AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: , ISSN Online: , ScienceHuβ,

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1 AGRICULTURE AND BIOLOGY JOURNAL OF NORTH AMERICA ISSN Print: , ISSN Online: , ScienceHuβ, Length-weight relationship, condition factor and dietary composition of Sarotherodon melanotheron, Rüppell, 1852 (Pisces: cichlidae) in Ologe Lagoon, Lagos, Nigeria. * 1 Ndimele, P.E., 1 Kumolu- Johnson, C.A., 2 Aladetohun, N.F., and 3 Ayorinde, O.A. 1 Department of Fisheries, Faculty of Science, Lagos State University, Ojo, Lagos. Nigeria. 2 Federal College of Fisheries and Marine Technology, Wilmont Point, Victoria Island, Lagos, Nigeria. 3 Nigerian Institute for Oceanography and Marine Research (NIOMR), Victoria Island. Nigeria. ABSTRACT Length Weight relationship (LWR), condition factor (k) and dietary composition of the black chin tilapia, Sarotherodon melanotheron (Rüppel, 1852) from Ologe lagoon, Lagos, Nigeria were investigated. The fish were collected monthly from fishermen for a period of two years (January, December, 2007). Gill nets, cast net, traps, hooks and lines were the gears deployed. 420 specimens of the fish species were collected and they were chilled with ice blocks at the point of collection and transported to the laboratory for analyses. Length Weight relationship (LWR) had significant correlation in the fish species and the growth exponent (b) was isometric. Condition factor (k) of the fish species for each year was higher than 1. Dietary composition using frequency of occurrence and numerical methods revealed that S. melanotheron is a planktivore depending mostly on the divisions; Chlorophyta, Bacillariophyta, Cyanophyta and Ochrophyta. This was further corroborated by the Geometric Index of Importance (GII) approach. Keywords: Length Weight relationship, condition factor, dietary composition, Sarotherodon melanotheron, Geometric Index of Importance INTRODUCTION Ologe lagoon is part of the lagoon system in Lagos, Nigeria but the least studied. It sustains a thriving artisanal fishery industry dominated by the Awori people of Lagos. However, there is little published work on the biology of fish fauna in Ologe lagoon. This necessitates the need to study this ecosystem continuously so as to develop strategies for effective management and conservation Length Weight relationship (LWR) of fishes are important in fisheries biology because they allow the estimation of the average weight of fish of a given length group by establishing a mathematical relation between the two (Beyer, 1987). They are also useful for assessing the relative well being of the fish population. Length Weight relationship has a number of important applications in fish stock assessment. Among these applications are estimating the standing stock biomass, and comparing the ontogeny of fish population from different region (Patrakis and Stergiou, 1995). The cichlids are important culturable fish species in tropical Africa. Although, their culture is not as popular as the catfish, however, they are important species in polyculture because of their prolific rate of reproduction. They multiply rapidly, providing food for the commercially viable catfish, thereby reducing the need for commercial feeds which constitutes about 70% of the recurrent expenditure in aquaculture. It thus becomes imperative to study the food and feeding habits of freshwater fish species like Sarotherodon melanotheron on a continuous basis to sustain and improve their relevance in aquaculture. The frequency of occurrence and numerical methods of estimating the relative importance of food items in the diets of fish have some short - comings (Gümüs et al, 2002). Specifically, the frequency of occurrence method tends to magnify the relative importance of small food items while numerical method under states the relative importance of large food biomass which may be the main diet of the fish. New methods of estimating the relative importance of food items in the diet of fish species which employs or combines more than one parameter have been developed

2 (Lima Junior and Goitein, 2001). Geometric Index of Importance (GII) is this category. Geometric Index of importance (GII) has some advantages over other commonly used indices for measuring the relative importance of food items in the diet of fish species because it has a mathematical foundation based on geometry, enabling the use of more than one quantitative parameter (Assis, 1995). It is easy to compute, each parameter involved is weighed equally and food items are ranked according to their overall importance in the stomach. Gümüs (2002) compared Geometric Index of Importance (GII) and Index of Relative Importance (IRI) and concluded that GII is more suitable for measuring the relative importance of food items in the diet of fish species because the discrimination strength of GII makes the relative importance of food items more visible and interpretable. Although, the length Weight relationship and feeding habits of Sarotherodon melanotheron have been studied in other habitats in Nigeria (Ugwumba and Adebisi, 1992; Ayoade and Ikulala 2007), no studies have been carried out on the biology of this fish species in Ologe lagoon. Apart from this, the analyses of the food and feeding habits of Sarotherodon melanotheron have always been done by conventional approach; frequency of occurrence and numerical methods with its attendant short comings. Therefore, this study aims at investigating some aspects of the biology of S. melenotheron in Ologe lagoon as well as analyse the diets using Geometric Index of Importance (GII) method which is a more objective diet analytical tool than the conventional methods. MATERIALS AND METHODS Study Area: Ologe lagoon (Fig. 1) with a surface area of about 9.4 square kilometers is located within the fourth lagoon system west of the Niger (Anetekhai et al, 2005). The main body of Ologe lagoon lies in Badagry between Longitude N and N and Latitude N and N. It opens up to the Atlantic Ocean via Lagos harbour and Badagry creek while its major source of water is River Owo. It sustains a thriving artisanal fisheries industry and serves as a source of water for domestic and industrial use, transportation, logging and sand dredging (Anetekhai et al, 2005) Sampling Procedure: The lagoon was divided into five sampling stations (Otto jetty, Imude, Gbanko, Agbara and Morogbo) so as to cover most parts of the lagoon (Fig 1). Samples of Sarotherodon melanotheron were collected monthly from January, 2006 to December, 2007, from catches of local fisherman using gill nets, cast net, traps, hooks and lines. Samplings were done from 06:00-18:00 GMT at 3hr intervals. Samples were chilled in ice blocks at the point of collection before being transported to the laboratory in the Department of fisheries, Lagos state University, Lagos, Nigeria for analysis. Identification of fish specimen was done using fish identification guide by Olaosebikan and Raji (1998) and FAO (1992). The weight of each specimen was taken using a top loading metler balance (model PN1200) to the nearest 0.1g after draining excess water with a pile of filter paper while standard length was measured in centimetre using a measuring board. The Length weight relationship (LWR) was estimated by using the equation: W = a L b Where W = Weight (g) L = Standard length (cm) a = Constant b = Growth exponent. The equation was linearised by a logarithmic transformation to give: Log e W = Log e a + b Log e L The value of the compiled growth exponent were used to calculate the condition factor, K K = 100W L b Where K = Condition Factor W = Total body weight (g) L = Standard Length (cm) b = Growth exponent The slopes of annual length - weight regression were compared to 3 using Student s t-test (Sokal and Rohlf, 1987) to determine whether species grew isometrically. Specimens were dissected and the gut taken out to remove the stomach. The contents were emptied into a Petri dish for analysis. The different food items eaten by the fish were identified under microscope by following the keys given by Ward and Whipple (1950), Pennak (1953) and Prescott (1962). Analysis was done using frequency of occurrence and numerical methods as described by Hyslop (1980) and Coastal et al (1992). N F i = i x 100% N where F i = Frequency of occurrence of the ith food items in the sample 585

3 N i = Number of stomachs in which the ith item was found. N = Total number of stomachs with food in the sample. F N i = i F x 100% Where N i = Numerical percentage of the ith food item in the space F i = Total number of ith food item F = Total number of all food items The food items consumed by Sarotherodon melanotheron was also evaluated using the index, Geometric Index of Importance (GII). GII combines the relative measures of food items and it is giving by this formula: n [ V i ] j i=1 GII j = n (Gümüs et al, 2002) Where V i = the value of the ith measure of food item category j, and n = the measure used in the analysis of each food item. The Percentage of total number and Percentage of frequency of occurrence are the relative measures of food items used in the estimation of GII. The GII value of each food item was estimated. The Shannon and Weaver diversity index was calculated using the Primer software with the formula given as: H = - [ (n i / N ) x Log e (n i / N )] (Shannon and Weaver, 1963) Wher H = Shannon and Weaver diversity index n i =the number of individuals of each species (the ith species) N = The total number of individuals or amount for the site Log e = The natural logarithm The species richness was also determined by means of primer software using Margalef s index (d) with the formula given as: S 1 d = (Margalef, Log e N 1968) Where d = Margalef s index S = The total number of species in the population. N = The total number of individuals in the population. RESULTS The results of the length - weight analyses are presented in Table 1.The length range for 2006 and 2007 are cm and cm respectively while the mean lengths were cm and cm respectively. The weight varied between g in 2006 and g in 2007 while the mean weights were g and g for 2006 and 2007 respectively. The correlation coefficients for both years was similar; 0.80 for 2006 and 0.81 for The values of b (growth exponent or regression coefficient) for the two years was similar; 3.12 for 2006 and 3.09 for 2007 and are not significantly different (p>0.05) from 3 while the condition factors were 2.39 and 2.38 for 2006 and 2007 respectively. A total of 440 stomachs of Sarotherodon melanotheron from Ologe lagoon were analysed. 338 (76.82%) of these stomachs had food items while 102 (23.18%) had empty stomachs. Table 2 shows that there are about four divisions of algae, and one zooplankton, exploited by Sarotherodon melanotheron in Ologe lagoon. Sand grains was also found in the stomach as well as some unidentified organism. Using the numerical method, the diets were mostly from the division chlorophyta (61.31%) and Bacillariophyta (17.73%). A zooplankton, copepod larvae occurred least (0.41%) in the diet. The frequency of occurrence method reveal that Selenastrum, an algae of the division chlorophyta (green algae) was the most important diet (76.71%), followed by two other green algae, Microspora (67.12%) and Closterium (67.12%) while copepod larve (19.18%) was least observed. Geometric index of importance (GII) was calculated for each of the food items identified in the stomach of Sarotherodon melanotheron (Fig. 2). The highest GII value (63.98) was recorded in selenastrum (Chlorophyta), followed by two other chlorophyta; Microspora (57.96) and Scenedesmus (50.57) while the least value (13.85) of GII was recorded in the only zooplankton (copepod larva) in the diet. The Shannon and weaver diversity index (H 1 ) for the diet of S. melanotheron was 3.2 while the species richness (d) of the food items was

4 Table 1: Length-Weight relationship and condition factor of Sarotherodon melanotheron in Ologe Lagoon, Lagos, Nigeria. Year Mean Mean N b k Correlation Length Weight (g) (r) (cm) Table 2: Summary of the stomach contents of Sarotherodon melanotheron in Ologe Lagoon Lagos, Nigeria. Frequency of Occurrence Numerical Method (A) CHLOROPHYTA (%) (%) Microspora Ankistrodesmium Selenastrum Closterium Staurastum Coelastrum Pediastrum Ulothrix Scenedesmus (B) CYANOPHYTA Merismopedia Anabaena Mycrocystis Spirulina (C) OCHROPHYTA Bidulphia Ophiocytium (D) BACILLARIOPHYTA Fragilaria Navicula Synedra Nitzchia Cyclotella Melosira Asterionella (E) COPEPODA Copepod larvae (F) Unidentified organism (G) Sand grains

5 Ologe NIGERIA Lagos Lekki Oshun Epe Bight of Benin A E Gulf Of Guinea N Otto Bridge (R 4) Agbara Imude (R 2 ) Ibiye Jetty Otto jetty (R 1 ) Obele (R 5 )Morogbo (R 3) Gbanko B Idoluwo Lagoon exit into Badagry creek 3 0 0S KEY:. A. Map of Lagos lagoon complex inset Ologe lagoon. B. Map of Ologe lagoon (enlarged) = Sample Stations Scale: 1:150,000 Fig 1: Map of Ologe lagoon. 588

6 Fig 2: Diet preference of Sarotherodon melanotheron by GII values DISCUSSION The correction coefficient (r) for LWR for both year is high for Sarotherodon melanotheron in Ologe lagoon which indicates that the length increases with increase in weight of the fish. This is in agreement with previous studies on different fish species from various water bodies: Fagade and Olaniyan (1972), Fagade (1983),, Layèyè (2006), Ayoade and Ikulala (2007). The values of b (growth exponent) for S. melanotheron for the two years are within the limits (2-4) reported by Tesch (1971) for most fishes. The b values are not significantly different (p> 0.05) from 3 which means that S. melanotheron grows isometrically. This agree with the studies of Layèyè (2006), Ayoade and Ikulala (2007). The mean condition factors (K) for Sarotherodon melanotheron is greater than 1 and this shows that the fish is above average condition within the lagoon (Wade, 1992). The K value recorded in this study agrees with the values reported by Ayoade and Ikulala (2007). The results of this study confirm that Sarotherodon melanotheron is a planktivore (Pauly, 1976; Ugwumba and Adebisi, 1992) because the diet consists mainly of phytoplankton and zooplankton (Table 2). The most important food category in the diet of S. melanotheron from Ologe lagoon is the division chlorophyta accounting for 61.31% of the total number of food items in the diets of the fish. Bacillariophyta, cyanophyta and Ochrophyta accounted for 17.73%, 8.28% and 6.97% respectively. This results is corroborated by the outcome of the frequency of occurrence method which revealed that the three most important food items in the diet of S. melanotheron ( that is, Selenastrum, Microspora and Closterium) belong to the division chlorophyta. This agrees with the study by Ayoade and Ikulala (2007). Futhermore, the inadequacies of the frequency of occurrence and numerical methods necessitate the need to estimate the relative importance of these food items by a more objective method. Geometric Index of Importance (GII) was employed and the values obtained further gave credence to the fact that the division chlorophyta are the most important food source of S. melanotheron in Ologe lagoon. According to the ecomorphology hypothesis, diet should be predictable from the morphology of the fish, particularly from morphological traits related to feeding such as mouth size, jaw shape and dentition (Ogunlaru et al 1997). Therefore, the domination of the food items of S. melanotheron from Ologe lagoon by phytoplanktonic algae must have been due to its possession of a terminal month which is well adapted for sucking, sieving and picking phytoplankton both within the water body and those attached to vegetation and other materials (submerge or floating). The gut (particularly the mid and hind gut) is extremely long indicating that it is an herbivore. Copepod larvae (zooplankton) were also found in the stomach of S. melanotheron from Ologe lagoon. This also agrees with earlier studies (Ugwumba and Adebisi, 1992; Oso et al, 2006). The Shannon and Weaver diversity index (H) of the food items in S. melanotheron was 3.2. This value is higher than the 1.2 reported in Ofori Danson and Kumi (2006). This result shows that the food items in 589

7 the diet of S. melanotheron from Ologe lagoon are more diverse than the one reported in Sakumo lagoon, Ghana by Ofori Danson and Kumi (2006). It can also be inferred that Ologe lagoon has a greater diversity of Planktons than Sakumo lagoon. However, the species richness (d), 2.3 recorded in this study is lower than those reported (5.3) in previous study (Ofori Danson and Kumi, 2006) REFERENCES Anetekhai, M. A.; Akin Oriola, G. A; Jimoh, A.A.; Akintola, S. L. and Kumolu Johnson, C. A. (2005): Preliminary report on Fish and Fisheries of Ologe lagoon, Lagos, Nigeria. Third International Conference of the Pan African Fish and Fisheries Association. Cotonou, Benin Republic. 10 th 14 th November, 2003, Assis, C.A. (1995): A generalized index for stomach content analysis. Fish. Sci. Mar. 60 (2-3): Ayoade, A.A. and Ikulala, A.O.O. (2007): Length-Weight relationship, Condition factor and stomach content of Hemichromis bimaculatus, Sarotherodan melanotheron and Chromidotilapia guentheri (Perciformes: Cichlidae) in Eleiyele Lake, Southwestern Nigeria. International Journal of Tropical Biology 55 (3-4): Beyer, J. E (1987): On length weight relationships. Part 1: Computing the mean weight of the fish of a given length Class. Fishbyte 5: Costal, J. L.; Almeida, P.R.: Moreira, F.M and Costal, M.L. (1992): On the food of the European eel, Anguilla anguilla (L.) in the upper zone of the Tagus estuary, Portugal. Journal of Fish Biology 41: Fagade, S.O. (1983): The biology of Chromidotilapia quentheri from a small lake. Arch. Hydrobiol. 97: Fagade, S.O. and Olaniyan, C.I.O. (1972): The biology of the West African shad, Ethmalosa fimbriate (Bowdich) in the Lagos lagoon, Nigeria. Journal of Fish Biology 4: FAO, (1992): Field guide to the freshwater fishes of Tanzania. Food and Agricultural Organization, Rome. pp 145. Gümüs, A; Yilmaz, M. and Polat, N. (2002): Relative importance of food items in feeding of Chondrostoma regium Heckel, 1843, and its relation with the time of annulus formation. Turkish Journal of Zoology 26: Hyslop, E.J. (1980): Stomach content analysis - A review of methods and their applications. Journal of Fish Biology 17: Lalèyè, P.A. (2006): Length - weight and Length - Length relationships of fishes from the Ouèmè River in Benin (West Africa). Journal of Applied Ichthology 22: Lima - Junior, S. E. and Goitein, R. (2001): A new method for the analysis of fish stomach contents. Maringã 23 (2): Margalef, R. (1968): Perspective in ecological theory. University of Chicago press, Chicago. 111p. Ofori - Danson, P.K. and Kumi, G.N. (2006): Food and feeding habit of Sarotherodon melanotheron, Rüpell, 1852 (Pisces: Cichlidae) in Sakumo lagoon, Ghana. West African Journal of Applied Ecology 10: Ogunlaru, A, Anetekhai, M.A.; Kumolu- Johnson, C.A.; Jimoh, A.A. and Whenu, O.O. (1997): Food, feeding habits and sex ratio of Chana obscura (Gunther) from Era swamps, Ojo Lagos, Nigeria. Journal of Prospects in science 1: Olaosebikan, B.D. and Raji, A. (1998): Field guide to Nigerian freshwaters fishes. Decency Printers and stationary Ltd, Ilorin, Nigeria. 105pp. Oso, J.A.; Ayodele, I.A. and Fagbuaro, O. (2006): Food and feeding habits of Oreochromis niloticus (L) and Sarotherodon galilaeus (L) in a tropical reservoir. World Journal of Zoology 1(2): Pauly, G. (1976): The biology, fisheries and potential for aquaculture of Tilapia in a small West African Lagoon. Aquaculture 71: Pennak, R.W. (1953): Freshwater Invertebrates of the United States: Ronal Press, New York. 769pp. Petrakis, G. and Stergiou, K.I. (1995): Weight-Length relationships for 33 fish species in Greek waters. Fisheries Research 21: Prescott, G.W. (1962): Algae of the Western Great Lakes Area Wm. C. Brown co, Pub. Dubuque, Lowa. 946pp. Shannon, C.E and Weaver, W. (1963): The mathematical theory of Communication. University of illinoris Press, Urbana. 125pp. Sokal, R.R. and Rohlf, F.J (1987): Introduction to Biostatistics. W.H. Freeman, New York, U.S.A. Tesch, W. (1971): Age and growth. In Methods for assessments of fish production in freshwaters. Ed Ricker, W.E. International Biological Programme, Oxford, England Ugwumba, A.A.A. and Adebisi, A.A. (1992): The food and feeding ecology of Sarotherodon melanotheron (Rüppell) in a small freshwater reservoir in Ibadan, Nigeria. Arch. Hydrobiology 124: Wade, J. W. (1992): The relationship between temperature, food intake and growth of brown trout, Salmo trutta (L); fed natural and artificial Pelletted diet in earth pond. Journal of Aquatic Science 7: Ward, H.B and Whipple, G.C. (1950). Freshwater biology. Wiley, London. 650pp. 590