Fisheries and Aquaculture Journal
Open Access

Differences in Phenotypic Characters of Nile Tilapia (Oreochromis niloticus L) in Three Ethiopian Rift Valley lakes; Screening Strains for Aquaculture

Megerssa Endebu^1*, Abebe Getahun² and Misikire Tessema^{3 *}Correspondence: Megerssa Endebu, Department of Aquaculture, Batu Fishery and Other Aquatic Life Research Center, East Shoa, Ethiopia, Tel: 251911044974, Email:

Author info »

Introduction

Nile tilapia (Oreochromis niloticus L.) is cultured worldwide and currently ranked second only to carps in global farmed food fish. The fish is indigenous species to Ethiopia and constitutes major proportion (65%) in the country’s fish production [1]. In the aquaculture development efforts of Ethiopia, wild O. nilotcus were collected from natural environments, especially from the Ethiopian rift valley lakes and stocked into ponds. In an attempt to select better performing strains for aquaculture, tilapia populations from different Ethiopian rift valley lakes showed different growth performances in pond culture. Growth performances of four O. niloticus populations of Ethiopian rift valley lakes (Hawassa, Chamo, Koka and Ziway) were evaluated in pond culture at Batu Fishery and other Aquatic Life Research Center [2] where the Chamo population was found to grow significantly faster than others. Similar studies were conducted to evaluate the growth performances of the tilapia populations of Ethiopian rift valley lakes in pond culture at different times for different experimental periods and found variation in growth performances [3,4] whereby the Koka and Ziway tilapia populations were mentioned as promising candidate populations for aquaculture development in Ethiopia compared to tilapia populations of Hora, Hawasa and Metehara lakes in Figure 1-3.

Figure 1: Location of the Ethiopian rift valley lakes.

Figure 2: Mean ± SD of total weight (gm) and TL (mm) of Nile tilapia (O. niloticus) populations of the three Ethiopian Rift valley lakes.

Figure 3 : O. niloticus samples of lakes Chamo (left), Koka (middle) and Ziway (right).

The three lakes, Chamo, Koka and Ziway are geographically isolated situated in different sub-drainage basins: Abaya-Chamo, Ziway-Shala and Awash basins, respectively, all within the Ethiopian Rift Valley [5]. Chamo has more diversified ichtyo fauna than other lakes in Ethiopia except Lake Abaya. There are six important fish species for fishery in Chamo. These, according to LFDP [6] are Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus), labeo (Labeo horie), African catfish (Clarias gariepinus), Bagrus (Bagrus docmak ) and Barbus (Labeobarbus intermedius). The O. niloticus, L. niloticus and C. gariepinus were numerically the three dominant species in the fish landings [7]. Koka harbors three commercially important fish species: Nile tilapia (Oreochromis niloticus), common carp (Cyprinus carpio) and African catfish (Clarias gariepinus) where O. niloticus were found in healthy state, C. gariepinus have shown signs of growth overfishing and C. carpio have shown under exploitation [8]. Indigenous fish species such as Nile tilapia (Oreochromis niloticus), Barbus (Labeobarbus intermedius), straightfin barb (Barbus paludinosus) and Garra (Garra dembecha), and introduced fish species such as African Catfish (Clarias gariepinus), Crucian carp (Carassius carassius), Common carp (Cyprinus carpio) and Tilapia zillii (Coptodon zillii) are found in Lake Ziway [9]. Among these species, Nile tilapia, African catfish, Crucian carp and Common carp are commercially important ones. Studies indicated [9] that the current annual fish production from Lake Ziway is declining, particularly the population of the Nile tilapia declined tremendously

Aquatic environment of the three lakes in terms of their basic morphometric features, altitude, water quality parameters and fish species diversity are different [10]. Under these different environmental conditions of the three lakes, tilapias are expected to develop different phenotypic and genetic characters. Phenotypic variation is wide in organisms spread in different geographical locations, and often involves ecologically relevant behavioral, physiological, morphological and life historical traits. Phenotypic plasticity can be inclusively defined as the production of multiple phenotypes from a single genotype, depending on environmental conditions [11].

Characterization of the tilapia population helps in utilization of the resource in aquaculture, and further contributes to protect the population in their natural environment. Hence, the objective of the present study was to investigate desired culture characteristics of O.niloticus of rift valley lakes in order to improve their productivityin aquaculture system with specific objective of characterizing theO.niloticus populations of Chamo, Koka and Ziway Lakes based ontheir phenotypic characters.

Materials and Methods

Description of the study areas

The fish were sampled from three Ethiopian rift valley lakes: Chamo, Koka and Ziway lakes from May, 2018 to March 2019. These water bodies were selected for their targeted Nile tilapia (O.niloticus.) populations to be used in the development of aquaculture in Ethiopia. Lake Chamo is situated in South most part of the Ethiopian rift valley lakes. The lake has surface area of about 297 km² [12] and recharged mainly by a feeder river called Kulfo. Lake Koka is a manmade reservoir located at about 90 km Southeast of Addis Ababa between 8° 18' 57" to 8° 28' 21" N and 39° 0' 0" E to 39° 9'18" E at an altitude of 1,590 m.a.s.l. It was constructed on Awash River in 1960 for thepurpose of hydro-electric power generation.

The reservoir has a surface area of about 255 km² with amaximum and mean depth of 14 m and 9 m, respectively [6]. Lake Ziway, spelled also as Zeway, Zway or Zwai (locally called as Lake Danbal) is located in the Ethiopian rift valley between 7° 52’ to 8° 8’N and 38° 40’ to 38° 56’E at an altitude of 1636 m a.s.l. with maximum length of 32 km and maximum width of 20km [6]. The lake is the second largest lake in Ethiopian rift valley after Abaya Lake, having an area of 434 km² and shoreline length of 137 km. The Lake is, however, the shallowest of the rift valley lakes with maximum and mean depth of 8.95 m and 2.5 m, respectively [6]. The lake has two feeder rivers, Meki River from Northwest and Katar River from East side, and has one outlet river in its Southern part, the Bulbula River, which seasonally flows into Abijata Lake.

Phenotypic characterization of the Oreochromis niloticus

Morphometric characters and meristic counts following described methods [11] were recorded from at least 150 fish samples of each of the tilapia populations of the three study lakes in Table 1.

Table 1: Morphometric and meristic characters of O. niloticus populations of the three lakes.

Along with the morphometric measurements, weight (TW) of each specimen was measured to the nearest 0.1 g. At least 150 fishes per lake were assessed. Condition factor of each fish was measured using the following equation:

K=100 (TW/TL₃)

Where, k=Fulton’s condition factor

TW=total weight in grams

TL=total length in centimeter

The fish were characterized based on the morphometric and meristic parameters. Values for the quantitative traits of the populations were expressed as mean and standard deviation as mean ± SD. Differences in mean values of the traits between the populations were analyzed in one-way analysis of variance (ANOVA) at significance level of p ≤ 0.05 using Tukey’s mean separation method [13,14].

Results and Discussion

In this phenotypic characterization, parameters including morphometric character indices, meristic counts, total weight total length, standard length and fish condition factor were analyzed from a total of 450 samples: 150 fish samples for each of the populations in Table 2.

Table 2: Means and standard deviations of quantitative phenotypic traits based on morphometric character indices and meristic counts.

Nile tilapia population of Lake Chamo were characterized by highest mean weight (412.24 ± 218.21 g), total length (27.81 ± 4.79 cm) and standard length (22.56 ± 4.17 cm), which differed significantly (p ≤ 0.05) from similar parameters of populations of lakes Koka and Ziway. The current mean total length of tilapia population of Lake Chamo is within the range of 19-43 cm length reported [7]. The Chamo population have also scored highest morphometric character indices of BD/SL,CPD/TL,Po-OL/ HL,PelFBL/SL,LLoDFS/SL,LLaDFS/SL,LLaDFR/SL,FiAFS/ SL,LLoAFR/SL and highest record of meristic character in PecFRC in which all the characters differed significantly (p ≤ 0.05) from the mean values measured from the populations of lakes Koka and Ziway. However, the population in Lake Chamo scored significantly (p ≤ 0.05) lowest mean values of BW/SL,TL/ SL and LLaDFR/SL from morphometric indices, and DFSC and AFRC from meristic characters. Generally, O. niloticus population from Lake Chamo were found to be larger in total length and weight, shorter at trunk region with respect to their standard length, dorso-vetrally deep, laterally compressed in body form as compared to other populations. They also had longest pre-orbital region, dorsal and anal fins as indicated in their morphometric indices.

Nile tilapia populations of Lake Koka scored mean weight of 259.17 ± 87.65 g, mean total length of 23.90 ± 2.63 cm and standard length of 19.17 ± 2.22 cm; values which were significantly (p ≤ 0.05) lower than that of Chamo population but higher than that of Ziway population. A mean total length that a fish of a given stock would reach if they were to grow indefinitely (L∞) was estimated to reach 44.5 cm for the O. niloticus population of Koka [8]and 28.1 cm for the O. niloticus population of Ziway [15]. Thesize differences between the population means in the current resultagrees with the above reports. Highest mean score of Fulton’scondition factor (K) was obtained in population of Lake Koka (1.83) and the value differed significantly (p ≤ 0.05) from that of the populations of lakes Chamo (1.78) and Ziway (1.75). The average K-values of O. niloticus were reported to vary over time; 1.87 for Koka population [16] and 1.89 [17] and 1.81 [15] for Ziway and 2.35 for Chamo [18]. The population of Lake Koka scored highest morphometric character indices of AL/SL, TL/ SL, DFBL/SL, CPW/TL, PelFL/SL and LLaAFR/SL but lowest mean values of HL/SL, BD/SL, CPL/TL, PecFL/SL, PelFBL/ SL, LLoDFS/SL, LLaDFS/SL, LLoAFS/SL, and LFiAFS/SL which were significantly different (p ≤ 0.05) from that of lakes Chamo and Ziway populations. As compared to populations of lakes Chamo and Ziway, the Koka O. niloticus population were generally found to have longer trunk region, laterally wide (fat), not dorso-ventrally deep, with shorter head and fin spines.

The tilapia population of Ziway were significantly (p ≤ 0.05) lower in their mean total weight (115.13 ± 47.14 g), mean total length (18.44 ± 2.46 cm) and standard length (14.94 ± 2.06 cm) than the lakes Chamo and Koka populations. The population had also lowest morphometric character indices of LLoDFR/SL, AFBL/SL, LLoAFR/SL and the lowest meristic counts of dorsal and pectoral fin rays which were significantly (p ≤ 0.05) different from mean values observed in that of Lakes Chamo and Koka populations. However, the population scored the highest mean value of OD/HL morphometric character index and the highest mean caudal fin ray count and differed significantly from that of lakes Chamo and Koka. Generally, O. niloticus population of Lake Ziway was relatively smaller in size, have shorter dorsal fin rays and wider orbit diameter with respect to their head length.

Morphometric characters in fish have been demonstrated to be influenced by environmental factors [19]. Chamo and Ziway are natural lakes while Koka is an artificial lake constructed for hydro-electric power generation. Aquatic environment of the three lakes in terms of their basic morphometric features, altitude, water quality parameters and fish species diversity are different [10]. The O.niloticus populations of the three lakes are accordingly isolatedfor centuries and developed different morphometric characters toadapt to their corresponding environmental conditions.

Fulton’s condition factor (K), which indicates the nutritional level and status of the fish over time, might be greatly influenced by environmental factors. The higher Fulton’s condition factor (K), observed in O. niloticus population of Lake Koka in the current study could be resulted as a function of better feed availability in artificial reservoirs than in natural lakes. Though the degree vary from lake to lake, anthropogenic impacts such as pollution due to silt and nutrient load from watershed areas, municipal waste, industries (tannery, flower culture), water level fluctuation and fishing pressures have directly or indirectly affected the fish community in the lakes [20]. Floodplains associated with the reservoirs are generally known to be most productive aquatic ecosystems. The K value of O. niloticus population of lakes Chamo, Koka and Ziway varied over time based on environmental changes [16-18].

Phenotypic adaptations of fish to their environment do not necessarily cause a change in genetic constitutions of the population [21] and hence phenotypic differences among populations cannot usually be taken as evidence of genetic differentiation. However, the O. niloticus populations of the three lakes are isolated for geological time that development of genetic differences among the populations is most likely. In genetic analysis using total mtDNA digestions, Seyoum and Kornfield [22] grouped O. niloticus of Ethiopia into different subspecies: O. n. cancellatus (Awash basin), O. n. filowa (Sodore hot springs), O. n. taita (Tana population) [23]using allozyme, clustered natural populations of O. niloticus inthe Ethiopian Rift valley (Lakes Ziway, Hawasa, Koka and Sodorehot springs) in one group and populations of Tana, Nile, Kenya inother group. The authors [20] considered the subspeciesclassification made by the former study [22] was premature.According to the species clustering of the later authors [23], the O.niloticus of Lake Chamo can be related to the Kenyan and Nilegroup since the Abaya-Chamo basin connects down to the ChewBahir and Turkana Lake in northern Kenya.

In a study of phylogenetic differentiation of wild and cultured Nile tilapia populations based on phenotype and genotype analysis [11], it was reported that phenotype analysis based on a large number of morphometric character indices and meristic counts can be used to discriminate fish populations up to the intraspecific level with the same results as the genotype analysis based on random amplified polymorphic DNA (RAPD) fingerprinting. Hence, the differences observed in phenotypic characters of the three O. niloticus populations in the present study based on the analysis made using 26 morphometric character indices, 8 meristic counts and four other morphometric characters indicates that the differences have also potential genetic bases.

Conclusion

Based on the parameters considered for characterization, Nile tilapia (O. niloticus) populations of lakes Chamo, Koka and Ziway differed in many phenotypic characters in their natural environments. As desired characters in aquaculture production, tilapia population of Lake Chamo had higher mean weight and length than population of Lake Koka followed by population of Lake Ziway.

The phenotypic characters are governed by genetic and/or environmental factors. Thus, it is important to confirm whether the populations could maintain these characters when grown under controlled environments.

Acknowledgments

p>This activity was jointly supported and monitored by Addis Ababa University and Agricultural Growth Program II (AGP- II) via Batu Fishery and other Aquatic Life Research Center of Oromia Agricultural Research Institute. Authors would like to thank Addis Ababa University, AGP-II and the Batu research center.

References

1. Abegaz H. Fish production from the perspective of Development Goals of Ethiopia. InEFASA 2015, Proceedings of the VIIth Annual Conference and Workshop of EFASA, Arba Minch, Ethiopia. 2015; pp: 5-16.
2. Tugie D, Endebu M, Hailu D, Lema A. Screening of Oreochromis niloticus strains for their important production traits in high stocking density and low CP feed quality without aerating devices inconcrete Tanks, Batu, Oromia, Ethiopia. Int J Fisheries and Aquatic Res. 2017;2(6):7-10.
3. Balkew K, Gjoen HM. Comparative studies on the growth performance of four juvenile Oreochromis niloticus L., (1758) strains in pond culture, Ethiopia. Int J Aquaculture. 2012;2(7):40-7.
4. Tugie D, Endebu M, Negisho T. Comparative study of growth performance of three Oreochromis niloticus populations under culture condition in concrete tanks, Zeway, Ethiopia. 2014;pp: 161-78
5. Ayenew T. Natural lakes of Ethiopia. Addis Ababa University Press. 2009; p. 206.
6. LFDP, Lake Fishery Development Plan. Lake management plans. Lake fisheries development project, phase II:Ministry of Agriculture, Addis Ababa, Ethiopia. 1997; pp: 49.
7. Dejene Z. Impact of fisheries and water quality changes on the management of Lake Chamo. 2008.
8. Tesfaye G, Wolff M. Stock assessment of fishery target species in Lake Koka, Ethiopia. Revista Rev Biol Trop. 2015;63(3):755-70.
9. Endebu M, Lema A, Genet T, Mitike A, Regassa B, Dejen E, et al. Fisheries baseline survey describing status of fisheries in Lake Zeway, Ethiopia. Fisheries Livest Prod. 2015;3(2):129.
10. Lemma B, Desta H. Review of the natural conditions and anthropogenic threats to the Ethiopian Rift Valley rivers and lakes. Lake Reserv Manag. 2016;21(2):133-51.
11. El-Zaeem SY, Ahmed MMM, Salama ME, El-Kader WN. Phylogenetic differentiation of wild and cultured Nile tilapia (Oreochromis niloticus) populations based on phenotype and genotype analysis. Afr J Agric Res. 2012; 7(19):2946-54.
12. Hailemicael A. Spatio-temporal analysis of Ethiopian rift valley Lake Chamo watershed utilization practices and environmental implications using geo-spatial technology. Department of Environmental Sciences, Andhra University, Viskhapatnam, India. PhD thesis. 2011. pp:143.
13. Kebede E, Mariam ZG, Ahlgren I. The Ethiopian Rift Valley lakes: chemical characteristics of a salinity-alkalinity series. Hydrobiologia. 1994;288(1):1-2.
14. Tesfaye G. Population dynamics and stock assessment of Nile tilapia, Oreochromis niloticus L. in three Rift Valley Lakes (Koka, Ziway and Langano). 2006;pp:80.
15. Tesfaye G, Tadesse Z. Length-weight relationship, Fulton’s condition factor and size at first maturity of tilapia, Oreochromis niloticus L. in Lakes Koka, Ziway and Langano (Ethiopian rift valley). Ethiop. J. Biol. Sci. 2008;7(2):139-57.
16. Tadesse Z. Studies on some aspects of the biology of Oreochromis niloticus L. (Pisces: Cichlidae) in Lake Ziway, Ethiopia. 1988;pp: 78.
17. Teferi  Y,  Admasu  D.  Length-weight  relationship,  body  condition and sex ratio of Tilapia (Oreochromis niloticus L.) in Lake Chamo, Ethiopia. Ethiop J Sci. 2002;25(1):19-26.
18. Robinson BW, Wilson DS. Experimentally induced morphological diversity in Trinidadian guppies (Poecilia reticulata). 1995;2(3): 294- 305.
19. Abera LH. Current Ecological Scenario of some Rift Valley Lakes of Ethiopia: A review. EC Agricul¬ture. 2016; 3(1): 570-80.
20. Allendorf FW. Conservation biology of fishes. Conser Biol. 1988; 2: 145-148.
21. Seyoum S, Kornfield I. Taxonomic notes on the Oreochromis niloticus subspecies-complex (Pisces: Cichlidae), with a description of a new subspecies. Can. J. Zool. 1992; 70: 2161-5.
22. Agnese JF, Adepo-Gourene B, Abban EK, Fermon Y. Genetic differentiation among natural populations of the Nile tilapia Oreochromis niloticus (Teleostei, Cichilidae). Heredity.1997;79: 88- 96.