Heterotis Research Articles

Comparative Study of the Proximate Composition and Sensory Evaluation of Fresh and Smoke-dried Fish Species from Omambala River, Anambra State, Nigeria

This study investigates the proximate composition and organoleptic properties of fish species from the Omambala River in Anambra State. A total of 40 fresh fish samples, specifically Clarias gariepinus and Heterotis niloticus, with a mean length of 25 cm and mean weight of 380 g, were analyzed. The fish samples, initially scaled, had their viscera removed and were washed in clean water before undergoing brining. This involved immersing the fish in a 75% saturated brine solution, prepared by dissolving 27 g of NaCl in 100 ml of water for 30 seconds. The samples were then smoke-dried in a smoking kiln. Proximate composition was assessed using standard methods from the Association of Analytical Chemists (AOAC), while organoleptic properties were evaluated using a 9-point hedonic scale. Data were collated and analyzed using a two-way analysis of variance (ANOVA) with GENSTAT version 4 software, and mean separation was performed using the Least Significant Difference at a 5% probability level. Results indicated that the proximate analyses revealed an increase in all nutrient compositions after smoke-drying, except for moisture and carbohydrates, which significantly decreased from 44.58% to 14.15% and from 37.10% to 7.88%, respectively, for C. gariepinus. In the case of H. niloticus, increases were noted in ash, fiber, fat, and protein, while moisture decreased significantly (p<0.05) from 44.87% to 17.89%. Organoleptic evaluation showed a preference for C. gariepinus, which had a significantly higher overall acceptability mean score of 8.40±0.66 compared to 6.70±2.26 for H. niloticus. This research demonstrates that smoke-drying fish effectively reduces moisture content, enhances nutrient composition, and improves organoleptic properties, thereby increasing shelf life. It is recommended that both C. gariepinus and H. niloticus be hygienically smoke-dried to maximize organoleptic qualities, nutrient composition, and shelf life, ultimately yielding better economic returns. Keywords: Nutrient composition, organoleptic properties, Smoking kiln, Fish species

Specific Diversity of Fish Ponds in the Haut-sassandra and Risks of Contamination by Potential Pathogens among Oreochromis niloticus (Tilapia)

Fishery and aquaculture products are an important source of protein in the human diet and a real source of income for producers. However, fish farming is still less well known among the Ivorian population, and does not yet benefit from technical assistance. This could have an impact on the quality of aquaculture resources. This study was therefore carried out firstly to assess the current state of fish farming in the Haut-Sassandra region, and then to evaluate contamination by potential bacterial pathogens of tilapia fish from fish ponds in this region. To this end, a survey was carried out from June to December 2022 using questionnaires. The survey consisted of direct interviews and farm visits to collect data. Tilapia fish were then sampled and analyzed. It emerged that fish farming is a fast-growing activity in the Haut-Sassandra region, but is practiced in a related way. It is mostly practiced by people aged between 35 and 50, most of whom have a primary education. Females account for 2.66%. The dominant system is extensive, practiced in dam and diversion ponds where several activities coexist. In this region, 100% Tilapia (Oreochromis niloticus), 21% Cameroon (Heterotis niloticus) and 48% Catfish (Clarias gariepinus) are found on all farms. Of the two pond types, the barrage ponds had the best characteristics. Microbiological analyses revealed the presence of potentially pathogenic species, notably Escherichia coli, Staphylococcus aureus Salmonella spp and Enterococcus in tilapia from these fish ponds. Fish farming is a fast-growing activity, but it needs special attention to meet the needs of the Ivorian population.

Analysis of Heavy Metals and Gene Expression of African Arowana Fish (Heterotis niloticus) obtained from Igbalegbe River, Ughelli, Delta State, Nigeria

Heavy metal pollution in aquatic ecosystems can be assessed with suitable biomarkers in fish. This study was carried out to determine the concentration of heavy metals and gene expression of African Arowana Fish (Heterotis niloticus) obtained from Igbalegbe River, Ughelli, Delta State, Nigeria using Atomic Absorption Spectrophotometer (Varian 220 Fast sequential) for the metals and Polymerase chain reaction (PCR) for the gene expression study. Results of the study showed that fishes in the downstream sectionof the river and the effluent discharge point recorded higher metal pollution Index (MPI) compared to the upstream station. The concentration of heavy metals in the fish tissue were generally within the limits of Food and Agricultural Organisation (FAO)/World health Organisation (WHO) except for that of Cadmium and Lead in the discharge station. The selected genes investigated were biomarkers for general stress (HSP70), xenobiotic metabolism (CYPA1), antioxidative defence (SOD), Insulin growth factor-1 (IGF-1) and hypoxia inducible factor (HIF) respectively. The expression of the genes revealed significant variations (P<0.05) in the fishes obtained from the different stations of the river. Some of the genes were down-regulated and suppressed while others were upregulated to enable the fish cope with stress while adapting to environmental pollution. Changes in biomarkers can therefore be considered as early signals of stress in the selected fish species.

Macro- and micro morphology of the olfactory organ of African bonytongue, Heterotis niloticus (Cuvier 1829), compared with other species of the family Osteoglossidae (Teleostei)

Osteoglossiformes (bonytongue fishes) possess many morphological specializations associated with functions such as airbreathing, feeding, and electroreception. The olfactory organ also varies among species, notably in the family Osteoglossidae. Herein, we describe the olfactory organ of an osteoglossid, Heterotis niloticus, to compare it with the olfactory organs of other osteoglossiforms. We demonstrate the presence of an olfactory rosette within the olfactory chamber. This structure consists of a short median raphe surrounded by olfactory lamellae, which possess dorsal lamellar processes. On the surface of the olfactory lamellae, there are secondary lamellae formed by the olfactory epithelium. Within the olfactory epithelium, two zones can be distinguished: parallel brands of sensory cells located in the cavities between the secondary lamellae and a nonsensory area covering the remaining part of the olfactory lamellae. The olfactory epithelium is formed by ciliated and microvillus olfactory sensory neurons, supporting cells, goblet cells, basal cells and ciliated nonsensory cells. Additionally, rodlet cells were observed. The results confirm large variability in terms of the olfactory organ of Osteoglossiformes, particularly of Osteoglossidae, and support the secondary lamellae evolution hypothesis within this family.

Early ontogeny of the African bony-tongue (Heterotis niloticus) and the effect of Artemia and rotifer live feeds on larval digestive enzyme activity and performance

High larval and fry mortality has been a major challenge to the commercial culture of the African bony-tongue (Heterotis niloticus). Research indicates inadequate feeding to be a possible cause of the high mortality rates of larvae/fry grown in captivity. An experiment was conducted to first describe the developmental stages of H. niloticus eggs and larvae until schooling, 6 days after hatching (DAH), at 26°C. The morphological development, survival, growth (weight gain and length), and swimming behavior of the larvae were monitored. A follow-up feeding trial was conducted with H. niloticus fry from 6 to 27 DAH involving four treatments: feeding with Artemia nauplii; a combined feed of 50% Artemia nauplii and 50% rotifers (w/w); feeding with rotifers; and no feeding. The activities of three digestive enzymes (trypsin, lipase, and amylase) were assessed in fry exposed to the live feed treatments. At hatching, the larvae had a large, vascularized yolk sac filled with yolk platelets, which occupied approximately one-third of the total body length of the abdominal cavity. Yolk platelet reabsorption started at 1 DAH and was complete at 6 DAH. Metamorphosis was completed at 6 DAH, and schooling behavior was observed. For the feeding trial, the fry that received Artemia nauplii underwent the fastest development until 27 DAH. Similarly, the survival rate was considerably higher in fry fed with Artemia nauplii than in those that received a combination of Artemia nauplii and rotifers or only rotifers. Overall, the survival rates for fry fed with Artemia nauplii and larvae co-fed were 72.7% ± 0.9% and 41.2% ± 3.3%, respectively. Fry did not survive until 27 DAH in the rotifer-fed and unfed treatment groups. Digestive enzyme activity differed significantly (p< 0.05) between treatments and sampling dates. All digestive enzymes were detectable at the onset of mouth opening (5 DAH) and fluctuated through the 7 and 9 DAH. Lower enzyme activity was observed when the fry were subjected to starvation or the rotifer treatment. Results indicate that Artemia nauplii is the best live feed organism for H. niloticus larviculture.

Mycological, Aflatoxin and Heavy Metals Composition of Dried Fish from Idi-ape Markets in Ilorin, Nigeria

Fish is a cherished and highly sort after food that is widely eaten among many communities in Nigeria and the world at large, with good nutritional values. This study is aimed at evaluating the mycological flora, aflatoxin, proximate composition and heavy metals content in different dried fish samples. A total of three samples were used in this study which are; Salvetinus fortinacis, Heterotis niloticus and Malapterurus electricus. Aflatoxin detection in samples were carried out using High Performance Liquid Chromatography. The proximate analysis was carried out to determine the percentage nutritional value in each of the samples. Heavy metals detection was carried out using Atomic Absorption Spectrometer Buck scientific model 230. The result of the mycological evaluation revealed that the mean fungal count of all samples ranged from 1.5 ± 0.71 to 22.5 ± 4.95 (x102 CFU/g). With H. niloticus having the highest while M. electricus had the least. The proximate analysis results revealed percentage moisture of samples ranged from 4.382 ± 0.02 to 6.869± 0.009 (%) with H. niloticus having the highest and S. fortinacis having least value. Ash ranged from 3.518 ±0.18 to 4.424 ± 0.06 (%) with H. niloticus having the highest and S. fortinacis having the least. Percentage carbohydrate ranged from 14.179 ± 0.26 to 15.728 ± 0.33 (%) with H. niloticuss having the highest and S. fortinacis having the least. Calorific value ranged 1270.115 ± 1.12 to 1407.66 ± 1.87 (KJ/100g) with H. niloticus having the highest and S. fortinacis having the lowest. Percentage lipid ranged from 10.549 ± 0.08 to 14.293 ± 0.10(%) with H. niloticus having the highest and S. fortinacis having the least. Percentage Crude fibre ranged from 22.389 ± 0.19 to 29.310± 0.03 (%) with S. fortinacis having the highest and H. niloticus having the least. Percentage Protein ranged from 35.529 ± 0.00 to 38.062 ± 0.00(%) with S. fortinacis having the highest and M. electricus having the least. The presence of mycotoxin producing fungi in the different dried fish samples led to the presence of different Aflatoxins (known carcinogenic toxin) in the samples which is of a threat to human health.

Aquaculture Development in Nigeria: The Second Biggest Aquaculture Producer in Africa

Today, fish farming has become one of the fastest-growing farming businesses, turning Nigeria into the second biggest aquaculture producer in Africa. Also, Nigeria is the leading country in the production of African catfish (Clarias gariepinus) and African bonytongue (Heterotis niloticus). The great quantity of land, inland water surface, and coastland, which are suitable for fish farming, have placed Nigeria at a very advantaged position to develop aquaculture further. Here, the development of brackish and marine aquaculture represents a promising field for future expansion. An adaptation of aquaculture development has to reduce the impact of climate change as outlined. Furthermore, disease management has to be urgently improved. Among others, the availability of commercial feed pellets is a bottleneck that has to be overcome. Unfortunately, Nigeria is far from self-sufficiency in its fish supply, with a deficit of about 2.5 million tons being imported, but national initiatives envision an expansion in the future to increase the supply of the population with high-quality protein and the prevention of malnutrition. This study identifies challenges and opportunities of the aquaculture subsector and tries to give some recommendations for future development, highlighting potential governmental interventions and support.

Genetic diversity of bonytongue fish Heterotis niloticus (Cuvier, 1829) in Cameroon, Central Africa

The African bonytongue (Heterotis niloticus) fish is the only species of the Osteoglossidae family in Africa. The characterization of this fish was carried out from January to June 2020 in Cameroon where this fish is distributed in native zones. This study aimed at contributing to the genetic characterization of Heterotis niloticus population in Cameroon. A total of 96 Heterotis niloticus were sampled from five regions namely Centre, South, Littoral, North and Far North. Caudal fins where randomly collected for genomic DNA (gDNA) extraction. Following standard procedures for simple sequence repeat markers available for this species, seven microsatellites were used for genotyping through Polymerase Chain Reaction (PCR) and electrophoresis. Genetic parameters were scored using the GenAlex 6.503 software and the population structure of Heterotis niloticus was assessed under STRUCTURE Version 2.3.4 software. The results showed that the local population of Heterotis niloticus in North-Cameroon has a higher number of allele (Na=6.00) and effective number of allele (Ne=3.66) while the highest Observed Heterozygosity (Ho) was observed for the population of Heterotis niloticus in the Far-North. The highest genetic distance is observed between the population of Far North and Centre, Far-North and South, Far-North and North. In general, similarity within the sub-population of Heterotis niloticus is higher than 65%. Genetically, the population of Heterotis niloticus in Cameroon was grouped into three genetic sub-populations based on microsatellites appraisal. Further investigations are suggested for analysis concerning productive traits for domestication and aquaculture purposes.

The Upemba National Park (Upper Congo Basin, DR Congo): An Updated Checklist Confirming Its Status as an African Fish Biodiversity Hotspot

An annotated checklist of the ichthyofauna of the Upemba National Park, draining part of the Upper Lualaba basin and situated in the southern part of the Democratic Republic of the Congo, is presented, based on a literature review, a re-examination of museum collections, and a study of recent collections (2012–2020). In total, 247 native and 1 introduced species, Heterotis niloticus, are reported. The native species belong to 78 genera, 26 families, and 15 orders. Of these, 45 species (18%) are endemic to the park, 35 species (14%) await formal description, and 5 taxa (2%) need further study to clarify their status. With 51 species, the Cyprinidae is by far the most species-rich family, followed by the Mormyridae (26), Mochokidae (26), Alestidae (18), Distichodontidae (18), Amphiliidae (17), and Cichlidae (16). The remaining families are represented by less than 15 species. Comments about the species distribution and the fish fauna shared with adjacent ecoregions are provided. Although the park provides some protection for the fish species living within its borders by limiting human access to the core zone, the annex and buffer zones are both subject to strong anthropogenic pressure. These observations underscore the need for the implementation and further elaboration of fish-related preservation guidelines and plans to enable better protection/conservation of the park’s ichthyofauna.

Air-breathing Behaviour in Heterotis niloticus Fingerlings: Response to Changes in Oxygen, Temperature and Exercise Regimes.

Air-breathing in fish is believed to have arisen as an adaptation to aquatic hypoxia. Although air-breathing has been widely studied in numerous fish species, little is known about the obligate air-breathing African bonytongue, Heterotis niloticus. In this way, we evaluated if abiotic factors and physical activity affect air-breathing patterns in fingerlings. The air-breathing frequency (fAB ) and behavioural responses of H. niloticus fingerlings were assessed in response to environmental oxygen, temperature, and exhaustion and activity in a series of experiments. The air-breathing behaviour of H. niloticus fingerlings under optimum water conditions was characterised by swift excursions lasting less than 1 s to the air-water interface to gulp air. The intervals between air-breaths were highly variable, ranging from 3 to 259s. Body size only slightly affected fAB , while hypoxia, hyperthermia, and exercise stress significantly increased fAB . Progressive hypoxia from 17.69 to 2.17 kPa caused a ~2.5 fold increase in fAB . Increasing temperatures to 27 and 32°C, from a baseline temperature of 22°C, significantly increased fAB from 0.4 ± 0.2 to 1.3 ± 0.5 and 1.6 ± 0.4 breaths min-1 , respectively. Lastly, following exhaustive exercise, fAB increased up to 3-fold. These observations suggest that H. niloticus fingerlings are very reliant on aerial oxygen, and their air-breathing behaviour is sensitive to environmental changes and activity levels.

Diet Composition and Dynamics in Fish Species of Ogun Coastal Water, Southwest, Nigeria

Diets composition and dynamics of Eugerres plumieri, Gobioides broussonnetii, Elops aurus, Oreochromis niloticus and Heterotis niloticus in Ogun Coastal water were examined. The fish species were obtained from local fishermen fortnightly between August and October, 2021. The fishes were immediately placed on iced chess after collection and identification before transporting to the laboratory for further examination. All the stomachs of the fishes examined and the contents were analysed using numerical and frequency of occurrence methods. Results indicated that O. niloticus and E. aurus fed on analogous foods which were principally macrophytes, Chlamydomonas species and Spirogyra. Other food items observed in all the fish species includes detritus, sand grains and insect parts. High similarity in the diets dynamics of E. aurus and E. plumieri indicated food competition between the fish species which they both showed high level of trophic flexibility and probably possess same ecological niche.

The gas bladder of Heterotis niloticus (Cuvier, 1829).

This work reports on the structural characteristics of the respiratory gas bladder of the osteoglossiform fish Heterotis niloticus. The bladder-vertebrae relationships are also analyzed. A slit-shaped orifice in the mediodorsal pharyngeal wall is surrounded by a muscle sphincter and serves as a glottis-like opening to the gas bladder. The dorsolateral internal surface of the gas bladder is lined by a parenchyma of highly vascularized trabeculae and septa displaying an alveolar-like structure. The trabeculae contain, in addition to vessels, numerous eosinophils probably involved in immune responses. The air spaces are endowed with a thin exchange barrier indicating a good potential for respiratory gas exchange. The ventral wall of the gas bladder is a well-vascularized membrane that exhibits an exchange barrier in the luminal face and an inner structure dominated by the presence of a layer of richly innervated smooth muscle. This is suggestive of an autonomous adjustability of the gas bladder ventral wall. The trunk vertebrae show large transverse processes (parapophyses) and numerous surface openings that lead into intravertebral spaces that become invaded by the bladder parenchyma. Curiously, the caudal vertebrae show a regular teleost morphology with neural and hemal arches, but have similar surface openings and intravertebral pneumatic spaces. The African Arowana hence rivals the freshwater butterfly fish Pantodon in its exceptional role of displaying postcranial skeletal pneumaticity outside of Archosauria. The possible significance of these findings is discussed.

Phenotypic polymorphism of African bony tongue fish Heterotis niloticus (Cuvier, 1829) in Cameroon rainforest region

The study on the phenotypic polymorphism of Heterotis niloticus was undertaken from February to May 2020 in the rain forest region of Cameroon. The main objective was to contribute to a better understanding of the genetic diversity of this adapted species for adequate breeding and preservation strategies. More specifically, the investigation aimed at evaluating the variability of phenotypic, morphometric and meristic features according to the study sites. Further, it was also in order to analyse the phenotypic variability, the structure, as well as the phylogenetic relationships among the Heterotis niloticus subpopulations. A total of 125 adult individuals were collected in three localities and characterized. Two (2) phaneroptic traits were observed, while 16 morphometric traits were measured and 5 meristic characters were counted. The results showed that there is a colour variability of eyes and body in Heterotis niloticus from the study area with a predominance of golden eyes (97.60%) and grey body (96.80%). The number of scales on the lateral line was higher in the individuals collected in Mbalmayo (38.67±1.46) than those in Ayos (37.70±0.95). Discriminant factor analyses and phylogenetic analyses revealed that the overall population studied is made up of 3 morphotypes cohabiting in the three localities; thus it was possible to establish the phylogenetic relationships that exist between them. Morphotypes 1 and 2 are closer while morphotypes 2 and 3 are far apart, showing a tendency of splitting genetic make up. The recorded diversity suggests that Heterotis niloticus from the study area constitutes a natural genetic resource having the interesting variability for further improvement and sustainable management.

Immunohistochemistry of the Gut-Associated Lymphoid Tissue (GALT) in African Bonytongue (Heterotis niloticus, Cuvier 1829).

Heterotis niloticus is a basal teleost, belonging to the Osteoglossidae family, which is widespread in many parts of Africa. The digestive tract of H. niloticus presents similar characteristics to those of higher vertebrates, exhibiting a gizzard-like stomach and lymphoid aggregates in the intestinal lamina propria. The adaptive immune system of teleost fish is linked with each of their mucosal body surfaces. In fish, the gut-associated lymphoid tissue (GALT) is generally a diffuse immune system that represents an important line of defense against those pathogens inhabiting the external environment that can enter through food. The GALT comprises intraepithelial lymphocytes, which reside in the epithelial layer, and lamina propria leukocytes, which consist of lymphocytes, macrophages, granulocytes, and dendritic-like cells. This study aims to characterize, for the first time, the leukocytes present in the GALT of H. niloticus, by confocal immuno- fluorescence techniques, using specific antibodies: toll-like receptor 2, major histocompatibility complex class II, S100 protein, serotonin, CD4, langerin, and inducible nitric oxide synthetase. Our results show massive aggregates of immune cells in the thickness of the submucosa, arranged in circumscribed oval-shaped structures that are morphologically similar to the isolated lymphoid follicles present in birds and mammals, thus expanding our knowledge about the intestinal immunity shown by this fish.

Nutritional Value, and Heavy Metal Contents of Fish from the Lower River Niger at Agenebode, Edo State, Nigeria

Fish constitutes a vital component of human diets due to their rich nutritional compositions. They serve as a remarkable source of proteins, vitamins, and fatty acids, which are indispensable for the effective growth and development of humans. The need to explore the nutritional compositions of various species of fish in different water bodies becomes paramount. Presently, consumer concern is not just on food's nutritional value but also on the safety level. Environmental contamination by heavy metals has become an issue of pressing concern in recent times. Heavy metals, due to their ubiquitous nature, are found in various water bodies as they are released from various anthropogenic activities. This work investigated the proximate compositions, mineral contents, and heavy metals concentrations of four different species of fish (P. annectens, L. niloticus, G. niloticus, and H. niloticus) collected from the lower Niger at Agenebode using standard procedures. The highest protein contents were in Gymnarchus niloticus (37.32%), while the least was in Heterotis niloticus (20.41%). Protopterus annectens had the highest carbohydrate content (34.55%), while Heterotis niloticus had the least (12.24%). The highest lipid content (14.41%) was in Gymnarchus niloticus. The highest concentration of potassium was 21.00 ppm. The concentrations of heavy metals in ppm ranged from 0.01 – 1.4 (Cd), 0.07 – 2.89 (Pb), 0.02 – 16.4 (Hg), 0.88 – 5.1 (Cu) and 1.2 – 8.23 (Zn). The concentrations of Hg, Cd and Pb in some of the samples investigated were higher than the permissible limits based on international standards. There is a pressing need for further study focusing on various species of animals and plants in the area due to the alarming contents of these metals; remedial measures could also be ensured for safety.

Localization of Acetylcholine, Alpha 7-NAChR and the Antimicrobial Peptide Piscidin 1 in the Macrophages of Fish Gut: Evidence for a Cholinergic System, Diverse Macrophage Populations and Polarization of Immune Responses

The recognition and elimination of invading pathogens are vital for host survival. Macrophages play a central role in host protection and cells functionally reminiscent of vertebrate macrophages are present in all multicellular organisms. A pattern responsible for bacterial recognition found on the surface of macrophages is CD14. These cells possess a repertoire of antimicrobial molecules stored in their granules and lysosomes. Polarization states observed in mammalian macrophages termed M1 and M2 also likely exist in fish macrophages. Markers for macrophage subtypes are slowly but definitively emerging in fish species. In the present study cell markers such as CD14, acetylcholine, alpha 7 acetylcholine nicotinic receptor (nAChR) subtype, the inducible nitric oxidase synthase (iNOS), and the antimicrobial peptide piscidin 1 are reported for the first time in the intestinal macrophages of both catfish Heteropneustes fossilis (Bloch, 1794) and the African bonytongue Heterotis niloticus (Cuvier, 1829) along the anterior and the posterior axis and the concentric muscle layers. Many antimicrobial effector responses of vertebrate macrophages including respiratory burst and NO induction are similar across the diverse animal taxa. Antibodies against calbindin coupled with ones to VAChT and tubulin revealed the localization of myenteric and submucosal plexuses, which are made up of enteric neurons, glial cells, and nerves near macrophages. Current studies allow for the elucidation of multiple roles of macrophages in disease models providing an insight into their in vivo function in fish.

Farming Features of African Bonytongue Fish <i>Heterotis niloticus</i> in Cameroon, Central Africa

The characterization of African bonytongue Heterotis niloticus fish farming was conducted in the Bi-modal agro-ecological zone of Cameroon from January to May 2021, Thirty-two fish farmers were interviewed and SPSS 6.2 Version was used to analyse the data. The results showed that the majority of fish farmers (81%) are men above 51 years, all of whom are Christians with more than fifty percent of them married. About 43% of them have university level education, and more than 6% of them considered the farming of Heterotis niloticus as their main income-earning activity. The main objective of Heterotis niloticus farming is sales (50%) and the uses (56%) of waged labour. A majority of the farmers produced reared African bonytongue in a polyculture system and 65% of them raised Heterotis niloticus in derivation ponds.

Studies on fish species diversity, abundance and Distributon along Onitsha axis of River Niger, Anambra State of Nigeria

A study on biodiversity, abundance and distribution was carried out in Onitsha Axis of River Niger in Onitsha North and South Local Government Area, Anambra State, Nigeria for a period of three months. The area was partitioned into Station I (Emejuru), Station II (Bridge Head) and Station III (Akpaka). Fish samples were collected weekly from July to September, 2019 with the aid of fisher folks using gill nets, cast nets, hook and lines and local traps. The results showed a total composition of 4,645 individuals belonging to 15 families and 31 species. Momyridae showed significance (p<0.05) species diversity with seven (7), followed by Bagridae (5) spp. with the remaining 13 families having one and two spp. Station III Akpaka recorded the highest fish diversity of 37%, followed by Station I Emejuru 34% and Station II Bridge head 29%. In terms of species abundance, Bagrus bayad 13.9% >bagrus docmak 8.8% >Chryschythys Nigrodigitatus7.2% >Bargus filamentous 4.5% >Malapters electricus 4.4% >Heterotis niloticus 4.0% >Orochromis niloticus 3.8% >Mormyrus macrophatalmus 3.3%) recorded the highest, followed by Heterobranchus bidorsalis, Mormyrus rume, Mormyrus tarpirus, Mormyrus senegalensis, Schibe mystus Synodontis clarias and Cithrinus citharus had 2.2%, 2.3%, 3.0%, 1.7%, 2.9%, 1.6% and 3.2% respectively, and Hypothermirus pissitacus the least with 0.4%. This research shows that the Onitsha axis of the River Niger is still rich in fish species diversity and abundance; hence concerted efforts should be made by the various government agencies to see that laws guiding the proper use of water bodies are enforced in the Onitsha axis of the River Niger, to enhance economics, conservation and sustainability.

Effects of stocking density on growth performance, feed utilization and economic profitability of juvenile Heterotis niloticus reared in a pen fish farming

Effects of stocking density on growth performance, feed utilization and economic profitability of juvenile Heterotis niloticus reared in a pen fish farming

Gill structure and neurochemical markers in the African bonytongue (Heterotis niloticus): A preliminary study

We have conducted a morphological and immunohistochemical study of the gills of juvenile specimens of the obligate air-breathing fish Heterotis niloticus. The study has been performed under normoxic and hypoxic conditions. The gills showed a reduced respiratory surface area by development of an interlamellar cellular mass (ILCM). The ILCM persisted without changes under both normoxia and hypoxia. Neuroepithelial cells (NECs), the major oxygen and hypoxia sensing cell type, were located in the distal end of the gill filaments and along the ILCM edges. These cells expressed 5HT, the neuronal isoform of the nitric oxide synthase (nNOS) and the vesicular acetylcholine transporter (VAChT). Furthermore, NECs appeared associated with nitrergic nerve fibres. The O2 levels did not modify the location, number or the immunohistochemical characteristics of NECs. Pavement cells covering the ILCM were also positive to nNOS and VAChT. The mechanisms of O2 sensing in the gills of Heterotis appears to involve several cell populations, the release of multiple neurotransmitters and a diversity of excitatory, inhibitory and modulatory mechanisms.