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.     

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.     

Cytoarchitectural organization of the electromotor system in the electric catfish (Malapterurus electricus)

Summary The cytoarchitectural organization of the electromotor system of the electric catfish (Malapterurus electricus) was investigated in order to obtain insight into the neuronal reorganization accompanying the functional transition of a presumptive previous motor system to an electromotor system eliciting electric organ discharge. The electric catfish possesses two giant electromotoneurons situated within the rostral spinal cord. Intracellular dye injections have revealed the enormous extension of the dendritic tree of electromotoneurons. About 50 primary dendrites span the entire lateral funicle and intermediate grey matter, and reveal an extensive contralateral projection. The giant dendritic tree (1.2 mm in rostrocaudal direction) presumably receives inputs from all ascending and descending pathways of the spinal cord. Electromotoneurons and motoneurons receive the same type of fibre inputs, and electromotoneurons and interneurons are connected through common presynaptic elements. The innervation pattern of the electromotoneurons and spinal motoneurons is similar. Synaptic terminals with round synaptic vesicles often reveal chemical contacts and gap junctions. Furthermore, dendrites of the two electromotoneurons form juxtapositions (ephapses) with each other and also with spinal interneurons. Our results suggest that the two electromotoneurons are homologous to median (primary) spinal motoneurons and are the central structures of the electromotor system within the central nervous system of the electric catfish. A high capability of information processing can be attributed to the giant dendritic trees from functional considerations. This presumably enables the electromotoneurons to elicit an electric organ discharge in different behavioural contexts with a minimum of functional reorganization.     

Observations on the food habits of Clarias gariepinus Burchell,the South African freshwater barbel (Pisces: Clariidae) in Transvaal

Clarias gariepinus is a general carnivorous feeder whose food consists mainly of fishes, terrestrial invertebrates, aquatic insects and zooplankton. The proportion in which these food items are eaten vary considerably and instances of emergency and preferential feeding are discussed. The barbel is an indiscriminate feeder and the presence of large quantities of non-animal material, which are of little food value to a carnivorous species, must be regarded as incidental.     

Protoancylodiscoides malapteruri n. sp. (Monogenea,Dactylogyridea, Ancyrocephalidae), parasite branchial de Malapterurus electricus Gmelin (Siluriformes,Malapteruridae), au Cameroun

Protoancylodiscoides malapteruri n. sp. Monogène parasite branchial du poisson électrique Malapterurus electricus Gmelin a été récolté au Cameroun dans une seule localité du bassin de la Sanaga. Ce parasite est caractérisé par la présence, au niveau du hapteur, de deux onchia (l'un ventral, l'autre dorsal), de quatre types d'uncinuli et, au niveau de l'appareil génital, d'un pénis tubulaire court, non enroulé, d'une pièce accessoire particulière, d'un canal déférent entourant la branche intestinale gauche et d'un vagin à ouverture latérale droite. La position systématique de ce Monogène au sein de l'ordre des Dactylogyridea est discutée et la diagnose du genre Protoancylodiscoides est modifiée. Protoancylodiscoides malapteruri n. sp., a monogenean gill parasite of Malapterurus electricus Gmelin in southern Cameroon, is described. This worm is characterised by the presence in the haptor of two onchia (one ventral and one dorsal) and four different types of uncinuli (hooklets), and in the genital system, a short tubular penis (never coiled), a special accessory piece, a vas deferens which winds arounds the left intestinal crus and a vagina with a lateral aperture on the right side. The systematic position of this monogenean within the order Dactylogyridea is discussed and the diagnosis of the genus Protoancylodiscoides is amended.     

The feeding ecology of the African lily trotter Actophilornis africanus (Gmelin) at Lake Naivasha, Kenya

The only feeding habitats available to African lily trotters, Actophilornis africanus (Gmelin), at Lake Naivasha are mats of the alien water fern, Salvinia molesta Mitch. This has replaced the native floating leaved water lily beds. Lily trotters were able to use these mats, taking invertebrate food items from the surface or turning plants over and pecking at the rootlets. Pecking rates and turning rates responded to the nature of the available food, with pecking rates high and turning rates low when terrestrial arthropods were found on the mat surface. Both pecking rates and turning rates were low when large aquatic food items, such as the swamp worm (Alma emeni Michaelsen), were available. Pecking rates and turning rates were both high when the predominant food items were aquatic insect larvae. The largest of these (hydrophilid larvae) were taken in preference to the smaller but commoner chironomid larvae. Colonization of the mats of S. molesta by invertebrates was low if the mats were affected by wind action but higher if they were constrained by enclosure or stranding; mats with higher invertebrate densities supported more feeding lily trotters.     

The food and feeding habits of two co-occurring marine catfish Galeichthys feliceps and G. ater (Osteichthyes: Ariidae) along the south-east coast of South Africa

The feeding-associated morphological structures of the two Galeichthys species were found to be similar in all respects. Interspecific competition for food was avoided through habitat separation. Habitat preference, as established by dietary analysis and fishing trials, was based on substratum type. Galeichthys feliceps fed over sandy and muddy substrata in marine and estuarine environments, while G. ater fed exclusively over marine reefs. The two species have different caudal fin structures which are probably evolutionary responses to habitat-associated behavioural requirements in the two different environments.
The diets of the two species were investigated and compared using calorific values of prey items. While both species fed predominantly on benthic crustaceans, polychaetes and molluscs, little dietary overlap occurred at the species level. In the estuarine environment, G. feliceps fed mainly on the anomurans Upogebia africana and Calianassa kraussi , crabs Hymenosoma orbiculare and Cleislosoma edwardsii , and several isopod species. In the marine environment G. feliceps fed mainly on two species of crabs, Thaumastoplax spiralis and Goneplax angulata , the echiurid Ochaetostoma capense and the sedentary polychaete Sternaspsis scutata. A high incidence of teleost scales in the diet of G. feliceps juveniles was found to be a consequence of scavenging rather than a lepidophagous habit. Galeichthys ater fed widely on several reef-associated crabs, isopods, polychaetes and cephalopods.     

The food, feeding habits and distribution of a siluroid catfish, Bagrus docmac (Forsskal), in the Kenya waters of Lake Victoria

Adult Bagrus docmac in the Nyanza Gulf of Lake Victoria feeds mostly on fish–Haplochromis spp. and Engraulicypris argenteus (Pelligrin). Juveniles prefer aquatic benthic invertebrates with Phyllogomphus aethiop.?(K.elys), Phanostoma senegalense(Brauer), Chironomus spp. and Caridina nilotica (Roux) dominating, followed by Chaoborus spp., Povilla adusla (Navas), Valvata spp. and Neoperla spio (Newman) in order of importance. B. docmac exhibits diurnal changes in feeding habits. It feeds actively during dusk and dawn, taking advantage of the twilight environment for successful feeding mission–a crespuscular feeding behaviour. Selectivity of food seems dependent on occurrence of prey items. The species has an ubiquitous distribution in the Gulf but occurs more frequently with increasing water depth and decreasing water temperature. The biomass of the predator shows little correlation with water conductivity. Bagrus docmac and the other important piscivorous species in the lake, Lates niloticus (L.), are mutually exclusive in their bathymetric distribution within the Gulf. They also have different preferences for water temperature and conductivity.     

Observations on the breeding habits of Clarias gariepinus (Burchell)

Clarias gariepinus (Burchell) can be stimulated to spawn in aquaria by hormonal treatment and the breeding habits could be observed. After pre-spawning activities such as the raising of dorsal fins and chasing of the female, the male folds around the head of the female and small batches of eggs are laid, followed by some gas bubbles. Eggs are distributed by the female over a wide area. This behaviour agrees with field observations. The final stimulant to spawning under natural conditions is thought to be a substance called petrichor dissolved in flood waters that have run over dry ground.     

Observations on the innervated face of the electrocyte of the main organ of the electric eel (Electrophorus electricus L.)

Summary The innervated face of electrocytes in the main electric organ of Electrophorus electricus L. was examined by light microscopy, both conventional and with Nomarski contrast, and by transmission and scanning electron microscopy. Acetylcholinesterase cytochemistry was used in the demonstration of the greater density of synapses over the caudal papillae. The various techniques contributed to a better understanding of the distribution and form of papillae and synapses at the posterior face of the electrocyte. Caudal papillae are longer and thinner than those at the rostral face, but it was not possible to recognize a different type sometimes referred to in the literature as small papillae. The contact of nerve endings with the electrocyte seems to be made predominantly on the terminal half of caudal papillae, however a smaller number occur elsewhere on the posterior face. Synaptic terminals frequently appear as round profiles, but may be also elongated, with or without bulges, usually occupying a depression, and separated from the post-synaptic membrane by a space of 60–100 nm, where an expansion may be found.     

Observations on feeding, growth and electric discharge of newborn Torpedo ocellata (chondrichthyes, batoidei)

Newly born and neonate Torpedo ocellata were obtained from gravid females caught during the autumn off the Mediterranean coast of Israel. The young torpedos, which weighed about 11 g, were fed with live Blennius pavo Risso, and doubled their weight in about 4 months. The behaviour of the torpedo during feeding was examined and photographed. When attacking a fish, the torpedo emerges from being buried in the sand and assaults the approaching prey. First, the prey is trapped under the torpedo and then directed towards the ray's mouth by its body movements. Newborn and neonate torpedos are able to discharge their electric organ. The amplitude of the discharge of one day-old fish is approximately 4 V. It increases dramatically during the first three weeks of life to 20 V, reaching an asymptotic level of about 26 V, by the end of the fourth month.     

Observations on the feeding, growth rate and habits of newly settled Octopus cyanea

This paper records observations on the behaviour of Octopus cyuneu caught in Hawa shortly after settlement from the plankton. The young animals rapidly establish homes on the bottom and defend these against their own species. Of a variety of food offered, crabs were most frequently (nearly always) taken; the animals always took the prey home to eat it. Records of diurnal activity show morning and evening peaks as in adults. There was a steady 2–3.5% daily increase in weight over the first six months (July-January) after settlement     

Interactions of feeding rates on growth,food conversion and body composition of the freshwater catfish Mystus vittatus (Bloch)

Food intake, growth, conversion efficiency and body composition of the non-air breathing catfish Mystus vittatus (Bloch) were studied in relation to different feeding levels. Fish weighing 817.9 ± 104.00 mg was found to consume a maximum of 156.0 mg live Tubifex worm/g day^-1. Geometrically derived feeding rates of 6.75, 23.00 and 26.00 mg dry food/g live fish day^-1 represent the maintenance, optimum and maximum levels respectively. The SDA increased from 6.75 mg/g day^-1 at maintenance to 13.50 mg/g day^-1 at maximum feeding rate. Starvation brougt about increase in body water content, while there was concomitant decrease in fat and crude protein.     

The primary structure of the hemoglobin of the electric eel (Electrophorus electricus)

The blood of the Electric Eel contains only one hemoglobin component. The primary structures of the alpha- and beta-chains are presented. These were separated by high-performance liquid chromatography, using a new kind of buffer system. The alpha-chains are acetylated, and consist of 142 residues, while the beta-chains are not blocked, and consist of 147 residues. The phylogenetic distances between these and the alpha- and beta-chains of human hemoglobin are 48 and 50% amino-acid exchanges, respectively. The relationship between primary structure and the Bohr effect and Root effect is discussed, especially the significance of the serine found in position F9 beta.     

The food and feeding habits of Tilapia species in the Lagos Lagoon

The food of Tilapia mariae (Boulenger), Tilapia guineensis * (Bleeker) and Tilapia melano-theron melanotheron * (Rupell) were investigated. It is shown that T. guineensis and T. m. melanotheron which were the more abundant species had similar food habits. The intensity of feeding of both species and the possible competition for food between them are discussed.     

The food and feeding habits of the Torrent frog, Amolops larutensis

The stomach contents of 661 Amolops larutensis (Blgr.) showed that this frog feeds on a wide range of terrestrial and aquatic animals of which insects form the greater part. Feeding was confined to the rocks and vegetation bordering the water-falls. Although adult frogs were capable of ingesting large prey up to a maximum length of 47.0 mm, they showed a definite preference for prey animals within the size-range of 1 to 6.5 mm length. No clear seasonal variation in the diet was found and it was suggested that the monthly fluctuations in the amount and type of prey ingested depend largely on the activity of the prey.     

Observations on feeding in a South African suctorial hoplonemertean, Nipponnemertes sp. (Family Cratenemertidae)

Marine hoplonemerteans were collected intertidally inAlgoa Bay, Port Elizabeth, South Africa in 1983.Algoa Living worms appear to belong to the genus Nipponnemertes, perhaps N. africanus (Wheeler, 1940). The external morphology and thestylet apparatus are described and illustrated. Laboratory observations showed that this speciesattacked and consumed two species of sympatricamphipods, Elasmopus pectenicrus and Hyalegrandicornis (the only two species tested). Thefeeding behavior was similar to that documented forother suctorial nemerteans that feed on amphipods. Onecomplete feeding sequence, from the initial strike tocompletion of feeding on H. grandicornis,took approximately 12 min: the proboscis struck theventral side of the amphipod, which was immobilized in<1 min; the head eventually wedged between thesternal plates, and the internal organs were evacuatedby suctorial action. The addition of E. pectenicrus andH. grandicornis as potentialprey for suctorial hoplonemerteans brings the totalknown number of amphipod species to 25, involving atleast ten families. A summary of all species ofAmphipoda known to be potential prey for suctorialhoplonemerteans is presented.