Aspects Of The Biology Of Heterotis niloticus Cuvier 1829 (Osteoglossiformes: Osteoglossidae) In The Anambra Flood River System, Nigeria

Abstract

Studies on some aspects of the biology of Heterots nilotcus in Anambra river were carried out for 22 months. Analysis of the stomach content of 546 species of H. niloticus in Anambra river established the preponderance o plantivorous crustacean, copepods and cladocera throughout the four maturation stages examined. Seasonal variations occurred in the dietary components of the fish. The length-weights relationship and the relative condition revealed that females had better conditon. The mean length and weght were 94.5 ± 60 cm (29 – 167 cm) and 120 ± 21.8g (10 – 250g) respectively. A sex ratio of 1:0.8 (M: F) at Otuocha was more pronounced than at Ogurugu and Nsugbe. Dgestive enzyme assays in the different gut regions (oesaphagus, stomach, pyloriccaeca, ileum and rectum) of H. niloticus showed an array of glycosidase (amylase, sucrase, malatase, lactase, cellulase); protease, (pepsin, trypsin, chymotrypsin) and lpases. The pattern of spread and relative activity of the enzymes is consistent with its planktophagous diet. Haematocrit values, haemoglobin concentrations, erythrocyte and leucocytes counts, mean cells haemoglobin concentrations, plasma protein, glucose, albumin and inorganic ion (sodium, chloride, calcium, potassium, magnesium, phosphorus) for H. niloticus were established. Correlations were found between some blood parameters and standard length.

Keywords: Heterotis niloticus, Length-weight relationship, Stomach content, Digestive enzymes, Haematology