Int. J. Aquat. Biol. (2019) 7(6): 332-341 ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.ij-aquaticbiology.com © 2019 Iranian Society of Ichthyology Original Article Demographic parameters and exploitation rate of five key fishes of Okpara Stream, Oueme River, Benin, West Africa Rachad Sidi Imorou1, Alphonse Adite*1, Edmond Sossoukpe2, Kayode Nambil Adjibade1, Hamidou Arame1, Stanislas Pejanos Sonon1 1Laboratory of Ecology and Aquatic Ecosystem Management (LEMEA), Department of Zoology, Faculty of Sciences and Technics, University of Abomey-Calavi, BP 526 Cotonou, Benin. 2Laboratory of Wetland Researches (LRZH), Department of Zoology, Faculty of Sciences and Technics, University of Abomey-Calavi, BP 526 Cotonou, Benin. s Article history: Received 22 September 2019 Accepted 8 December 2019 Available online 2 5 December 2019 Keywords: Growth parameters Exploitation rate Length at first capture Management Recruitment Abstract: The current study was carried out on Okpara Stream in Northern Benin to evaluate the demographic factors with inferences on fisheries status of five dominant fish species, which were sampled monthly intervals for 18 months. Asymptotic length (L∞) ranged from 36.23 cm (Brycinus macrolepidotus) to 18.8 cm (Hemichromis fasciatus). Growth rates (K) varied between 1.6 yr-1 and 0.66 yr-1 with growth performance index (Φ’) ranging from 2.4 to 3.1. Theoretical age at length zero (t0) varied -0.95 year for Marcusenius senegalensis to -0.59 year for Shilbe intermedius. Except for B. macolepidotus, total mortalities were higher than 2 year-1 and length at first capture (L50) ranged 7.72-12.09 cm. Marcusenius senegalensis and S. intermedius showed one annual peak of recruitment, whereas H. fasciatus, Oreochromis niloticus and B. macrolepidotus displayed two peaks. The results indicated that the stocks of these five species were underexploited. However, the low length at first capture (L50) recorded for some species, requires the implementation of early fisheries management scheme to assure a sustainable exploitation of these fishes. Introduction In most regions of the world, fishing is one of the foremost activity for human subsistence because of generating substantial incomes for grassroots (Ekouala, 2013). As reported by FAO (2018), in year 2016, global world fish production reached 171 million metric tons that was estimated at about 362 billion US dollars. In Benin, fisheries appeared to be a key component of rural activities and the fishery’s sector contributed substantially to the national economy. Indeed, total production of inland and marine fisheries reached 42400 tons estimated at about 42,400,000,000 FCFA or 80,761,904 USD (FAO, 2019). Moreover, the increase of the African population in general and that of Benin in particular, has led to a high fishing pressure and to the overexploitation of inland and marine fish resources (Welcomme, 2001). Thus, in addition to the drastic decrease of the fish production in most water bodies, exploitable stocks were dominated by small-sized *Correspondence: Alphonse Adite DOI: https://doi.org/10.22034/ijab.v7i6.642 E-mail: alphonseadite@gmail.com individuals (Dulvy et al., 2003; Mullon et al., 2005; Chikou, 2006; FAO, 2010; Sossoukpe et al., 2013). Therefore, a rational management scheme of the fish stocks is needed to assure the conservation and the sustainable exploitation of the fish resources. In fish population stock, estimating parameters such as asymptotic length (L∞), growth coefficient (K), fishing/natural mortalities (F/M) and exploitation rate (E), are means of conservation and management (Abohwere and Falaye, 2008; Tah et al., 2010). These fish stock management tools are powerful instruments for development policies and decision making in fisheries sector. Data on age and growth are particularly important for describing the status of a fish population and for predicting the potential yield of the fishery. They also facilitate estimation of production, stock size, recruitment and mortality (Lowe-McConnel, 1987). Though several aspects of the fish population dynamic and community structure have been 333 Int. J. Aquat. Biol. (2019) 7(6): 332-341 investigated in many aquatic ecosystems in Benin, little is known about the demographic parameters and exploitation rate of marine and inland fish species. Such studies have been restricted to few species such as Galeoides decadactylus, Sardinela madarensis and Chloroscombrus chrysurus from the marine environment (Sossoukpe et al., 2016a, b; 2017), Sarotherodon melanotheron from Lac toho (Lederoun et al., 2015), S. galileus from Lac Doukon et Lac Togbadji (Lederoun et al., 2016) and Tilapia guineensis, Hemichromis fasciatus, Eleotris vittata, Clarias gariepinus, Chrysichthys auratus, Hepsetus odoe, Parachanna obscura and Heterotis niloticus from Sô River (Hazoume, 2017). Okpara Stream is the main tributary of the Oueme River, and in spite of its fisheries importance and degradation pressures, little is known about the demographic parameters and exploitation rates of its fish stocks. As reported by Sidi Imorou et al. (2019a), Okpara Stream dwelled 53 species belonging to 29 genera and 14 families. Dominant species are Hemichromis fasciatus (29.49%), Marcusenius senegalensis (16.43%), Shilbe intermedius (10.44%), Oreochromis niloticus (8.90%) and Brycinus macrolepidotus (9.23%) aggregating numerically 74.49% of the fish community total relative abundance (Sidi Imorou et al., 2019b). These species display a high commercial, economic and nutritional importance for the grassroots. Therefore, the current study aims to investigate growth rates, mortality coefficients and exploitation rates of the five key fish species, namely H. fasciatus, M. senegalensis, S. intermedius, O. niloticus and B. macrolepidotus of Okpara Stream to gather fisheries documentation that will contribute to ensure successful management of these fishes. Materials and Methods Study area: This study was carried out on Okpara Stream, a tributary of Oueme River (200 Km), located between 8°14'-9°45'N and 2°35'-3°25'E. This riverine water belongs to the Northern hydrographic system and traverses the Borgou Province of Northern Benin and that of Zou in Central Benin. Annual ambient temperature around the stream averaged 26.6°C and the low temperatures were recorded in December and January. The climate is tropical and comprised two seasons: the dry season in November to April and wet season in May to October. The annual pluviometry averaged 1200 mm, peaked at about 1300 mm in July, August and September. The soil is covered by a wooded savanna characterized by the presence of Parkia biglobosa, Khaya senegalensis and Vitellaria paradoxa. Also, the plant community comprised marshy meadows, bamboo and fallow bushes. The Okpara stream is the main source of fish resources for the grassroots and provides water for irrigated agriculture. In addition, a dam was built on the stream to supply the surrounding populations with drinking water. Sampling sites: Five sampling sites were selected (Fig. Figure 1. Location of Okpara’s stream and sampling sites. Site 1= Perere Township, Site 2 = Gadela village (Parakou Township), Site 3= Kpassa village (Tchaourou Township), Site 4= Yarimarou village (Tchaourou Township), and Site 5 = Sui village (Tchaourou Township). 334 Sidi Imorou et al./ Demographic parameters of five fishes from Okpara Stream 1) based on localities, accessibility, fisheries importance and level of site degradations (Sidi Imorou et al., 2019a). Site 1 is situated in Perere town at Okpara up stream and site 2 is located in Parakou town at Gadela village (Okpara up stream) about 2 km from SONEB dam. Site 3 is located at Kpassa village where a dam was built to serve as a source of drinking water for the populations of Tchaourou and Parakou towns and surrounding villages. Site 4 is situated around Okpara downstream at Yarimarou village (Tchaourou town) where the dam withdraws its water. Site 5 is also located around Okpara downstream at Sui village of Tchaourou. At these five sites, samplings were done in the “aquatic vegetation habitat” at the edge of the stream and in the “open water habitat” exempt of vegetation and characterized by a high depth. Fish collection and identification: Fish samplings were done for 18 months by monthly intervals in all habitats at the five sampling sites with experimental gillnet and seine (Sidi Imorou et al., 2019a, b). In addition, fish samplings were directly made in fishermen artisanal captures by taking one third of each fisherman catches. All rare and uncommon species were included in the sample (Okpeicha, 2011). Fishing gears such as gillnets, seines, cast nets, hooks, and traps were used by the fishermen to collect the fishes. After collection, the fish samples were first identified in situ using fish identification references such as Van Thielen et al. (1987), Skelton (1993), and Lévêque and Paugy (2006). The fish assemblages were preserved in a cooler and then transported to the Laboratory of Ecology and Management of Aquatic Ecosystem to confirm the identifications. The valid scientific names of the fish species have been confirmed on Fishbase (Froese and Pauly, 2018). In the laboratory, length of each specimens was measured to the nearest 1 mm with a measuring board, weighted to the nearest 1 g with an electronic scale (Camry) and preserved in 10% formalin and latter in 70% ethanol to make easier other biological observations such stomach content analysis and aspects of reproductive biology (Schreck and Moyle, 1990; Murphy and Willis, 1996). Data analysis: Basic parameters are length-weight relationship (LWR), age-based growth, mortality (Z), exploitation rate (E), and condition factor (K) (Ricker, 1975). Length data were combined monthly and converted into length frequencies with a constant class interval of 2 cm. The mean lengths and weights of classes were used for data analysis using accepted FiSAT’s format (Gayanilo and Pauly, 1997). Growth parameters (L∞, K and t0) and growth performance index (’): Growth parameters are important to determine the stock state. The model of von Bertalanffy (1938) of ELEFAN I program in FiSAT II is the most used in studies of fish’s growth: TL = L∞{1 − exp[−K(t − t0)]} (King, 1995) Where, TL (cm) is the total length of the fish, L∞ (cm) = asymptotic length of fish, L∞ = maximum length that a fish could reach if it lived many years, K (yr-1) = growth coefficient, and t0 (yr) = theoretical age of the fish individual when its length is zero. T0 is determined by the following Pauly’s equation: log10(−t0) = −0.392– 0.275 Log10L∞ − 1.038 Log10K (Pauly, 1979). Where t0 (yr) is the age of the fish at various lengths and calculated by the inverse of von Bertalanffy growth equation. K and L estimates were used to determine the growth performance index (') of the species (Munro and Pauly, 1983; Pauly and Munro, 1984) according to the formula: ’ = Log10K+ 2Log10 L∞ Where ’ is growth performance index. This index is an indicator of fish’s well-being. Mortality parameters: The instantaneous annual rate of total mortality (Z) was evaluated by the construction of linearized curve of length converted into catch (Sparre and Venema, 1992). Instantaneous natural mortality rates (M) were determined by Pauly’s (1980) empirical equation: Log10M = -0.0066 – 0.279 Log10L∞ + 0.6543 Log10K + 0.463 Log10T With T = annual temperature of Okpara stream waters. The fishing mortality (F) rate was determined by the formula: F = Z-M Probability of capture (L50), longevity (Tmax) and epxloitation rate (E): Estimates of length at first 335 Int. J. Aquat. Biol. (2019) 7(6): 332-341 capture (L50) were derived from capture probabilities generated by FiSAT’s capture curve analysis. The estimate of the average growth coefficient K was used to generate longevity as follows: Tmax = 3/K (Anato, 1999). The exploitation rate (E) was calculated by FiSAT from the linearized curve of length converted to capture curve of each species: E = F/Z, with F = fishing mortality and Z = annual total mortality. This value gives a rough estimate of whether the stock is overexploited or not (Pauly, 1983). When E>0.5, the stock is overexploited. When E is approximately equal to 0.5, the yield is optimized and F is approximately equal to M (Gulland, 1971). Results Growth parameters: Growth parameters are shown in Table 1. The asymptotic length, L∞ ranged 18.8 (H. fasciatus) to 36.23 cm (B. macrolepidotus). The values of growth rates (K) varied between 0.66 yr-1 for S. intermedius and 1.6 yr-1 for M. senegalensis. Growth performance index (') ranged 2.4 for H. fasciatus and 3.1 for O. niloticus. The theoretical age at length zero (t0) varied -0.95 (M. senegalensis) to -0.59 year (S. intermedius). Longevity, instantaneous mortality and exploitation rates: The length converted catch curves (Fig. 2) generated the value of total mortality (Z), natural mortality (M), fishing mortality (F) and exploitation rate that are presented in Table 2. For most species (4/5), Z were higher than 2 year-1 excepted for B. macolepidotus (1.79 yr-1) and the higher value of Z is 3.65 yr-1 for M. senegalensis. The natural mortality ranged from 2.786 (M. senegalensis) to 1.441 yr-1 (S. intermedius), and the fishing mortality (F) ranged 1.50 yr-1 for H. fasciatus and 0.36 yr-1 for O. niloticus. The exploitation rates ranged 0.44 for H. fasciatus to 0.16 for O. niloticus. These rates were weak compared to the optimum (E = 0.5) when fishing mortality is equal to natural mortality (F = M) (Pauly and Munro, 1984). The values of longevity were relatively high Table 1. Growth parameters of von Bertalanffy function output by FiSAT of exploited fishes in Okpara Stream (Oueme River, North-Benin) in comparison to populations from other African waters. Species Locality Country L∞ (cm) K (yr-1) t0 (yr) ' References B. macrolepidotus Okpara stream Benin 36.23 0.73 -0.68 2.98 Current study Lake Ayame I Cote d’Ivoire 32 0.46 - 2.67 Tah et al. (2010) H. fasciatus Okpara stream Benin 18.8 0.88 -0.67 2.40 Current study Lake Nokoue Benin 16.75 1 - 2.45 Niyonkuru (2007) So stream Benin 18.38 0.96 -0.48 2.51 Hazoume (2018) Lake Ayame I Cote d’Ivoire 27 0.57 - 2.62 Tah et al. (2010) Ebrie Cote d’Ivoire 25 0.85 - - Villanueva (2004) M. senegalensis Okpara stream Benin 18.90 1.6 -0.95 2.76 Current study O. niloticus Okpara stream Benin 35.18 1.2 -0.90 3.1 Current study Lake Ayame I Cote d’Ivoire 35.5 0.48 - 2.78 Tah et al. (2010) Lake Victoria Kenya 61.3 0.35 - - Getabu (1992) Tanguiga Reservoir Burkina Faso 17.6 0.46 - 2.15 Bajot and Moreau (1997) S. intermedius Okpara stream Benin 25.2 0.66 -0.59 2.62 Current study Lake Nokoue Benin 26 0.7 - 2.67 Niyonkuru (2007) Table 2. Longevity, mortality and exploitation rate of the five key fishes of Okpara Stream (Oueme River, North-Benin). Species Tmax (yr) Z (yr-1) M (yr-1) F (yr-1) E Z/K L50 (cm) L50/L∞ B. macrolepidotus 4.11 1.79 1.39 0.4 0.22 2.45 7.90 0.22 H. fasciatus 3.41 3.45 1.95 1.50 0.44 3.92 8.78 0.47 M. senegalensis 1.88 3.65 2.786 0.86 0.24 2.28 10.54 0.56 O. niloticus 2.50 2.30 1.941 0.36 0.16 1.92 7.72 0.22 S. intermedius 4.55 2.13 1.441 0.69 0.32 3.23 12.09 0.48 Tmax = Longevity, Z= total mortality, M=natural mortality, F=fishing mortality, E=exploitation rates, L50=Length at first capture, K=growth coefficient, L∞= asymptotic length. 336 Sidi Imorou et al./ Demographic parameters of five fishes from Okpara Stream and the highest was found for S. intermedius (Tmax = 4.55 year) and the lowest value was found for M. senegalensis (Tmax = 1.88 year). The ratio between Z and K was superior to 1 for the five species and ranged from 1.92 (O. niloticus) to 3.92 (H. fasciatus) (Table 2). With regards to the ratio between L50 and L∞, the lowest value was recorded for B. macrolepidotus and O. niloticus (L50/L∞ = 0.22) and the highest value was recorded for M. senegalensis (L50/L∞ = 0.56) (Table 2). Length at first capture and recruitment: The length at first capture (L50) is the estimate length of fishes at 50% probability of capture (Fig. 3). In this study, the highest L50 was recorded for S. intermedius (12.09 cm) and the lowest one for O. niloticus (7.72 cm) (Table 2). The recruitment structure (Fig. 4) of fishes showed one annual peak of recruitment for M. senegalensis and S. intermedius. Species like H. fasciatus, O. niloticus and B. macrolepidotus showed two peaks of recruitment in a year (Fig. 4). Discussions The asymptotic length (L∞ = 18.8 cm) value recorded for H. fasciatus, the dominant species, agreed with that reported by Hazoume (2017) in the Sô River (18.38 cm) in Benin. However, these values of L∞ were lower than those reported by Villanueva (2004) in Ebrie Lagoon (25 cm) and by Tah et al. (2010) in Lake Ayame I (27 cm) in Ivory Coast. Also, the value recorded for O. niloticus (35.18 cm) in this study agreed with that reported by Tah et al. (2010) in Lake Ayame I (35.5 cm) of Ivory Coast. In contrast, O. niloticus showed higher L∞ = 64.6 cm in Lake Victoria in Kenya (Getabu, 1992) while S. intermedius exhibited an asymptotic length (25.2 cm) nearly identical to that reported by Niyonkuru (2007) in Lake Nokoue (26 cm) in Benin. In this study, the growth rates (K) between 1.6 and 0.66 yr-1 recorded for these key species were higher than those reported by Tah et al. (2010) in Lake Ayame, by Villanueva (2004) in Ebrie Lagoon, by Getabu (1992) in Lake Victoria and by Bajot and Moreau (1997) in Tanguiga Reservoir of Burkina Faso. Nevertheless, in the current study, H. fasciatus displayed a lower growth rate (0.88) compared to those of Lake Nokoue (1.0) and Sô River (0.96). This A B C D E Figure 2. Length converted catch curves of dominant fishes of Okpara Stream (Oueme River, North-Benin): A = Hemichromis fasciatus; B =Marcusenisius senegalensis; C = Schilbe intermedius; D = Oreochromis niloticus; E = Brycinus macrolepidotus. 337 Int. J. Aquat. Biol. (2019) 7(6): 332-341 could be explained by the fact that in transitory ecosystems such as coastal lagoons (Lake Nokoue, brackish sites of Sô River), fishes quickly reach their maximum size with shorter life span than those living in freshwaters (Longhurst and Pauly, 1987; Tah et al., 2010). In addition, the high abundance of H. fasciatus in Okpara River could cause intraspecific food competition, reducing the growth rate of this top- A B C D E Figure 3. Probability of capture and length of first capture of fishes in Okpara stream (Oueme River, North-Benin): A = Hemichromis fasciatus; B =Marcusenisius senegalensis; C = Schilbe intermedius; D = Oreochromis niloticus; E = Brycinus macrolepidotus. A B C D E Figure 4. Recruitment patterns of dominant fishes in Okpara Stream (Oueme River, North-Benin): A = Hemichromis fasciatus; B =Marcusenisius senegalensis; C = Schilbe intermedius; D = Oreochromis niloticus; E = Brycinus macrolepidotus. 338 Sidi Imorou et al./ Demographic parameters of five fishes from Okpara Stream carnivorous species. The growth performance index (') ranged between 2.40 (H. fasciatus) and 3.1 (O. niloticus). The ' fall within 2.65<'<3.32, the range of ' values reported by Baijot and Moreau (1997) for slow-growing fish species. The ecosystem disturbances factors could have negatively affected the well-being of the fishes and leading to reduced growth performances. Most of these degradation factors of Okpara Stream were the dumping of domestic garbage, the withdrawal of water by SONEB, a Benin Water Company, the withdrawal of water for irrigation, the use of chemical fertilizers/pesticides for agriculture, the introduction of invasive exotic fishes such the O. niloticus and the proliferation of water hyacinth, an invasive floating plant. The average value of ' recorded in this study agreed with to those reported by Hazoume (2017) in Sô River in Benin and by Adeyemi et al. (2009) in Gbedikere Lake in Nigeria exhibiting average growth performances ' = 2.75 ± 0.41 and ' = 2.79 ± 0.19, respectively. However, the current value of ' in Okpara Stream was lower than those reported by Ahouansou Montcho et al. (2011) in Pendjari River in Benin and by Du Feu (2003) in Kainji Lake where ' values averaged 3.22 ± 0.31 and 3.19 ± 0.31, respectively. Inversely, Niyonkuru (2007) found an average value of ' = 2.58 ± 0.19, lower than that recorded in this study. These differences could be mainly attributed to environmental conditions and food availability. Overall, fish longevity (Tmax) ranged between 1.88 yr (M. senegalensis) and 4.55 yr (S. intermedius). These values were lower than those reported by Hazoume (2017) on Sô River where Tmax was higher and reached 11.66 yr, probably because the Sô River floodplains stand as breeding and nursery/growing grounds for several fish species. In Okpara Stream, natural mortality (M) of fishes was higher than those of the Sô River by Hazoume (2017). These results imply that as natural mortalities (M) of fishes increase, longevities (Tmax) decrease. In the current investigation, for all species, natural mortalities (M) were greater than fishing mortalities (F) and the exploitation rates (E) were lower than 0.5. As results, stocks of B. macrolepidotus, H. fasciatus, M. senegalensis, O. niloticus and S. intermedius were underexploited in Okpara Stream (Tah et al., 2010). Villanueva (2004) and Tah et al. (2010) came up with the same observation and trends in some West African lagoons/estuaries such as Lake Ayame I of Ivory Coast. Nevertheless, in the current study, for each species, the ratio of total mortality (Z) to K is greater than 1, leading to a situation where mortalities dominated growth (Barry and Tegner, 1989). With regards to length at first capture (L50), species such as B. macrolepidotus and O. niloticus had L50 of 7.9 and 7.72 cm, respectively. These values were lower than those reported by Tah et al. (2010) in Lake Ayame I, L50 = 11.57 and L50 = 14.03 cm for B. macrolepidotus and O. niloticus, respectively. Recruitment are occurred throughout the year with two peaks per year for the majority of species (H. fasciatus, O. niloticus and B. macrolepidotus), indicating two main periods of spawning. This observation agreed with the findings of many African fisheries biologists (Pauly, 1982; Welcomme and De Merona 1988; Ahouansou Montcho et al., 2011) who found that tropical fish species reproduced twice a year, and mainly during the wet season. In the current study, all the five fish species displayed some exploitation rates (E = F/Z) ranging between 0.16- 0.44, less than 0.5, suggesting that the stocks of these fishes in Okpara Stream were underexploited (Pauly and Moreau, 1997). Conclusion The relatively high growth rates (K) and growth performance index (') displayed by B. macro- lepidotus, M. senegalensis, H. fasciatus, O. niloticus and S. intermedius indicated that these fish species showed a good adaptation to ecological condition of Okpara Stream. Also, the low exploitation rates (K) indicated that the stocks of these fishes in Okpara Stream were underexploited. Nevertheless, the low length at first capture (L50) of some fishes such O. niloticus, B. macrolepidotus and H. fasciatus is harmful for the survival, the conservation and the 339 Int. J. Aquat. Biol. (2019) 7(6): 332-341 sustainable exploitation of these species. Early fisheries management scheme should be implemented to guaranty the “ecological health” of the fish community and its sustainable exploitation. References Abohweyere P.O., Falaye E.A. (2008). Population parameters of Macrobrachium vollenhovenii in the Lagos–Lekki Lagoon System. Nigeria Journal of Fisheries International, 3: 27-33. Adeyemi S.O., Bankole N.O., Adikwu I.A., Akombu P.M. (2009). Age, growth and mortality of some commercially important fish species in Gbedikere Lake, Kogi State Nigeria. International Journal of Lakes and Rivers, 2(1): 45-51. Ahouansou Montcho S., Chikou A., Lalèyè P.A., Linsenmair K.E. (2011). Population structure and reproductive biology of Schilbe intermedius (Teleostei: Schilbeidae) in the Pendjari River, Benin. African Journal of Aquatic Science, 36(2): 139-145. Anato C.B. (1999). Les Sparidae des côtes béninoises: milieu de vie, pêche, présentation des espèces et biologie de Dentex angolensis Poll et Maul, 1953. Thèse de Doctorat d’État es Sciences, Faculte des Sciences 1060 Tunis, Tunisie. 277 p. Baijot E., Moreau J. (1997). Biology and demographic status of the main fish species in the reservoirs of Burkina Faso. In: E. Baijot, J. Moreau, S. Bouda (Eds). Hydrological Aspects of Fisheries in Small Reservoirs in Sahel Region. Technical Centre for Agricultural and Rural Cooperation, Commission of the European Communities, Wageningen, Netherlands. pp: 79-109. Barry J.P., Tegner M.J. (1989). Inferring demographic processes from size-frequency distributions: simple models indicate specific patterns of growth and mortality. Fishery Bulletin, 88: 13-19. Chikou A. (2006). Étude de la démographie et de l’exploitation halieutique de six espèces de poissons- chats (Teleostei, Sliluriformes) dans le delta de l’Ouémé au Bénin. Thèse doctorat en science, Université de Liège, Belgique. Du Feu T. (2003). Gaining a quick overview of the Lake Kainji Fishery, Nigeria: the use of length frequency data. In : M.L.D. Palomares, B. Samb, T. Diouf, J.M. Vakily and D. Pauly (eds.). Fish biodiversity: local studies as basis for global inferences. ACP-EU Fisheries Research Report, 14. 281 p. Dulvy N-K., Sadovy Y., Reynolds J-D. (2003). Extinction vulnerability in marine Populations; Fish and Fisheries, 4: 25-64. Ekouala L. (2013). Le développement durable et le secteur des pêches et de l'aquaculture au Gabon: une étude de la gestion durable des ressources halieutiques et de leur écosystème dans les provinces de l’estuaire et de l’ogooué maritime. Thèse pour l’obtention du titre de docteur en géographie Université du Littoral côte d’opale école doctorale sesam (e.d n°73) laboratoire T.V.E.S (e.a n°4477). 408 p. FAO (2010). La situation mondiale des pêches et de l’aquaculture, département des pêches et de l’aquaculture, Rome. 244 p. FAO (2018). The State of World Fisheries and Aquaculture 2018 - Meeting the sustainable development goals. Rome. Licence: CC BY-NC-SA 3.0 IGO. http://www.fao.org/fishery/facp/BEN/en#CountrySect or-Statistics. Froese R., Pauly D. (2018). FishBase. World Wide Web electronic publication. www.fishbase.org, Editors version (06/2018). Gayanilo F.C., Pauly D. (1997). The FAO ICLARM Stock Assessment Tools (FISAT) reference manual. FAO Computer Information Series. Getabu A. (1992). Growth parameters and total mortality in Oreochromis niloticus (L) from Nyanza Gulf, Lake Victoria. Hydrobiologia, 232: 91-97. Gulland J.A. (1971). The fish resources of the ocean West Polyfleet, survey Fishing News (books) Ltd. FAO Technical Paper, 97. 428 p. Hazoume R.U.S. (2017). Diversité, organisation trophique et exploitation des poissons de la rivière Sô au Benin (Afrique de l’Ouest). Thèse de doctorat de l’Université d’Abomey-Calavi, Benin. 162 p. Lederoun D., Chikou A., Vreven E. Snoeks J., Moreau J., Vandewalle P., Lalèyè P. (2015). Population parameters and exploitation rate of Sarotherodon melanotheron melanotheron rüppell, 1852 (Cichlidae) in Lake Toho, Benin. Journal of Biodiversity and Environmental Sciences, 6(2): 259-271. Lederoun D., Lalèyè P., Vreven E., Vandewalle P. (2016). Length-weight and length- length relationships and condition factors of 30 actinopterygian fish from the Mono basin (Benin and Togo, West Africa). Cybium, 40: 267-274. Lévêque C., Paugy D. (2006). Distribution géographique et affinités des poissons d’eau douce africains. In: C. 340 Sidi Imorou et al./ Demographic parameters of five fishes from Okpara Stream Lévêque, D. Paugy (ed.). Les poissons des eaux continentales. Diversité, écologie, utilisation par l’homme, Éditions IRD, Paris. 521 p. Longhurst A.R., Pauly D. (1987). Ecology of Tropical Oceans. Academic Press, San Diego, CA. 406 p. Lowe-McConnel R.H. (1987). Ecological studies in tropical fish Communities, Cambridge University Press, London. 73 p. Mullon C., Fréon P., Cury P. (2005). The dynamics of collapse in world fisheries. Fish and fisheries, 6: 111- 120. Munro J.J., Pauly D. (1983). A simple method for comparing the growth of fishes and invertebrates. Fishbyte, 1(1): 5-6. Murphy B.R., Willis D.W. (1996). Fisheries Techniques. Second Edition. American Fisheries Society, Bethesa, Maryland. Niyonkuru C. (2007). Étude comparée de l’exploitation et de la démographie des poissons Cichlidés dans les lacs Nokoué et Ahémé au Bénin. Thèse de Doctorat en Gestion de l’Environnement, Université d’Abomey- Calavi, Bénin. 199 p. Okpeicha S.O. (2011). Biodiversité et exploitation des poissons du barrage de la SUCOBE dans la commune de Savè au Bénin. Master en hydrobiologie, Faculté des Sciences Techniques, Université d’Abomey-Calavi. Pauly D. (1979). Theory and management of tropical multispecies stocks: A review, with emphasis on the Southeast Asian demersal fisheries. ICLARM Studies and Reviews. International Center for Living Aquatic Resources Management, Manila. No. 1. 35 p. Pauly D. (1980). On the interrelations between natural mortality, growth parameters and mean environmental temperature in 175 fish stock. Journal du Conseil International pour l’Exploration de la Mer, 39(2): 175- 192. Pauly D. (1982). Studying single-species dynamics in a tropical multispecies context. In: D. Pauly, G.I. Murphy (Eds). Theory and Management of Tropical Fisheries. ICLARM Conference Proceedings, 9: 33-70. Pauly D. (1983). Some Simple methods for the assessment of tropical fish Stock. FAO Fisheries Technical Paper No. 234. 52 p. Pauly D., Moreau J. (1997). Méthodes pour l'évaluation des ressources halieutiques. Cépaduès Editions: Toulouse. 288 p. Pauly D., Munro J.L. (1984). Once more on the comparison of growth in fishes and invertebrates. Fishbyte, 2: 21- 22. Ricker W.E. (1975). Computer and interpretation of biological statistics of fish population. Bulletin of Fisheries Research Board of Canada, 315-318. Schreck C.B., Moyle P.B. (1990). Methods for Fish Biology. American Fisheries Society, Bethesa, Maryland. Sidi Imorou R., Adite A., Arame H., Chikou A., Adjibade N.K., Sonon P.S. (2019a). Ichthyofauna of Okpara Stream, a Tributary of Oueme River, Benin, West- Africa. International Journal of Sciences, 8(5): 53-66. Sidi Imorou R., Adite A., Adjibade N.K., Arame H., Sonon P.S., Abou Y. (2019b). Fish biodiversity and community structure of Okpara stream, Oueme River, Benin, West Africa: Risk of high predation and food- web alteration. Journal of Biodiversity and Environmental Sciences, 1-18. Skelton P.H.A. (1993). Complete Guide to the Freshwater Fishes of Southern Africa. Southern Book Publishers. Sossoukpe E., Aissan N.A. Adite A., Fiogbe E.D. (2017). Diagnosis, Growth and Exploitation Rate of the Sapater (Chloroscombrus chrysurus, Linnaeus 1766) Fishing by Purse Seine in the Nearshore Waters of Benin. International Journal of Advanced Fisheries and Aquatic Science, 3(1): 73-89. Sossoukpe E., Nunoo F.K.E., Ofori-Danson P.K., Fiogbe E.D., Dankwa H.R. (2013). Growth and mortality parameters of P. senegalensis and P. typus (Sciaenidae) in nearshore waters of Benin (West Africa) and their implications for management and conservation. Fisheries Research, 137: 71-80. Sossoukpe E., Djidohokpin G., Fiogbe E.D. (2016a). Demographic parameters and exploitation rate of Sardinella maderensis (Pisces: Lowe 1838) in the nearshore waters of Benin (West Africa) and their implication for management and conservation. International Journal Fisheries and Aquatic Studies, 4: 165-171. Sossoukpe E., Sidi Imorou R., Adite A., Fiogbe E.D. (2016b). Growth, Mortality and Exploitation of the African Lesser Threadfin Galeoides decadactylus (Pisces, Polynemidae) Fishing by the Gill Net "Soovi" in Benin Nearshore Waters. Journal of FisheriesSciences.com, 10(3): 31-37. Sparre P., Venema S.C. (1992). Introduction to tropical fish stock assessment. Part 1. Manual, FAO Fisheries Technical paper, 306. No 1, Review 1, FAO Rome. 376 p. 341 Int. J. Aquat. Biol. (2019) 7(6): 332-341 Tah L., Joanny T. G., Douba V.N, Kouassi J. N., Moreau J. (2010). Preliminary estimates of the population parameters of major fish species in Lake Ayame I (Bia basin; Cote d’Ivoire). Journal of Applied Ichthyology, 26: 57-63. Van Thielen R., Hounkpe C., Agon G., Dagba L. (1987). Guide de détermination des Poissons et Crustacés des Lagunes et Lacs du Bas-Bénin. Direction des Pêches, Cotonou. Villanueva M.C.S. (2004). Biodiversité et relations trophiques dans quelques milieux estuariens et lagunaires de l’Afrique de l’Ouest: Adaptation aux pressions environnementales. Thèse de doctorat, I.N.P. École Nationale Supérieure Agronomique de Toulouse, France. 224 p. Von Bertalanffy L. (1938). A quantitative theory of organic growth. Human Biology, 10: 181-213. Welcomme R.I., De Merona B. (1988). Fish communities of rivers. In: C. Leveque, M.N. Bruton, G.W. Ssentongo (Eds). Biology and ecology of African freshwater fishes. ORSTOM, Paris. pp: 251-272. Welcomme R.L. (2001). Inland Fisheries. Ecology and Management. FAO and Fishing News Books, Blackwell Science Ltd, Oxford. 358 p.