls, controls and MLI groups. Taken together, these results indicate that long-term exposure to low or high light intensity light suppresses spermatogenetic process and that this inhibition is due to reduced secretory activity of LH cells in the pituitary gland and androgen secretion in the testis of the fish O. mossambicus.

This study investigated the extent of changes in haemato-biochemical and immunological parameters of O. mossambicus fed with M. oleifera-based diets pre and post-challenge with different concentrations of A. hydrophila. Moringa oleifera powdered leaves were added to five experimental diets at 0%, 3%, 6%, 9% and 12%, designated D1, D2, D3, D4 and D5, respectively. Each diet was randomly fed to triplicate groups of 45 fish (33.46 ± 1.57 g) for 45 days. There were no significant differences (P > 0.05) in WG, FCR and SGR between treatments. There was an increase in WBC, RBC, HGB and HCT with increasing M. oleifera levels. No significant changes (P > 0.05) were observed in AST, ALT, ALP and LDH levels between treatments. After 45 days, fish from each treatment were injected with varying concentrations (0, 1 × 106 cfu, 1.5 × 106 cfu, 3 × 106 cfu and 4 × 106 cfu ml˗1) of Aeromonas hydrophila. There was a significant decline in RBC, HGB and HCT of fish in the D1-D3 compared to the D4 and D5 groups. There was an increase in AST, ALT, ALP and LDH in the D1-D3 groups while no significant changes (P > 0.05) were observed in the D4 and D5 groups between bacterial concentrations. Survival rate was lower in the D1-D3 compared to the D4 and D5 groups, indicating that immunity was enhanced in fish fed with the highest M. oleifera inclusion levels. NBT and lysozyme activities were also lower in the D1-D3 groups compared to the D4 and D5 groups. The enhancement of immunity is attributed to the presence of biologically active compounds with immunostimulatory properties. The phytochemistry of the M. oleifera revealed high levels of total polyphenol, total phenols, total flavonoids, carotenoids, vitamins C and E.

Specimens of spinycheek grouper Epinephelus diacanthus (Teleostei: Epinephelidae) and the Mozambique tilapia, Oreochromis mossambicus (Teleostei: Cichlidae) were reported in this study to show the case of head deformity in individuals of Epinephelus diacanthus collected from waters in the vicinity of Jubail City, Saudi Arabia. Individuals of Oreochromis mossambicus were obtained from the fish market, which are originally collected and brought from the neighbouring Sultanate of Oman have shown pugheadness deformity. The specimen of Epinephelus diacanthus shown to have short neurocranium, absence of upper jaw and normal lower jaw, with the mouth nearly closed. The specimen of Oreochromis mossambicus showed short neurocranium and a normal upward directed upper and lower jaws. The mouth was nearly closed, with the two sides being stuck, which means that the deformity has a significant effect on the mechanism of mouth operation. The case of O. mossambicus is considered more severe than the case of E. diacanthus in spite of missing few bony elements. The possible causes for such deformities are discussed. The first new documented record of Epinephelus diacanthus in the Arabian Gulf waters is reported based on one specimen with total length 420 mm, which has been collected by gill net on the coast of Jubail City. Morphometric and meristic data are provided.

We investigated the effects of dietary enriched with Shilajit in three dose levels: 2.0, 4.0, and 6.0 g kg−1 in the basal diet on growth rate, non-specific immune response, and disease resistance for 60 days in Oreochromis mossambicus against an opportunist pathogen, Aeromonas hydrophila. The results showed that the Shilajit enriched diets at 4.0 and 6.0 g kg−1 diets significantly (p

In the present study, growth performance, serum biochemical, hematological parameters and disease resistance against S. iniae in Mozambique tilapia were determined after 60-day feeding period with ethanol extract propolis supplemented diets. Growth performance increased (P 0.05). Total protein, values in serum found significantly higher in P2 group (9.31 ± 0.66 g dL−1) compared to the P0 (7.49 ± 1.66 g dL−1). The highest serum cholesterol value was obtained in P4 (206.76 ± 24.57 mg dL−1) group and found significantly different from P0 (169.79 ± 17.11 mg dL−1). The lactate dehydrogenase, lysozyme and myeloperoxidase activity significantly increased in P1, P2, P4 and P8 groups. The highest lysozyme and myeloperoxidase activity values were obtained in P2 and P4 groups (for lysozyme 255.44 ± 3.41 mg L−1, 260.55 ± 4.29 mg L−1 and for myeloperoxidase 145.01 ± 3.82 U L−1 151.35 ± 4.17 U L−1 respectively) and found significantly different from P0 group. Propolis supplementation to the diets showed no differences on other serum biochemical parameters such as glucose, triglyceride, glutamic pyrivic transaminase and glutamic oxaloacetic transaminase. After challenge with S. iniae, fish fed with 2 and 4 g kg−1 propolis showed significant survival rates (72.55% and 68.63%, respectively) compared with other groups. This study indicates that growth performance and non-specific immune response of Mozambique tilapia can be enhanced by dietary supplementation with propolis and that the optimal level would be 2 g kg−1.

The induction of triploidy in red hybrid tilapia (Oreochromis mossambicus × Oreochromis niloticus) using electric-shock at different duration (3, 5, 10, 15 and 20 min) is reported in this study. Triploidy induction was attempted by exposing fertilized egg to electric field maintained at 12 V at approximately 4 min after fertilization. The efficiency of triploidization was confirmed by counting the number of chromosomes and affirmed by assessing erythrocyte biometrics of one month old fingerlings. The result obtained shows that shock duration of 10 min was most effective as it induced triploidy in 87% of the fish in this group with a hatching rate of 68%. The chromosome count of induced triploids was 3n = 66 while diploid fish had 2n = 44. Also, many erythrocyte biometrics of the triploid hybrid tilapia were significantly larger than those of the diploid groups (between 12 and 56% increments). Out of all the erythrocyte parameters measured or calculated, the cell major axis had the highest percentage of erythrocytes (91.4%) that were within the exclusive triploid range (12.61–15.98 μm). Hence, despite the dominant oval shape of both diploid and triploid erythrocytes, discrimination of the entire fish groups was accurately done by solely accessing the exclusive range of the cell major axis. It was concluded that application of an electric field of 12 V for 10 mins was better for triploidization of the red hybrid tilapia eggs.

The purpose of the present study is to extend knowledge on the adverse effects of nanoparticles by evaluating genotoxicity as environmental risk assessment in Oreochromis mossambicus. Fish were exposed to sublethal concentrations of the selected nanoparticles, namely silicon dioxide (SiO2NPs-12mg/L), aluminium oxide (Al2O3NPs-4mg/L), titanium dioxide (TiO2NPs-16.4mg/L) and iron oxide (Fe3O4NPs-15mg/L) for short-term (24, 72 and 96 h) and long-term durations (15, 30 and 60 days). Genetic damages such as cytoplasmic, nuclear and DNA damage were measured in the erythrocytes of fish by using standard genotoxicity tests such as micronucleus test and comet assay. The frequencies of micronuclei along with nuclear and cytoplasmic abnormalities were scored and compared with the control group. The intensity of micronuclei along with other nuclear and cytoplasmic anomalies are found to be increased significantly (pOreochromis mossambicus.

This study investigated the potential of Artemisia afra on growth and disease resistance in Oreochromis mossambicus . Phytochemical analysis of A. afra was also undertaken. Five A. afra -based diets designated as D1, D2, D3, D4 and D5 were formulated and randomly fed to triplicate groups of 45 fish (32.5 ± 1 g). At the end of feeding, Food Conversion Ratio and Specific Growth Rate values were not significantly different (F 15,4 = 0.6, p > 0.05; F 15,4 = 0.45, p > 0.05, respectively) between D1 and the other diets. Weight gain and feed intake were higher in D1, D2 and D3 than in D4 and D5, but no significant difference (ANOVA, p > 0.05) was found between treatments. This suggests that safe dosages were used. Phagocytosis and lysozyme activity were higher in fish fed D4 and D5 than those fed D1 and the other diets. White blood cells were also higher in fish fed the A. afra -based diets. To test for disease resistance, fish from each dietary treatment were injected with varying concentrations (0, 1 × 10 6 cfu, 1.5 × 10 6 cfu, 3 × 10 6 cfu, 4 × 10 6 cfu mL ˗1 ) of Aeromonas hydrophila . Relative percentage survival and the survival rate of O. mossambicus were higher in fish fed D4 and D5, indicating that the use of A. afra -based diets enhanced immunity of O. mossambicus . This is because A. afra contained a number of biologically active compounds that act as immunostimulants. High levels of total polyphenol (70.32 ± 3.5 mg 100 g ˗1 ), total phenols (88.65 ± 5.32 mg 100 g ˗1 ), total flavonoids (181.5 ± 4.13 mg g ˗1 ) and alkaloids (29.63 ± 3.58 g kg ˗1 ) were recorded in A. afra .

The present study aim to compare the growth and biosynthetic ability of long-chain polyunsaturated fatty acids (LC-PUFA) of red tilapia (Oreochromis mossambicus♀ × O. niloticus♂) at different salinities. An 8-week feeding trial was conducted on the juvenile red tilapia (initial weight about 10.5 g) reared at 0, 15 and 30 parts per thousand (ppt) salinity fed with two isonitrogenous (32%) and isolipidic (9%) diets. The diet with vegetable oil was named VO, specifically rapeseed oil, without LC-PUFA but rich in C18 PUFA precursors, the other diet with fish oil was named FO rich in LC-PUFA. At the end of feeding trial, irrespective of diet, fish reared at 30 ppt showed significantly higher weight gain and specific growth rate and lower feed conversion ratio than those reared at 15 ppt or 0 ppt (p

The destruction of microbial communities within the gut of farmed tilapia (Oreochromis mossambicus) by Streptococcus agalactiae infection can result in considerable impacts to the health of the host. It is necessary to find a more effective treatment to improve the gut biome of farmed tilapia. We applied a tilapia culture method incorporating microorganisms in the diet and tracked gut bacteria over a 15-week period. A model of S. agalactiae infected individuals was constructed by detecting blood parameters and actual observation. Good’s coverage index (> 0.98) and < 1 % of reads was indicated by rarefaction curves. Healthy fish with no inclusion of microorganisms in the diet as reference group (RG), we assessed the effects of microorganisms on gut bacterial profiles and described changes in microbial richness and diversity via a comparison of the gut microbiota profiles of infected tilapia with (PD) and without (CG) the addition of microorganisms. An abnormal gut bacterial profile was associated with higher prevalence of infection by S. agalactiae, the lower Vibrio in PDs compared to the CGs, Spongiimonas spp. was present in all PDs and in the 3- and 6-week CGs, Photobacterium spp. appeared in all CGs and in the PDs at 3 and 6 weeks, Synechococcus, Shewanella, Spirochaeta, Psychromonas, Psychrilyobacter, Kiloniella, Allofrancisella, Candidatus Hepatoplasma, and Aliivibrio genera were only observed in the PDs, but Carboxylicivirga and Arcobacter were only detected in the CGs. Infected fish cultured using the combined microorganisms displayed significantly greater gut microbial species richness and diversity (Chao1; p-value < 0.001. Shannon’s; p-value < 0.001). The survival ratio of PDs (> 60 %) were higher than CGs. The application of the combined microorganisms within the diet of cultured O. mossambicus may therefore benefit their health by promoting a gut microbiome of greater diversity and increasing their resistance to disease.

Background. Gillnets of mesh sizes (6.9 to 12.7 cm) are used in individual boats in Sri Lankan reservoirs targeting exotic cichlid species, Oreochromis mossambicus (Peters, 1852) and Oreochromis niloticus (Linnaeus, 1758), which dominate the fisheries. The mesh composition of gillnets varies from boat to boat and from season to season making catch samples in individual boats are under the influence of different selectivity patterns. As such, the conventional procedure of correcting length frequency samples using the overall mean selectivity pattern in the fishery is not precise in estimating growth parameters. The presently reported study aimed at assessing cichlid stocks in three tropical reservoirs accounting for gillnet selectivity of individual sampled boats. Materials and methods. Length frequency data obtained from each boat were corrected for the combined selectivity of the fleet of gillnets of different mesh sizes used in the boat during the sampling occasion. For predicting optimal fishing strategies using a yield-per-recruit approach, probabilities of capture determined from the array of fishing mortality in the length-structured virtual population analysis was incorporated. Results. Length frequency data corrected for overall gillnet selectivity in sampled boats gave reliable estimates of von Bertalanffy growth parameters. Based on these estimates, mortality parameters were determined and the overall gear selection pattern was deduced from the array of fishing mortality in the length-structured virtual population analysis. Optimal fishing strategies were determined incorporating overall probabilities of capture in the relative yield-per-recruit (Y′ × R–1) analysis. Conclusion. The overall gillnet selection pattern of a sampled boat offers a methodology for reliable estimation of growth parameters. Although both cichlid species are caught in gillnets simultaneously, Y′ × R–1 analyses predicted increase of exploitation rate for one species while its decrease for the other species perhaps due to influence of other factors such as fish behaviour and fishers’ choice of specific areas for fishing. This analysis provides a methodology of a more precise length-based stock assessment in future research.

Cortisol is the principal glucocorticoid released due to various forms of environmental as well as aquacultural stressors in fish. The aim of the present investigation was to determine cortisol‐induced alterations along the luteinizing hormone (LH)‐secreting cells–ovary axis in the tilapia Oreochromis mossambicus. Administration of cortisol to stripped O. mossambicus for a period of 22 days during the ovarian cycle caused significantly higher number of follicles with chromatin nucleoli (stage I) compared to those of initial controls and controls. Whereas the number of follicles at perinucleolar (stage II) and vitellogenic (stage IV) stages did not differ significantly between controls and cortisol‐treated fish, the number of follicles at cortical alveolar stage (stage III) was significantly lower in cortisol‐treated fish than in controls. While the stage V follicles (maturation stage) were absent in initial controls, their presence in controls was concomitant with intensely labelled LH‐secreting cells in the proximal pars distalis (PPD) region of the pituitary gland during prespawning phase. However, cortisol‐treatment resulted in complete absence of stage V follicles associated with weakly immunoreactive LH‐content in the PPD region of the pituitary gland during prespawning phase. These results suggest that chronic cortisol‐ treatment causes suppression of LH‐secreting cells activity and blocks progression of vitellogenic follicular development process in O. mossambicus.

In the present study, the tilapia Oreochromis mossambicus were exposed to food deprivation for a period of 6 or 12 days and changes in the luteinizing hormone (LH) immunoreactivity in the proximal pars distalis (PPD) of the pituitary gland and the testicular activity were examined. Intensely immunoreactive LH content was noticed in the PPD of the pituitary gland in the initial controls, controls on days 6 and 12, and fasting fish on day 6, whereas the LH immunoreactivity was moderate or weak in fasting fish on day 12. In addition, although the mean gonadosomatic and hepatosomatic indices among different experimental groups did not show any statistically significant difference, the mean numbers of spermatogonia, spermatocytes, and spermatids were significantly lower in food-deprived fish on days 6 or 12 compared to those of controls. The inhibition of the spermatogenesis was accompanied by the presence of abundant spermatozoa in the lumen of seminiferous tubules of the testis in food-deprived fish, whereas the occurrence of spermatozoa was relatively infrequent in initial controls and controls. Furthermore, refeeding to food-deprived fish on day 6 onwards resulted in occurrence of few intensely stained LH secreting cells and significantly higher numbers of spermatocytes and spermatids concomitant with sparse spermatozoa in majority of tubules compared to those of food-deprived fish. These results suggest that prolonged exposure to food-deprivation causes suppression of the LH secretory activity in the pituitary gland and disruption in the spermatogenesis in O. mossambicus.

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.

The present investigation was conducted with a view to produce a female-free population and to test the heredity of body colour in tilapia. In this study, 6-day-old red tilapia were fed diets incorporated with 0, 25, 50, 75 and 100 mg/kg diet of a synthetic androgen, 17α-methyltestosterone (17α-MT), for 30 days. Administration was followed by 120 days of rearing in nylon hapas where hormone-free diet was given. At the end of the 120-day rearing, 17α-MT at 50 ppm induced 100% sex reversal, whereas 25, 75 and 100 mg/kg resulted in incomplete sex reversal. Immersion of newly hatched red tilapia fry in an aqueous solution of 17α-MT at 200 μg/L for 1 h produced 73% males; however, when given to 2-day-old fry, it yielded 78% males. The results indicate that oral administration of 17α-MT is more effective than treatment by immersion to produce male dominant red tilapia populations. Treatment of red tilapia with the androgen did not indicate any definite trend in the gonado-somatic index of both males and females. The results of progeny testing indicate that red tilapia does not belong to either XX-XY or WZ-ZZ sex determination systems, the two most common sex determination systems that exist in fish. When mating, Oreochromis mossambica (black tilapia) and red hybrid tilapia produced F1 progeny with a brown colour, the intermediate colour between the two parental body colours. When F1 hybrids were interbred, the three phenotypes got separated in the F2 generation with a 1 black/2 brown/1 red phenotypic ratio as expected of a single autosomal gene with incomplete dominant gene action. The importance of monosex male red tilapia farming and body colour inheritance is also discussed.

Nutrients are absorbed through transporters located in the brush border of intestinal absorptive epithelial cells. These transporters are complexes of proteins that control the uptake or removal of different compounds through cell and organelle membranes. Ingested proteins are catabolized to short-peptide and amino acids, which are absorbed through specified intestinal transporters. Two key complexes in this process are the B0AT (encoded by the SLC6A19 gene) and B0,+AT (encoded by the SLC3A1 and SLC7A9 genes), that transfer neutral and cationic amino acids. This research was conducted in Mozambique tilapia (Oreochromis mossambicus), with the aim of characterizing the dynamic of their expression along different intestinal sections at different time-points after feeding, in different water salinities. Our results demonstrated the dynamic of gene expression patterns along the intestine, with significant salinity effect on the genes encoding to the B0,+AT. Differences in expression levels with time after feeding were found in all three genes, with the highest expression observed at 6 h after feeding, in the middle intestine. Some of our results differ from what was expected based on data from mammalian organisms, and with only few previous studies on these transporters in any fish species, this is one of the first steps toward characterization of their regulation in fish. Statement of Relevance The results can lead to better food utilization.