Int. J. Aquat. Biol. (2020) 8(4): 262-271 ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.ij-aquaticbiology.com © 2020 Iranian Society of Ichthyology Original Article Ageing Nile tilapia (Oreochromis niloticus): A comparative study between scales and otoliths Khaled Y. Abouelfadl1, Walid Aly*2,1Alaa G.M. Osman3 1Aquatic Ecology Department, Faculty of Fish and Fisheries Technology, Aswan University, Egypt. 2Fisheries Biology Lab., Fisheries Division, National Institute of Oceanography and Fisheries, Egypt. 3Department of Zoology, Faculty of Science, Al-Azhar University (Assiut Branch), Assiut, Egypt. s Article history: Received 7 June 2020 Accepted 21 August 2020 Available online 2 5 August 2020 Keywords: Relative precision Percent agreement Age groups Longevity Abstract: This study is the first to compare age estimates based on scales and otoliths of the Nile tilapia, Oreochromis niloticus, from Lake Nasser, Egypt. Ageing precision between readers was estimated by calculating the percent agreement between three independent readers, and the coefficient of variation (CV) ages estimated from otoliths and scales. The relation between the total length of fish and the radius of its scale and otolith was determined and appeared to be linear. The estimated age composition of the O. niloticus included six age groups estimated using scales and five age groups estimated by otoliths. The relative precision (CV and SD) of ages estimated from otolith was higher than that from scales. Higher percentages of agreement of overall annuli identification and age assignment between readers were noted in otoliths comparing to that in scales. Scale showed some inaccurate estimation in the age of fish older than 4. The precision and bias information in this study will be beneficial to fisheries professionals in assessing the age of Nile tilapia and other cichlids in the future. Introduction Growth and age studies investigate the essential demographic characteristics to examine and assess the structure of fish populations (Maceina and Sammons, 2006). Estimating the age of fish is a common technique used to model its population dynamics and productivity by understanding fish longevity, growth and mortality rates i.e. an accurate understanding of these metrics needs precise age information (Campana, 2001). If a population that is or will come under considerable fishing pressure is to be studied, it is imperative that ageing should be done accurately as it is the most important parameters upon which recommendations can be based for the rational exploitation of a fish species. Many structures have been used for age estimation of fishes, including scales, various fin rays, fin spines, vertebrae, opercle, and otoliths. Ageing of fishes from subtropical and tropical regions have been reported via annual increments in such calcified structures, for example, scales (Ilieş et al., 2014), dorsal and pectoral *Correspondence: Walid Aly E-mail: walid.soton@gmail.com spines (Metcalf and Swearer, 2005), vertebral centra (Branstetter and Stiles, 1987; Bahuguna, 2013), opercular bones (Gómez-Márquez et al., 2008), and otoliths (Pilling et al., 2003; Fowler, 2009). A comparison of these various calcified structures has been performed in many species to obtain valuable information on the accuracy and bias of such age estimating structures (Kruse et al., 1993; Abecasis et al., 2008; Lozano et al., 2014). Studying the variation in age estimations using different calcified structures provide collateral evidence for the validity of the ageing method (Campana, 2001). Significant variation in age estimates based on different calcified structures indicates inaccurate ageing methodologies, imprecise ageing structures, or problems associated with interpretation (Muir et al., 2008). Balancing the accuracy and precision of the ageing method with sample size limitation is the main criteria to select the proper method for determination of age and growth in fishes (Zymonas and McMahon, 2009). Tilapias are the main species produced in Egypt 263 Int. J. Aquat. Biol. (2020) 8(4): 262-271 and contributed about 31% of the total wild fish catch in 2017 (GAFRD, 2017). Nile tilapia (Oreochromis niloticus) is widely distributed in all fresh and brackish water bodies in Egypt (El-Sawy, 2006). While various aspects of the biology of O. niloticus and other commercially important tilapias have been thoroughly studied in Egypt (El-Sawy, 2006; El- Bokhty et al., 2013; Hassan and El-Kasheif, 2013; El- Kasheif et al., 2015; Hussian et al., 2019; Shalloof et al., 2020), there were no comparative studies to validate used O. niloticus ageing methods based on calcified structures. The present work aims to compare scales and otoliths as reliable calcified materials for estimating the age of O. niloticus from Lake Nasser by obtaining information on the accuracy and bias of such age estimating structures which can provide collateral evidence for the validity of these ageing methods. Materials and Methods Sampling and data collection: A total of 266 Nile tilapia were collected from Lake Nasser during 2018 from local fishermen. They were caught using trammel and gill nets which are the main commercial fishing gears used to catch this species in the lake. For each fish specimen, total length (TL) was measured to the nearest 0.1 cm and total body weight (Wt)) to the nearest 0.1 g. Fish samples were transported to the laboratory and stored at -20ºC. In the laboratory, several scales (8–10) were removed from each fish sample from the area below the pectoral fin (Abecasis et al., 2008) and stored in individually labelled envelopes. Scales were then cleaned in dilute aqueous ammonia solution, rinsed, and dried. All scales showing signs of regeneration were eliminated. Cleaned scales were kept between two clean slides. Digital images of at least three scales for each fish sample were obtained using a camera (ABBOT DEC2000) mounted on a binocular stereomicroscope (Zeitess 530). The radius of the scale was measured on the digital image. Both sagittas were recovered intact from each fish sample by exposing the otoliths capsules by applying an incision on the dorsal side of the head. Otoliths then washed in water and cleaned from all extraneous tissue, and dried, labeled, then stored in plastic vials. Digital images were obtained using a camera (ABBOT DEC2000) mounted on a binocular stereomicroscope (Zeitess 530) for each pair of otoliths, submerged in 50% glycerol and illuminated with oblique reflected light. The clearest image was chosen for interpretation. The radius of the otolith was measured on the digital image. Age determination: Each scale and otolith were read twice by three different readers separately (no previous knowledge of count, or length of the sample). Each reader assigned each fish to an annuli class based on the number of opaque zones of the scale or the otolith (Murie and Parkyn, 2005). Aging precision between readers was estimated by calculating: (1) the percent agreement between three independent readers and (2) The coefficient of variation (CV) (Kimura and Lyons, 1991). Results Out of 266 examined fish, 136 were females (51.1%), and 130 males (48.9%). The total length (TL) of the samples ranged 13.5-48.0 cm with an average of 20.75±8.61 cm. The total weight (TW) varied 46.6- Table 1. Coefficient of variation (CV), percentage of agreement, and standard deviation of age group estimation by different readers based on scales and otoliths reading. Age group Scales Otoliths CV Agreement SD CV Agreement SD I 34.2% 68.7% 0.56 16.2% 88.5% 0.38 II 30.2% 58.4% 0.68 11.1% 86.1% 0.39 III 17.2% 58.5% 0.59 12.2% 80.4% 0.50 IV 16.1% 61.0% 0.67 5.8% 82.7% 0.37 V 10.2% 70.1% 0.62 0.0% 100.0% 0.00 VI 10.4% 71.3% 0.62 - - - Total 24.8% 64.7% 0.62 11.6% 87.5% 0.33 264 Abouelfadl et al./ Scale and otolith-based ageing of Nile tilapia 2301.7 g with an average of 652.96±537.2 g. The total length of males ranged between 13.5 and 48.0 cm and their total weight between 46.6 and 2301.7 g while females TL ranged between 14.0 and 45.5 cm TW between 56.3 and 2055.3 g. The TL for females and males did not differ significantly (T-test t=0.66, P<0.05) (Fig. 1). The relationship between total length and the radius of its scales and otolith was determined and appeared to be linear. The correlation coefficient of the linear relationship was lower in scales (r2=0.93) than that of otolith (r2= 0.98) (Fig. 2). The otoliths and scales of O. niloticus showed annual rings, each ring composed of a faint broader growth zone and a dark opaque line (Fig. 3). The estimated age composition of the O. niloticus represented by the samples, including six age groups estimated using scales and five age groups estimated by otoliths (Table 1). The relative precision (CV and SD) of ages estimated from otolith was higher than Figure 1. Length frequency of Oreochromis niloticus from Lake Nasser during 2018. Figure 2. The relation between scales and otoliths radius and the total body length of Oreochromis niloticus from Lake Nasser during 2018. 265 Int. J. Aquat. Biol. (2020) 8(4): 262-271 that of scales (Fig. 4). A higher percentage of agreement of overall rings identification and age assignment between readers was noted in otoliths (87.5%) comparing to that of scales (64.7%) (Table 1). Calculating the agreement percentage between readers in the identification of each ring and assignment of each age group in both otolith and scales showed that higher percentages were recorded in otoliths reading reaching to 100% in the determination of age group V while the same group in scale had 71.1% agreement and the lowest percentage of agreement was recorded in the age group III with 84.4% in otoliths and 58.5% in scales (Table 1). The relationship between the assigned age groups and the total body length was determined and appeared to be linear. The correlation coefficient of this linear relationship for of scales (r2=0.91) was lower than that of otolith (r2= 0.93) (Fig. 5). The proportion of fish in each age group increased from the group I to group II, then it decreased gradually with increasing age groups where the second year of the age (age II) had the highest frequency percentage of 37.6 and 43.6% for age estimation by scales and otoliths, respectively (Fig. 6). Fifty-six samples were assigned to age group I using both scales and otoliths and they had mean TL of 17.5 cm while group II had some differences where the number of assigned samples were less when scales were used instead of otoliths (100 and 110, respectively) and the mean TL were 25.2 and 25.9, respectively, but these differences were not significant. Furthermore, significant differences (P<0.05) was noted in samples assigned to age group Table 2. Mean and standard deviation of total body weight, total body length, hard structure radii, and number and frequency (%) of fishes of Oreochromis niloticus assigned to each age group based on scales and otoliths reading. Age Scales Otolith Total weight (g) Total length (cm) Radius (mm) No % Total weight Total length Radius (mm) No % (Min-Max) Mean±SD (Min-Max) Mean±SD (Min-Max) Mean±SD (Min-Max) Mean±SD (Min-Max) Mean±SD (Min-Max) Mean±SD I (46.6-336.0) 116.8±35.3 (13.5-20.0) 17.5±2.4 (0.116-0.157) 0.138±0.012 56 21.1 (46.6-336.0) 116.8±35.3 (13.5-20.0) 17.5±2.5 (0.091-0.139) 0.120±0.016 56 21.1 II (157.4- 551.7) 332.5±118.3 (20.5-29.5) 25.2±3.1 (0.156-0.372) 0.242±0.059 100 37.6 (157.4- 639.0) 366.1±139.2* (20.5-30.8) 25.9±3.3 (0.139-0.230) 0.188±0.027 116 43.6 III (480.7-891.2) 680.9±59.4 (30.0-35.0) 32.1±1.6 (0.286-0.397) 0.357±0.038 54 20.3 (555.8-947.5) 749.5±95.4* (31.0-36.0) 33.4±5.5* (0.185-0.289) 0.253±0.037 46 17.3 IV (803.0-1236.0) 995.8±135.7 (35.3-39.5) 36.9±3.2 (0.366-0.540) 0.436±0.045 24 9.02 (888.0-1904.0) 1240±406.2** (36.5-42.5) 39.2±7.5* (0.258-0.361) 0.326±0.031 28 10.5 V (1082.2-2059.4) 1649.4±304.5 (40.0-45.0) 42.8±4.1 (0.401-0.592) 0.486±0.062 22 8.27 (1582.0-2301.7) 1985.7±223.7* (44.0-48.0) 45.6±10.8* (0.361- 0.437) 0.395±0.0.24 20 7.5 VI (1939.5-2301.7) 2118.4±170.7 (45.5-48.0) 46.8±6.8 (0.543-0.630) 0.591±0.036 10 3.76 - - - - - Significant compared with scales * P<0.05, **P<0.01 Figure 3. A scale (A) and an otolith (B) of Oreochromis niloticus with annual rings, each ring composed of a faint broader growth zone and a dark opaque line. 266 Abouelfadl et al./ Scale and otolith-based ageing of Nile tilapia III and higher (Table 2) where the frequency of samples and mean TL of each age group varied significantly between scale and otolith-based age estimation (Table 2). This variation is noted in the last assigned age group which was the group V in scales- based estimation while it was group VI in otolith- based estimation. Discussions In the present study, the otoliths and scales of O. niloticus showed rings, each ring composed of a faint broader growth zone and a dark opaque line. Many factors were reported to be correlated with ring formation in fish’s hard structures, including changes in temperature, total dissolved solids, food quantity, and changes, associated with the cycle of wet-dry seasons (Karakiri and von Westernhagen, 1989; Lecomte et al., 1989; Gauldie et al., 1990; Yosef and Casselman, 1995; Admassu and Casselman, 2000). Indeed, seasonal variations are less intensive in the subtropics and tropics than in the temperate regions. However, regular climatic fluctuation occurs in many tropical freshwaters (Oppenheimer, 1989). This fluctuation may follow either a uniannual or multiannual cycle, lead to the formation of one or more macrozones or checks in the calcified structures of the fish (Admassu and Casselman, 2000). In addition, fluctuation in body condition associated with spawning activity has also been considered an important factor especially in tropical and subtropical areas, where ring formation has often been attributed to the reproduction, particularly in cichlid fishes (Garrod, 1959; Pannella, 1974; Hecht, 1980). The results of both scales and otoliths-based age estimation in the present study showed that the growth of O. niloticus in Lake Nasser followed the pattern shown by cichlids in other systems (El-Sawy, 2006; El-Bokhty et al., 2013; Hassan and El-Kasheif, 2013; Figure 4. The coefficient of variation (CV%), percent agreement, and the standard deviation (STDEV) in age estimation by different readers based on scales (A) and otoliths (B). Figure 5. The relation between total body length and the assigned age group using scales and otoliths of Oreochromis niloticus from Lake Nasser during 2018. Figure 6. Age composition of Oreochromis niloticus from Lake Nasser based on scales and otolith reading. 267 Int. J. Aquat. Biol. (2020) 8(4): 262-271 El-Kasheif et al., 2015). Growth during the first year is extremely rapid, reaching almost one third (17.5 cm) of its maximum length. The advantage of this growth pattern is the ability of juveniles to avoid the intense predation by rapidly attaining a size large enough (Hecht, 1980). After sexual maturation, the growth rate decreases with an asymptotic length being approached early on in life (Booth et al., 1995). This study is the first to use two different tools simultaneously to assess the quality of ageing information of O. niloticus. All age estimation of this species in different water bodies in Egypt used scale method except Anonymous (1997) and Khalifa (2000) who used otoliths for ageing O. niloticus from Qarun and Wadi El-Raiyan Lakes. Generally, most of the earlier studies of fishes age and growth used scales for age estimation due to ease of collection, process, and avoids sacrificing the specimens. Emphasis on proper animal care in the fisheries profession would justify use of the scale in areas where other tools provide similar results, or even in areas where scales are slightly less precise (Kruse et al., 1993). In this study, the comparison between age estimates using scales and otoliths showed that otoliths were more accurate for age determination of O. niloticus. It was found that otolith-based age estimates would be more precise than scale-based estimates as the average precision estimates for scales (CV=24.8%) is twice more than that of otoliths (11.6%). Our results are in accordance with the growing evidences that the scale as a tool of age estimation may be unreliable under certain growth conditions. Many studies have suspected on scale ageing due to difficulties in reading annuli, low precision (Lowerre-Barbieri et al., 1994), and that scale ages may become inaccurate when growth becomes asymptotic. As scale growth is proportional to body growth, in older fish annuli become crowded on the scale edges making scale interpretation difficult. As a result, true age can be misestimated, especially in species that growth is concentrated in early life history like O. niloticus (Beamish and McFarlane, 1987; Shepherd, 1988). Moreover, several studies have reported that scales can provide unreliable estimates of fish age because of the lack of a distinct cold season, as annuli are formed during cold months when growth is slow, likely results in scale annuli that are indistinguishable for some fish populations in subtropical and tropical areas (Huish, 1954; Schramm and Doerzbacher, 1985). Several studies reported that otoliths are the most reliable ageing structure in several temperate as well as tropical fish species (Beamish, 1979; Brothers, 1979; Kalish, 1989; Cailliet et al., 2001; Phelps et al., 2007; Gunn et al., 2008; Fowler, 2009). Age estimation of O. niloticus from tropical and subtropical lakes using calcified structures are more challenging when compared to temperate species, where, in many cases, the between-reader agreement is above 90% (Bwanika et al., 2007). Nevertheless, the ageing precision (CV=11.6 %, the agreement between readers=87.5%, and SD=0.33) for O. niloticus using otoliths in this study indicated comparable to that of the majority of studies ageing fish using otoliths (Campana, 2001). This precision estimate is reflected by 100% agreement obtained between readers for age 5 years. The ageing precision results for scales and otoliths in the present study were similar to those of different species (Hecht, 1980; Boxrucker, 1986; Welch et al., 1993; Booth et al., 1995; Abecasis et al., 2008) which reported that the percent of accurate agreement for scale readers is always less than that of otolith readers. The age composition of the catch is used in age- structured stock assessments, which can be used to estimate exploitable biomass. The results of this study showed that the proportion of fish in each age group increased from the group I to group II, then it decreased gradually with increasing age groups. This pattern is following the classical dome shaped catch curve which is an indicator of two oppositely directed drives: the process of recruitment and the influence of mortality. The process of recruitment results in the formation of the left (rising from group I to group II) region on the catch curve. At a sufficiently mature age, the age group to which recruits belong almost completely transits into the harvested stock. Approximately at this age, the catch curve goes past 268 Abouelfadl et al./ Scale and otolith-based ageing of Nile tilapia the maximum and starts to decrease monotonously (Sukhanov, 2016). Age-length keys for O. niloticus developed in this study showed high variability between tools in assigning ages to fish >30 cm TL. Great variation in the length-at-age key of O. niloticus from Lake Nasser is noted in the previous longevity and age estimation studies as they all were solely based on scale (Table 3). This variation may have resulted from the inaccuracy of the estimation method and /or a combination of both extrinsic factors such as the variable abiotic conditions experienced by the fishes in different areas of the lake and intrinsic factors such as genetic variation between the individuals themselves. Much of the extrinsic intra-year variation in the growth of Oreochromis spp. was linked to flood intensity and duration (Booth et al., 1995). In the present study, age frequency distributions of O. niloticus based on scales were different from those based on otoliths, nevertheless, scale ages can fulfil a manager's need for information about population age composition if the oldest age-groups (>4) are combined. However, the scale is not sufficiently precise to assess the ages of individuals in a population, and does not, for the most part, accurately recognize older O. niloticus in Lake Nasser. Conclusion This study is the first to compare age estimates based on scales and otoliths of the Nile tilapia. Otoliths are recommended for the best age estimates due to its higher precision of age estimates compared to scales. If nonlethal techniques for estimating age are required, scales can provide close age estimates for fish in comparison to otolith age estimates, but they may still inaccurately estimate the age of fish older than age 4. The precision and bias information in this study will be beneficial to fisheries professionals in assessing age of Nile tilapia and other cichlids in the future. References Abecasis D., Bentes L., Coelho R., Correia C., Lino P. G., Monteiro P., Gonçalves J. M. S., Ribeiro J., Erzini K. (2008). Ageing seabreams: a comparative study between scales and otoliths. Fisheries Research, 89: 37- 48. Adam E.A. (2004). Stock assessment of some important commercial fish species of Lake Nasser, Egypt. Ph.D. thesis, Faculty of Science, Assiut University. 262 p. Admassu D., Casselman J.M. (2000). Otolith age determination for adult tilapia, Oreochromis niloticus L. from Lake Awassa (Ethiopian Rift Valley) by interpreting biannuli and differentiating biannual recruitment. Hydrobiologia, 418: 15-24. Agaypi M.Z. (1992). Studies on length-weight relationship of Oreochromis niloticus and Sarotherodon galilaeus of the High Dam Lake. Working Report of Fishery Management Center, Aswan, Egypt, 1: 11-24. Anonymous. (1997). Investigation of Lake Qarun ecosystem. Final Report Submitted to USAID. National Institute of Oceanography and Fisheries, Cairo, Egypt. 247 p. Bahuguna P. (2013). Age determination and growth rate of freshwater fish Puntius conchonius (Ham.-Buch) by a use of trunk vertebrae. Periodic Research, 2: 46-51. Beamish R.J. (1979). Differences in the age of Pacific hake Table 3. Length at age (cm) of Oreochromis niloticus reported by different authors in Lake Nasser. I II III IV V VI VII Tool Size parameter Author 18.9 31.1 41.4 47.8 52.3 54.7 56.7 Scales Total length Talaat (1979) 19.4 27.0 32.6 37.2 39.0 Scales Standard length- 1984/1985 Adam (2004) 6.9 20.3 29.8 36.5 41.3 44.7 47.2 Scales Standard length Latif and Khallaf (1987) 17.3 25.4 30.9 34.7 37.3 39.0 40.2 Scales Total length -Males Yamaguchi et al. (1990) 16.8 25.2 31.1 32.9 34.6 35.5 36.1 Scales Total length -Females Yamaguchi et al. (1990) 21.8 26.3 30.6 39.0 Scales Total length Agaypi (1992) 14.3 19.4 23.7 29.4 33.5 37.8 Scales Total length Mekkawy et al. (1994) 17.7 24.2 31.3 36.7 Scales Standard length-1994/1995 Adam (2004) 17.3 25.8 32.2 37.7 Scales Total length Shenouda et al. (1995) 15.6 23.2 27.6 31.8 Scales Standard length- 1999/2000 Adam (2004) 17.5 25.2 32.1 36.9 42.8 46.8 Scales Total length Present study 17.5 25.9 33.4 39.2 45.6 Otoliths Total length Present study 269 Int. J. Aquat. Biol. (2020) 8(4): 262-271 (Merluccius productus) using whole otoliths and sections of otoliths. Journal of the Fisheries Board of Canada, 36: 141-51. Beamish R.J., McFarlane G.A. (1987). Current trends in age determination methodology. In: R.C. Summerfelt, G.E. Hall (Eds.). Age and Growth of Fish. Iowa State University Press: Ames, IA. pp: 15-42. Booth A.J., Merron G.S., Buxton C.D. (1995). The growth of Oreochromis andersonii (Pisces: Cichlidae) from the Okavango Delta, Botswana, and a comparison of the scale and otolith methods of ageing. Environmental Biology of Fishes, 43: 171-78. Boxrucker J. (1986). A comparison of the otolith and scale methods for aging white crappies in Oklahoma. North American Journal of Fisheries Management, 6: 122-25. Branstetter S., Stiles R. (1987). Age and growth estimates of the bull shark, Carcharhinus leucas, from the northern Gulf of Mexico. Environmental Biology of Fishes, 20: 169-81. Brothers E. B. (1979). Age and growth studies on tropical fishes. Stock Assessment for Tropical Small-Scale Fisheries, 119-36. Bwanika G.N., Murie D.J., Chapman L.J.. (2007). Comparative age and growth of Nile tilapia (Oreochromis niloticus L.) in lakes Nabugabo and Wamala, Uganda. Hydrobiologia, 589: 287-301. Cailliet G.M., Andrews A.H., Burton E.J., Watters D.L., Kline D.E., Ferry-Graham L.A. (2001). Age determination and validation studies of marine fishes: do deep-dwellers live longer?. Experimental gerontology, 36: 739-64. Campana S.E. (2001). Accuracy, precision and quality control in age determination, including a review of the use and abuse of age validation methods. Journal of fish biology, 59: 197-242. El-Bokhty E.E.B., Ibrahim A., El-Bitar T. (2013). Assessment of Oreochromis niloticus caught off Lake Borollus, Egypt. Global Veterinaria, 10: 708-15. El-Kasheif M.A., Authman M.M.N., Al-Ghamdi F.A., Ibrahim S.A., El-Far AM. (2015). Biological Aspects and Fisheries Management of Tilapia Fish Oreochromis niloticus (Linnaeus, 1758) in El-Bahr El-Faraouny Canal, Al-Minufiya Province, Egypt. Journal of Fisheries and aquatic Science, 10: 405-44. El-Sawy W.M.T. (2006). Some biological aspects of dominant fish populations in Lake Edku in relation to prevailing environmental conditions. M.Sc. thesis, Faculty of Science, Zagazig University. 231 p. Fowler A.J. (2009). Age in years from otoliths of adult tropical fish. In: B.S. Green, B.D.Mapstone, G. Carlos, G.A. Begg (Eds.). Tropical fish otoliths: information for assessment, management and ecology . Reviews: Methods and Technologies in Fish Biology and Fisheries, 11.Springer. pp: 55-92 GAFRD (2017). General Authority For Fish Resources Development. Fish Statistics 2017 Yearbook, Ministry of Agriculture. Egypt. 27. 118 p. Garrod D.J. (1959). The growth of Tilapia esculenta Graham in Lake Victoria. Hydrobiologia, 12: 268-98. Gauldie R.W., Coote G., West I.F., Radtke R.L. (1990). The influence of temperature on the fluorine and calcium composition of fish scales. Tissue and Cell, 22: 645-54. Gómez-Márquez J.L., Peña-Mendoza B., Salgado-Ugarte I.H., Arredondo-Figueroa J.L. (2008). Age and growth of the tilapia, Oreochromis niloticus (Perciformes: Cichlidae) from a tropical shallow lake in Mexico. Revista de Biología Tropical, 56: 875-84. Gunn J.S., Clear N.P., Carter T.I., Rees A.J., Stanley C.A., Farley J.H., Kalish J.M. (2008). Age and growth in southern bluefin tuna, Thunnus maccoyii (Castelnau): direct estimation from otoliths, scales and vertebrae. Fisheries Research, 92: 207-20. Hassan A., El-Kasheif M. (2013). Age, growth and mortality of the cichlid fish Oreochromis niloticus (L.) from the River Nile at Beni Suef Governorate, Egypt. Egyptian Journal of Aquatic Biology and Fisheries, 17: 1-12. Hecht T. (1980). A comparison of the otolith and scale methods of ageing, and the growth of Sarotherodon mossambicus (pisces: Gchlidae) in a Venda impoundment (Southern Africa). African Zoology, 15: 222-28. Huish M.T. (1954). Life history of the black crappie of Lake George, Florida. Transactions of the American Fisheries Society, 83: 176-93. Ilieş I., Traniello I.M., Sirbulescu R.F., Zupanc G.K.H. (2014). Determination of relative age using growth increments of scales as a minimally invasive method in the tropical freshwater Apteronotus leptorhynchus. Journal of Fish Biology, 84: 1312-25. Kalish J.M. (1989). Otolith microchemistry: validation of the effects of physiology, age and environment on otolith composition. Journal of Experimental Marine Biology and Ecology, 132: 151-78. Karakiri M., von Westernhagen H. (1989). Daily growth 270 Abouelfadl et al./ Scale and otolith-based ageing of Nile tilapia patterns in otoliths of larval and juvenile plaice (Pleuronectes platessa L.): influence of temperature, salinity, and light conditions. Rapports et Procès- verbaux des Réunions du Conseil International pour l'Exploration de la Mer, 191: 390-99. Khalifa U.S. (2000). Management and population dynamics of some exploited fish species in Wadi El- Raiyan lakes. Ph.D. thesis, Faculty of Science, Cairo University. 246 p. Kimura D.K., Lyons J.J. (1991). Comparisons of scale and otolith ages for Walleye Pollock. AFSC Processed Report: 91-06. Kruse C.G., Guy C.S., Willis D.W. (1993). Comparison of otolith and scale age characteristics for black crappies collected from South Dakota waters. North American Journal of Fisheries Management, 13: 856-58. Latif A.F.A., Khallaf E.A. (1987). Growth and mortality of Tilapia species in Lake Nasser. Journal of Faculty of Science, Almenofeya University, Shebeen Alkoom, Egypt, 1: 34-53. Lecomte F., Meunier F.J., Rojas-Beltran R. (1989). Some data on the growth of Arius proops (Ariidae, Siluriforme) in the estuaries of French Guyana. Aquatic living resources, 2: 63-68. Lowerre-Barbieri S.K., Chittenden M.E. Jr, Jones C.M. (1994). A comparison of a validated otolith method to age weakfish, Cynoscion regalis, with the traditional scale method. Fishery Bulletin, 92(3): 555-568. Lozano I.E., Vegh S.L., Dománico A.A., Ros A.E. (2014). Comparison of scale and otolith age readings for trahira, Hoplias malabaricus (Bloch, 1794), from Paraná River, Argentina. Journal of Applied Ichthyology, 30: 130-34. Hussian M.A., Aly W., Morsi H.H. (2019). Feeding on phytoplankton profile of two African Cichlids in large reservoir, Lake Nasser, Egypt. Egyptian Journal of Aquatic Biology and Fisheries, 23: 451-64. Maceina M.J., Sammons S.M. (2006). An evaluation of different structures to age freshwater fish from a northeastern US river. Fisheries Management and Ecology, 13: 237-42. Mekkawy I.A.A., Mohamad S.H., Abass F.F., Okasha S.A. (1994). Some biological aspects of Oreochromis niloticus (Linnaeus, 1758) from Lake Nasser, Egypt and the effect of lake impoundment. Bulltin of Faculty of Science, Assiut University, 23: 101-42. Metcalf S.J., Swearer S.E. (2005). Non‐destructive ageing in Notolabrus tetricus using dorsal spines with an emphasis on the benefits for protected, endangered and fished species. Journal of fish biology, 66: 1740-47. Muir A.M., Ebener M.P., He J.X., Johnson J.E.. (2008). A comparison of the scale and otolith methods of age estimation for lake whitefish in Lake Huron. North American Journal of Fisheries Management, 28: 625- 35. Murie D.J., Parkyn D.C. (2005). Age and growth of white grunt (Haemulon plumieri): a comparison of two populations along the west coast of Florida. Bulletin of Marine Science, 76: 73-93. Oppenheimer M. (1989). Climate change and environmental pollution: physical and biological interactions. Climatic Change, 15: 255-70. Pannella G. (1974). Otolith growth patterns: an aid in age determination in temperate and tropical fishes. In: T.B. Bagenal (Ed). The ageing of fish, Unwin Brothers. pp: 28-39. Phelps Q.E., Edwards K.R., Willis D.W. (2007). Precision of five structures for estimating age of common carp. North American Journal of Fisheries Management, 27: 103-05. Pilling G.M., Grandcourt E.M., Kirkwood G.P. (2003). The utility of otolith weight as a predictor of age in the emperor Lethrinus mahsena and other tropical fish species. Fisheries Research, 60: 493-506. Schramm H.L.Jr, Doerzbacher J.F. (1985). Use of otoliths to age black crappie from Florida. In: Proceedings of the Annual Conference Southeastern Association of Fish and Wildlife Agencies. pp: 95-105. Shalloof K.A.S., El-Far M.A., Aly W. (2020). Feeding habits and trophic levels of cichlid species in tropical reservoir, Lake Nasser, Egypt. The Egyptian Journal of Aquatic Research, 46(2): 159-165. Shenouda T.S., Azim M.E., Abbas F.F., Adam E.A. (1995). Comparative age and growth studies on two tilapia species from the High Dam Lake within twenty years and signs of their overfishing. Journal of Egyptian German Socity of Zoology, 18: 15-44. Shepherd J.G. (1988). An exploratory method for the assessment of multispecies fisheries. ICES Journal of Marine Science, 44: 189-99. Sukhanov V.V. (2016). Age-distribution models for fish in catches. Russian Journal of Marine Biology, 42(2): 111- 116. Talaat K.M.M. (1979). Application of Some Growth Models on Tilabia Populations in Lake Nasser and Some Other Areas of Egyptian Inland Waters. M.Sc. thesis, Faculity of Science, Alexandria University. 182 271 Int. J. Aquat. Biol. (2020) 8(4): 262-271 p. Welch T.J., van den Avyle M.J., Betsill R.K., Driebe E.M. (1993). Precision and relative accuracy of striped bass age estimates from otoliths, scales, and anal fin rays and spines. North American Journal of Fisheries Management, 13: 616-20. Yamaguchi Y., Hirayama N., Koike A., Adam E.A. (1990). Age determination and growth of Oreochromis niloticus and Sarotherodon galilaeus in High Dam Lake, Egypt. Nippon Suisan Gakkaishi, 56: 437-43. Yosef T.G., Casselman J.M. (1995). A procedure for increasing the precision of otolith age determination of tropical fish by differentiating biannual recruitment. In: D.H. Sector, J.M.Dean, S.E. Campana (Eds). Recent developments in fish otolith research. University of South Carolina, Columia. pp: 247-269. Zymonas N.D., McMahon T.E.. (2009). Comparison of pelvic fin rays, scales and otoliths for estimating age and growth of bull trout, Salvelinus confluentus. Fisheries Management and Ecology, 16: 155-164.