Haematological profile of Heterobranchus bidorsalis (Geoffroy St. Hilaire 1809) was determined. Haematocrit values, haemoglobin concentrations, erythrocyte and leucocyte counts, mean cell haemoglobin concentration, sodium and potassium ions concentrations were 24.75±1.23%, 5.43±0.25 g/100 ml, 1.99±0.52 10"/mm 3 and 7.25±0.60 10 4 /mm 3 , 22.11±0.77%, 802.52±36.97 and 83.54±5.05 mgfl, respectively.H. bidorsalis fingerlings were subjected to a range of salinities, 0, 3, 6, 9, 12 and 15 ppt. The optimum salinity range for survival and good growth performance was determined as 0-3 ppt. Survival was > 85% from 0-9 ppt with no significant differences (P> 0.05), but decreased progressively as salinity increased.Qualitative and quantitative assays of digestive enzymes in the different regions of H. bidorsalis guts revealed an array of carbohydrases, proteases and lipases. Enzyme activity was restricted to the stomach, duodenum and ileum with fewer enzymes recorded in the stomach. The pattern of distribution and relative activity of enzymes correlated with its euryphagous diet.Parasitological examinations conducted on the skin and internal organs of H. bidorsalis yielded a variety of parasites which included three protozoans, two monogeans, six digeneans, four cestodes, two nematodes, two annelids and four copepods. No acanthocephalan infection was detected. Protocephalus sp. (Cestoda) and Allocreadium sp. (Trematoda) had the highest prevalence (>81%) followed by digenean metacercaria (35%).The implications of these results in relation to the aquaculture potential of this catfish is discussed.

Analyses of stomach contents of (1093) Heterotis niloticus (Cuvier 1829) in the River Ogbese, Owena Reservoir and Mahin Lagoon (southwestern Nigeria) established it as a benthic feeder in the river and a planktonic feeder in the reservoir and lagoon. There was a preponderance of zooplankton, accounting for > 80% occurrence and > 25% of total volume in the stomachs of specimens from all habitats; this suggests a microphagous habit. Digestive enzyme assays in the different gut regions (oesophagus, stomach, pyloric caeca, ileum, rectum) of H. niloticus revealed an array of glycosidases (amylase, sucrase, maltase, lactase, cellulase); proteases (pepsin, trypsin, chymotrypsin) and lipases were also detected. The pattern of distribution and relative activity of the enzymes is consistent with its planktophagous diet. Haematocrit values, haemoglobin concentrations, erythrocyte and leucocyte counts, mean cell haemoglobin concentration, plasma protein, glucose and albumin, inorganic ion (sodium, chloride, calcium, potassium, magnesium, phosphorus) concentrations of pond-cultured H. niloticus were established. Correlations were found between some blood parameters and standard length.

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.

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