Received: 13 November 2017 | Revised: 7 February 2019 | Accepted: 22 March 2019 DOI: 10.1111/lre.12271 ORIGINAL ARTICLE Some aspects of reproduction and feeding habits of Nile tilapia (Oreochromis niloticus) in three dams in Uasin Gishu County, Kenya Nicholas N. Gichuru1,2 | Julius O. Manyala2 | Philip O. Raburu2 1Kenya Marine and Fisheries Research Institute, Kisumu, Kenya Abstract 2Department of Fisheries and Aquatic Knowledge of the fisheries status of dams within Uasin Gishu County was needed Sciences, University of Eldoret, Eldoret, prior to the government's plan to introduce fish and fisheries in the area. The dams Kenya were constructed in the 1950s and stocked with tilapia for local consumption, recrea‐ Correspondence tion and control of macrophytes. The Nile tilapia (Oreochromis niloticus) was selected Nicholas N. Gichuru, Kenya Marine and Fisheries Research Institute, Pipeline area, for the present study due to its establishment success and popularity in the Kenyan near Kisumu International Airport, Kisumu, market. Water samples were collected at subsurface levels for phytoplankton analy‐ Kenya. Email: [email protected] sis and compared with the phytoplankton found in the stomachs of O. niloticus, re‐ vealing the food preference of the fish in a natural environment. Fish samples were collected with gillnets and beach seines. The results of the present study identi‐ fied the most important food items for the fish were Chlorophyceae (green algae), Bacillariophyceae (diatoms) and Cyanophyceae (blue‐green algae). The fish exhibited a relative condition factor of about 1.00, indicating their robustness or well‐being in the dams. The LM50 was reached at 18–20 cm class interval, which coincides with the most critical breeding biomass needing some kind of protection for sustainable management of the fishery. KEYWORDS feeding habits, Oreochromis niloticus, reproduction, Uasin Gishu dams 1 | INTRODUCTION dependent on the rainfall pattern (LaFranchi, 1996). To this end, fish production statistics of reservoirs in Kenya is lacking or inadequate. The majority of riverine, dams and small lake fisheries are small scale The fish currently found in reservoirs either has accidentally escaped in magnitude. A significant part of production is not commercialized, from culture conditions or was stocked in an effort to increase fish or else is marketed through informal channels, thereby not being re‐ supply (FAO, 1998). flected in national economic statistics. As a result, these fisheries Stocking of fish in Uasin Gishu County was done during the are regarded as low‐value economic activities (Allan et al., 2005). colonial era (1950s). Most of the dams were stocked with tilapi‐ Nevertheless, FAO (2010) has underscored the importance of inland ine species (mainly Oreochromis niloticus (Linnaeus 1757) and fisheries in regard to the livelihoods of people in both developed Coptodon zilli) by the “White settlers”. There are no records indi‐ and developing countries, even though irresponsible fishing prac‐ cating when this was done (Machuka, E. pers. comm.). Tilapia is a tices, habitat loss and degradation, water abstraction, drainage of hardy fish species, being resistant to low dissolved oxygen con‐ wetlands, dam construction and pollution often act synergistically, centrations in natural bodies and ponds (Balarin & Hatton, 1979; compounding the individual effects. Riverine fishing is particu‐ Witte et al., 1992). The fish also can withstand high carbon diox‐ larly important to poor households because it provides food not ide levels (Fish, 1956). Other gases tolerated by these fish include Lakes & Reserv. 2019;24:181–189. wileyonlinelibrary.com/journal/lre © 2019 John Wiley & Sons Australia, Ltd | 181 182 | GICHURU ET AL. ammonia, methane and hydrogen sulphide produced by decaying 1.1 | Study area organic matter. The fish is widely distributed from the near East (Israel, Palestine) to rivers and lakes in most parts of Africa. It has Uasin Gishu County lies across the equator in one of Lake Victoria's been introduced to other parts of the world because of its wide North catchment areas at an altitude of 1,250–1,850 m above sea adaptability in tropical and subtropical regions, including Asia, level. The rivers draining into it are tributaries of the Yala River, which the Caribbean and the Americas, through aquaculture develop‐ drains into Lake Victoria via the Yala Swamp. The area receives an ment (FAO, 2006; Khallaf & Alne‐na‐ei, 1987; Popma & Lovshin, annual rainfall of 900 to 1,100 mm, and the general climate of the 1996). Cichlids/tilapiines are “small brood” spawners that pro‐ area is characterized by two seasons, including a wet season (April– duce batches of eggs at frequent intervals. They generally occupy September) and dry season (October–February; Onyango, 1999). a “territory” and often make nests where they spawn and guard their eggs (Lowe‐McConnell, 1987). Oreochromis niloticus was essentially stocked in Uasin Gishu 2 | MATERIALS AND METHODS for sport fishing and local consumption, while C. zilli was stocked to control aquatic weeds in the dams (Machuka, E. per comm.). The Three (3) dams were selected for the present study on the basis of Kenyan government identified promotion of fish production as a their size (i.e. large [>100 acres in size]; medium [between 20 and key to economic development, fondly referred to as the “blue econ‐ 100 acres]; small [<20 acres]) and anthropogenic activities (level of omy”. Nevertheless, information on fish and fisheries in Uasin Gishu human disturbance). Other secondary factors were the ownership County is scanty or entirely lacking. Accordingly, the present study status. Kesses Dam and Kerita Dam are communally owned, while was conducted to generate information for preparing sound fisher‐ Chebigut Dam is a privately owned waterbody (Figure 1). Kesses ies production and management plans for long‐term exploitation. It Dam covers an area of about 500 acres, being located around is the intention that the results of the present study will also be use‐ 0°17′0.263″ North, and 35°19′0.852″ East, at an altitude of about ful in aquaculture development. 2,192 m (GPS readings, etrex Garmin model). Kerita Dam is a FIGURE 1 Location of the three study dams in Uasin Gichu County, Kenya GICHURU ET AL. | 183 medium‐sized dam covering an area of about 35 acres and located being thoroughly stirred until an evenly distributed mixture was around 0°19′0.294″ North and 35°24′0.329″ East, at an altitude attained. One millilitre of the mixture was examined under a com‐ of about 2,240 m. Chebigut Dam is a small reservoir, covering an pound microscope. A counter (Sedgewick‐Rafter cell 550) with area of about 10 acres. It is located around 0°33′0.984″ North and one hundred (100) counting cells was used to count individuals 35°22′0.394″ East, at an altitude of about 2,185 m. The distance of each food item. Food items were first classified into families from Kesses Dam to Kerita Dam is about 20 km by road, while and then into their respective genera. Minute food items were Chebigut Dam is about 42 km from Kerita Dam by road (Figure 1). counted in 10–20 randomly picked counting cells, with their mean Sampling was done monthly from December 2011 to April values calculated and multiplied by 100, and the result then being 2012 except for January 2012 because of logistic problems. As multiplied by the dilution factor. For medium to large food items, sampling was done in the dry season when the dam's environ‐ 20–40 randomly picked cells were counted, their mean value ob‐ mental conditions were relatively stable, the failure to sample tained, and then multiplied by 100, and subsequently multiplied in January did not significantly affect the results within and be‐ by the dilution factor. For very large food items, the entire cells tween the months. The dams were divided into three distinct (100) were counted and then multiplied by the dilution factor. For sampling areas, including the inlet, mid‐water and outlet sectors extra large food items (i.e., those that could be seen by a naked of the dams. One‐litre plastic bottles were used to collect water eye), the items were visually identified, except for those not at the subsurface water column in duplicates. Samples were col‐ clearly visible to the eye, for which a dissecting microscope was lected in the littoral and open water regions of the dams. The used to aid identification. Consumed detritus were estimated as samples were immediately preserved in Lugol's iodine solution percentages they could occupy in the fish stomach. and left to settle for 48 hr to allow particulate matter to settle. Principal component analysis (PCA) was used to perform multi‐ The lower water layer (40–100 ml) containing the settled algae variate analysis to identify variables responsible for major variations was decanted into glass vials and stored in a cool, dark room for in the dams. The “Past” programme/package was used to draw the subsequent analysis. The known volume of the concentrated graph highlighting the variations in relation to correlated variables, sample was used to identify and count the phytoplankton, using making it possible to compare water quality between the three dams a compound microscope (model ULTRA SWIFT LITE‐M3200). The and the major variables responsible for variations in the dams. The phytoplankton in the water column was compared to the phyto‐ fish natural food selectivity was calculated using Ivlev's electivity/ plankton in the fish stomachs, with the data used to determine selectivity index (Ivlev, 1961), defined as: the fish food preferences. The fish were caught using gillnets ranging from 2 to 4 inch stretched mesh size. The fish sampling Ei = ri −Pi ∕ ri +Pi (1) method borrowed heavily from the sampling methods recom‐ mended by Sparre and Venema (1992), with nets being set during where ri = relative abundance of a prey in a predator's diet; Pi is the day in duplicates at the inlet, mid‐water and outlet regions prey's relative abundance in the ecosystem; Ei ranges from −1 to and left for two to three hours before removal.