On a new species of electric catfish from Kainji, Nigeria, with some observations on its biology

A new species of electric catfish, Malapterurus minjiriya , from Kainji, Nigeria, is described and a key for separating it from the two other known species is given. Notes on some aspects of the biology of the electric catfishes in Lake Kainji, Nigeria are included.     

The food and feeding habits of Hydrocynus forskahlii Cuvier and Hydrocynus brevis Günther in Lake Kainji, Nigeria

The diets and modes of feeding of Hydrocynus forskahlii Cuvier and Hydrocynus brevis Günther are described. Both species are mainly piscivorous in Lake Kainji. H. forskahlii feeds largely upon small clupeids though very large specimens prey more heavily upon the characid Alestes baremose. H. brevis preys upon a wide variety of species by swallowing them whole but also attacks large fish and bites pieces from them. Sexual dimorphism in H. brevis is described. The effects of predation upon the fish stock of Lake Kainji by Hydrocynus species are discussed.     

Temporal patterning of electric organ discharges in the African electric catfish, Malapterurus electricus (Gmelin)

This paper is the first detailed analysis of situation-specific temporal patterning of electric organ discharges (EODs) in a strong electric fish. Using a resident-intruder paradigm EODs were recorded during interactions between dyads composed of Malapterurus electricus (Gmelin) and four different types of fish: (1) conspecifics; (2) large prey-type mid-water fish, goldfish ( Carassius auratus , Linnaeus 1758) and tilapia ( Oreochromis melanotheron , Rüppel, 1852); (3) a sympatric competitor, Polypterus palmas (Ayres 1850) and (4) a larger, threatening catfish, Clarias sp.
An analysis of the EODs emitted showed that in the presence of conspecifics the average EOD volley consisted of a single long-duration, low frequency train of EODs. The presence of the midwater fish (goldfish and Tilapia) elicited volleys consisting of two short trains, and P. palmas elicited long duration volleys with two trains and long inter-train intervals. Finally, an attacking Clarias resulted on average in volleys consisting of two high-frequency trains of EODs. With nonconspecific partner species resident electric catfish emitted volleys with more pulses, more trains that were longer in duration and higher in frequency than the EODs in volleys emitted by intruder electric catfish with the same species stimulus fish.     

Notes on the biology of the mayfly Povilla adusta in West Africa

A study of the mayfly Povilla adusta Navas in five West African lakes showed at least one population (in Barombi Mbo) with a clear lunar periodicity of emergence, and at least one without, at Kainji Lake. The seasonal distribution of Povilla eggs in fish stomachs at Kainji implies a delayed effect of lake level on adult numbers. The relatively small size and short generation time (probably three months) of Povilla in Barombi Mbo, by comparison with the same species in Lake Victoria, may be related to the higher temperature of Barombi Mbo. The eggs of bdelloid rotifers were found attached to Povilla larvae from some of the lakes.     

Food and feeding of the mormyrid fishes of Lake Kainji, Nigeria, with special reference to seasonal variation and interspecific differences

The feeding habits of mormyrids from Lake Kainji, Nigeria, are discussed in relation to the decreased abundance of these fish since impoundment in 1968. Evidence is presented of both intra-specific seasonal variation in diet and inter-specific trophic divergence. These variable factors are discussed in relation to the degree of success achieved by certain species in the lake.     

The effects of the formation of Lake Kainji (Nigeria) upon the indigenous fish population

The changes in the species composition and structure of the fish population resulting from the damming of the River Niger at Kainji are illustrated and discussed. The main changes are shown to be a decline in the numbers of bottom feeding insectivores, especially the Mormyridae and an increase in the numbers of omnivores, predators and planktivores. The detailed specific changes within all the major families are examined. A brief comparison is made between the changes in the fish population following Lake Kainji's formation and the effects of the formation of other African man-made lakes     

Haematology and habits in catfish of the genus Synodontis

African catfish of the genus Synodontis vary in their habits, from inverted plankton eaters to normally oriented benthos eaters. Haemoglobin concentrations and red cell counts vary between populations of one species, and between species of differing habits. Synodontis schall from the well-aerated White Nile had lower haemoglobin concentrations than members of the same species from Lake Kainji, Nigeria. Synodontis membranaceus , an inverted plankton eater, had lower haemoglobin concentrations than the bottom dwelling S. filamentosus and S. nigrita. Species with intermediate habits, such as S. batensoda and S. ocellifer had intermediate concentrations of haemoglobin.
It is suggested that these differences in haemoglobin concentration are a result of differing habits. Those species that enter poorly aerated water are stimulated to make more haemoglobin.     

The effect of the impoundment of Lake Kainji, Nigeria, on the indigenous species of mormyrid fishes

SUMMARY. Changes in the numbers and species composition of mormyrid fishes since the impoundment of the Niger (Lake Kainji) are analysed. An initial decline after impoundment appears to have been reversed and these fish are now increasing. The increase is, however, restricted to a few species only; many forms common in the river are still declining or have disappeared altogether. Marked seasonal variations in abundance are described and possible explanations discussed.     

Episodic electric discharges in the course of social interactions: an example of Asian clariid catfish

Function of weak electric discharges is conclusively proved only for two fish orders - Mormyriformes and Gymnotiformes. Every specimen of the two groups emits electric discharges continuously or quite regularly for location, orientation and communication. The function of weak episodic electric discharges in other groups of weakly electric fish - Rajiformes, Uranoscopidae and Siluriformes, remains the puzzle since Darwin. Recent experiments made it possible to expand the list of weakly electric fish with episodic discharges. The range of behavioral situations accompanied with electric emission has been expanded as well. For instance, Asian catfish, Clarias macrocephalus, emit episodic discharges while in aggressive and spawning behavior. Asian catfish females emit the special burst of electrical discharges as a part of mating ritual. This burst cannot serve as an invitation to spawning or synchronization of reproductive products release, because females emit it after the sperm ejection. If females would need males' help for eggs release, it could be suggested that discharges assist in their mutual efforts. Since the electric field strength near fish is higher than fish's non-specialized electrical sensitivity thresholds, other hypotheses are possible. For example, it could be suggested that electric fields would make sperm or eggs more active. To proceed in our conception about episodic discharges function, new hardware and software are needed.     

Changes in recreational catfish Silurus glanis harvest rates between years 1986–2017 in Central Europe

The European catfish Silurus glanis is an important fish species in both commercial and recreational fisheries. Catfish is a spreading species that was reported to potentially benefit from increasing temperatures. The goal of this study was to estimate long‐term changes in harvest rates of catfish in Central Europe. This study used individual mandatory angling logbooks collected by the Czech Fishing Union in the Czech Republic (Central Europe) over the course of years 1986–2017 (32 years) to assess harvest rates of catfish. This study discovered that harvest of catfish has been increasing over time. Moreover, rivers that previously showed zero harvested catfish are beginning to display higher harvest rates of catfish. Increasing average air temperature and angling effort in the study area have positively affected harvest rates of catfish. The increased harvest of catfish could not be reliably explained by intensive fish stocking. In conclusion, while other studies show that many fish species are negatively affected by human activities and therefore show decreased harvest rates, catfish angling seems to benefit from anthropogenic changes.     

Monopolar electric discharges of the catfish <Emphasis Type="Italic">Parasilurus asotus</Emphasis> (Siluridae,Siluriformes)

Electric discharges in the catfish Parasilurus asotus are registered for the first time. The discharges are monopolar pulses of a 50–300 ms duration which corresponds to the frequency characteristics of ampoules of electroreceptors in these catfish. Electric generation is discovered only upon the aggressive-defensive behavior of not less than two species. In solitary fish no discharges were observed neither at prolonged continuous registration (longer than 24 h each) nor at mechanical stimulation. The hypothesis is discussed of a potential mechanism of active (under use of their own electric discharges) monitoring of water conductivity with a relative sensitivity on the order of 0.0002%. This hypothesis may be applied to an explanation of anomalous group behavior of these catfish before earthquakes.     

Comparison of two methods of attaching telemetry transmitters to the Mekong giant catfish, Pangasianodon gigas

For conservation and successful stock enhancement of endangered species, an understanding of the movement patterns and behavior of the target species is indispensable. The Mekong giant catfish, Pangasianodon gigas, is endemic to the Mekong Basin and now is threatened with extinction. Although biotelemetry using acoustic transmitters and receivers is expected to reveal its movement patterns and behavior, the most suitable attachment method for the transmitter to the catfish is unknown. In this study we examined the effects of external attachment and surgical implantation on the survival and growth of the catfish, compared with those in control individuals, in an earthen fish pond for approximately 2 months. No fish died during the experimental period. Furthermore, we found no fungal infections in any fish and no significant differences in growth rate among treatment and control fish. However, all transmitters of externally tagged fish were lost during the experimental period. In contrast, transmitters of some surgically implanted fish remained in the peritoneal cavity. In conclusion, the surgical implantation technique is suitable for long-term monitoring of the catfish.     

Electrical activity of the broadhead catfish Clarias macrocephalus during paired aggressive-defensive interactions: Effects of illumination and chemical alarm signal

We studied the effects of illumination and alarm pheromone on emition of specialized electric discharges in the broadhead catfish Clarias macrocephalus (Clariidae, Siluriformes) during aggressive-defensive interactions. The discharges were recorded with a special hardware in two adult fish of a similar size placed into an aquarium, during a period of 24 h, under alternating 30-min-long light (700 lx) and dark periods. The electrical activity of the broadhead catfish was found to be higher in the dark than under the light; by the end of the trial, the frequency of electrical discharges gradually decreased. The overall number of discharges recorded in different pairs of the fish was significantly different, which is evidence of individual variability in the electrical activity. Changes in the illumination regime in many cases increased the emition of electrical discharges, which could be a result of a stress-response. However, the stimulation of the fish by alarm pheromone (extract of the skin, 0.5 g/l) caused no pronounced changes in the electrical activity. It is supposed that aggressive motivation caused in the broadhead catfish by the presence of another individual of the same species dominated over the defensive response initiated by the alarm pheromone and, thus, dominated in the development of the electrical response.     

The evolution of electroreception and bioelectrogenesis in teleost fish: a phylogenetic perspective

According to current phylogenetic theory, both electroreceptors and electric organs evolved multiple times throughout the evolution of teleosts. Two basic types of electroreceptors have been described: ampullary and tuberous electroreceptors. Ampullary‐type electroreceptors appeared once in the common ancestor of the Siluriformes+Gymnotiformes (within the superorder Ostariophysi), and on two other occasions within the superorder Osteoglossomorpha: in the African Mormyriformes and in the African Notopteriformes. Tuberous receptors are assumed to have evolved three times; all within groups that already possessed ampullary receptors. With the exception of a single catfish species, for which studies are still lacking, all fish with tuberous electroreceptors also have an electric organ. Tuberous electroreceptors are found in the two unrelated electrogenic teleost lineages (orders Gymnotiformes and Mormyriformes) and in one non‐electrogenic South American catfish species (order Siluriformes). Electric organs evolved eight times independently among teleosts: five of them among the ostariophysans (once in the gymnotiform ancestor and in four siluriform lineages), once in the common ancestor of Mormyriformes, and in two uranoscopids. With the exception of two uranoscopid genera, for which no electroreceptive capabilities have been discovered so far, all electric organs evolved as an extension of a pre‐existing electroreceptive (ampullary) condition. It is suggested that plesiomorphic electric organ discharges (EODs) possessed a frequency spectrum that fully transgressed the tuning curve of ampullary receptors, i.e. a signal such as a long lasting monophasic pulse. Complex EOD waveforms appeared as a derived condition among electric fish. EODs are under constant evolutionary pressure to develop an ideal compromise between a function that enhances electrolocation and electrocommunication capabilities, and thereby ensures species identity through sexual and behavioural segregation, and minimizes the risk of predation.     

Lake Kainji,Nigeria; A summary of the changes within the fish population since the impoundment of the Niger in 1968

The relative composition of the major fish families in Lake Kainji between 1974 and 1975 is analysed and compared with pre- and post-impoundment data collected by previous workers. Trends in the fishery are assessed, and it is concluded that the cichlids, particularly Sarotherodon (= Tilapia) galilaeus Artedi, are becoming the dominant commercially valuable fish. No evidence was found of a significant recovery in the formerly abundant citharinids.The value of the sampling technique is discussed and criticised in relation to under-assessment of certain species, notably S. galilaeus. The Schilbeidae were found to be one of the most numerous families in the lake but are commercially under-exploited.Department of Zoology, University of Reading     

Seasonal fluctuations in taxonomic and functional diversity in assemblages of catfishes in the Venezuelan Arauca River Floodplain

The Arauca River harbors a considerable fish biodiversity, yet it remains poorly sampled and the knowledge about its fish communities is incomplete. We studied the taxonomic and functional composition and diversity of catfish assemblages in one lotic and one lentic habitat of a segment of this floodplain during one hydrological cycle, from August 2014 to August 2015, comprising six samplings using gillnets, and identified the relationships between catfish traits and the environment based on five limnological variables. The functional structure was studied through 11 morphological measures and the species diets. We identified 31 catfish species and nine trophic groups. There were significant differences in species composition and diversity between habitats and months, but the functional structure of the catfishes was only determined by the temporal variability. The functional structure of the catfish assemblages was ordered by morphological traits related to locomotion, habitat use, and trophic ecology and these traits were correlated with the limnological variables, supporting the existence of environmental filters. Integrating the taxonomic and functional perspectives can provide a more complete picture of the ecological patterns of freshwater fish assemblages in the Neotropics and can help us predict how these assemblages might change in response to anthropogenic alterations of the environment.     

Cloning and characterization of myogenic regulatory genes in three Ictalurid species

We report sequence, tissue expression and map-position data for myogenin, MYOD1, myostatin and follistatin in three Ictalurid catfish species: channel catfish (Ictalurus punctatus), blue catfish (I. furcatus) and white catfish (Ameiurus catus). These genes are involved in muscle growth and development in mammals and may play similar roles in catfish. Amino acid sequences were highly conserved among the three Ictalurid species (>95% identity), moderately conserved among catfish and zebrafish (approximately 80% identity), and less conserved among catfish and humans (approximately 40-60% identity) for all four genes. Gene structure (number of exons and introns and exon-intron boundaries) was conserved between catfish and other species for all genes. Myogenin and MYOD1 expression was limited to skeletal muscle in juvenile channel catfish, similar to expression patterns for these genes in other fish and mammalian species. Myostatin was expressed in a variety of tissues in juvenile channel catfish, a pattern common in other fish species but contrasting with data from mammals where myostatin is primarily expressed in skeletal muscle. Follistatin was expressed in juvenile catfish heart, testes and spleen. All four genes contained polymorphic microsatellite repeats in non-coding regions and linkage analysis based on inheritance of these microsatellite loci was used to place the genes on the channel catfish linkage map. Information provided in this study will be useful in further studies to determine the role these genes play in muscle growth and development in catfish.     

The need for research and monitoring on the impacts of translocated sharptooth catfish,Clarias gariepinus,in South Africa

The sharptooth catfish, Clarias gariepinus (Burchell, 1822), is a widespread African freshwater fish species which occurs naturally from the Nile to the Orange River. Through translocation aquaculturists, farmers, anglers and engineers have helped to extend its range into many South African rivers where it did not occur naturally and where it is now an alien invasive species. Being a very hardy fish species it will have a major impact on a range of aquatic, amphibian and avian biota, impacts that should not be under-estimated and which urgently require study. Ironically, the illegal introduction of catfish into some dams has impacted on sport fisheries for another alien: bass. There is also a serious potential impact from alien catfish on freshwater eels. Anglers and farmers need to be educated about the adverse consequences of introducing catfish and a serious look needs to be taken at interbasin transfers of biota by engineers.     

Retinal projections in the electric catfish (Malapterurus electricus)

Summary The poorly developed visual system of the electric catfish was studied with silver-degeneration methods. Retinal projections were entirely contralateral to the hypothalamic optic nucleus, the lateral geniculate nucleus, the dorsomedial optic nucleus, the pretectal nuclei including the cortical nucleus, and the optic tectum. The small size and lack of differentiation of the visual system in the electric catfish suggest a relatively small role for this sensory system in this species.     

A study of the hydration and thermodynamics of warm-water and cold-water fish collagens.

The hydrated volumes, Vh, of collagens extracted from various fish species were calculated by using the Simha-Einstein equation, and it was found that the hydration of warm-water fish collagen is greater than that of cold-water fish collagen (halibut). Although the intrinsic viscosities of warm-water fish (bigeye-tuna, carp and catfish) collagens are almost the same, the hydrated volume of bigeye-tuna collagen is approx. 1.5 and 3 times those of carp and catfish collagens respectively. The extent of hydration at 20 degrees C is in the following order: bigeye tuna greater than carp greater than catfish greater than halibut. The various thermodynamic activation parameters (delta G*, delta H* and delta S*) were calculated and it was found that they are useful for determining the exact denaturation temperature. It was calculated that the denaturation temperatures of halibut, bigeye-tuna, carp and catfish collagens are 17, 31, 32 and 26-30 degrees C respectively. The variations of hydration, intrinsic viscosity, denaturation temperature and the thermodynamic parameters with the variation of concentration of catfish collagen were also thoroughly examined. The change of thermodynamic parameters from coiled-coil to random-coil conformation upon denaturation of collagen were calculated from the amount of proline and hydroxyproline residues and compared with viscometric results.