No 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

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.

Species richness and human activities in natural environments are among the most important recreational needs. Monthly studies of aquatic fauna, artisanal fisheries and tourism characteristics was conducted during wet and dry seasons, over a two year period in the three landscapes along the 6817.7 m length of Agbokum waterfalls by using a close-ended pre-coded survey instrument. Through MANOVA analysis of the 1780 respondents we found strong positive association between peoples visits to the recreational areas and the type of landscape in which the respondents felt happy. People who felt happier in landscape dominated by waterfalls, visit the middle reaches of the river for outdoor recreation more often while people who feel happy in landscapes dominated by slow water current with an extensive wide area and floodplains, visit downstream reaches of the waterfalls more often. Activities performed more often along downstream reaches include fishing, bathing/swimming, boating and hunting while more frequent activities in the middle reaches (waterfalls) include taking photographs, picnics, enjoying nature, outing with family and friends, looking at view, resting and relaxing. A total of 5484 fish representing 22 species belonging to 16 genera from 9 families were sampled with 10 species being restricted to wet season and only 1 in the dry. The number of taxa and individuals present at upstream, midstream and downstream reaches were 16 (2003), 13 (1034), 17 (2447), respectively. <i>Tilapia zillii</i>, <i>Clarias gariepinus</i> and <i>Labeo coubie</i> dominated overall catch constituting 35.5%. Twenty five operational boats counted during the period of study, were only used downstream by 25 full-time fishermen, 87 part-time, 44 shoreline fishermen and 36 assistant fishermen. Common gears were the hook and line constituting 45.8%, cast and dip net (10.1%) bailing (8.7%), gill nets (7.3%), seine net (6.4%) Traps (5.5%), lift net (4.7%) Dip nets (0.9%), poisoning (2.8%), cutlass (3.3%) and spear (1%). Seasonally occurring aquatic fauna include crustaceans (<i>Atya gaboneensis</i> and <i>Palaemon paucidens</i>) (23.5%) oysters (<i>Etheria elliptica</i>) (15.4%), clams (<i>Galacea paradoxa</i>) (20.8%), Manatee (<i>Trichechus senegalensis</i>) (2.5), <i>Hippopotamus amphibious</i> (1.8%), Otter (<i>Lutra macullicolis</i>) (0.5%), Crocodyles (<i>Crocodylus niloticus</i>, <i>Crocodylus cataphractus</i> (Aligata) and <i>Osteolaemus tetraspsis</i>) (18.8%). The nile monitor (<i>Varanus nilaticus</i>), aquatic snake (<i>Anoscopus sp</i>), and three species of water turtle (<i>Kimxys erosa</i>, <i>Pelumedusa sp</i> and <i>Peliosus sp</i>) (21.6%). Relatively higher faunal densities and species richness in the upstream and downstream reaches coupled with waterfalls in middle reaches can makes Agbokum waterfalls a touris...

Bacterial infection among the most common cultured mudfish Clarias gariepinus in Africa, has become a cause of concern, because it constitutes the largest economic loss in fish farms. In order to provide useful biological data of the pathogens for good management practices, samples were collected monthly between January 2008 and December 2009 in three monoculture nursery ponds, located in three different positions: upriver (A, grassland), mid-river (B, mixed forest and grassland) and downriver (C, rainforest) along 200km length of Cross River floodplains, Nigeria. A total of 720 fingerlings between 15.1 and 20.7g were analyzed to determine the degree of infection. The bacterial pathogens were taken from their external surfaces, and were isolated and identified by standard methods. The caudal fins of fingerlings from pond A had the highest bacterial load (5.8x10 3 cfu/g), while the least counts (1.2x103cfu/g) were identified on the head of fish from pond C, with Flexibacter columnaris as the major etiological agent. Pseudomonas fluorescens, Aeromonas hydrophila, Escherichia coli, Staphylococcus aureus and Micrococcus luteus were identified as co-isolates with P. fluorescens as dominant (0.7x10 2 cfu/mL) co-isolates in pond water. Clinical signs of five white spots with red periphery appeared on the external surface of infected fish. All the fish sampled, died after 4 to 9 days. There was no significant difference in the bacterial counts between different ponds, but the difference between fish organs/parts examined was significant. Fish from these ponds are therefore potentially dangerous to consumers and highly devalued, with the economic impact to producers. Preventive methods to avoid these infections are recommended.