Abundance, length weight relationships and Fulton's condition factor of the freshwater cichlid Sarotherodon galilaeus (Pisces: Teleostei: Perciformes) from a sand dragged man made lake of Southern Benin, West Africa
Condition factors and growth trends indices such as allometry coefficients are decisive fisheries management tools that evaluate the well being of fishes, their establishment and the quality of their habitat. We investigated the condition factors and length weight relationships of a freshwater tilapine cichlid, Sarotherodon galilaeus, that has naturally colonized the artificial lake of Ahozon (South Benin) S. galilaeus individuals has been sampled every month in the "aquatic vegetation" and in the "open water" habitats with seines, cast nets, gill nets and hooks. This species dominated Lake Ahozon and made about 85.21% of the fish community. Fish sizes showed significant spatial (F1,5548=57106.9, p=0.0001) and seasonal (F2,5547=82,06, p=0.0001) variations and smaller sizes (18.65+ 5.76mm SL) were recorded in the "aquatic vegetation" considered as the spawning ground for S. galilaeus. In Lake Ahozon, length weight regression equations gave slopes b ranging between 2.636 and 3.081 indicating that S. galilaeus exhibited both allometric and isometric growth. Also, the species exhibited spatial (F1,5548=94.510, p=0.0001) seasonal (F2,5547=7.163, p=0.001) ontogenetic (F2,5547=63.591, p=0.0001) and sexual (F1,3781=8.275, p=0.001) variations of condition factors (K) that mostly depend on the availability of food resources. The prominence of the species and its condition factors indicated that S. galilaeus is wellestablishment in Lake Ahozon. The improvement of growth performance and well being for a sustainable fisheries/aquaculture in Lake Ahozon require the protection of the foraging and spawning grounds, the prevention against organic and chemical pollution, the introduction of predators to prevent overpopulation of S. galilaeus, the fertilization of the lake and a planned harvest of the fish stock. *Corresponding Author: Alphonse Adite alphonseadite@gmail.com Journal of Biodiversity and Environmental Sciences (JBES) ISSN: 2220 6663 (Print) 2222 3045 (Online) Vol. 8, No. 5, p. 75 87, 2016 http:/www.innspub.net J. Bio. Env. Sci. 2016 76 Gbaguidi et al. Introduction The freshwater cichlid, Sarotherodon galilaeus (Pisces: Teleostei: Perciformes) is a worldwide SubSaharan African tilapine species that occurs in the Nile Basin, Niger River, Senegal and Casamance rivers of the Senegal Republic, Gambia River, Geba River in Guinea Bissau, Konkoure River in Guinea Conakry, Oubangui River in Central Africa, Ogun, Cross, Benoue, Logone and Chari rivers in Nigeria (Fryer and Iles, 1972; Lowe McConnell, 1987; Leveque et al. 1992; Leveque, 1997; Snoeks, 2000) Also, this species inhabits lakes Mobutu,Turkana in the Democratic Republic of Congo (RDC) Lake Tchad, and in many water bodies of Benin (Leveque et al. 1992) S. galilaeus (Linne, 1758) species belongs to the family Cichlidae, Percoidei Sub order, Perciformes Order, Acanthopterygii Super Order and Actinopterygii Subclass. This species exhibits a grew silvery color on the fins and sides and juveniles show some black vertical lines on the sides (Leveque et al. 1992; Leveque, 1997) About body ratio, the head length is 32.5 39.0% the standard length, body height is 43.0 56.5 the standard length and pectoral length is 36.0 50.0% the standard length. In Benin, S. galilaeus occurs in rivers Mono, Oueme, Niger, So and in natural Lakes such as TohoTodougba, Ahouangan, Toho, Hlan, Azilli, Doukon and the coastal lagoon (Leveque et al. 1992; Van Thielen et al. 1987; Adite and Van Thielen, 1995; Adite and Winemiller, 1997) Particularly, in TohoTodougba Lagoon (SouthBenin) of the total annual fish catches estimated at 387 metric tons, about 73% (283 metric tons) was S. galilaeus, making this species the most valuable commercial fish resources in this water body (Adite and Winemiller, 1997) In addition, S. galilaeus has naturally colonized and dominated a sand dragged artificial freshwater lake of Ahozon Village (Ouidah City, County of Pahou) in Southern Benin where the species is well established and reproduce actively (Gbaguidi and Adite, in press) Lake Ahozon is an abandoned and neglected artificial water body resulted from a progressive accumulation of running water in an extensive hole, created by sand dragging activities, and where S. galilaeus dominated the fish community (Gbaguidi et al. in press) In Lake Ahozon, S. galilaeus showed a sexratio of (0.60:1) and sizes at sexual maturity (L50) were about 131mm and 106mm, respectively, for males and females. In this man made water body, S. galilaeus spawned all seasons and batch fecundity ranged between 42 oocytes and 1,149 oocytes. The species foraged mainly on algae (blue green algae, green algae, desmids, diatoms) sand particles and detritus (Gbaguidi and Adite, in press; Gbaguidi et al. in press) However, despite the fisheries and commercial importance of this species, and the high numeric abundance in this man made lake, nothing is known about the length weight relationships, the growth trends and the condition factors of S. galilaeus in this unmanaged artificial lake. Indeed, condition factors and length weight relationships of fishes are important tools for fishery management and reflect habitat conditions (Abowei, 2010a, 2010b) Also, the growth factors and associated structural indices assess the plumpness or well being of the species and hence, are response of the physiological conditions of fishes (Tesch, 1971; Abowei, 2009) Consequently, length weight models and condition factors could be used as indicators to evaluate the productivity and the "ecological health" of aquatic ecosystems (Deekae and Abowei, 2010) More importantly, condition factors consistently affect the spawning cycle and are robust predictors of fecundity, reproduction, growth and mortality in fishes, and have been widely used as a measure of feeding intensity (Abowei, 2009) As a result, length weight models and condition indices of fishes are valuable community structure tools used for management decision in fisheries and to evaluate the overall establishment of a naturally colonized or introduced fish species (Schreck and Moyle, 1990) The present study was carried out to assess the plumpness/well being and growth trends of the freshwater cichlid, Sarotherodon galilaeus (Linne, 1758) in the man made lake of Ahozon (South Benin) using the Fulton's condition factor and the matrixes J. Bio. Env. Sci. 2016 77 Gbaguidi et al. of length weight regression equations of the species. Inferences have been made for fisheries management and aquaculture valorization. Materials and methods Study area The man made lake of Ahozon (SouthBenin) is the study habitat, located in Ouidah City, Pahou County (Fig. 1a) The city of Ouidah extended about 364 km2 and comprises on its South, the Atlantic Ocean and the mangrove lined coastal lagoon (Capo chichi, 2006) Fig. 1. Map showing: (a) Ouidah City in South Benin and the study location, the manmade lake of Ahozon, and (b) the sampling sites: Site 1 and Site 2 aquatic vegetation habitats; Site 3 and Site 4 Open water habitats. J. Bio. Env. Sci. 2016 78 Gbaguidi et al. The climate is sub equatorial with two (2) wet seasons (April to July; mid September to October) with a peak usually recorded in June, and two (2) dry seasons (December to March; August to mid September) Yearly mean rainfall was about 1307.3 mm. Ambient temperatures ranged between 25degC and 33.6degC and monthly evaporation varied from 59.2 to 145 mm (Akoegninou et al. 1993) The study area comprises some sandy soils, red ferric soils and a vast swampy soil, located at the coastal zone, and extended from Cotonou city (South Benin) to Ouidah. Currently, this swamp undergoes sand dragging activities, considered as an ecological disaster. Plantations such as Elaeis guineensis (palm tree) and Coco nucifera (coconut tree) producing oil for industries, were common in the study area (Adite and Van Thielen, 1995) Also, intense agriculture dominated by corn, tomatoes, beans, groundnuts etc. occurred in the study region. Likewise multispecies fisheries dominated the environment of Ouidah and took place in the brackish coastal lagoon and in some freshwater lakes such as Toho Todougba, Ahouangan and Dati. Though not widespread, fish culture was encountered with couple of fish ponds constructed in swampy areas. In Southern Benin, Lake Ahozon (Fig. 1a and 1b) lies between two water bodies, Lagoon Toho Todougba (15 km2) a freshwater lake, and the coastal lagoon (60 km2) a brackish water, both about 5 km apart from Lake Ahozon. GPS tracking revealed that Lake Ahozon (06deg22'52"N 002deg10'34"E) covered about 0.165845 km2 (Fig. 1b) These kinds of man made lakes, in general neglected and abandoned by the owners, originated from sand dragging activities, and the resulting hole receives every wet season, a huge volume of running waters. Evaluation of water quality indicated that Lake Ahozon had depths varying between 16.2 240 cm (mean: 80.19 cm) and transparencies ranging from 16.2 to 60.5 cm (mean: 36.63 cm) Water temperatures ranged between 28.2degC and 38.7degC (mean: 33.25degC) pH between 6.7 and 9.7 (mean: 7.51) dissolved oxygen between 0.73 and 11.8 mg/l (mean: 5.43 mg/l) and conductivity between 50 and 560 m/cm (mean: 240 m/cm) (Gbaguidi et al. in press) In the man made lake of Ahozon, the "aquatic vegetation" habitat showed muddy bottoms whereas the "open water" habitat exhibited sandy muddy bottoms with dominance of sand. Dominant phytoplankton genera in Lake Ahozon were Navicula, Peridinium, Scennedesmus, Pinnularia, Spirogyra, Cosmarium, Melosira, Synechocystis, Microcystis, Oscillatoria, Euglena, Phacus, Surirella and Lychmophora and zooplanktons were dominated by Trichocerca, Keratella, Brachionus and copepods. Benthic macro invertebrates recorded were chironomid larvae and a Gasteropod mollusk, Melanoide tubercularis. Aquatic vegetation was dominated by Cyperus crassipes, Cyperus rotundus, Fuirena umbellata, Andropogon gayanus, L