~ 346 ~  International Journal of Fisheries and Aquatic Studies 2015; 3(2): 346-352  ISSN: 2347-5129 (ICV-Poland) Impact Value: 5.62  (GIF) Impact Factor: 0.352 IJFAS 2015; 3(2): 346-352 © 2015 IJFAS www.fisheriesjournal.com Received: 16-09-2015 Accepted: 18-10-2015 Imaobong E Ekpo Department of Fisheries & Aquatic Environmental Management, University of Uyo, P. M. B 1017, 520001, Akwa Ibom State – Nigeria. Mandu A Essien-Ibok Department of Fisheries & Aquatic Environmental Management, University of Uyo, P. M. B 1017, 520001, Akwa Ibom State – Nigeria. Ezekiel E Effiong Department of Fisheries & Aquatic Environmental Management, University of Uyo, P. M. B 1017, 520001, Akwa Ibom State – Nigeria. Correspondence Imaobong E Ekpo Department of Fisheries & Aquatic Environmental Management, University of Uyo, P. M. B 1017, 520001, Akwa Ibom State – Nigeria. Biology of bigmouth sleeper, Eleotris vittata (Dumѐril, 1861) (Pisces: Eleotridae) in the lower Cross River, Nigeria Imaobong E Ekpo, Mandu A Essien-Ibok, Ezekiel E Effiong Abstract Between May and December 2014, the abundance, condition factor, length-weight relationship, food and feeding habits of the bigmouth sleeper, Eleotris vittata were studied in the lower Cross River, Nigeria. Data generated were subjected to statistical analyses analysis at 0.05 probability level. A total of 231 specimens were collected and examined. The highest number was recorded in the month of December (79 specimens; 34.20%) while September (2 specimens; 0.87%) had the least. The highest monthly condition factor was recorded in June (1.56) while November (1.30) had the lowest. E. vittata had total length and total weight ranges of 8.10-110.30cm and 5.07-342.70g respectively. Seasonal variation in abundance of E. vittata was higher (121 specimens; 52.38%) during the wet season than the dry season (110 specimens; 47.62%). The results obtained from the length-weight relationship graph showed that the growth pattern of the fish was negatively allometric with b values of 0.16 obtained at P<0.05. There was moderate correlation between the length and weight of the specimens as the correlation coefficient (r) was 0.5586. Feeding intensity was highest in the month of June (88.89 %GRI) and lowest in September (50.00 % GRI). The gut contents revealed that 5 food items were ingested of which three were of primary importance (crustaceans 78.83 %IFD, Pisces 18.88 %IFD and molluscs 10.32 %IFD) while the rest of the items (nematode 4.42 %IFD and macrophytes 3.51 %IFD) were of secondary importance. Hence, E. vittata is an invertivore-piscivore. Keywords: Eleotris vittata, feeding habits, size variation, condition factor, lower Cross River 1. Introduction The family Eleotridae (Perciformes) comprises about 35 genera and 155 species which inhabit tropical and subtropical areas worldwide. [1, 2] reported the family Eleotridae as being among the world’s most widely distributed fish. They occurred throughout most of the West African coastline and can be found worldwide in tropical and subtropical regions, but are rarely found in temperate areas [3, 4] . In the Nigerian coastal waters, Eleotrid species comprise Bostrychus africanus, Dormitator lebretonus, Eleotris vittata and Eleotris danganensis [5] and they are found in both fresh and brackish waters [6, 7] classified E. vittata as a creeklet-dominated species while working in the intertidal fish communities of the Cross River estuary. Data of the functional Length-Weight Relationship (LWR) is important for fish stock assessment [8] , estimation of growth rates and age structure [9] , calculation of the standing stock biomass [10] , condition indices [11, 12] and several other aspects of fish population dynamics [13, 14] . Like any other morphometric characters, the LWR can be used as a character for the differentiation taxonomic units and the relationship changes with the various development events in life such as metamorphosis, growth and onset of maturity [15] . Condition factor, K is an index of the degree of fatness or well-being of a species [16] . The study of condition factor is important to understand the life cycle of fish species, contribute to an adequate management of the species and to maintain the ecosystem equilibrium [17] . This factor is calculated from the relationship between the weight of a fish and its length, with the intention of describing the “condition” of that individual fish [18] . Different values in K of a fish indicate the state of sexual maturity, the degree of food sources availability, age and sex of some species [19] . The study of the food and feeding habits of aquatic species is a subject of continuous research because it constitutes the basis for the development of a successful fisheries management programmed on fish capture and culture [20] . Nature offers a great diversity of organisms that are used as food by fish, and these differ in size and taxonomic groups [21, 22] observed that the dietary analysis of organisms in their natural habitat enhances the understanding of the