Gymnarchus Research Articles

Assessment of microplastic-contaminated liver through gene expression profiling of four commercial fish species in the Lagos Lagoon, Nigeria

Microplastic (MP) occurrence in the Lagos Lagoon has been on a progressive increase in recent years. The potential impacts and hazards of MPs on commercially available fish species from the Lagoon have been understudied. This study aims to assess molecular damage due to microplastic accumulation in the liver of four commercial fish species (Oreochromis niloticus, Chrysichthys nigrodigitatus, Clarias gariepinus, and Gymnarchus niloticus) sourced directly from the Lagoon. The results revealed that MP load in the liver of the fish species ranged between 7.2 ± 1.9 and 9.5 ± 4.4 particles/individual, with G. niloticus recording the maximum concentration. The observed extracted MPs are predominantly black and blue fibres while the Fourier Transform Infrared spectroscopy revealed polyethylene dominance in the plastic polymers. Relative gene expression results revealed statistically significant downregulation of the CYP 1a gene and upregulation of the HSP 70 gene in all the microplastic-laden liver samples except in G. niloticus. The findings from this study suggest that microplastic contamination in fish tissues may exacerbate cellular toxicity in commercially available biota in the Lagos Lagoon, thereby calling for urgent measures to curb microplastic and ultimately plastic pollution. However, there's a need for in-depth research on the effects of environmentally relevant microplastics on edible fish tissues to further elucidate their molecular impact.

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.

Približan sastav i organoleptičke osobinesušene ribe Aba (Gimnarchus Niloticus)

This study investigates the quality composition of Aba knife fish (Gymnarchus Niloticus) predominant in South-eastern Nigeria. The fish sample require proper processing techniques to preserve their organoleptic qualities for a substantial period. The objective of the study was to investigate the influence of oven-drying process on the proximate and organoleptic qualities of Gymnaruchus Niloticus. The studied fresh fish fillets were rinsed in clean water, brined and spread in trays before taken for oven drying. An oven drier (FALC STF-F-52) was used for the oven-drying process. Analyses of proximate compositions (moisture content, crude lipid, crude protein, ash content and crude fiber) were carried out on the fresh and oven dried fish samples. The study showed that oven drying decreases the moisture content to a safe level of 38.13 ± 0.01% dry basis(d.b), and increase the crude protein content (18.23±0.01), fat content (4.34±0.01), ash content (3.40±0.01), carbohydrate content (35.96±0.01) of the investigated fish samples. There were no crude fibre contents (0.00) in the fresh fish samples. Therefore, the oven drying process had no noticeable effect on the fibre content. The oven dried fish samples were rated high in terms of taste, aroma, colour, texture and general acceptability by the panel of assessors. The significance of the obtained results as well as recommendations for further studies were offered.

Fish Mummies in the Collections of the Náprstek Museum – Preliminary Report

The National Museum – Náprstek Museum of Asian, African and American Cultures, Prague, keeps within its collection four ancient Egyptian fish mummies. The specimens were recently examined using computed tomography as a part of the Atlas of Egyptian Mummies Project in the Czech Collections. Preliminary results of the examination using the most advanced, non-destructive radiological methods indicated that the original taxonomical determination of the mummified fish, examined previously by the team led by Eugen Strouhal in the 1970s, as Polypterus sp. (and Gymnarchus niloticus) was not confirmed. Recently, the specimens were classified as belonging to the Siluriformes order.

Abundance, Distribution, Morphometric, Feeding Evaluation and the Reproductive Strategies of Gymnarchus niloticus in the Lower River Niger at Agenebode, Edo State Nigeria

The study of the numerous areas of biology of fish produces ample and relevant information that aids scientist to explore, know and maintain the survival, growth, continuity and sustainability of life of various fish species. A total of 94 specimens of Gymnarchus niloticus were collected from River Niger at Agenebode during the sample period that ranged from 14 – 94 cm total length (54.88± 17.92); weighed 424 - 2281g (1569.61 ± 422.85). The length weight relationship (LWR) of G. niloticus in this study showed a negative (b<3) allometric growth pattern. Out of the 94 specimens analysed 54 males and 40 females were examined with a ratio of 1:1.4. Insects and decapods were the major food of the juveniles of Gymnarchus niloticus while the major food of preference of the sub adults and adults were Fish and insects with 27.12%, and 27.97% by FO. Gymnarchus niloticus possesses a single ovary in the female and single testis in the male which is often referred to as unpaired gonad. Fecundity ranged between 620 to 1378 eggs with a mean of 957.69 ± 112.31 eggs in females. The relationship between fecundity (F) and weight (W) and fecundity and standard length (SL) showed that fecundity is more related to weight than length of fish. Log F = 820.66 + 0.11 W and Log F = 151.23 + 5.31 SL. Fecundity had a positive significant correlation (P<0.05) with both somatic weight (r = 0.714) and standard length (r = 0.657) of fish. Ova diameter showed a ranged between 3.5 and 7.9 mm with a mean of 4.72 ± SD1.69 mm and it had significant relationship (P<0.05) with total weight, gonad weight and maturity stage. Gymnarchus niloticus in the Lower River Niger at Agenebode showed that G. niloticus has an unpaired gonad in both sexes, a gonochoristic reproductive pattern. Fecundity is low and the ova are large. They are small brood spawners with asynchronous breeding strategy. The attributes of G. niloticus obtained from this study reveals that the fish species is a good candidate for fish culture.

CONSTRAINTS ON FISH PREFERENCE AND CONSUMPTION PATTERN IN LAGOS STATE, NIGERIA

Fish is one of the main key ingredients on global menu consumed by rich and poor people. This study examined constraints associated with fish preference and consumption pattern in Lagos State, Nigeria. Multi-stage sampling procedure was used to select 112 respondents for the study. Data were collected on types of fish preferred, respondents’ income, constraints and forms of fish consumed using a structured questionnaire. Frequency counts, percentage, mean and Pearson Product Moment Correlation (PPMC) were used to analyze the data. Result revealed that the most preferred frozen, fresh and processed fish were Mackerel (x̄ = 1.46), Clarias spp (x̄ = 0.85) and fried fish (x̄ = 1.38), respectively. Most of respondents’ income (30.4%) fell between N10,001 to N20,000. Inadequate power supply (x̄ = 1.69), high cost of fish (x̄ = 1.58), and poor income (x̄ = 1.56) were some of the constraints that affected fish consumption in the study area. Mackerel (94.5%), fried fish (74.9%) and Gymnarchus niloticus (37.8%) were the most consumed form of frozen, processed, and fresh fish respectively. Result of PPMC showed that relationship exists between consumers’ income level (ᵡ2 = 0.008; r = 0.398; and P≤ 0.05) and consumption of fish. Also, there exists a difference (P≤ 0.05) in the consumption pattern of fish between rural and urban consumers (t = -2.109; df = 109; and P = 0.037). The study concluded that consumers’ income level and access to power supply posed great challenge to consumption and preference for fish in the study area. Government should intensify effort in providing stable power supply.

Gross Anatomy and Histological Features of Gymnarchus niloticus (Cuvier, 1829) from the River Niger at Agenebode in Edo State, Nigeria

This study was conducted to record the anatomy and histological features of the gastrointestinal tract of the trunk fish Gymnarchus niloticus captured at Agenebode in the Lower River Niger, Edo State. The gastrointestinal tract was segmented into the mouth, oesophagus, stomach, pyloric caeca, and intestine. The slender (taeniform) body that is fuller at the head tappers at its end. There are no spines on this fish, and the fins used for locomotion are the dorsal fins and not the typical pectoral fins as in other fish. The oesophagus, stomach, pyloric caeca, intestine, and cloaca (anterior, intermediate, posterior, and rectum) were analysed for histological examination. The stomach had significantly higher villi and thicker inner circular muscles compared to the intestine and oesophagus. The lamina propria was thickest in the stomach which is significantly higher when compared with the oesophagus, but not with the intestine. However, the intestine showed significantly thicker outer longitudinal muscle, while gastric glands were observed only in the stomach. The histological features were closely associated with the functions of the different segments of the gastrointestinal tract. In conclusion, the histological features of the gastrointestinal tract of G. niloticus are consistent with the feeding habit of a carnivorous fish. In conclusion, the GIT is a complex structure composed of organs that reveals that it is a higher vertebrate created for a hardy survival, consistent with the feeding habit of a carnivorous fish. The histology reveals a GIT formed by four conspicuous layers from the inside to the outside of the mucosa, submucosa, and an inner longitudinal layer of the muscularis and the outer circular of the muscularis typical of higher vertebrates.

Anthropogenic Influences on Physico-Chemical Quality, Fish and Macrophyte Diversities of River Adofi, Southern Nigeria.

&lt;b&gt;Background and Objective:&lt;/b&gt; Freshwater systems support agriculture, industry and even human existence. Pollution due to human activities affect the quality of water bodies thereby threatening biodiversity. This study, therefore, investigated the anthropogenic influences on physico-chemical quality, fish and macrophyte diversities of River Adofi. &lt;b&gt;Materials and Methods:&lt;/b&gt; Three sampling stations along River Adofi at Ejeme-Aniogor (Station 1), Utagba-Uno (Station 2) and Umuleke-Ossissa (Station 3) were selected based on ecological features and the presence of human activities. Water samples were collected fortnightly for 6 months and water quality was determined. Fish and macrophyte species were collected and diversity indices were calculated. &lt;b&gt;Results:&lt;/b&gt; Physico-chemical parameters were significantly different (p<0.05) in all three stations except for magnesium, calcium and nitrate. Temperature, total dissolved solids, conductivity, COD, total alkalinity and magnesium were higher (p<0.05) in Station 2 at Utagba-Uno where a rubber factory effluent discharges into the river. Out of 15 families, 18 genera and 26 species of fish collected &lt;i&gt;Oreochromis &lt;/i&gt;species were more abundant, followed by &lt;i&gt;Gymnarchus niloticus&lt;/i&gt;. Mokochidae and Clariidae had higher diversities than other families. Macrophytes recorded were 53 taxa from 21 families and 33 genera with emergent and submerged life forms dominating. Poaceae dominated with nine species. Shannon index increased with increasing species richness and evenness with both fish and macrophytes evenly distributed. &lt;b&gt;Conclusion:&lt;/b&gt; Lower diversity of fish species observed in Station 2 may be due to influences of effluent discharges into the river while domestic and agricultural activities enhanced abundance and diversity of fish and macrophytes at Station 3.

Ultrastructure of the Anisakid nematode, Raphidascaroides sp (Nematoda: Anisakidae) from the freshwater fish Rhinogobius ocellatus (Fowler, 1937) with attendant histopathological alterations in Lekki Lagoon, Lagos, Nigeria

The objective of this study is to report the parasitic infections in the gobiid fish with histopathogical changes and the SEM description of the recovered parasites for possible unreported morphological details and for the purpose of control measures in the fish species. Fishes were procured, dissected and examined parasitologically. The nematode, Raphidascaroides sp was the only recovered parasite from the intestine of the gobiid fish. Fixation of the parasites was done in 2.5% glutaldehyde and were post fixed in 1% Osmium tetraoxide, sputter coated and examined with the Scanning Electron Microscope. The infected tissues were also fixed in Bouins fluid.The overall prevalence of infections was 70.7%. Male specimens of the fish species were more susceptible to infections (71.4%) than the female specimens (66.6.) The Raphidascaroides sp. ultrastructure revealed three lips with dentigerous ridges.The two ventrolateral lips measures 68.6 and 69.7 µm while the third lip has a length of 55.1 µm with corresponding breadth of 66.0 µm, 40.5 µm and 59.3 µm respectively. The histopathological alterations in the fish species revealed goblet cell hyperplasia and moderate lymphocytic infiltration of the lamina propria.The dominant and only parasite recovered from the fish host is Raphidascaroides sp, an anisakid nematode whose pathological consequences is mild owing to lack of holdfast organs in nematodes. The ultrastructural description of the parasites is the first report in Nigeria. There is a conclusion that there may be similar food and feeding habits of the fish, Rhinogobius ocellatus with Gymnarchus niloticus with a report of the same parasites in its intestinal mucosa.

Structural diversity of olfactory organs in Osteoglossiformes

AbstractOsteoglossomorpha, an ancient Teleostei group, exhibits many ancestral structural features. Herein, we describe the diversity in morphology of olfactory organs of air‐breathing Pantodon buchholzi, Arapaima gigas, and Gymnarchus niloticus in terms of adaptations to short ventures out of water and compare the results with the water‐breathing Osteoglossum bicirrhosum. We demonstrate the presence of olfactory rosettes within the olfactory chamber in all studied species and additionally a peculiar cudgel‐shaped structure in P. buchholzi. The typical olfactory rosette with centrally located elongate median raphe and two rows of olfactory lamellae was found only in P. buchholzi. In A. gigas, the olfactory lamellae arranged in semicircular manner were merged to small median raphe. Osteoglossum bicirrhosum and G. niloticus lacked median raphe, while the olfactory lamellae were ordered nearly parallel or circular, respectively. Olfactory epithelium lining the olfactory lamellae was unfolded only in P. buchholzi and G. niloticus. In contrast, in O. bicirrhosum and A. gigas convexities formed by nonsensory cells and concavities made by the sensory component were observed. Among the olfactory sensory neurons, ciliated and microvillus neurons were found in all studied species. Crypt‐like cells were noted only in P. buchholzi, whereas rod‐like cells were unique for A. gigas. The substantial morphological variation of the olfactory organ structure and ultrastructure in the studied osteoglossiforms may be explained by the early division of Osteoglossomorpha within Teleostei and long‐term, independent evolution within the families.

Nilonema gymnarchi (Nematoda: Philometridae) and trace metals in Gymnarchus niloticus of Epe lagoon in Lagos State, Nigeria

The presence of trace metals in the sediment, water, and biota of the Epe lagoon has been recently linked to oil exploration and municipal perturbations around the lagoon. The study was aimed at assessing the concentrations and associated health risks of Fe, Zn, Cu, Ni, Pb, Cd, Cr, Mn, Co and V in the water, sediment, and Gymnarchus niloticus of Epe lagoon and to evaluate the role of the enteric parasite Nilonema gymnarchi in bioaccumulation of the metals in the fish. The temperature, pH, redox potential, conductivity, turbidity, dissolved oxygen (DO), total dissolved solids (TDS), and salinity were determined in-situ using a handheld multi-parameter probe (Horiba Water Checker Model U-10). The concentrations of Fe, Zn, Cu, Ni, Pb, Cd, Cr, Mn, Co, and V were determined in the surface water, bottom sediment, Gymnarchus niloticus, and its enteric parasites, Nilonema gymnarchi in Epe lagoon using the Flame Atomic Absorption Spectrometer (Philips model PU 9100). The bioaccumulation factors and target hazard quotients of the trace metals in the infected and uninfected fish were estimated and compared. The intestinal tissue sections of the infected and uninfected fish were examined using a binocular dissecting microscope (American Optical Corporation, Model 570) using hematoxylin and eosin (H&E) stain. Biochemical markers such as reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and lipid peroxidation (MDA) were determined in the liver of the infected and uninfected fish. The SOD level was higher in the uninfected fish than the infected ones supports the indications deduced from the bioaccumulation analysis. Strong positive correlations between SOD and most of the metals- Fe (0.916), Zn (0.919), Cu (0.896), and Ni (0.917) suggests that the metals may have inflicted more toxicity in the uninfected. The histopathological comparisons made between the uninfected and infected fish showed consistency with the outcomes of other comparisons made in this study. These evidence were marked by tissue alterations in the infected fish ranging from no observed changes to mild alterations, while the uninfected exhibited more severe tissue injuries such as hemorrhagic lesions, severe vascular congestion, edema, the increased connective tissue of the submucosa, and vascular congestion. The condition factors of the infected (0.252) and uninfected (0.268) fish indicated slenderness and unfitness possibly due to environmental stressors such as trace metals. The parasitized fish showing better-coping potentials than the uninfected, coupled with the significant bioaccumulation interferences exhibited by the parasite Nilonema gymnarchi is an indication that the parasites may be a good metal sequestration agent for the fish and can be used to forestall the significant health hazard quotient posed by the current level of iron and the synergy of all metals analyzed in the lagoon.

Ichthyofauna composition of Alape River, Igbokoda, South West Nigeria

Objectives: To study ichthyofauna composition of Alape River, Igbokoda, Ilaje Local Government Area of Ondo State, Nigeria. Method: Sampling was done for a period of three months, from the month of November 2019 to January 2020. Data for this study were based on the record of fish caught by local fishermen. Findings: A total of twenty thousand, four hundred and nine (20,409) individual fishes of six species (Heterotis niloticus, Clarias gariepinus, Chrysichthys nigrodigitatus, Gymnarchus niloticus, Oreochromis aureaus and Hepsetus odoe), belonging to six families (Arapaimidae, Clariidae, Claroteidae, Gymnarchidae, Cichlidae and Hepsetidae) were recorded for the whole period of study. The over-all comparison among the months of study shows that January recorded the highest catch (6,919) with an over-all relative percentage abundance of 33.9%, followed by December (6,871) with 33.67%. The least catch (6,619) was observed in the month of November with a relative percentage abundance of 32.43%. The study showed that Clarias gariepinus and Oreochromis aureus were dominant fish species, Chrysichthys nigrodigitatus was sub-dominant, Heterotis niloticus and Hepsetus odoe were occasional while Gymnarchus niloticus was rare in River Alape. The results of this study showed that the river has low fish species composition and abundance in spite of the size of the river. Considering this fact, there is need for further survey to cover more months. There is also a need to evolve strategies for effective utilization and proper management of the river for optimum fish production, sustainability and conservation. Keywords: Ichthyofauna; Abundance; Composition; Alape River

Biodiversity of Fish Fauna in River Niger at Agenebode, Edo State, Nigeria

The River Niger is blessed with diverse fish species and aquatic life. The study of the fish fauna and biodiversity along the River Niger was conducted from October 2016 to December 2018. A total of 35 species belonging to 18 families were obtained from this study. New to this River as regards literature are the family Solidae and Catostomidae. The sole fish (Solea solea) (0.16%) with only 1 representation while the Catastomids were represented by 3 species; Ictiobus niger (1.73%), Ictiobus cyprinellus (2.20%), Ictiobus bubalus (2.52%). Other species obtained were the Mormyrus rume 3.93%, Polyterus bichir (2.99%) and Protopterus annectens (7.08%). The most abundant of species observed was Gymnarchus niloticus (8.49%) of the family Gymnarchidae while the least was Solea solea (0.16%). The biodiversity indices revealed that Station 2 had the most evenly distributed species and the most of diverse species though Station 1 had the most number of species. Station 3 however had the least of species obtained. It is concluded the River Niger is still productive and in good condition, capable of maintaining and managing fish species according to condition factor.

Numerical study on vortex structure of undulating fins in stationary water

The Gymnarchus Niloticus fish(GNF) with long dorsal-fin undulating generally cruises with high efficiency and extra-ordinal maneuverability while keeping its body for straight line. In the paper the unsteady flow field of undulating fins in stationary water is calculated by Large Eddy Simulation and dynamic grid technique with diffusion-based smoothing model. The thrust produced by undulating fins is measured at wave amplitude of 850, and the unsteady flow field around undulating fins on middle cross section at wave amplitude of 850 at a series of phase angles is measured by phase-locked PIV in the stationary water. The thrust calculated by numerical simulation is in good agreement with hydrodynamics experiments. The streamwise vortex structure and its evolution on cross sections calculated by numerical simulation qualitatively agree well with PIV experiments. The numerical results at wave amplitude 300 indicates there are three kinds of vortexes in the flow field, i.e. streamwise vortex, crescent vortex and toroidal vortex. Vortex characteristic and its temporal and spatial evolution is described, and the vortex structure and its relationship with thrust, heave force is analyzed.

Dynamics of heavy metal Pollution in Tropical lagoon of Gulf of Guinea, West Africa

In this study the accumulation of Iron (Fe), Zinc (Zn), Cobalt (Co), Chromium (Cr), Cadmium (Cd), Lead (Pb) and Nickel (Ni) in sediment, water, some fish samples (Schilbe mystus, Mormyrus rume, Gymnarchus niloticus, Cynoglossus senegalensis, and Chrysichthys nigrodigitatus ) and an aquatic plant Eichhornea crassipes collected from Lekki lagoon, Lagos Nigeria were examined. Heavy metals in the water, sediment, some selected fish and an aquatic plant were determined seasonally across nine sampling Stations; in the gills, liver and muscles of the fish species and in the root stem and leaves of Eichhornea crassipes using an atomic absorption spectrometer (AAS). Heavy metals concentrations in the sediment and water varied significantly, both spatially and seasonally. Metal concentrations varied between species and body parts while Co, Cr and Pb were not detected. Ni was found in the liver and gills of S. mystus and M. rume and Cr in the gills of G. niloticus only. In Eichhornea crassipes , metals detected were in the order: root>leaves>stem for Fe, Zn, Cr, and Cd; root>stem>leaves for Pb and Ni while Co was not detected. Heavy metal presence in Lekki Lagoon calls for monitoring of activities within and around the lagoon and policy development towards the sustainable ecosystem health services. Keywords: Pollutants, Heavy metals, Eichhornia crassipes, Bioaccumulation, Lekki lagoon

Polycyclic Aromatic Hydrocarbons in Smoked Ethmalosa fimbriata and Gymnarchus niloticus from Selected Fish Markets in the Niger Delta, Nigeria

Polycyclic aromatic hydrocarbon (PAH) concentrations in edible muscles of two smoked fish species (Ethmalosa fimbriata and Gymnarchus niloticus) collected from different fish markets in the Niger Delta in Nigeria were determined. The aim of the study was to ascertain the PAH composition and consequent potential human health risk through dietary ingestion of these smoked fish species. The Σ16 PAH concentrations varied from 237 to 965 µg kg−1. The compositional pattern of PAHs in the fish species showed the prevalence of 2–4 ring PAHs over 5–6 ring PAHs. The carcinogenic potency (BaPTEQ) values ranged from 5.4 to 122 µg kg−1 and 27 to 102 µg kg−1 for E. fimbriata and G. niloticus, respectively, while the mutagenic potency (BaPMEQ) values varied from 2.8 to 135 µg kg−1 and 20 to 83.2 µg kg−1 for E. fimbriata and G. niloticus, respectively. The estimated incremental lifetime cancer risk from the ingestion of these fish samples varied from 1.04 × 10−9 to 2.34 × 10−8 which suggested that there is no considerable cancer risk arising from the ingestion of these fish species.

Karyotype of the african weakly electric fish, &lt;i&gt;Gymnarchus niloticus&lt;/i&gt; (Osteoglosiformes: Gymnarchidae) from Oluwa River, Nigeria

Bonytongue fishes of the order Osteoglossiformes provide an interesting clade for evolutionary study considering their wide distribution and their basal position in the general Teleostei phylogeny. Lack of adequate information on the cytogenetics of this group of fishes has been a limiting factor to the understanding of karyotype evolution of the clade. In this study, karyotype of Gymnarchus niloticus, the only species in the family Gymnarchidae collected from Oluwa River was investigated in order to increase the knowledge of karyotype pattern in the family. Metaphase chromosomes were obtained from the anterior portion of the kidney after injecting the fish intraperitoneally with 0.05% colchicine. Slide preparation followed the conventional Giemsa staining technique while digital images of the chromosomes were processed using Mirosoft Excel and Photoshop. The result revealed a karyotype of 2n = 54 (26m+14sm+14sta) which was significantly different in chromosome number and in chromosome macrostructure from the karyotype of 2n = 34 (34m/sm) reported for G. niloticus from Lekki Lagoon. The wide difference in chromosome number and in chromosome structure observed in G. niloticus from these two locations is not a common occurrence among closely related fish species. These two karyotypes therefore raise a question of the possibility of another species in the family Gymnarchidae.Keywords: Cytogenetics, Chromosomes, Bonytongues, Osteglossomorpha

Lumbering on land costs elephant seals dear

In the transition from a terrestrial lifestyle to an existence beneath the waves, elephant seals (Mirounga angustirostris) are pretty far along. With a streamlined body, blubber for insulation and the ability to carry extensive oxygen supplies for lengthy dives, elephant seals are as well equipped as many whales and dolphins. However, when the colossal mammals haul themselves onto gently shelving beaches to mate and give birth, the tables turn against them. ‘There is an energetic consequence to becoming aquatic; it becomes easier to swim but harder to walk’, says Frank Fish from West Chester University, USA; the question was, how hard? Having previously filmed and analysed the movements of relatively diminutive harbour and grey seals, which are about one-tenth the size of elephant seals, Fish and graduate student Kelsey Tennett teamed up with Dan Costa from the University of California, Santa Cruz, USA, to get up close and personal with the gigantic mammals in California's Año Nuevo State Park.‘It was in January, the time when males are trying to mate with females and the females are pupping’, says Fish, recalling how the massive seals weren't too bothered by the scientists and their cameras; they had other things on their minds. Setting up a camera about 6–12 m from a seal that was taking a brief rest after dragging itself across the sand, the team waited until the animal showed signs of moving again before filming. ‘We could tell when the animal was about to move because it would start to rise up with its head and chest’, says Fish. Having filmed the seals humping along before collapsing on the sand, Fish then dashed into shot behind the animal with a 0.5 m long stick, so that Tennett could calculate the size of the animal and measure its movements back in the lab.Analysing the seals’ cumbersome manoeuvres, Fish realised that each elephant seal initially reared its head and chest up before allowing its torso to slump forward to initiate a charge. As its chest crashed down, the animal then flexed its body like an inchworm to shift its hindflippers forward, allowing it to push down on the sand with its pelvis as the wave of movement travelled forward along its body. This then allowed it to thrust its chest, head and neck back off the sand, using its foreflippers like crutches, ready to lurch forward once again and initiate the next cycle. Sometimes the animals could only manage a few ‘strides’ covering 5–10 m before grinding to a halt, while some males maintained speeds of up to 2.5 m s−1 over 30–40 m in pursuit of a female or rival.But what did all of this mean for the giant animals’ efficiency as they thundered across the sand – were they more or less efficient than smaller seals? Fish and Tennett teamed up with physicist Anthony Nicastro, also from West Chester University, to answer the question. They calculated that the elephant seals were using approximately 40 times more energy at any instant to shuffle along at speeds of about 2 m s−1 (which equates to 0.6 times their body length), than smaller grey seals scuffling about at a similar speed – relative to their body size – of 1.3 m s−1.‘Bigger is not always better, particularly when you are highly adapted for swimming rather than terrestrial locomotion’, says Fish, adding that elephant seals are paying an energetic penalty for their aquatic lifestyle. And, having scrutinised the largest seals in the northern hemisphere, Fish is keen to visit their even more gigantic relatives in the south. ‘I want to see if they [southern elephant seals] have reached a limit in how big a seal can be’, he says.

Manta rays bank like planes to take turns

![Figure][1] A manta ray ( Mobula birosris ). Photo credit: Frank Fish. It might seem like the stuff of 1960s science fiction, but the US Navy is intrigued by the stealth and manoeuvrability of manta rays. These colossal creatures could inspire the next generation of autonomous

Molecular evolution of globin genes in Gymnotiform electric fishes: relation to hypoxia tolerance

BackgroundNocturnally active gymnotiform weakly electric fish generate electric signals for communication and navigation, which can be energetically taxing. These fish mainly inhabit the Amazon basin, where some species prefer well-oxygenated waters and others live in oxygen-poor, stagnant habitats. The latter species show morphological, physiological, and behavioral adaptations for hypoxia-tolerance. However, there have been no studies of hypoxia tolerance on the molecular level. Globins are classic respiratory proteins. They function principally in oxygen-binding and -delivery in various tissues and organs. Here, we investigate the molecular evolution of alpha and beta hemoglobins, myoglobin, and neuroglobin in 12 gymnotiforms compared with other teleost fish.ResultsThe present study identified positively selected sites (PSS) on hemoglobin (Hb) and myoglobin (Mb) genes using different maximum likelihood (ML) methods; some PSS fall in structurally important protein regions. This evidence for the positive selection of globin genes suggests that the adaptive evolution of these genes has helped to enhance the capacity for oxygen storage and transport. Interestingly, a substitution of a Cys at a key site in the obligate air-breathing electric eel (Electrophorus electricus) is predicted to enhance oxygen storage of Mb and contribute to NO delivery during hypoxia. A parallel Cys substitution was also noted in an air-breathing African electric fish (Gymnarchus niloticus). Moreover, the expected pattern under normoxic conditions of high expression of myoglobin in heart and neuroglobin in the brain in two hypoxia-tolerant species suggests that the main effect of selection on these globin genes is on their sequence rather than their basal expression patterns.ConclusionResults indicate a clear signature of positive selection in the globin genes of most hypoxia-tolerant gymnotiform fishes, which are obligate or facultative air breathers. These findings highlight the critical role of globin genes in hypoxia tolerance evolution of Gymnotiform electric fishes.