Int. J. Aquat. Biol. (2017) 5(3): 228-235DOI: ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.ij-aquaticbiology.com © 2017 Iranian Society of Ichthyology Original Article Comparative assessment of diet and condition factor of Cyprinus carpio and Oreochromis leucostictus in Lake Naivasha, Kenya James Last Keyombe*1, 2,1Yasindi W. Andrew2, Oyugi O. Dalmas3 1Lake Turkana Research Station, Kenya Marine and Fisheries Research Institute, P.O. Box 205 - 30500, Lodwar, Kenya. 2Department of Biological Sciences, Egerton University, P.O. Box 536 - 20115, Egerton, Kenya. 3Migori County, Fisheries and Livestock Development, P.O. Box 210 - 40400, Suna-Migori, Kenya. Article history: Received 22 January 2017 Accepted 30 M ay 2017 Available online 2 5 June 2017 Keywords: Feeding Detritus Algae Zooplankton Phytoplankton Plant materials Abstract: The study compared and assessed the diet and condition factors of two fish species, Oreochromis leucostictus and Cyprinus carpio, in Lake Naivasha. Fish samples were collected monthly using gill nets (35-70 mm mesh size) from July to December 2013. Stomach contents of all the specimens were analysed using the point method. Results indicated that detritus was the most abundant food item in the diet of both O. leucostictus and C. carpio accounting for 50% and 63%, respectively, while benthic macroinvertebrates contributed the least with each fish having 2%. Rooting and digging behaviour of the carp probably led to both C. carpio and O. leucostictus ingesting the suspended detritus as their main source of food with C. carpio outcompeting O. leucostictus due to its prolific nature and better adaptability to benthic conditions. Fulton’s condition factor of all the fish samples had values of >1. A comparison of the two fish species showed C. carpio had a condition factor of 1.51 while O. leucostictus had 1.32. The higher condition factor of C. carpio in Lake Naivasha is an indication that the fish have better tissue energy reserves, greater reproductive potential and higher survival rates compared to O. leucostictus with a lower condition factor. Introduction The blue spotted tilapia, Oreochromis leucostictus, is an exotic species of Lake Naivasha. It established itself quickly when it was first introduced, unintentionally, in the lake in 1956 from Lake Victoria Basin and has been present to date (Njiru et al., 2006). Reason for its quick establishment after the introduction has not been exhaustively studied. Currently, it is the most abundant tilapiine fish species in the lake (Oyugi et al., 2011). Other tilapiine species introduced in the 1950s were Tilapia zillii, Oreochromis niloticus and O. spirulus niger (Gunther) (Hickley et al., 2008). There was a hybrid produced between O. leucostictus and O.s. niger (Gunther) which became abundant in the early 1960s but due to back crossing with O. leucostictus, it disappeared by 1972 (Hickley et al., 2008). The purpose for the introduction of O. s. niger was to provide a forage fish * Corresponding author: James Last Keyombe DOI: https://doi.org/10.22034/ijab.v5i3.265 E-mail address: katalitsa@yahoo.com for the American largemouth bass, Micropterus salmoides. O. leucostictus and T. zillii used to form an important fishery in the lake (Muchiri and Hickley, 991), with both species being commercially exploited using gill nets by fishermen. They have however been replaced from the commercial fishery by the invasive common carp, Cyprinus carpio (Oyugi et al., 2014). The common carp which was accidentally introduced in the year 1997 from a fish farm at the catchments of River Gilgil has the largest populations and is the main component in the lake’s commercial fishery (Oyugi et al., 2014). Among the commercially important fish species of the lake, O. leucostictus is the most desired by the local community for consumption. This is because it has fewer bones in its flesh compared to C. carpio and is tastier (Waithaka et al., 2015). However, its population has been on a decrease probably due to the invasion by the C. carpio 229 Int. J. Aquat. Biol. (2017) 5(3): 228-235 in the lake (Oyugi et al., 2014). The C. carpio interfered with the O. leucostictus breeding grounds through increasing turbidity of the water when feeding, and this could have reduced O. leucostictus spawning areas (Oyugi et al., 2014). Interactions between fish species and between them and planktonic organisms are frequently revealed through dietary studies. Gut content analysis which provides evidence of whether the invading population has increased pressure on prey items or increased competition for resources (Britton et al., 2007), is also lacking in this lake. Similarly, common carp has had various impacts in Lake Naivasha ecosystem since its introduction (Oyugi et al., 2012). However, knowledge of the effects of their interaction with O. leucostictus is limited. Therefore, the aim of this study is to assess the diet and condition factor of O. leucostictus and C. carpio in Lake Naivasha, to facilitate informed decision making processes for effective management of the fisheries resources. Materials and Methods Study area: Lake Naivasha is a shallow freshwater body, situated in the eastern arm of the Great Rift Valley in Kenya (0o46'S, and 36o20'E). It lies at an altitude of about 1890 m above the sea level. The Lake covers a surface area varying between 120 Km2 and 160 Km2 depending on the dry and wet seasons, respectively (Harper and Mavuti, 2004). The lake’s mean depth varies between 4-6 m (Hickley et al., 2008). It lies in an endorheic basin but its freshness is mainly maintained by the inflows from the catchment area, biogeochemical sedimentation and the underground seepage (Hickley et al., 2008). Lake Naivasha is a complex basin consisting of four lakes that include Oloidien, Crescent Lake, the main Lake Naivasha and Sonachi. Rivers Malewa and Gilgil are the most important feeders of the lake (Fig. 1). Karati River flows into the lake intermittently. The lake is surrounded by a Cyperus papyrus swamp which covers an area of 64 km2, but this can vary largely depending on rainfall intensity, livestock and prevailing wildlife populations in the riparian zone (Harper and Mavuti, 2004). The six sampling stations in both the main Lake Naivasha and crescent lake which were used in this study are indicated in Figure 1. These stations are Malewa (00o43'49.9"S 036o21'32.1"E), Korongo (00o 44'22.6"S 036o19'28.9"E), Hippo Point (00o47'14.0"S 036o18'56.8"E), Mid Lake (00o46'30.8"S 036o20' 49.9"E), Sher 00o49'19.1"S 036o21'49.4"E) and Crescent (00o45'39.8"S 036o24'31.2"E). Malewa and Korongo sampling stations are located approximately 100 m from the shore and characterized by floating Figure 1. A map of Lake Naivasha showing the sampling sites. 230 Keyombe et al./ Diet and condition factor of C. carpio and O. leucostictus in Lake Naivasha, Kenya mats of water hyacinth (Eichhornia crassipes), salvinia (Salvinia molesta) and papyrus (C. papyrus) vegetation. They are characterized by muddy substrate, decayed plant materials and silt. The average depths of the stations are 3 and 3.5 m, respectively. Sher Bay and Crescent Lake are fairly sheltered from the wave action of the main lake and are characterized by calm waters occasionally invaded by the floating mats of E. crassipes and detached C. papyrus especially during strong winds at high water levels. The average depths in these stations are 2.5 and 3 m, respectively. The substrate is mainly silt and sand. Sampling and data analyses: Fish samples were collected monthly using gill nets (mesh size OF 35, 40, 50, 60 and 70 mm) from Malewa, Korongo, Hippo Point, Mid Lake, Sher and Crescent sampling stations between July and December 2013. The variation in net mesh sizes allowed fish of different sizes to be caught. The nets were set at the first sampling station of the day at 7:00 am and hauled six hours later at 1:00 pm. The nets were then set at 1:30 pm and hauled at 7:30 for the second station of the day. Two stations were sampled per day. Six hours was the adequate time to ensure enough fish for sampling were caught in the nets during the day. Immediately after retrieving the net, each fish caught was weighed in grams using an electronic weighing scale (Digitron T745) to the nearest 0.1 grams. The total length of each fish was measured to the nearest centimeter using a measuring board. The sampled fish were then eviscerated and their sex determined according to Witte and Van Densen (1995) as outlined in Table 1. In the laboratory, fish stomachs were removed, fullness index determined using the modified method of Hyslop (1980), and preserved in labeled plastic vials with 5% formalin for further analysis. Condition factor (K) was estimated following Le Cren (1951): K =W/Lb Where K is the condition factor, W is the total body weight of fish in grams, L the total length in centimeters and b is the regression slope. Data on gut contents was tested for normality and homogeneity of variance using MS Excel 2010 and chi-square. The differences in the contribution of each food item were tested using Quadratic fit. Descriptive and inferential data analysis was conducted using MS Excel 2010. In all the analyses, 95% level of significance was used as the critical point for rejection of the null hypotheses. Results Contribution of food items: During the period of July to December 2013 the gut contents of 153 O. leucostictus and 162 C. carpio were analysed. Detritus, algae and zooplankton were the most abundant food types in the guts of the two fish species, Table 1. The ovarian maturity stages of Oreochromis leucostictus and Cyprinus carpio (Witte and Van Densen, 1995; Bonneau, 1999; Donkers, 2004). Description Maturity stage O. leucostictus C. carpio I Cannot differentiate sex Immature, gonad tissue developing II Small ovary, tube like. Eggs not visible Gonad non-vascularised III Ovary larger, occupies 1/3 of body cavity. Eggs visible as yellow granules Eggs/milt visible IV Ovary dull grey. Occupies ½ of body cavity. Eggs visible as yellow granules Mature, vascularised but not running V Ovary large. Greenish in colour. Occupies almost entire body cavity Running ripe Golden green eggs extruded on applying pressure to abdomen VI Red wrinkled ovary Spent 231 Int. J. Aquat. Biol. (2017) 5(3): 228-235 with fish of all sizes including the dietary items in their diet (Fig. 2). Detritus contributed the highest proportion in the diet of both O. leucostictus and C. carpio in all the sampling stations. Despite O. leucostictus and C. carpio having diversified their feeding habit to include mainly detritus and phytoplankton, higher plant materials still contributed significant portion of food items consumed by the fish in Lake Naivasha. Spatial variation in diet composition: There was minimal spatial variation in the composition of the food items consumed by both C. carpio and O. leucostictus in Lake Naivasha. Detritus dominated C. carpio diet in both the inshore (Crescent, Korongo, Malewa, Sher, Hippo point) and offshore (Mid lake) sampling stations. The lowest composition of detritus was at Korongo and the highest at Sher sampling stations at 61% and 75%, respectively. The other important food items in the guts of C. carpio were zooplankton, benthic invertebrates and plant 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% C. carpio O. leucostictus P e r c e n ta g e c o m p o s it io n Fish species Benthic Invertebrates Plant materials Zooplankton Algae Detritus Figure 2. The dietary composition of (a) Cyprinus carpio and (b) Oreochromis leucostictus in Lake Naivasha from July to December 2013. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% P e r c e n ta g e c o m p o s it io n Sampling site Benthic Invertebrates Plant materials Zooplankton Algae Detritus Figure 3. The relative food contribution in the guts of Cyprinus carpio at different sampling stations in Lake Naivasha from July to December 2013. 232 Keyombe et al./ Diet and condition factor of C. carpio and O. leucostictus in Lake Naivasha, Kenya materials. Zooplankton abundance ranged from 1-8% in all sampling stations. Zooplankton in the guts of C. carpioat Crescent, Korongo and Malewa sampling stations constituted 8%, 4% and 3%, respectively. Carps from Mid lake, Sher and Hippo point sampling stations had 2%, 1% and 2% of zooplankton as their gut contents (Fig. 3). The results revealed no significant differences between the food items ingested by C. carpio in all the sampling stations (P<0.05). The important food items of O. leucostictusin all sampling stations was detritus at Sher (52%) followed by algae at Hippo point (35%) and zooplankton at Mid lake (24%). Benthic macroinvertebrates and higher plant materials constituted insignificant proportions of O. leucostictus food each at 4%. The results showed no significant differences between the food items 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% P e r c e n ta g e c o m p o s it io n Sampling site Benthic Invertebrates Plant materials Zooplankton Algae Detritus Figure 4. The relative contribution of food items in the guts of Oreochromis leucostictus at different sampling stations in Lake Naivasha from July to December 2013. 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 C. carpio Female C. carpio Male C. carpio O. leucostictus Female O. leucostictus Male O. leucostictus C o n d it io n fa c to r ( S E ) Fish species Figure 5. The condition factor of Oreochromis leucostictus and Cyprinus carpio in Lake Naivasha from July to December 2013. 233 Int. J. Aquat. Biol. (2017) 5(3): 228-235 ingested by O. leucostictus in all the sampling stations (P<0.005). No significant spatial variation was detected between the other food items. Further analyses revealed that detritus was the most important food item for O. leucostictusin all the sampling stations (Fig. 4). Condition factor: All the fish samples collected had condition factor value of > 1. Cyprinus carpio had a condition factor of 1.51 while that of O. leucostictus was 1.32. The females of C. carpio had a K-value of 1.53 while female O. leucostictus 1.35. Similarly, male C. carpio had a K-value of 1.52 while males of O. leucostictus had 1.33 (Fig. 5). Discussion The highest proportion of phytoplankton was consumed in the open waters compared to the areas closer to the shore. This could be due to the openness and lack of free floating macrophytes in these off shore sampling stations allowing for more light penetration hence more phytoplankton biomass compared to areas closer to the shore where macrophytes shade the water from direct sunlight and inhibiting phytoplankton development. The higher percentages of plant materials consumed in the near shore areas (Korongo and Hippo point) than in the open deeper areas of the lake (Sher Bay, Oserian and Crescent Island) could be due to the infestation and presence of water hyacinth and other macrophytes as compared to the open lake which only receives floating macrophytes occasionally especially during strong winds. There was no significant difference in the amount of detritus in the diet of both fish in all the sampling stations. However, slightly higher detritus amounts were recorded in the near shore areas. This could be attributed to the decaying of plant materials abundant at the littoral zone. Occasionally, the decayed plant materials and other sediments are usually carried to the deeper waters through lake mixing particularly by wind thus distributing the detritus throughout the lake. This could explain the almost equal contribution of detritus in all the sampling station within the lake. An earlier study by Njiru et al. (2006) found that C. carpio in Lake Naivasha had diversified its diet by feeding on plant materials (40%), plant seeds (17%), detritus (12%) and fish remains (11%). However, according to Muchiri (1990), O. leucostictus feed on detritus as the principal component of their diet. Detritus is the most abundant food material available to fish in the lake and its importance has been previously also noted by Malvestuto (1974) and Siddiqui (1977). Of the other dietary constituents, algae, especially planktonic forms, were predominant. Fish body condition varies seasonally depending on changes in gonadal development, food availability, and other environmental factors (Pope and Willis, 1996). The two fish species had K-values above 1. The results showed that both species were in good condition. According to Braga (1986) and Efitre et al. (2009), values of the condition factor vary according to seasons and are influenced by environmental con- ditions. The favourable physicochemical parameters in Lake Naivasha may therefore have been a catalyst for the good condition factor of the two fish species. The physico-chemical parameters of Lake Naivasha measured in this study were within the tolerable range for both O. leucostictus and C. carpio (Edwards and Twomey, 1982). In a study of O. leucostictus in Lake Naivasha, Siddiqui (1977) found all stages of gonad maturation all year round and did not observe any seasonal fluctuation in relative condition factor, which he attributed to a constant proportion of fish with gonads in different stages of development. According to Nathaniel et al. (1998), the condition factor of gravid females was within the range 1.6 and 2.0 irrespective of the location of sampling in the Victoria reservoir (Uganda). The condition factor of 1.52 for C. carpio in this study is in agreement with the results from Victoria reservoir. Based on the results of this study, it can be concluded that the habit of C. carpio of rooting or digging in the bottom has had a negative effect on the environmental condition of Lake Naivasha through increase in turbidity and decrease in oxygen in the water column. This has in turn led to both fish species in the study consuming the suspended detritus as their 234 Keyombe et al./ Diet and condition factor of C. carpio and O. leucostictus in Lake Naivasha, Kenya main source of food with C. carpio outcompeting O. leucostictus due to its prolific nature and better adaptability to such conditions. The higher condition factor of C. carpio in Lake Naivasha is an indication that the fish have better tissue energy reserves, greater reproductive potential and higher survival compared to O. leucostictus with a lower condition factor. 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(2017) 5(3): 228-235 E-ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.ij-aquaticbiology.com © 2017 Iranian Society of Ichthyology چکیده فارسی در Oreochromis leucostictus و Cyprinus carpio چاقی ضریب و غذایی رژیم ایمقایسه ارزیابی توسعه کنیا نایواشا، دریاچه 3لماسا، اویوگی او. د2. آندرودبلیویاسیندی ، *1،2جیمز لست کیومبه .، لودوار، کنیا205-30500، صندوق پستی ی کنیاو شیالت اییدریایستگاه تحقیقاتی دریاچه تورکانا، انیستیتو تحقیقاتی علوم 1 .، اگرتون ، کنیا536-20115ی، دانشگاه اگرتون، صندوق پستی علوم زیست گروه2 .، کنیامیگوری-، سونا210-40400، صندوق پستی منطقه میگوری و دامداری توسعه شیالتاداره 3 چکیده: ارزیابی ودر دریاچه نایواشا کنیا Oreochromis leucostictusو Cyprinus carpio ماهی و ضریب چاقی دو گونه رژیم غذاییدر این مطالعه . ندصید شد 2013( از ماه جوالی تا دسامبر مترمیلی 35 -70)فاصله گره تا گره تور گوشکیر با استفاده ازهای ماهی ماهانه نمونهمقایسه شد. دو ررژیم غذایی هغذایی در ترین اقالم فراوان تریتیدکه . نتایج نشان داد ندتحلیل شد اینقطهبا استفاده از روش ها تمامی نمونهمحتویات معده شدند. شامل میبرا هر گونه درصد را 2مهرگان کفزی حداقل که بی، درحالیبوددرصد 63و 50به ترتیب با O. leucostictusو C. carpioگونه بهرا معلق هایتریتید از O. leucostictusو C. carpioگونه دو که هر شود میبه این منجر احتماالً کپور معمولیزنی رفتار ریشه کنی و نقب نسبت به بسترو سازگاری بهتر به شرایط توانایی ذاتیعلت به C. carpio در این رقابت با این وجودنمایند، استفاده عنوان غذای اصلی O. leucostictus مقدار آن در که گونه نشان داد دو ضریب چاقیمقایسه بود. 1از بیشتر هاماهی تمامی نمونه فولتونضریب چاقی .برتری دارد C. carpio 51/1 در وO. leucostictus 32/1 ضریب چاقی باالتر .باشدمیC. carpio ذخایر بافتی انرژیتیکی، دهندهدر دریاچه نایواشا نشان .استتر ضریب چاقی ایینپ مقداربا O. leucostictus در مقایسه با و نرخ بقای باالتر پتانسیل تولید مثلی .گیاهی مواد فیتوپالنکتون، زئوپالنکتون، جلبک، پوده، تغذیه، :کلمات کلیدی