Benedict Obeten Offem

Bio: Benedict Obeten Offem is an academic researcher from Cross River University of Technology. The author has contributed to research in topics: Clarias gariepinus & Species richness. The author has an hindex of 11, co-authored 27 publications receiving 360 citations.

Diet, size and reproductive biology of the silver catfish, Chrysichthys nigrodigitatus (Siluformes: Bagridae) in the Cross River, Nigeria

Abstract: The silver catfish, Chrysichthys nigrodigitatus (Lacepede: 1803) is a highly valued food-fish included among the dominant commercial catches exploited in major rivers of Africa. To provide useful biological data for management, samples were collected monthly between January (2005) and December (2007) in three zones: I: Upper Cross River (grassland), II: Middle Cross River (mixed forest and grassland), and III: Lower Cross River (rainforest)) along 200 km length of the Cross River, Nigeria. Data from 1 248 specimens were processed using: allometric coefficient (b), gonado-somatic index, Fulton's condition factor and diversity indices. Male dominance was observed in all populations; C. nigrodigitatus reached maturity at 11.5cm (male) and 16.7cm (female) total length. Gonado-somatic index was higher for females with a peak in the early rains. The breeding period was between April and August with mean fecundity ranging between 4522 ±1924 eggs and 20321 ± 5543 eggs. This was directly related to total length and weight by the regression models: F = 2365.88 + 560.22 log L and F = 5025.81 +56.34 log W respectively. Exponential equations for length-weight relationships were Wt=- 1.997 Lt 2.206 (Zone I), W = -2.831 Lt 3.040 (Zone II) and Wt= -2.245 Lt 2.995 (Zone III). The mean allometric coef- ficient (b) showed significant departure from cubic value (negative allometry) for Zone I while Zones II and III showed no difference, indicating isometry. Dominant items in the diet were fish and fish parts constituting 21.6% with Food Richness and Gut Repletion Index of 18 and 100% respectively, in all zones. Diet Breadth of 0.802 (Zone I), 0.922 (Zone II) and 0.910 (Zone III) indicate a high trophic flexibility that enables switching from one diet to another according to availability. Mean condition factor for males varied from 0.718 ±0.117 minimum in Zone I to 0.996 ±0.062 maximum in Zone III. Forest inland wetlands (Zone II and III) of Cross River provided better condition for C. nigrodigitatus. Rev. Biol. Trop. 56 (4): 1785-1799. Epub 2008 December 12.

Influence of Seasons on Water Quality, Abundance of Fish and Plankton Species of Ikwori Lake, South-Eastern Nigeria

Abstract: This study is aimed at assessing the effect of seasons on quality of lake water in relation to changes in fish, plankton abundance and environmental variables. Standard methods were used to analyze monthly fish, plankton and water samples collected from Ikwori Lake during wet and dry seasons for 24 months (January 2008 to December 2009). All measured water parameters except dissolved oxygen (3.3 ± 0.10mgl-1), total dissolved solids (103.2 ± 2.22mgl-1), acidity (4.44 ± 3.91mgl-1), color (60.33 ± 8.38pt. co) and pH (5.8 ± 0.119) showed significant seasonal variation. The highest values of the parameters occur between February and March (dry season) and lowest between May and August (wet season). In addition, total phytoplankton (cells/litre), were significantly more during the dry season than the wet. Out of 16 fish species sampled, 7 species were restricted to dry season, only one i.e. Polypterus senegalus was recorded in the wet while 8 species occurred in both seasons. Seasonal differentiation in the richness and diversity indices of all species sampled revealed higher values for the dry season than the wet. Therefore, the influence of season is important in the management of water quality, plankton and fish production of the aquatic system.

Toxicity of Lead to Freshwater Invertebrates (Water fleas; Daphnia magna and Cyclop sp ) in Fish Ponds in a Tropical Floodplain

Abstract: Acute toxicity of Pb to the water flea; (Daphnia sp) and Copepod, (Cyclop sp) both important component of zooplankton diet of fish was determined by static assay. A positive relationship between percentage mortality and exposure concentration was found in all tests. Mean 24-h LC50, 48-h LC50 and 96-h LC50 values were 2.51 ± 0.0.04 mg l−1, 1.88 ± 0.06 mg l−1 and 1.65 ± 0.19 mg l−1 for Daphnia spp and 3.11 ± 0.03 mg l−1, 2.97 ± 0.05 mg l−1 and 2.61 ± 0.09 mg l−1 for Cyclop spp, respectively. For all tested species did the LC50 values decrease with time; the decrease was more marked for Daphnia spp. Observed symptoms include spiral movement followed by change of body colour to white and rapid disintegration of the skin. The Daphnia spp. appear to be more sensitive to Pb poison than Cyclop spp. The results showed that concentrations of Lead (Pb) in excess of 0.19 mg l−1 and 0.30 mg l−1 can be potentially harmful to Daphnia magna and Cyclop spp respectively.

Length-weight Relationship, Condition Factor and Sex Ratio of Forty Six Important Fishes in a Tropical Flood River

Abstract: A study was conducted on the length-weight relationship, condition factor and the sex ratio of 14,466 fish representing 46 species bel onging to 28 genera from 16 families of economically important freshwater fishes inhabiting the 200 km length of Cross River inlands wetlands, Nigeria. Fish s amples were collected with art isanal gears (gillnets, cast nets, seine net s) during J anuary 2006 and December, 2007. 87.5% of the species sampled had more males than females. The estimated b v alue (allometry coefficient) of the equation W =aL ranged between 1.92 a nd 3. 65 w ith mean and mode values of 2.6 ± b 0.32 and 3 respec tively. 65% of the samp les had condition f actor gr eater t han the m ean (0.77 ± 0.12). Fish Sp ecies o f C ross River inland wetlands are therefore do minated by male p opulations, growth trend is mostly isometric (exhi bit dimensional equality of the b ody parameters) and can be d escribed as being in goo d condition.

Plankton- Based Assessment of the Trophic State of Three Tropical Lakes

Abstract: In developing countries, lakes being important sources of water supply and fishing are vulnerable to anthropogenic impact, yet knowledge of their trophic state in relation to changes in species composition, and environmental variables, are limited. This study is aimed at assessing the trophic status of lakes by monthly sampling of three lakes located along the floodplain of Cross River, Nigeria between January 2008 and December 2009. Samples were analyzed for water quality parameters, zooplankton and phytoplankton composition and distribution. Results were subjected to community structure analysis using trophic state index, species richness and diversity indexes. Essential primary productivity nutrients, nitrates, sulphates and phosphates were highest in Ejagham Lake, and lowest in Ikot Okpora Lake. Dominant phytoplankton species Oscillatoria lacustria (Cyanophyceae), Cyclotella operculata (Bacilliarophyceae) and zooplankton Keratella tropica, Keratella quadrata, Filinia longiseta, Branchionus anguillaris and Trichocerca pusilla (rotifers) all typical of eutrophic communities were recorded in high densities in Ejagham Lake in both dry and wet seasons while Cladocerans, Bosmina longirostris and Moina micrura and copepods considered indicators of oligotrophy and mesotrophy were recorded in large numbers in Ikot Okpora and Obubra Lakes respectively. Higher values of species richness, Evenness and Shannon-Wiener diversity index for both phytoplankton and zooplankton, were recorded in Ejagham Lake during the dry season than wet. Also values of the Trophic state index were generally highest at the Ejagham Lake in the savanna region of the floodplain and lowest at Ikot Okpora in the forest region of the floodplain. Forest region is therefore a limiting factor in the productivity of lakes in the tropics.

Bioindicators: the natural indicator of environmental pollution

Abstract: Bioindicators are living organisms such as plants, planktons, animals, and microbes, which are utilized to screen the health of the natural ecosystem in the environment. They are used for assessing environmental health and biogeographic changes taking place in the environment. Each organic entity inside a biological system provides an indication regarding the health of its surroundings such as plankton responding rapidly to changes taking place in the surrounding environment and serving as an important biomarker for assessing the quality of water as well as an indicator of water pollution. Even the health of aquatic flora is best reflected by plankton, which acts as an early warning signal. In this review we have tried to explain the concept behind Bioindicators and plankton, with particular emphasis on their potential to be used as Bioindicators for water quality assessment and outcomes relating to this.

Rev. Biol. Trop. (Int. J. Trop. Biol. ISSN-0034-7744) Vol. 54 (3): 000-000, September 2006Scanning electron microscopy of damage caused by Mesocyclops thermocyclopoides (Copepoda: Cyclopoidea) on larvae of the Dengue fever vector Aedes aegypti (Diptera: Culicidae)

Abstract: This study was funded by the vicerrectoria de Accion Social, vicerrectoria de Investigacion, Universidad de Costa Rica, and PNUD.

Toxic heavy metals: impact on the environment and human health, and treatment with conducting organic polymers, a review

Abstract: Water pollution by heavy metals has many human origins, such as the burning of fossil fuels, exhaust gases of vehicles, mining, agriculture, and incineration of solid and liquid wastes. Heavy metals also occur naturally, due to volcanoes, thermal springs activity, erosion, infiltration, etc. This water contamination is a threat for living beings because most heavy metals are toxic to humans and to aquatic life. Hence, it is important to find effective techniques for removing these contaminants in order to reduce the level of pollution of the natural waters. In this work, we have reviewed the toxicity of several heavy metals (mercury, lead, cadmium, chromium, nickel), their impact on the environment and human health, and the synthesis and characterization methods of conducting organic polymers (COPs) utilized for the removal of heavy metals from the environment. Therefore, this review was essentially aimed to present recent works and methods (2000–2020) on the environmental impact and toxicity of heavy metals and on the removal of toxic heavy metals, using chemically and/or electrochemically synthesized COPs. We have also stressed the great interest of COPs for the removal of toxic heavy metals from waters.

A Systematic Revision of the African Species of the Genus Clarias (Pisces; Clariidae)

Abstract: A systematic revision of the African species of the genus Clarias (Pisces;Clariidae) , A systematic revision of the African species of the genus Clarias (Pisces;Clariidae) , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی