Effect of Commercial Feed on Sexual Maturity of Two Tilapia Species (Oroechromis niloticus and Oreochromis tanganicae) 
Jonathan Nkhoma1 
,
Confred G. Musuka2 
,
Confred G. Musuka2
1. Matero Residential Area, Muchinga Road, House No. 3262, Lusaka, Zambia
2. The Copperbelt University, School of Natural Resources, P.O. Box 21692, Kitwe, Zambia
Author Correspondence author
International Journal of Aquaculture, 2014, Vol. 4, No. 16 doi: 10.5376/ija.2014.04.0016
Received: 29 Mar., 2014 Accepted: 30 Apr., 2014 Published: 02 Jun., 2014
2. The Copperbelt University, School of Natural Resources, P.O. Box 21692, Kitwe, Zambia
Author Correspondence author
International Journal of Aquaculture, 2014, Vol. 4, No. 16 doi: 10.5376/ija.2014.04.0016
Received: 29 Mar., 2014 Accepted: 30 Apr., 2014 Published: 02 Jun., 2014
© 2014 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:
Nkhoma and Musuka, 2014, Effect of Commercial Feed on Sexual Maturity of Two Tilapia Species (Oroechromis niloticus and Oreochromis tanganicae), International Journal of Aquaculture, Vol.4, No.16: 96-101 (doi: 10.5376/ija.2014.04.0016)
Abstract
An experiment was conducted for twelve weeks (90 days) in hapas inserted in the semi-concrete ponds to evaluate the effect of commercial feed on the sexual maturity of two tilapia species, Oroechromis niloticus and Oreochromis tanganicae. Results indicated that the final mean body weight was 73.65g for O. niloticus and 66.30g for O. tanganicae respectively. First maturity in both species was observed in the sixth week and the smallest fish matured at 34g and 73mm for O. niloticus, while for O. tanganicae, it was 42g and 111mm. Length at first maturity was 136mm for O. niloticus and 129mm for O. tanganicae. Maturity stages were macroscopically identified into three stages (immature, maturing and mature) and at the end of the trial, 73% of O. niloticus and 58% of O. tanganicae were in the reproductive process (mature). The gonadosomatic index (GSI) mean value for O. niloticus was higher than that of O. tanganicae. However, there was no significant difference (p>0.05) between GSI values.
Keywords
Commercial feed; Sexual maturity; Effects; Tilapia species; Oroechromis niloticus; Oreochromis tanganicae)
Tilapia is the common name applied to three genera of family Cichlidae: (Sarotherodon; Oreochromis and Tilapia) including about 70 species (Meyer, 2002). Tilapias are the second most important farmed fish after carp (El-Sayed, 2002) that is one of the most important food fish in the world, especially in Europe and Asia (Currie, 1991). Carp production is growing rapidly in Asia, increasing from 5.537 million t in 1990 to 16.313 million t in 2001, an annual growth rate of 11 per cent (Dey et al., 2005).
In Zambia, as in many parts of the world wild Oreochromis species are the major cultured tilapia species because they are readily acceptable by consumers throughout the country (Mudenda, 2004). They are good candidate species for pond culture due to their high adaptability to a wide range of environments, tolerance to harsh conditions (low water quality and high stocking densities), handling, ease reproduction and fast growth (El-Sayed, 2002).
One of the major problems in tilapia culture, is the tendency of females to mature and reproduce at small sizes (Popma and Lovshin 1995).In that study authorsobserved that, in tilapia sexual maturity is a function of age, size, and environmental conditions. Furthermore, they reported that tilapia populations in large lakes mature at a later age and larger size than the same species raised in culture ponds (Popma and Lovshin 1995). For instance, O. niloticus matures at about 10 to 12 months and 350 to 500g in several East African lakes but the same population culture in ponds will reach sexual maturity at an age of 5 to 6 months and 150 to 200g (Popma and Lovshin, 1995). A study conducted by Hepher and Pruginin (1982) observed that some tilapias species can also reach sexual maturity in 3 to 6 months, and spawn before they reach a marketable size when grown in ponds and controlled cultured conditions. When growth is slow in culture ponds, sexual maturity will be delayed by a month or two but fish may spawn at weights as low as 20g (Mair and Little, 1991). According to Hepher and Pruginin (1982), their early maturation and prolific “wild” spawning produce such large number of small fry as to cause stunting of the entire tilapia population and often of other species in the pond. Similarly, Baroiller and Toguyeni (1996) reported that the early sexual maturity of Oreochromis species leads to overcrowding and stunting resulting in limited economic yields for fish farms since energy is directed towards reproduction instead of somatic growth.
Manissery et al., (2001) and Muchlisin et al., (2006) showed that nutrition plays a major role in the reproductive performance of fish. Early sexual maturity in tilapias can be achieved by feeding them commercial feed with all the required nutrients to support growth. In Tilapia species sexual maturity advances in stages and gonad maturation has been categorised into 6 stages where stage (I) consists of immature or virgin fish, stage (II) are fish beginning maturation, (III) is a developing phase, (IV) pre-spawning stage (V) spawning stage and (VI) post spawning stage (Duponchelle and Legendre,1996; Nyakuni, 2009). The present study, focused on the role played by commercial feed on sexual maturity of Oreochromis niloticus and Oreochromis tanganicae.
1 Materials and Methods
The experiment to determine the effect of commercial feed (Namfeed) on sexual maturity of Oreochromis niloticus and Oreochromis tanganicae (mean wt. 30g), was conducted in six hapas placed in semi-concrete outdoor ponds for 12 weeks (90 days) at the National Aquaculture Research and Development Centre (NARDC) in Mwekera on the Copperbelt Province, Zambia.
The study was a two by two factorial run in a Completely Randomized Design (CRD) with three replicates. Fish were sampled by using a scooping net at fortnight intervals. Weight and length were measured using an analytical balance and measuring board, while maturity was checked by stripping or massaging the fish on the belly.
Water quality parameters were taken and the figures recorded using a Horiba U-10 water quality checker that measures six parameters: pH, Temperature, Dissolved Oxygen, Electrolytic Conductivity, Turbidity and Salinity. The water quality checker sensor measures by being directly submersed in the water as opposed to collecting samples. pH, water temperature and dissolved oxygen were measured twice per day, in the morning (at 08:00 hours) and afternoon (at 14:00 hours) by dipping a probe of the oxygen meter about 20 cm into the water.
One-hundred and eighty (180) juvenile Oreochromis niloticus and Oreochromis tanganicae, with an individual average weight of 30g were used in the experiment. 30 fingerlings, locally provided by the NARDC, were randomly distributed among the hapas measuring 4m×2m×1m. Fish were acclimatized to the rearing environment for a period of two weeks before the beginning of the trial.
Throughout the experimental period, fish were fed with a commercial feed (Namfeed) at the rate of 5% of their total biomass, twice per day (at 09:00 and at 15:00hrs) for 5 days in a week. Clove (herbal spice) was used to anesthetise the fish to minimize stress during sampling. At the beginning and at the end of the experiment 10% of the fish were individually weighed and dissected to remove the gonads. The gonads were weighed using the analytical balance and results recorded for the calculation of GSI. The relative gonad weight or gonadosomatic index, an index of reproductive maturity was calculated by using the formula: GSI = (Gonad weight (g)/Body weight of fish (g) × 100 according to Singh and Dhawan (1996). Gonadosomatic index has been considered as reliable estimate for gonadal maturity and spawning of any species. The gonadosomatic index increased with the maturation of fish and reaches to its maximum at the peak period of maturity (Mishra and Saksena, 2012).
Fish were anesthetised using Clove (herbal spice) to minimize physical injury and stress. Stripping of sperms and eggs method was used to determine the stages of sexual development in fish. The fish were stripped by applying gentle pressure to the abdomen between the pelvic fin. When the eggs or milt came out with pressure on the abdomen, the fish was considered to have reached maturity.
Fish belonging to maturity stage onwards were considered as mature and used for the purpose of calculating the size at first maturity.
The water quality parameters included were: water temperature, dissolved oxygen and pH.
The statistical model used in the experiment was as follows:
Yij = µ + τi + βj + (τβ)ij + εij
Where: Yij = observed response variables
µ= overall mean
τi= the effect of feed on O. niloticus (i=1,2)
βj = the effect of feed on O. tanganicae (j=1,2)
(τβ)ij = interaction between two species
ε= experimental error
Statistical Package for Social Scientists (SPSS) version 16.0 was used to analyze the data on body weight, length, first maturity and Gonadosomatic index. A two-way analysis of variance (ANOVA) was used to determine whether there was any significant difference in the variables measured among the experimental groups.
2 Results and Discussion
Figure 1 shows the changes in mean weight of fish over 12 weeks experimental period. The initial mean weights of fish were 30g for both species while final body weights were 73.65g for O. niloticus and 66.30g for O. tanganicae.
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Slow growth was observed in both species in the first four weeks of trial. However, the species showed faster growth in the sixth week. Based on the results of growth it was clear that O. niloticus performed better than O. tanganicae. Higher growth could partly be influenced by effective feed utilization and gonadal development (Figure 1). However, final weight showed no significant difference (p>0.05) between the two species.
The smallest O. niloticus matured at the weight and standard length of 34g and 73mm while that of O. tanganicae, it was at the weight and standard length of 42g and 111mm respectively, an indication that some fish matured earlier than others. The present study showed that O. niloticus reaches sexual maturity at a smaller size and younger age than O. tanganicae. This present study was in agreement with that conducted by Al Hafedh et al (1999), which revealed that fish that grew fast matured earlier. According to the Popma and Lovshin (2005), O. mossambicus reached sexual maturity at a smaller size and younger age than O. niloticus and O. aureus. Morales (1991) also reported that the tilapias attained their sexual maturity at three months old with a total length of 8 to 16 cm. The results of the present study were also in agreement with de Graff et al. (1999) who reported that the first maturation size for reared Nile tilapia was between 30 and 50 g.
However, at the end of the experimental period, the length at first maturity at which 50% of the fish population reaches sexual maturity (L50) was observed to be 136mm for O. niloticus and 129mm for O. tanganicae (Figure 2).
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The results of the present study therefore disagree with the results obtained by Popma and Lovshin (2005). The differences in length at first sexual maturity could be attributed to the differences in genetical and environmental conditions such as food supply and changes in water quality parameters such as temperature, pH and dissolved oxygen.
The gonadal development for O. niloticus showed that 12 % were in immature (I) stage, 15 % were in maturing (II) stage and 73 % were in mature (III) stage (Figure 3).
In a similar manner, the gonadal development for O. tanganicae showed that, 17 % of the fish were in immature (I) stage, 25 % were in maturing (II) stage and 58 % were in mature (III) stage (Figure 4).
The maturity stages of these tilapia species were classified macroscopically and three stages were observed, which was in agreement with the results reported by Pena-Mendoza et al., (2005), but disagree with Shalloof and Salama (2008) for O. niloticus and Olele (2010) for S. galilaeus. These differences arose probably because the sexual maturity was a function of the size and could have been influenced by the abundance and seasonal availability of food, temperature, photoperiod and other environmental factors at different localities (Pena-Mendoza et al., 2005). Seventy-three (73 %) percent of O. niloticus had matured and were in the reproductive process compared to fifty-eight (58 %) percent for O. tanganicae. Maturity peak of both species was observed in October, which was associated with warm temperature and onset of the rain season culminating into a rise in water levels.
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In a similar manner, the gonadal development for O. tanganicae showed that, 17 % of the fish were in immature (I) stage, 25 % were in maturing (II) stage and 58 % were in mature (III) stage (Figure 4).
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The maturity stages of these tilapia species were classified macroscopically and three stages were observed, which was in agreement with the results reported by Pena-Mendoza et al., (2005), but disagree with Shalloof and Salama (2008) for O. niloticus and Olele (2010) for S. galilaeus. These differences arose probably because the sexual maturity was a function of the size and could have been influenced by the abundance and seasonal availability of food, temperature, photoperiod and other environmental factors at different localities (Pena-Mendoza et al., 2005). Seventy-three (73 %) percent of O. niloticus had matured and were in the reproductive process compared to fifty-eight (58 %) percent for O. tanganicae. Maturity peak of both species was observed in October, which was associated with warm temperature and onset of the rain season culminating into a rise in water levels.
The gonadal weight and gonadosomatic index was calculated by using gonad and body weight (Gonad/body weight * 100) and the average values for O. niloticus was found to be 1.07 and 1.53, while that for O. tanganicae was 0.86 and 1.41 respectively. Gonadosomatic index is a very important parameter for understanding gonad development of fish (Begum et al., 2008). There was no significant differences (p>0.05) between gonadosomatic index values of O. niloticus and tanganicae. Both growth performance in terms of somatic and maturation were higher in O. niloticus than in O. tanganicae. That could be due to differences in uptake and utilization of feed between these species.
The mean water quality parameters during the entire experimental period are presented in Table 1.
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Tilapias are more tolerant to a wide variety of environmental conditions and to the extreme growth and development is affected (Popma and Lovshin 1995). Water temperature influences the physico-chemical and biological factors of water body. Water temperature also has a major influence on the amount of food consumed by a fish (Jobling, 1998). When fish are fed to satiation, growth at the preferred temperature is typically three times greater than at 22℃. Maximum feed consumption at 22℃ is only 50 to 60% as great as at 26℃ (Popma and Lovshin 1995). Reproduction is also inhibited at water temperatures below 20oC, slowed at waters temperature of 21 to 24oC and most frequent growth is recorded in waters above 25oC. The ranges of mean values for water temperature in different months in the present study were: 23.34±0.76 to 25.46±0. These values were more or less similar to those reported by Paul (1998), Rahman (1999), Kohinoor (2000) and Kohinoor et al., (2004).
The ranges of mean value of dissolved oxygen concentrations were found to be from 4.92±0.94 to 6.19±1.17mg/L, which was similar to findings reported by several researchers (Rahman, 2000; Kohinoor, 2000; Kohinoor et al., 2004). Low dissolved oxygen is usually the first water quality constraint to growth in intensively managed ponds as a result, maturation was affected indirectly. Most tilapia species are tolerant to dissolved oxygen levels as low as 0.5mg/L, which was not tolerable for most other cultured fish (Popma and Lovshin, 2005). In the case of the present study, the values for dissolved oxygen concentration were within the optimum level (4.92±0.94 to 6.19±1.17mg/L).
The pH in all the hapas was alkaline throughout the experimental period and the values ranged from 7.39±0.06 to 7.50±0.03. Tilapia seems to grow best in water that was near neutral or slightly alkaline (Popma and Lovshin, 2005). The ranges and mean values of pH in the present study were alkaline indicating the productive nature of water.
3 Conclusion
The aim of the study was to determine the effect of commercial feed on sexual maturity of tilapia species (O. niloticus and tanganicae) reared in hapas. The present study showed that O. niloticus matured at a smaller size than O. tanganicae and the mean values of growth weight and gonadosomatic index. However, there was a difference in terms of gonadosomatic index and gonad mean weight. Maturity stages were macroscopically identified into three stages (immature, maturing and mature) and at the end of the experimental period, 73% of O. niloticus and 58% of O. tanganicae were in the reproductive process (mature).
Acknowledgement
The authors wish to extend their heartfelt thanks to staff and management of NARDC and the Copperbelt University for their invaluable moral, material and financial support to the research team.
Al Hafedh Y. S. M, Siddiqui A. Q., and Al-faiady M. Y., 1999, ‘Effects of Dietary Protein Levels on Gonad Maturation, Size and Age at First Maturity, Fecundity and Growth of Nile Tilapia’, Aquacult. Int., 7: 319-332
http://dx.doi.org/10.1023/A:1009276911360
http://dx.doi.org/10.1023/A:1009276911360
Begum M., Pal H.K, Islam M.A. and Alam M.J., 2008, Formulation of quality fish feeds from indigenous raw materials and their effects on growth and maturity of Mystusgulio, J. Bangladesh Agril. Univ. 6(2): 355–360
Baroiller J.F. and Toguyeni A., 1996, Comparative effects of a natural steroid, 11ß-hydroxy-androstenedione (11ß-OH-A4) and a synthetic androgen, 17α-Methyl-testosterone (17α-MT) on sex-ratio in Oreochromis niloticus. In: Pullin, R.S.V., Lazard, J., Legendre, M., AmonKothias, J.B., Pauly, D. (Eds), Third International Symposium on Tilapia in Aquaculture. ICLARM Conference Proceeding 41, 11-16 November, 1991. Abijan, Cote d’Ivoire, pp. 344-351
Currie C.K., 1991, The Early History of the Carp and Its Economic Significance in England. The Agricultural History Review Vol. 39, No. 2 (1991), pp. 97-107. Published by: British Agricultural History Society. Article Stable URL:http://www.jstor.org/stable/40274806
Dey M.M., Paraguas F.J., Bhatta R., Alam F., Weimin M., Piumsombun S., Koeshandrajana S., Dung L.T.C., and Sang N.V., 2005, Carp Production in Asia: Past Trends and Present Status. In: Penman, D.J., M.V. Gupta and M.M. Dey (eds.) 2005. Carp Genetic Resources for Aquaculture in Asia. WorldFish Center Technical Report 65, 152 p.http://www.worldfishcenter.org/Pubs/CarpGen/CarpGenetics.pdf.
Duponchelle F., and Legendre M., 1996, Oreochromis niloticus (Cichlidae) in Lake Ayame, Cote D’ivoire: Life History Traits of a strongly diminished population.The life History Traits of strongly diminished populations of Oreochromis niloticus in Lake Ayame - Cote Divore. Available from http://www.mnhn.fr/sfi/cybium on 29/04/2014
El-Sayed A. M., 2002, ‘Effect of stocking density and feeding levels on growth and feed efficiency of Nile tilapia (Oreochromis niloticus L.) fry’. Aquaculture Research, 33:621-626
http://dx.doi.org/10.1046/j.1365-2109.2002.00700.x
http://dx.doi.org/10.1046/j.1365-2109.2002.00700.x
Hepher B., and Pruginin Y., 1982, Tilapia culture in ponds under controlled conditions pp. 185-203 In: Pullin, R.S.V. and. Lowe-McConnell, R.H. (eds), The Biology and Culture of Tilapias. ICLARM Conference Proceedings 7, 432. International Center for Living Aquatic Resources Management, Manila, the Philippines
Hossain M.A., Rahmatullah S. M., Islam M.S., Kabir A.K.M.A. and Dewan S., 1997, Impact of chapila (Gadusia chapra Ham.) on growth of carps in polyculture. Bangladesh J. Fish. Res., 1(2): 19-23
Jobling M., 1998, Feeding and Nutrition in Intensive Fish Farming. pp 66-113. In: K.D. Black and A.D., Pickering (editors). Biology of Farmed Fish. London: Sheffield Academic Press. CRC press. 415p
Kohinoor A.H.M., 2000, Development of culture technology of three small indigenous fish-Mola (Amblypharyngodon mola), Punti (Puntius sophore) and Chela (Chela cachius) with notes on some aspects of their biology. Ph.D.Thesis. Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh
Kohinoor A.H.M., Islam M.L., Wahab M.A., and Thilsted S.H., 1998, Effect of mola (Amblypharyngodon mola) on growth and production of carp in polyculture. Bangladesh J. Fish., 2(2): 119-126
KohinoorA.H.M., Momtaz Begum and Hussain M.G., 2004, Culture potentials of gulsha (Mystus cavasius) in monoculture management under different stocking densities. Bangladesh J. Fish. Res., 8(2): 95-100
Mair G.C., and Little D.C., 1991, Population control in farmed tilapia, NAGA, ICLARM Quarterly, 17(4): 8-13
Manissery J. K., Krishnamurthy D., Gangadhara B., and Nandeesha M.C., 2001, Effects of varied levels of dietary protein on the breeding performance of common carp (Cyprinus carpio). Asian Fisheries Science 14: 317-322
Meyer D. E., 2002, Technology for successful small-scale tilapia culture (CRSP Research Report 02-179). CRSP (Aquaculture Collaborative Research Support Program). [Abstract from originalpaper published in: D. Meyer (Ed). 6to Simposio oamericano de Acuacultura Proceedings: Tilapia Sessions, 22-24 August 2001. Tegucigalpa, Honduras, pp. 97-106]
Mishra S., and Saksena D.N., 2012, Gonadosomatic index and fecundity of an indian major Carp Labeo calbasu in Gohad Reservoir. The Bioscan 7(1): 43-46, 2012. An International Journal of Life Sciences. www.thebioscan.in
Mishra A., and Singh U.P., 2002, Effect of feeding on spawning of common carp. Indian J. Fish., 49(3)
Morales D.A., 1991, La Tilapia en México. Biología, Cultivo y Pesquerías. AG, México, D.F. 190 pág
Muchlisin Z.A., Hashim R., and Chong A. S. C., 2006, Influence of dietary protein levels on growth and egg quality in broodstock female Bagrid catfish (Mystus nemurus Cuv. & Val). Aquaculture Research 37: 416– 418
http://dx.doi.org/10.1111/j.1365-2109.2005.01382.x
http://dx.doi.org/10.1111/j.1365-2109.2005.01382.x
Mudenda C.G., 2004, Economic perspective of aquaculture development strategy of Zambia. FAO/ZAM/TCP 3006
Noakes D. L. G., and Balon E. K., 1982, Life histories of tilapias: an evolutionary perspective. pp 61-82. In: Pullin, R.S.V. and Lowe-McConnell, R.H. (eds.). The Biology and Culture of Tilapias. ICLARM Conference Proceedings 7, International Center for Living Aquatic Resources Management, Manila, Philippines, 432p
Nyakuni L., 2009, Habitat utilization and Reproductive Biology of Nile Tilapia (Oreochromis Niloticus) in Albert Nile, Nebbi District. A Dissertation submitted to Graduate School in partial fulfillment for the award of Master of Science degree in Zoology (Fisheries and Aquatic Sciences) of Makerere University
Olele N. F., 2010, Reproductive biology of Sarotherodon galilaeus (Artedi, 1757) in Onah Lake, Delta State, Nigeria. J. Applied Sci. Res., 6: 1981-1987
Paul S., 1998, Comparison between carp polyculture system with silver carp (Hypopthalmicthys molitrix) and with small indigenous fish mola (Amblypharyngodon mola). M.S. Dissertation, Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh. pp.85
Pena-Mendoza B., Gomez-Marquez J.L., Salgado-Ugarte I.H., and Ramirez-Noguera D., 2005, Reproductive biology of Oreochromis niloticus (Perciformes: Cichlidae) at Emiliano Zapata dam, Morelos, Mexico. Rev. Biol. Trop., 53: 515-522
Popma T. J., and Lovshin L. L., 1995, “Worldwide Prospects for Commercial Production of Tilapia”. International Center for Aquaculture and Aquatic Environments. Department of Fisheries and Allied Aquacultures. Auburn University, Alabama 36849. December, 1995. 42p
Rahman M.M., 1999, Effects of species composition on pond ecology and growth of fish in Carp-SIS polyculture systems. M.S. Dissertation, Department of Fisheries Management, Bangladesh Agricultural University, Mymensingh. 92pp
Shalloof K.A.S. and Salama H.M.M., 2008, Investigations on some aspects of reproductive biology in Oreochromis niloticus (Linnaeus, 1757) inhabited Abu-Zabal Lake, Egypt. Global Vet., 2: 351-359
Singh R., and Dhawan A., 1996, Effect of formulated feed on growth and ovarian maturation in common carp, Cyprinus carpio communis Linn. Indian J. Fish., 43(4): 349-353
Shinkafi B.A., Ipinjolu J. K and Hassan W.A., 2011, Gonad Maturation Stages of Auchenoglanis occidentalis (Valenciennes 1840) in River Rima, North-Western Nigeria. Journal of Fisheries and Aquatic Science, 6: 236-246
http://dx.doi.org/10.3923/jfas.2011.236.246
http://dx.doi.org/10.3923/jfas.2011.236.246
Thomas C., 2010, Using Kafue Bream in aquaculture. http://www.thefishsite.com/articles/1105/using-emoreochromis-andersonii-em-kafue-bream-in-zambia
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