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The effects of replacing high percentages (50%, 75% or 100%) of dietary protein from fish meal with soy protein concentrate on growth, diet utilization, and carcass composition of the African catfish, Clarias gariepinus, was evaluated. Supplemental methionine was added to the diet formulation in which soy protein concentrate replaced 100% of fish meal protein. Diets were formulated (420 g crude protein/kg and 17.5 kJ gross energy/g dry diet) and fed to catfish fingerlings (13.1±0.5 g) to apparent satiation twice daily for 70 days. Replacement of 50% and 75% of fish meal protein with soy protein concentrate did not affect growth, feed utilization or carcass composition, which were similar (P > 0.05) to those fed with the control diet. At 100% replacement, growth and feed utilization were depressed and slightly inferior hematological characteristics were observed, compared with the other treatments. Liver histology of catfish fed any of the diets showed no alternations. Results indicate that 75% of...

Two aquatic plants: water fern, Azolla africana and duckweed, Spirodela polyrrhiza were evaluated as feedstuffs in production diets for Nile tilapia, Oreochromis niloticus fingerlings. Eleven diets (30% crude protein) containing fish meal protein substituted at a rate of 5, 10, 20, 30, and 100% for either of the plant ingredients were formulated. A diet without any of the plant ingredients served as the control. Nile tilapia fed diets containing duckweed showed superior growth performance. There were no significant differences (P > 0.05) in growth responses of fish fed either 10% duckweed and 5% water fern dietary inclusion or the control diet. There was a growth depression in fish with increased dietary inclusion of both plants. The most cost-efficient diet was obtained in a diet with 30% duckweed dietary inclusion. Results of this study indicated that duckweed and water fern could be substituted for fish meal protein up to 10% and 5%, respectively, in low-cost diets for Nile tilapia without com...

Stomach contents analyses of 330 specimens of the electric catfish, Malapterurus electricus (Gmelin 1789) (standard length, 10.1-30.5 cm) collected in Mahin Lagoon (southwestern Nigeria) established it as a bottom feeder. A preponderance of insects and prey fish, which accounted for 100% occurrence and > 18% of total volume in the stomachs of specimens, suggested a predatory habit. Carbohydrases (amylase, maltase), chitinase, proteases (pepsin, chymotrypsin, trypsin) and lipases were detected in different gut regions with different activity, which correlated with its predatory diet. KEY WORDS: digestive enzymes, stomach contents, food, electric catfish, Malapterurus electricus.

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, ...

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±0.52 106/mm3 and 7.25±0.60 104/mm3, 22.11±0.77%, 802.52±36.97 and 83.54±5.05 mg/1, 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 relati...

The dietary habits of the giant African clariid catfish, Heterobranchus bidorsalis (Geoffroy St. Hilaire 1809) inhabiting Owena Reservoir (Southwestern Nigeria) were investigated. Stomach content analyses established that it had an euryphagous diet. The diet comprised mainly plankton, insects, fish and detritus although, plant parts, benthic invertebrates and tadpoles were consumed. Detritus was very prominent accounting for between 68.1–74.5% occurrence and 13.9–19.6% volume in all sizes of fish examined, which indicated that it was a benthic feeder. There was a progression from planktivorous diet in fish below 12 cm standard length (SL) through a transitional insectivorous phase (SL, 12–27 cm) to a predominantly piscivorous diet in fish above 27 cm SL. It was capable of filter feeding only when young but later became predatory, consuming appropriately sized prey organisms as it grew older. No seasonal variation was established in food preference of any size of fish.