DOUMBIA Lassina et. al. /International Journal of Modern Sciences and Engineering Technology (IJMSET) ISSN 2349-3755; Available at https://www.ijmset.com Volume 1, Issue 8, 2014, pp.36-45 Feeding strategy of two catfish species taxonomically and morphologically similar Schilbe mandibularis (Günther, 1867) and Schilbe intermedius Rüppell, 1832 coexisting in Agnébi River (Côte d’Ivoire) DOUMBIA Lassina1 BAMBA Yacouba2 Université Nangui Abrogoua Université Nangui Abrogoua UFR-Sciences et Gestion de l’Environnement UFR-Sciences et Gestion de l’Environnement Abidjan, République de Côte d’Ivoire Abidjan, République de Côte d’Ivoire [email protected] [email protected] OUATTARA Allassane3 GOURENE Germain4 Université Nangui Abrogoua Université Nangui Abrogoua UFR-Sciences et Gestion de l’Environnement UFR-Sciences et Gestion de l’Environnement Abidjan, République de Côte d’Ivoire Abidjan, République de Côte d’Ivoire [email protected] [email protected] Abstract: Feeding habits of Schilbe mandibularis and Schilbe intermedius in Agnébi River were studied during two years of sampling. The coefficient of emptiness, index of preponderance of Natarajan & Jhingran and that of Schoener helped to analyze and compare the diets of the two species of Schilbe. In terms of diet overall, both species have an omnivore tendency. Food preferences vary from station and also from one season to the other highlighting the opportunism of species studied. Regarding the size of individuals, juveniles and adults feeding behavior varies from one medium to another. The overall nutritional profile of both species indicates the general trend with an emphasis of piscivory in Schilbe intermedius for an eclectic tendency of Schilbe mandibularis. Keywords: Côte d’Ivoire, Agnébi River, Feeding strategy, Schilbeidae, Schilbe mandibularis, Schilbe intermedius. 1. INTRODUCTION: Knowledge of the natural environment fish food is an essential step to understanding their biology and ecology [1]. In addition, the Schilbeidae are one of the groups of freshwater and brackish water fish economically more important worldwide [2]. In Côte d'Ivoire, two species of the genus Schilbe were identified by Sangaré [3] and more recently by Gourène et al. [4]. This is Schilbe intermedius Rüppell, 1832 and Schilbe mandibularis (Günther, 1867) two sympatric species in the area of study that is the Agnébi River. Also, to Vanga [5], these fishes contribute appreciably to the production of inland fisheries landed in Côte d'Ivoire. Indeed, they are popular organoleptically by local residents of the study area [6]. Previous investigations on the diet of this type of fish [3]; [7]; [8]; [9], [10]; [11]; [12] are fragmentary. According to Doumbia [13], two species taxonomically and morphologically similar and occupying the same habitat can interfere with each other in relation to food. The purpose of this study is to verify the sharing of food resources between Schilbe mandibularis and S. intermedius from the general profile and dietary behaviors in different seasons and the various habitats are the three study sites and in the age classes. Two assumptions were made. Due to the opportunism of the species studied, there will be a difference in the composition of stomach contents. It is among the specimens of the juvenils as the most important diet similarity we must observe. 2. MATERIALS AND METHODS: Study site: Figure 1 shows the location of the Agnébi River and sampling stations selected (Gbessé, Pont-auto- route and Armébé).The Agnébi River is located between 5 and 7 degrees north and 4 and 5 ° West longitude latitude [14]. The Gbessé station to the upper is on the Kavi. This tributary of the Agnébi River been drying up during the long dry season. The station Pont auto-route (middle stream) at significant discounts during the long dry season. The water is summarizing a stream of water from a depth less than 30 cm. As for the © IJMSET-Advanced Scientific Research Forum (ASRF), All Rights Reserved “IJMSET promotes research nature, Research nature enriches the world’s future” 36 DOUMBIA Lassina et. al. /International Journal of Modern Sciences and Engineering Technology (IJMSET) ISSN 2349-3755; Available at https://www.ijmset.com Volume 1, Issue 8, 2014, pp.36-45 Armébé station (lower course) is characterized by the permanence of water that is certainly tied to the great depths (7 m on average). Note that the selection of study sites was preceded by a survey of six months. N Figure 1: Location of sampling stations on Agnébi River (based on [4]). Sampling and stomach contents analysis Test fisheries were conducted for 24 months stations deductions Agnébi River. During monthly outings, two batteries mesh nets: 10, 12, 15, 20, 30, 35, 40 and 50 were placed at 17h, visited the next day at 7h am for nights fisheries and re-visited before be raised to 13h for the days of fishing. During the various missions, fish caught were identified according to Lévêque et al. [15] and Gourène et al., [16]. Specimens randomly selected for the study of stomach contents were measured and dissected. Their stomachs were removed, weighed and stored in bottles containing a 5% formalin solution. Of a total of 921 analyzed stomachs, 211 from specimens Schilbe mandibularis and 710 individuals from S. intermedius. Regarding the analysis strictly stomach contents, each stomach was drained on absorbent paper, weighed and carefully opened under a dissecting microscope. After a first selection in this loop that eliminates the stomach contents too degraded by digestive juices, the different fractions of stomach contents deductions were identified, counted and weighed after spin on blotting paper. The data were presented in the form of: - Emptiness coefficient (ec): It allows to assess the feeding activity of the species and to identify their feeding behavior. Indeed, the emptiness ratio is the percentage of empty stomachs on the total number of stomachs examined [17]. Its formula is as follows: ec = number of empty stomachs x 100 © IJMSET-Advanced Scientific Research Forum (ASRF), All Rights Reserved “IJMSET promotes research nature, Research nature enriches the world’s future” 37 DOUMBIA Lassina et. al. /International Journal of Modern Sciences and Engineering Technology (IJMSET) ISSN 2349-3755; Available at https://www.ijmset.com Volume 1, Issue 8, 2014, pp.36-45 Number of stomachs analyzed - Corrected occurrence percentage [17] and [18]: Fc = (Fi / ΣFi) x 100 with Fi = (ni / NT) Fi is the frequency of prey i n is the number of stomachs containing prey i and NT is the total number of full stomachs examined; - Weight percentage [19]: W = Wi / Wt x 100 Where Wi = total weight of prey i and Wt = total weight of all prey. As blended index taking into account the two percentages described above, we chose the index of preponderance of Natarajan and Jhingran [20]. This index was used by Kouamélan et al. [21] in a study of the eating habits of three Mormyridae to Lake Ayame. Its formula is as follows: According to Linton et al. [22], the index of Schoener [23] is the best estimator of food niche overlaps between 7 and 85%. Moreover, the use of this index is recommended by Hurlbert [24]. The degree of dietary overlap was determined using the index Schoener whose formula is as follows: α= 1 – ½ ∑ │Pij - Pik│ Pij = proportion of taxa i in the stomach contents of the species j Pik = proportion of taxa i in the stomach contents of the species k The higher the value of the index of Schoener [23] approach 1 plus the diet overlap is important. Size classes are defined based on the smallest size at first maturity determined by Ouattara [25]. He argues that people regarded as juvenils have a standard length of less than 123 mm (the smallest size at first sexual maturity). All specimens whose standard lengths greater than or equal to 123 mm are adults. The chi-square test which according to Scherrer [26] applies to both frequencies than proportions (percentages) was used to compare the emptiness coefficients between the two species studied [27]. The Spearman rank correlation test (Statistica version 7.1 program) was used to compare the diets according to the variables considered. 3. RESULTS AND DISCUSSION: For a total of 211 stomachs Schilbe mandibularis analyzed, 101 were empty. So the factor of emptiness is 47.87%. In Schilbe intermedius, we worked on 710 and 474 stomachs were empty. This corresponds to a coefficient of emptiness 66.76%. Worth X² = 3.11 to p = 0.05, the coefficients of emptiness do not present significant difference. General diet Table 1 shows the results of analysis of food containing stomachs expressed in index of dominance and classification propose by Rosecchi and Nouanze [17]. The general diet of the species studied has 11 major classes of prey and 11 orders of insects. The index of prey balance indicates the dominance of fish © IJMSET-Advanced Scientific Research Forum (ASRF), All Rights Reserved “IJMSET promotes research nature, Research nature enriches the world’s future” 38 DOUMBIA Lassina et. al. /International Journal of Modern Sciences and Engineering Technology (IJMSET) ISSN 2349-3755; Available at https://www.ijmset.com Volume 1, Issue 8, 2014, pp.36-45 (67.08%) in the diet of Schilbe intermedius. Animals debris (25.17%) are secondary prey. In contrast, in Schilbe mandibularis, fruits (32.25%) and animal debris (28.71%) are the preferred prey. Fishes (24.62%) are secondary prey. As for insects, they occupy a rank of accidental prey with 13.38% in S. mandibularis to 5.88% in S. intermedius. Hymenoptera are the most abundant order as in the regime of S. mandibularis (4.70%) than in S. intermedius (1.78%). The Schoener index of 0.552, indicating a diet overlap between species studied. Similarly, the Spearman rank correlation coefficient reveals similarity of interspecific diet (N = 21; rs = 0.729, p = 0.0001).