Department of Aquatic Sciences and Fisheries Technology

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    Seroprevalence of circulating taeniid antigens in pigs and associated risk factors in Kongwa district, Tanzania
    (Elsevier, 2019-10-29) Maganira, Justine; Mwang'onde, Beda; Kidima, Winifrida; Mwita, Chacha; Hoglund, Johan
    The aim of this study was to investigate exposure to porcine cysticercosis (PC) and associated risk factors in the Kongwa District, eastern-central Tanzania. For the first time a cross-sectional investigation of the seroprevalence in pigs using a commercial genus specific cysticercosis enzyme linked immunosorbent assay (apDia Ag-ELISA) was undertaken in eastern-central Tanzania. Moreover, the identity of suspected T. solium cysts from pigs in the study area were confirmed by sequencing parasites’ mitochondrial cox1 gene. Structured questionnaires and direct observations were used to investigate risk factors associated with parasite transmission. A total of 102 pig-keeping households were surveyed during the dry season between July and August 2017 and 126 households in the rainy season between March and April 2018. Of the 447 examined pigs, 77 (17%, 95% C.I. 14%e20%) tested positive in the ELISA. Seroprevalence was higher in pigs examined during the rainy (21%, 95% C.I. 16%e26%) than dry (12%, 95% C.I. 7%e17%) season (p ¼ 0.019). Eight cyst-positive-pigs were confirmed to be infected with T. solium by sequencing. Risk factors associated with PC seropositivity included origin of piglets or pigs (OR ¼ 0.27, 95% C.I. 0.13 e0.42, p ¼ 0.001), socioeconomic factors and pig production system (OR ¼ 0.22, 95% C.I. 0.07e0.37, p ¼ 0.005) and sanitation and hygiene practices (OR ¼ 0.19, 95% C.I. 0.04e0.34, p ¼ 0.014). This study has recorded a high Taenia spp. seroprevalence in pigs in Kongwa suggesting the presence of people in the community carrying the adult parasite, Taenia solium. Our findings also suggest risk of infection by T. solium to people in urban centres and cities consuming pigs from rural areas in Kongwa. The high seroprevalence in Kongwa calls for further studies on taeniasis and cysticercosis in the human population in order to determine suitable control strategies
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    Soil contamination by Taenia solium egg DNA in rural villages in Kongwa district, Tanzania
    (Taylor & Francis, 2020-06-04) Maganira, Justine; Kidima, Winifrida; Mwita, Chacha; Halvarsson, Peter; Hoglund, Johan
    The presence ofTaenia solium DNA from eggs in soils around the households in four Tanzanian villages in Kongwa district were analysed in relation to seasonal fluctuations and infection risk implications. A total of 192 pooled soil samples from five sampling points per household were examined by droplet digital Polymerase Chain Reaction (ddPCR) from 96 pigkeeping households both during the dry and rainy seasons. The pooled samples were first processed by a flotation-double sieving technique, followed by screening for worm DNA employing universal primers targeting the mitochondrial cytochrome c oxidase subunit I (cox1) gene of human taeniid species and some other helminths. All DNA positive samples were later confirmed by a specific ddPCR probe assay targeting the mitochondrial cox1 gene of T. solium. A total of 17.2% (n = 33) samples were positive with the universal ddPCR, whereas T. solium DNA was confirmed by the specific ddPCR only in 3.1% (n = 3) of the surveyed households. The detection of T. solium DNA in this study spells out a low risk of exposure to T. solium eggs from contaminated household soil. Based on our results, ddPCR seems to be a promising technology for screening T. solium eggs in soil.
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    Testing the performance of environmental DNA metabarcoding for surveying highly diverse tropical fish communities: A case study from Lake Tanganyika
    (John Wiley & Sons Ltd, 2019-10-02) Doble, Christopher; Hipperson, Helen; Salzburger, Walter; Horsburgh, Gavin; Mwita, Chacha; Murrell, David; Day, Julia
    Background and Aims: Environmental DNA (eDNA) metabarcoding provides a highly sensitive method of surveying freshwater fish communities, although studies to date have largely been restricted to temperate ecosystems. Due to limited reference sequence availability and challenges identifying closely related and rare species in diverse tropical ecosystems, the effectiveness of metabarcoding methods for surveying tropical fish communities from eDNA samples remains uncertain. To address this, we applied an eDNA metabarcoding approach to survey Lake Tanganyika's (LT) species‐rich littoral fish communities. Materials and Methods: As this system contains many closely related species, particularly cichlid fishes, we used four primer sets including a cichlid‐specific primer set (Cichlid_CR). A reference database was built for the 12s, 16s, and control region for 358 fish species including over 93% of known cichlids. Results and Discussion: In silico and in situ results demonstrated wide variability in the taxonomic resolution of assignments by each primer with the cichlid‐specific marker (Cichlid_CR) enabling greater species‐level assignments for this highly diverse family. A greater number of non‐cichlid teleost species were detected at sites compared to the visual survey data. For cichlid species however, sequencing depth substantially influenced species richness estimates obtained from eDNA samples, with increased depths producing estimates comparable to that obtained from the visual survey data. Conclusions: Our study highlights the importance of sequencing depth and local reference databases when undertaking metabarcoding studies within diverse ecosystems, as well as demonstrating the potential of eDNA metabarcoding for surveying diverse tropical fish communities, even those containing closely related species within evolutionary radiations.
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    Life history shifts in an exploited African fish following invasion by a castrating parasite
    (John Wiley & Sons Ltd., 2020-09-24) Gabagambi, Nestory; Skorping, Arne; Mwita, Chacha; Kihedu, Kwendwa; Mennerat, Adele
    Evolutionary theory predicts that infection by a parasite that reduces future host survival or fecundity should select for increased investment in current reproduction. In this study, we use the cestode Ligula intestinalis and its intermediate fish host Engraulicypris sardella in Wissman Bay, Lake Nyasa (Tanzania), as a model system. Using data about infection of E. sardella fish hosts by L. intestinalis collected for a period of 10 years, we explored whether parasite infection affects the fecundity of the fish host E. sardella, and whether host reproductive investment has increased at the expense of somatic growth. We found that L. intestinalis had a strong negative effect on the fecundity of its intermediate fish host. For the noninfected fish, we observed an increase in relative gonadal weight at maturity over the study period, while size at maturity decreased. These findings suggest that the life history of E. sardella has been shifting toward earlier reproduction. Further studies are warranted to assess whether these changes reflect plastic or evolutionary responses. We also discuss the interaction between parasite and fishery-mediated selection as a possible explanation for the decline of E. sardella stock in the lake.
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    The status and health burden of neurocysticercosis in Mbulu district, northern Tanzania
    (BioMed Central (BMC), 2018) Mwang'onde, Beda; Mwita, Chacha; Nkwengulila, Gamba
    Objective: The objective of this study was to assess the extent and health burden of neurocysticercosis in the general community of the Mbulu district, northern Tanzania. About 1051 randomly select participants were screened for human cysticercosis. The Cysticercus Western Blot IgG and Computed Tomography scan were used to detect infection by cysticerci. The DALYs was used to assess the community’s health burden vis-a-vis neurocysticercosis. Results: The sero-prevalence of HCC was 16.27%. About 76% of 25 selected human cysticercosis sero-positives had neurocysticercosis suggestive lesions on CT scan and 74% had history of epilepsy. Epilepsy caused 2.8 years of life lost and 2.2 healthy years of life lost due to disability per 1000 person-years in Mbulu. The average DALYs imposed due to neurocysticercosis and epilepsy were 3.0 and 3.9 per 1000 person-years, respectively. Neurocysticercosis is a serious public health concern in northern Tanzania.
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    Validation of droplet digital Polymerase Chain Reaction for the detection and absolute quantification of Taenia solium eggs in spiked soil samples
    (Elsevier, 2019-09-14) Maganira, Justine; Mwang'onde, Beda; Kidima, Winifrida; Mwita, Chacha; Nkwengulila, Gamba; Hoglund, Johan
    To enable the detection of taeniid eggs in environmental samples, a sensitive technology is required. In this study, we validated the effectiveness of a digital droplet Polymerase Chain Reaction (ddPCR) assay for detection, identification and absolute quantification of taeniid DNA from artificially contaminated soils with varying numbers of taeniid eggs using a set of universal primers, JB3 & JB4.5. The results showed that the number of cox1 copies detected increased gradually for both species with the number of taeniid eggs added to the different soil types. The highest cox1 DNA copies recovery for Taenia solium and T. lynciscapreoli was from the sand soil with lowest recovery being observed in clay soils. Therefore, ddPCR is a promising technology for screening of taeniid eggs from soil samples collected in the environment irrespective of the soil type and the number of eggs. The potential of the ddPCR protocol to detect taeniid egg DNA in spiked soil samples has great practical application for taeniid egg screening in soils from endemic areas. However, when universal primers are used in screening environmental samples, the identity of ddPCR positive samples must be confirmed by sequencing. In addition, more validation studies using species-specific primers and field soil samples is recommended.
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    Detection of Porcine Cysticercosis in Meat Juice Samples from Infected Pigs
    (Springer, 2021-02-15) Maganira, Justine; Kidima, Winifrida; Mwita, Chacha; Hoglund, Johan
    Background Seroprevalence of porcine cysticercosis has been generally studied using enzyme-linked immunosorbent assays (ELISA) detecting either antigens or antibodies in sera. However, serum is not always readily available. The objective of this study was to assess the diagnostic potential of meat juice in detecting porcine cysticercosis using a cysticercosis antibody ELISA. Methods Sera and meat juice samples from 13 different organs/tissues were collected from nine pigs naturally infected with cysticercosis and from six uninfected pigs reared under hygienic conditions. The sensitivity of the cysticercosis antibody ELISA in detecting porcine cysticercosis in meat juice samples was compared to that in serum samples from the same pigs. Results Using sera, cysticercosis was detected in all nine pigs harbouring cysticerci, but not in those reared under hygienic conditions. The sensitivity of the ELISA was highest in meat juice extracted from the diaphragm (100%), heart (89%) and neck muscle (78%) of the nine infected pigs, whereas it varied between 0 and 44% in the other samples. Conclusion To the best of our knowledge, this is the first study for T. solium cysticercosis serology to use meat juice. Our results show that meat juice from pig carcass organs or muscles is a promising diagnostic specimen for the detection of porcine cysticercosis. More studies including a large sample size of pigs with varying degrees of cysticercosis infection are needed to further prove this concept.
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    The role of fish-poultry integration on fish growth performance, yields and economic benefits among smallholder farmers.
    (Taylor & Francis, 2019-04-15) Shoko, Amon P.; Samwel Mchele Limbu; Lamtane, Hieromin A.; Kishe-Machumu, Mary A.; Sekadende, Baraka; Ulotu, Eusebia E.; Joram, Masanja C.; Mgaya, Yunus D.
    Aquaculture practices from sub-Saharan Africa are characterised by low production, owing to improper technology. Production can be increased through integrating fish farming with other existing on-farm activities, particularly livestock husbandry. We assessed the role of fish-poultry integration on all male Nile tilapia, Oreochromis niloticus growth performance, yields and economic benefits among smallholder farmers in sub-Saharan Africa, Tanzania. The study also compared phytoplankton species composition, abundance and biomass between the fish-poultry integration and non-integrated system. After 180 days of the experiment, all male O. niloticus cultured under fish-poultry integration exhibited significantly higher growth rates than those in the non-integrated system (p < 0.05). Gross fish yield (GFY), net fish yield (NFY) and net annual yields (NAY) obtained from fish-poultry integration were significantly higher than those from non-integrated system (p < 0.05). Partial enterprise budget analysis revealed that fish-poultry integration was more profitable than the non-integrated system. Moreover, fish-poultry integrated system produced significantly higher phytoplankton abundance and biomass than those from the non-integrated system. Results demonstrate that rural smallholder farmers can achieve higher growth rate, farm net yields and income by integrating all male O. niloticus with other on-farm activities than practising a stand-alone fish culture system.
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    Fasting enhances cold resistance in fish through stimulation of lipid catabolism and autophagy
    (Wiley, 2019-01-07) Lu, Dong-Liang; Ma, Qiang; Ning, Li-Jun; Wang, Jing; Li, Ling-Yu; Li, Jia-Min; Han, Si-Lan; Sun, Sheng-Xiang; Samwel Mchele Limbu; Li, Dong-Liang; Qiao, Fang; Chen, Li-Qiao; Zhang, Mei-Ling; Du, Zhen-Yu
    In cold environments, most homeothermic animals increase their food intake to supply more energy to maintain body temperature, whereas most poikilothermic animals such as fishes decrease or even stop feeding under cold stress. However, the physiological value of fasting during cold resistance in poikilotherms has not been explained. Here, we show that moderate fasting largely enhanced cold resistance in fish. By using pharmacological (fenofibrate, mildronate, chloroquine and rapamycin) and nutritional approaches (fatty acids diets and amino acids diets) in wild‐type or specific gene knock‐out zebrafish models (carnitine palmitoyltransferase‐1b‐deficient strain, CPT1b−/−, or autophagy‐related protein 12‐deficient strain, ATG12−/−), we verified that fasting‐stimulated lipid catabolism and autophagy played essential roles in the improved cold resistance. Moreover, suppression of the mechanistic target of rapamycin (mTOR) pathway by using rapamycin mostly mimicked the beneficial effects of fasting in promoting cold resistance as either the physiological phenotype or transcriptomic pattern. However, these beneficial effects were largely reduced when the mTOR pathway was activated through high dietary leucine supplementation. We conclude that fasting helps fish to resist cold stress by modulating lipid catabolism and autophagy, which correlates with the mTOR signalling pathway. Therefore, fasting can act as a protective strategy of fish in resisting coldness.
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    Aquaculture and Fisheries Extension. In: Mgaya, Y.D. and Mahongo, S.B. (Editors), Lake Victoria Fisheries Resources: Research and Management in Tanzania.
    (Springer, 2017-11-29) Shoko, A.P.; Mgaya, Y.D.; Samwel Mchele Limbu; Hoza, R.
    The dwindling catch from Lake Victoria has caused an insufficient fish supply to the population of the Lake Victoria basin, Tanzania. The decrease in catch rates and demand for fish has created room for fish farming practices at both small and commercial scales in the Lake Basin. This chapter provides a result-oriented status of aquaculture research and development efforts made by the government and Non-Governmental Organizations (NGOs) in the Lake Basin from the colonial era to the present. The chapter also highlights strengths, weaknesses, opportunities and challenges (SWOCs) to aquaculture development in the basin. Results show that the basin has a high potential for fish farming development due to suitable characteristics for fish farming. Fishponds are the common culture system used in fish farming in the basin. The ponds are stocked with either Nile tilapia Oreochromis niloticus or African sharptooth catfish, Clarias gariepinus, reared in monoculture or polyculture. A system of integrated aquaculture-agriculture (IAA) farming is also practised in some areas of the basin. The yield from the lake basin has increased with time due to improved pond management techniques. However, more room is available for further increase pending the adoption of technology and improved extension services. Fish farming could help to reduce fishing pressure on capture fisheries in the main lake and contribute significantly to the conservation of the lake’s biodiversity. Ultimately, fish farming will generate income for the people, which is in line with the government’s efforts to alleviate poverty in the country.
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    Biodiversity Indicators: Plankton and Macroinvertebrates in Lake Victoria, Selected Satellite Lakes and Rivers. In: Mgaya, Y.D. and Mahongo, S.B. (Editors), Lake Victoria Fisheries Resources: Research and Management in Tanzania.
    (Springer, 2017-11-29) Mgaya, Y.D.; Samwel Mchele Limbu; Lugomela, C.V.; Kayanda, R. J.; Ngupula, G.W.
    Plankton and macroinvertebrates are used as biodiversity indicators on account of their sensitivity to changes in aquatic ecosystems. This chapter assesses the changes in the diversity, abundance and distribution of plankton and macroinvertebrates in the inshore and offshore areas of Lake Victoria, selected satellite lakes and rivers within the lake basin. Samples for both plankton and macroinvertebrates were collected during dry and wet seasons between 2000 and 2006. The results indicated that cyanobacteria were most diverse in both seasons. Microcystis spp., Planktolyngbya spp. and Anabaena spp. were the most dominant cyanophyte species at the sampled sites. The dominant phytoplankton (cyanobacteria) are less digestible and provide poor quality food for the fish; that may have contributed to the reduction or loss of planktivorous haplochromines and tilapiines that once flourished in Lake Victoria. Zooplankton community composition in the lake is dominated by rotifers and cyclopoid copepods, in both inshore and offshore areas. The dominance of cyclopoid copepods is important in the production and sustainability of small fishes and larvae that utilize these organisms as a food base. Macroinvertebrate abundance has shifted from an oligochaete and insect dominated community in 1984 to a community dominated by molluscs. The occurrence of a relatively high abundance of low-oxygen tolerant macroinvertebrate taxa at inshore and offshore stations is an indication of deteriorating water quality water quality conditions due to eutrophication and pollution processes. There is a need for a reduction in nutrient loads and pollutant inputs into the lake in order to ensure the ecosystem health.
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    Fish Biology and Life History Indicators. In: Mgaya, Y.D. and Mahongo, S.B. (Editors), Lake Victoria Fisheries Resources: Research and Management in Tanzania.
    (Springer, 2017-11-29) Katunzi, E.F.B.; Mgaya, Y.D.; Mkumbo, O.C.; Samwel Mchele Limbu
    Life history traits like growth, reproduction, food and mortality are principal factors in the survival of the fish. This chapter examines the life history indicators of three commercial fish species in Lake Victoria, namely Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus) and the cyprinid known as ‘Dagaa’ (Rastrineobola argentea). The size at first maturity for Nile perch has been declining due to stress in the population caused by heavy exploitation, changes in food availability and deteriorating water quality parameters, particularly dissolved oxygen concentration. The fish exhibits ontogenic shifts in food. R. argentea has an offshore surface dwelling behaviour with about 68% found distributed in waters of more than 40 m depth. Its size at first maturity varies from place to place. R. argentea breeds throughout the year but with distinct peaks during the rainy season. An increase in fecundity has been observed in Nile tilapia and it is considered a mechanism to compensate for the intensive fishing pressure in the lake. Studies indicate an increase in size and growth parameters for Nile tilapia despite the heavy fishing pressure as a result of increased demand in local and foreign markets. The success of the species could be due to the ability of the species to expand their niche. It has diversified its food to include Caridina nilotica, chironomids, chaoborids, molluscs and bottom detrital matter. An ecosystem approach guided by a precautionary principle is required in order to manage the fishery resources in Lake Victoria and to ensure their sustainability.
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    Molecular cloning and functional characterization of elongase (elovl5) and fatty acyl desaturase (fads2) in sciaenid, Nibea diacanthus (Lacepède, 1802)
    (Elsevier, 2019-02-10) Lin, Zhideng; Zou, Weiguang; Huang, Yisheng; Samwel Mchele Limbu; Han, Fenglu; Wen, Xiaobo
    In the present paper, we investigated the molecular cloning and functional characterization of elongase of very long chain fatty acid (elovl) and fatty acyl desaturase (fads) genes in a marine teleost, Nibea diacanthus. The elongase cDNA sequence encoded a polypeptide of 294 amino acids exhibiting Elovl5 activity, which effectively elongated both C18 (18:2n−6, 18:3n−3 and 18:3n−6) and C20 (20:4n−6 and 20:5n−3) polyunsaturated fatty acids. The desaturase cDNA sequence specified a polypeptide of 445 amino acids indicating Δ6 desaturation activity, which coul converted C18:2n−6 and C18:3n−3 to C18:3n−6 and C18:4n−3, respectively. Tissue distribution analysis by quantitative real-time PCR revealed that the elovl5 was primarily expressed in intestine and liver, while the fads2 was mainly expressed in liver and brain. These results increase our knowledge of the ability of endogenous highly unsaturated fatty acids (HUFA) biosynthesis in marine carnivorous fish.
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    Effects of α‐lipoic acid on growth performance, body composition, antioxidant profile and lipid metabolism of the GIFT tilapia (Oreochromis niloticus) fed high-fat diets.
    (Aquaculture Nutrition, 2019-01-18) Xu, Fangning; Xu, Chang; Xiao, Shusheng; Lu, Maixin; Samwel Mchele Limbu; Wang, Xiaodan; Du, Zhen-Yu; Qin, Jian G.; Chen, Li-Qiao
    The wide use of lipid as a non‐protein energy substitute has led to lipid metabolic problems in cultured tilapia. Therefore, studies that reduce the effects of high‐fat diets in genetically improved farmed tilapia (GIFT) are required. This study evaluated the optimum level and effects of dietary α‐lipoic acid (α‐LA) on growth performance, body composition, antioxidant capacity and lipid metabolism of GIFT tilapia. The basal diet (120 g/kg lipid) was supplemented with six concentrations of α‐LA at 0 (control), L300, L600, L900, L1200 and L2400 mg/kg diet to make the experimental diets, which were fed to GIFT tilapia juveniles (initial body weight: 0.48 ± 0.01 g) for 8 weeks. The weight gain of fish improved significantly in the L300 than other dietary treatments. The intraperitoneal fat index and lipid content of fish fed on the L2400 diet decreased significantly than those fed on the control diet. The activities of superoxide dismutase and glutathione peroxidase (GSH‐Px) in serum and liver were significantly higher in fish fed on the L300 diet than the control. The reduced GSH content of fish fed on the L300 in serum and liver was significantly higher than those fed on control diet. The malondialdehyde content in serum and liver was significantly lower in L300 than in the control. The adipose triglyceride lipase gene was significantly up‐regulated in fish fed on the L2400, but the diacylglycerol acyltransferase 2 gene was down‐regulated in adipose. The liver‐type fatty acid‐binding protein gene in the liver was significantly up‐regulated in fish fed on the L300 and L600 diets. Moreover, the acyl‐coenzyme A oxidase gene in liver was significantly up‐regulated in fish fed on the L300, L600, L900 and L1200 diets. Polynomial regression analysis indicated that 439–528 mg/kg α‐LA is an appropriate dosage in high‐fat diet to improve growth performance and relieve lipid oxidative damage by accelerating lipid catabolism and reducing lipid synthesis in GIFT tilapia.
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    Forskolin reduces fat accumulation in Nile tilapia (Oreochromis niloticus) through stimulating lipolysis and beta-oxidation
    (Elsevier, 2018-12-26) Zhang, Han; Wen, Jia-Jing; Zhang, Yun-Ni; Samwel Mchele Limbu; Du, Zhen-Yu; Qin, Jian-Guang; Chen, Li-Qiao
    High fat diets are commonly used in aquaculture to reduce feed cost in Nile tilapia, but impair its lipid homeostasis. This study evaluated the role of forskolin on reducing fat accumulation in Nile tilapia (Oreochromis niloticus) by using in vitro and in vivo experiments. The use of 50 μM forskolin in vitro increased free fatty acid and glycerol release, but decreased triglyceride in adipocytes and hepatocytes. The adipose triglyceride lipase (ATGL), protein kinase cAMP-dependent type I regulatory subunit alpha (PKAR I) and other genes related to β-oxidation (peroxisome proliferator activated receptor alpha, PPARα and carnitine O-palmitoyltransferase 1, CPT1) were significantly up-regulated. After feeding a high-fat diet for six weeks, O. niloticus were fed with 0 (control), 0.5 and 1.5 mg/kg forskolin for two weeks to determine whether forskolin could reduce fat accumulation in vivo. Fish fed the two levels of forskolin decreased significantly the hepatosomatic and mesenteric fat indices. The total lipid in the whole fish and liver together with the serum glycerol content were lower in fish fed on forskolin than in the control. The fish fed on forskolin diets exhibited smaller areas of lipid droplets in adipose and liver tissues. Lipolysis related genes (ATGL, hormone-sensitive lipase, HSL; monoacylglycerol lipase, MGL; and protein kinase cAMP-activated catalytic subunit, PKAC) and β-oxidation genes (PPARα; fatty acid binding protein 1, FABP1; and CPT1) in the adipose were up-regulated. Similarly, in the liver lipolysis genes such as ATGL and PKAR I and β-oxidation genes (PPARα, FABP1, CPT1 and acyl-CoA oxidase, ACO) showed an increasing trend with the increase of forskolin doses. This study indicates that forskolin can reduce fat accumulation in the adipose and liver by stimulating lipolysis and β-oxidation in O. niloticus.
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    The comparisons in protective mechanisms and efficiencies among dietary α-lipoic acid, β-glucan and L-carnitine on Nile tilapia infected by Aeromonas hydrophila
    (Elsevier, 2018-12-13) Lu, Dong-Liang; Samwel Mchele Limbu; Hong-Bo, Lv; Ma, Qiang; Chen, Li-Qiao; Zhang, Mei-Ling; Du, Zhen-Yu
    Dietary α-lipoic acid (LA), β-glucan (Gluc) and l-carnitine (L-Ca) are commonly used additives to promote fish growth and stress resistance in aquaculture production. However their mechanisms and efficiencies in helping fish to resist diseases have not been compared before. In this study, we fed Nile tilapia (Oreochromis niloticus) with diets containing appropriate doses of LA, Gluc and L-Ca for five weeks and further intraperitoneally injected the fish with Aeromonas hydrophila. After dietary treatment, none of the additives affected the fish growth, but dietary Gluc and L-Ca reduced protein and lipid body contents in fish, respectively. After A. hydrophila challenge, all fish treated with the three dietary additives showed higher survival rate, but those fed on dietary L-Ca had lower survival than those fed on LA and Gluc diets, indicating high protection efficiency of LA and Gluc. The protective mechanisms of the three feed additives were quite different under A. hydrophila infection. Dietary LA induced higher total antioxidant capacity and higher mRNA expression of anti-oxidative genes than other additives in liver and also activated partly the immune function in serum and spleen. Gluc largely increased the immune function by activating the immunity enzymes in serum, inducing inflammation in liver and increasing the expression of immune genes in spleen and head kidney. Gluc also increased partly the antioxidant capacity in serum and liver and lipid catabolism in liver. L-Ca largely increased lipid catabolism in liver while it increased partly the antioxidant capacities in serum and liver. Taken together, these results indicate that, dietary LA, Gluc and L-Ca have various protective mechanisms and differ in their efficiencies on resisting A. hydrophila infection in Nile tilapia.
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    Dietary Aspilia mossambicensis and Azadirachta indica supplementation alters reproductive performance and induces gonadal histopathological effects in Nile tilapia (Oreochromis niloticus)
    (Wiley, 2018-12-07) Kapinga, Imani Benedict; Samwel Mchele Limbu; Madalla, Nazael Amos; Kimaro, Wahabu Hamisi; Mabiki, Faith Philemon; Lamtane, Hieromin Amon; Tamatamah, Rashid Adam
    The use of medicinal plants to control reproduction in aquaculture have recently received considerable attention because they are biodegradable, safe, effective and locally available. However, information on their effects on gonadal characteristics and histological features in fish is currently limited. The present study evaluated the gonadal characteristics and histological changes of Nile tilapia, Oreochromis niloticus gonads fed on Aspilia plant, Aspilia mossambicensis and Neem tree, Azadirachta indica. Juvenile fish were fed diets supplemented with four doses (1.0, 2.0, 4.0 and 8.0 g/kg diet) of A. mossambicensis or A. indica leaf powders at 3% of their body weight daily for 90 days to examine absolute fecundity (AF), relative fecundity, gonadosomatic index (GSI) and histology of gonads. The antifertility phytocompounds in the two plants were quantified by using standard methods. Results indicated that, all doses of A. indica and A. mossambicensis used reduced significantly AF and GSI values (p < 0.05). Dose‐dependent histological alterations of gonads were noticed in both plants starting from doses of 2.0 g/kg in males and 4.0 g/kg in females. The highest percentages of total flavonoids (23.7%) and alkaloids (14.2%) were obtained from A. indica ethanol extract (p < 0.05). Taken together, dietary supplementation with A. mossambicensis and A. indica leaf powders alter gonadal characteristics of O. niloticus and histology triggered by alkaloids and flavonoids. Farmers interested in using the two plants to control prolific breeding should limit the dose inclusion to 2 g/kg to avoid severe effects on fish testis and ovaries.
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    Dietary oils modify lipid molecules and nutritional value of fillet in Nile tilapia: a deep lipidomics analysis.
    (Food Chemistry, 2018-11-02) Liu, Y; Jiao, J-G.; Gao, S; Ning, L-J.; Samwel Mchele Limbu; Qiao, F; Chen, Li-Qiao; Zhang, M-L; Du, Zhen-Yu
    The nutritional value of fish fillet can be largely affected by dietary oils. However, little is known about how dietary oils modify lipid molecules in fish fillets. Through biochemical and lipidomics assays, this study demonstrated the molecular characteristics of fillet lipids in Nile tilapia fed with different oils for six weeks. High 18:2n-6 and low 18:3n-3 deposition in phosphoglycerides resulted high 18:2n-6/18:3n-3 ratio in tilapia. Dietary n-3 VLCUFAs intake increased its deposition at sn-1/3 of triglycerides and at sn-2 of phosphatidylcholines. Irrespective of dietary oil, 16:0 was distributed preferentially at the outer positions of glycerol backbone. High 18:2n-6 accumulated at sn-2 position for fish fed with n-3 PUFA-enriched oils. High 18:3n-3 deposited at sn-1/3 in TG, sn-1 in phosphatidylethanolamines, while at sn-2 in phosphatidylcholines. Together, dietary oils change the composition and positional distribution of fatty acids on the glycerol backbone, and change nutritional value of fish for human health.
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    Nutrient release from the sediments and biological nitrogen fixation; advancing sources of eutrophication in Lake Victoria, Tanzania.
    (Wiley, 2018-11-05) Salome, Shayo; Samwel Mchele Limbu
    Intensification of anthropogenic activities in the three riparian countries bordering the shoreline of Lake Victoria is exacerbating eutrophication in the main body of the lake. The present study evaluated the importance of sediments and biological nitrogen fixation as sources of nutrient enrichment into Lake Victoria in Magu, Mwanza and Kayenze bays influenced by different anthropogenic activities, over a period of 7 months. Kayenze Bay is a relatively pristine site, while higher anthropogenic activities occur in the Magu Bay and Mwanza North Bay areas. Sediment cores were retrieved from each sampling site and transported to the laboratory for nutrient concentrations and flux analyses. In situ nitrogen fixation rates also were measured in the water column. The results indicated the sediment–water interface in Magu Bay exhibited significantly higher concentrations of nitrate‐N and a net release of nitrate‐N, compared to Mwanza North Bay and Kayenze Bay (p < 0.001). The sediment–water interface in Magu Bay also exhibited a significant net release of total phosphate towards the water column, compared to Mwanza Bay (p < 0.001). The sediment–water interface in Mwanza North Bay exhibited higher ammonium‐N concentrations, and net release of ammonium‐N and total nitrogen than did Magu and Kayenze Bays (p < 0.001). The sediment–water interface in Mwanza and Magu Bays exhibited higher total nitrogen and soluble reactive phosphate concentrations than Kayenze Bay (p < 0.001). Their sediments also released net fluxes of soluble reactive phosphate to the water column than did Kayenze Bay (p < 0.001). In contrast, the Kayenze Bay sediments acted as a sink of ammonium‐N from the water column, compared to Mwanza North and Magu Bays (p < 0.001). Biological nitrogen fixation rates were significantly higher during the rainy season than the dry season (p < 0.05), although no spatial variations in biological nitrogen fixation existed among the three sites (p > 0.05). The present study indicated the water column and sediments in Magu Bay and Mwanza North Bay, characterized by high anthropogenic activities are rich in nitrate‐N, ammonium‐N, total nitrogen and soluble reactive phosphate, compared to the relative pristine Kayenze Bay. Anthropogenic activities and sediments may well be important sources of nutrients enrichment to the overlaying waters, thereby enhancing eutrophication of Lake Victoria. Management strategies are required to reduce external releases and internal nutrient fluxes to enhance the lake ecosystem health.
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    The metabolic regulation of dietary L-carnitine in aquaculture nutrition: present status and future research strategies.
    (Wiley, 2018-09-26) Ling-Yu, Li; Samwel Mchele Limbu; Qiang, Ma; Li‐Qiao, Chen; Mei‐Ling, Zhang; Zhen-Yu, Du
    L‐carnitine is a multi‐functional nutrient which plays a leading role in fatty acid metabolism in mammals and other eukaryotes. Its main physiological function is to promote fatty acid β‐oxidation to produce energy, which reduces body fat content and improves body weight without affecting moisture content in whole body and muscle. In recent years, its dietary supplementation in aquaculture nutrition has been studied in different cultured species. It has been proved that L‐carnitine can improve growth and increase lipid utilization rate in some aquatic animals. However, such beneficial effects of dietary L‐carnitine are limited or absent in other species. The reasons for the conflicting results obtained on L‐carnitine functions in aquatic animals need to be elucidated. This review explores comprehensively the different physiological functions of L‐carnitine in various aquatic animals. In the end, research strategies are provided to elucidate the existing conflicts on dietary L‐carnitine application in aquaculture nutrition in order to promote its utilization in aquatic feed industry.