Vol. 6(4), pp. 46-54,April, 2014 DOI: 10.5897/IJFA2013.0397 Article Number:DF9115E44221 International Journal of Fisheries and ISSN 2006-9839 Copyright ©2014 Aquaculture Author(s) retain the copyright of this article http://www.academicjournals.org/ijfa Full Length Research Paper Diet composition, ontogenetic dietary shifts and morphometric relationships of the Nile barb Barbus bynni (Forsskål, 1775) (Pisces: Cyprinidae) in Lake Abaya, Ethiopia Elias Dadebo 1*, Seble Bancha 2, Abinet Wolde-Senbet 2 and Yosef Teklegiorgis 3 1Department of Biology, Hawassa University, P. O. Box 5, Hawassa, Ethiopia. 2Department of Biology, Wolaita Sodo University, P. O. Box 138, Wolaita Sodo, Ethiopia. 3Department of Animal and Range Sciences, Hawassa University, P. O. Box 336, Hawassa, Ethiopia. Received 7 November, 2013; Accepted 7 April, 2014 Food and feeding habits of Barbus bynni (Forsskål, 1775) were studied in Lake Abaya, Ethiopia, from January to February, 2010 (dry season) and May to June, 2010 (wet season). From a total of 292 fish samples, 251 (86.0%) contained food in their guts. Macrophytes, insects and detritus were the dominant food categories both during the dry and wet seasons. Macrophytes and detritus occurred in 78.1 and 73.3% of the guts, and constituted 30.4 and 29.3% of the total food volume, respectively while insects occurred in 72.5% of the guts and accounted for 29.2% of the total volume. Zooplankton occurred in 37.5% of the guts but they constituted only 4.6% of the total volume of food categories. No seasonality in diet was observed, however, there was an ontogenetic change in diet. In juveniles, the contribution of food of animal origin was relatively high, whereas in adults the contribution of plant materials was dominating. The relationships between total length (TL) and total weight (TW) of males, females and both sexes combined were curvilinear and statistically significant (P < 0.001). The relationships between TL and fork length (FL), TL and standard length (SL) and FL and SL were all linear and statistically significant (P < 0.001). The growth pattern of B. bynni in Lake Abaya was allometric because the slope of the relationship (b) was 3.25, which is a value considerably higher than 3. Key words: Barbus bynni , diet composition, feeding habits, Lake Abaya, morphometric relationships. INTRODUCTION The Nile barb Barbus bynni (Forsskål, 1775) is a the Nile (Golubtsov and Krysanov, 1993; Bailey, 1994). In benthopelagic freshwater fish widely distributed in the Ethiopia, the species is widely distributed in the Southern Nile system and in lakes that were once connected to Rift Valley Lakes, Abaya and Chamo, the *Corresponding author. E-mail: [email protected] Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Dadebo et al. 47 Figure 1. Map of Africa with horn of Africa region highlighted (a), map of Ethiopia with the southern rift valley lakes area indicated (b), maps of Lakes Abaya and Chamo with the sampling area in Lake Abaya shown (c). Omo River and the rivers that drain into the Nile system and 2) to provide basic information on morphometric (Golubtsov et al., 1995; Getahun, 2007; Golubtsov and relationships of this species in Lake Abaya. Habteselassie, 2010). African barbs belong to the genus Barbus and are divided into small and large barbs. The division is MATERIALS AND METHODS supported by cytogenetics, the smaller barbs having 50 chromosomes while the large barbs have 150 (Berrebi Study area and Valiushok, 1998). B. bynni belongs to the large Barbus group sensu (Banister, 1973). Lake Abaya (Latitude: 5°30’ - 6°30’ N and Longitude: 36°30’ - 38°30’E) is the largest Ethiopian Rift Valley Lake located in the Although B. bynni is commercially important in Lake southern part of the Ethiopian Rift Valley, east of the Guge Abaya, no study has been conducted on the biology and Mountains, at an elevation of 1,285 m (Figure 1). The Bilate River ecology of the species. No published information is that rises from the southern slope of the Gurage Mountains is the available on the food and feeding habits and major influent of the lake (Baxter, 2002). The town of Arbaminch morphometric relationships of B. bynni in African water lies on its southwestern shore. The lake has a maximum length of 60 km, width of 20 km, and a catchment area of 17,300 km 2 bodies in general and in Lake Abaya in particular. (Tudorancea et al., 1999). The surface area of the lake is 1,162 The aim of this work was, therefore, 1) to investigate km 2, with a maximum depth of 13 m (Baxter, 2002). the food and feeding habits of B. bynni in Lake Abaya, There are a number of islands in this lake, the largest being Aruro; 48 Int. J. Fish. Aquac others include Gidicho, Welege, Galmaka, and Alkal. The lake is Volumetric analysis reddish in color due to high load of suspended clay particles. Lake Abaya does not always have an outflow, but in some years, it Food items that were found in the guts were sorted into different overflows into Lake Chamo. Nech Sar National Park, known for its food categories, and the water displaced by a group of items in wild life and bird life surrounds the lake, which is also fished by each category was measured in a partially filled graduated cylinder local people. The ichthyo-fauna of Lake Abaya, and also that of the (Bowen, 1983). The volume of water displaced by each category of neighbouring Lake Chamo, is Soudanian species (Beadle, 1981). food item was expressed as a percentage of the total volume of the The fish species are more diverse than that of the other rift valley gut contents (Bowen, 1983). The importance of different food lakes of the country probably due to a previous inter-connection of categories was determined by categorizing the TL of the fish into Lakes Abaya, Chamo, Chew Bahir and Turkana with the Nile four size classes (I: 10.0 to 19.9 cm, II: 20.0 to 29.9 cm, III: 30.0 to system (Beadle, 1981). There are 21 fish species found in Lakes 39.9 cm and IV: 40.0 to 49.9 cm) and the total volume of food in Abaya and Chamo and the inflowing rivers (Golubtsov and each size class was determined. The volumetric contribution of Habteselassie, 2010). The commercially important species are each of food category was then expressed as a percentage of the Oreochromis niloticus (Linnaeus, 1758), Labeo horie (Heckel, total volume of food consumed in each size class. 1847), Bagrus docmak (Forsskål, 1775), Clarias gariepinus (Burchell, 1802) and Lates niloticus (Linnaeus, 1758). According to Tudorancea et al. (1999), the lake has a secchi disc Statistical analysis depth of 19 cm and a pH of 8.7 with conductivity (K25 ) of 800 µS/cm. The area in which the lake lies is mainly volcanic in origin Chi-square test was used to compare frequency of occurrences of while the waters of the lake are permanently turbid due to heavy the different food categories during the dry and wet seasons (Sokal colloidal suspension of ferric oxide and the high turbidity of the lake and Rohlf, 1995). Similarly, the non-parametric Mann-Whitney’s U greatly reduces primary productivity and fish production (Schröder, test was used to compare the volume of the different food 1984). categories consumed during the dry and wet seasons since the data did not satisfy the assumption of equal variance to employ a parametric test. Fish sampling and measurements Dietary overlap between different length-classes was calculated using Schoener Diet Overlap Index (SDOI) (Schoener, 1970; Sampling was done four times, twice during the dry season Wallace, 1981): (January and February) and twice during wet season (May and June). In the shallow littoral area, a beach seine (25 m long and 3 α m wide with a mesh size of 0.6 cm) was used for sampling, while = 1-0.5 (1) Nordic survey multi-mesh monofilament nylon gillnets (Appelberg et al., 1995) were used in the pelagic area of the lake (Figure 1). The Where α is percentage overlap, SDOI, between length classes x multi-mesh gillnets consisted of twelve randomly distributed panels and y, pxi and pyi are proportions of food category (type) i used by of the mesh sizes 5, 6.25, 8, 10, 12.5, 15.5, 19.5, 25, 29, 35, 43, x and y, and n is the total number of food categories. Overlap in the and 53 mm (bar mesh). Each panel was 2.5 m long, and hence the index is generally considered to be biologically significant when α total length (TL) of each net was 30 m. The nets were 1.5 m deep value exceeds 0.60 (Mathur, 1977). 2 with a total area of 45 m . The depth of the water where the gillnets were set ranged between 3 to 5 m about 1.5 km inward from the littoral sampling station. They were set around 7.00 am and pulled Morphometric relationships around 3.00 pm. A total of 292 fish were collected. Fish were then removed from the gillnets shortly after landing. The TL, fork length Length-weight relationship was calculated using the following (FL) and standard length (SL) were measured to the nearest mm, formula: while total weight (TW) was measured to the nearest gram. b TW = aTL (2) Food and feeding Where TW is total weight (g), TL is total length (cm), and a and b Since B. bynni has no distinct stomach, contents of the entire gut are intercept and slope of the length-weight regression equation, were taken and preserved in 5% formalin immediately after respectively.