African Journal of Aquatic Science 2009, 34(1): 97–101 Printed in South Africa — All rights reserved Copyright © NISC (Pty) Ltd AFRICAN JOURNAL OF AQUATIC SCIENCE ISSN 1608–5914 EISSN 1727–9364 doi: 10.2989/AJAS.2009.34.1.10.735 Haematological characteristics of African bony tongue, Heterotis niloticus (Teleostei: Arapaimidae), in south-western Nigeria EO Ayotunde 1 *, OA Fagbenro 2 and BO Offem 1 1 Department of Fisheries, Faculty of Agriculture, Cross River University of Technology, Calabar, PMB 102, Obubra Campus, Cross River State, Nigeria 2 Department of Fisheries and Wildlife, Federal University of Technology, PMB 704, Akure, Ondo State, Nigeria * Corresponding author, e-mail: eoayotunde@yahoo.co.uk Received 13 June 2008, accepted 11 October 2008 Introduction The African ‘bony tongue’, Heterotis niloticus (Cuvier 1829) (Teleostei: Arapaimidae), is a tropical species inhabiting swamps, the lower reaches of rivers, flood plains and creeks where the current is not strong. It grows to about one metre in length and exceeds 6 kg in weight in natural water bodies in the tropics; it is microphagous and feeds mostly on plankton, benthic material, algae, invertebrates, seeds and plant debris. It has the ability to leap high out of the water. The hardiness of this fish, coupled with its fast growth rate, makes it suitable for aquaculture. The flesh is fairly tough and dry with low oil content and a strong flavour (Reed et al. 1967). A knowledge of the haematological and serolog- ical characteristics of Heterotis niloticus is important in determining health status, in toxicological and parasitolog- ical investigations as well as in the selection of brooders for breeding purposes and the separating of the sexes. The use of haematology values as an indicator for diagnosing disease and stress-induced conditions in fish has received considerable attention (Kori-Siakpere 1985, Rambhaskah and Rao 1990, Erondu et al. 1993, Fagbenro et al. 1993, Ayotunde and Ochang 2004). Changes in the cellular composition of blood have been associated with environ- mental stress (Casillas and Smith 1977, Hilmy et al. 1980), dietary deficiency and starvation (Smith 1968, Weinberg et al. 1976) and disease (Amend and Smith 1975, Lester and Budd 1979). Van Vuren et al. (1994) stated that the haematological evaluation of fish blood provides valuable information concerning the physiological response of fish to changes in their external environment. According to these authors the haematological variables are well known for their clinical value in prognosis and diagnosis. Investigations into rapid diagnosis of fish diseases through serological techniques have progressed very slowly in fish clinical studies. Serological tests may determine the presence of antigen in the tissue of fish microorganisms and the presence of antibodies against particular antigens within the blood of fish (Ronald 1989). This study was undertaken to establish reference haematological, plasma biochemical and serological profiles for Heterotis niloticus as a basis for future comparative studies. This species is a new candidate in fish culture in Nigeria, and its growth rate and the biological conditions necessary for its culture are still under investigation. Materials and methods Twenty-five healthy Heterotis niloticus, identified using the taxonomic key by Reed et al. (1967), were obtained from Osun State Ministry of Agriculture and Natural Resources Fish Farm, Osogbo, south-western Nigeria. On the basis of their appearance and the absence of obvious signs of disease, all specimens were considered to be healthy. Standard lengths (SL) were measured to the nearest 1 cm using a measuring board and they were weighed to the nearest 1 g on a top-loading balance. They ranged in mass from 301 to 610 g (mean 429 g) and in length from 30.4 to 39.5 cm (mean 34.2 cm). It is difficult to harvest H. niloticus bigger than 700 g to 1 kg in fish farms in Nigeria. Haematological characteristics — including red and white blood cells counts, haemoglobin, haematocrit, mean cell haemoglobin concentration, mean cell volume, mean cell haemoglobin, protein, glucose, albumin, sodium, chloride, potassium, magnesium and phosphorus — were established from an examination of 25 adult Heterotis niloticus collected at a fish farm. The red and white blood cell counts did not positively correlate with the physical parameters of length and weight. There were significant correlations between the blood cells, haemoglobin and pack cell volume. The blood group, genotype and agglutination test results were 92% Rh-O + and 8% Rh-O – , respectively, and were similar to the pattern in humans. Keywords: agglutination, aquaculture, biochemical analysis, fish diseases, plasma chemistry, serology, water quality