Mormyroidea

The term Mormyriformes derives from Greek mormyros, μορμύρος, μόρμυρος, a species of fish that would probably be Lithognathus mormyrus, and from Latin forma, with the same connotation as the English form. Its synonymy Mormyridae is considered the valid taxonomic status according to the Integrated Taxonomic Information System or ITIS of North America. Although several authors included it within the taxonomic category "order" until after the second half of the 20th century, it is considered as a "superfamily" since the mid 1990s. == Distribution and ecology ==

Ecology This superfamily has a wide adaptability and can be found in freshwater river systems "with high concentrations of suspended solids and reduced transparency", a water hardness of up to 20 °dH and a salinity level of less than 1%. The habitats of these fishes are dominated by mud and/or sandy substrates, plant debris, marginal grasses, filamentous algae or clumps of aquatic plants, 1n 1909, George Albert Boulenger visited the Congo and described forty-seven endemic species, fourteen of them in northern West Africa in the Congo region, eight in West Africa on the Congo and other rivers, seven in the Nile, six in both the Nile and Lake Chad and the Niger and Senegal, and two in Lake Victoria. In 2003, Didier Paugy, Christian Lévêque, and Guy G. Teugels published a regional synthesis of West African fishes and identified a total of fifteen genera with 41 species in Lower Guinea and fourteen genera with 44 species in West Africa. In 2006, Christian Lévêque and Didier Paugy analyzed the composition of the fish fauna in the most representative rivers and lakes of the main ichthyological provinces of Africa and determined the presence of fifteen species in the Nile, fourteen in Chad, twenty-seven in Niger, sixteen in the Volta River, ten in the Konkouré River, thirteen in the Jong, eight in the Sassandra, ten in the Bandama, fifteen on the Sanaga, twenty-two on the Ogôoué, six on the Ruaha, 109 on the Congo, and ten on the Zambèze. Additionally, within the freshwater or epicontinental species of the richest African aquatic systems, 19 of them are found in the Niger River, 75 in the Congo River and 16 others in the Zambezi River. In 2008, Melanie L. J. Stiassny, Guy G. Teugels and Carl Hopkins evaluated the geographic distribution of genera in the subfamily Mormyrinae and indicated that at least fourteen are found in Lower Guinea; the remainder can be found in Congo as in the case of Genomyrus, Angola as in Heteromormyrus, Nilo-Sudan as in Hyperopisus and Cyphomyrus, and South Africa as in Cyphomyrus. In addition, the same authors indicated that at least six species in the subfamily Petrocephalinae are in Lower Guinea, while in 2012, several researchers from the universities of Regensburg and Heidelberg, in conjunction with the South African Institute for Aquatic Biodiversity, indicated the presence of several new species in the rivers Luongo, Lufubu, Zambezi, Boro, Cunene, Thoage, and the Okavango Delta. ==Morphology==

Sizes and shapes The superfamily Mormyridae has a high diversity within its more than 200 species and subspecies, with a range of sizes and shapes that varies according to the family of membership and their respective genus. The smallest can measure around in their adult stage, while the largest can reach , although a specimen belonging to Gymnarchus niloticus which reached a size of is known to exist in the Loumbila reserve, near Ouagadougou. • The genera Campylomormyrus, Gnathonemus and Mormyrus possess a particularly prominent extending mouth that usually consists of a flexible fleshy elongation attached to the lower jaw and is equipped with touch and probably taste sensors, which is why they are popularly called "elephant-nose fishes". • The genera Mormyrops, Brienomyrus, Hippopotamyrus, Marcusenius, Petrocephalus, and Pollimyrus possess small barbs and usually lack the extended mouthparts of elephantfishes, hence they are called "Nile river pikes". with a brain-to-body mass ratio ranging from 1/52 to 1/82, and possibly associated with the ability to interpret bioelectrical signals. Since the pioneering work of Michael Pius Erdl in 1846, several researchers have made efforts toward describing the development of this organ and its functionality. Thus, based on the analysis of larvae and embryos of Pollimyrus (Marcusenius) Isidori, it is known that "the brain develops very rapidly: the corpus cerebelli (c.cer) and cerebellar structures, i.e. eminentia granularis (e. gr), lobus caudalis (lc) and transitorius (lt), lobi lineae lateralis (lll), are formed in 40 days, whereas valve development needs 180." They possess a hypertrophy in the cerebellum, which the literature refers to as mormyrocerebellum or gigantocerebellum, "probably related to his unique electrogenic and electroreceptive abilities" and to the large size of the valve, which in turn relates to the electrosensory system present in these fish. It has been found that for species living in oxygen-deficient aquatic environments, they protect their brains from damage caused by hypoxia through efficient use of existing oxygen. Electric organs with the central nervous system in green, the electroreceptors in blue, and the electric organ in red. In this species, the electroreceptors are at highest density in the 'elephantnose' snout, which is actively moved to help locate prey. Such an organ is evolutionarily derived from muscle cells, and there is a degree of convergent evolution in form and function with the Gymnotiformes of South America, especially in the sensory apparatus for detecting and processing electrical signals involving electrocommunication and electrolocation processes. Tuberous organs These fish have two types of tuberous electroreceptor: the Knollenorgan and the Mormyromast. Both organs are found in adult individuals, where they are lightly covered by epithelial cells and skin, while their sensitivity ranges from 0.1 mV and 10 mV/cm/ Tens of Hz up to more than a kHz. It is composed of a set of receptor cells that can reach between 40 and 60 microns in diameter; these are located under the skin and have a sensitivity of approximately 0.1 mV/cm. The mormyromast appeared under the name Schnauzenorgan ('Snout organ') in a paper by Walter Stendell in 1914, where he described it as a combination of the sensory and glandular apparatus for a species of Mormyrus. This organ is one of the most abundant in mormyriforms, with a high concentration of electroreceptors in the epidermis per cm2: for example, for Gnathonemus petersii there are about 2000 per cm², versus a maximum of 50 receptors per cm² for ampullary organs and knollenorgans. == Behavior ==

Communication Some species of mormyriformes, predominantly in the mormyridae family, are sociable, attentive and intelligent, whereas the gymnarchidae are solitary, unintelligent and even aggressive. Such electric fields provide these fish with a specialized sensory system for communication and orientation. EODs are useful for orientation, finding food and communication, whose frequency is variable; fields allow them to locate objects and react to other animals in turbid waters – or waters of reduced transparency – where their vision is affected by the presence of organic matter and suspended solids. This system is a recurrent subject of scientific research, particularly in the field of inter- (and intra-) species communication, as well as in studies of electrophysiology and behavior. EODs are often pulsatile, with frequencies exceeding 130 Hz for the most aggressive, Feeding . Feeding generally consists of small invertebrates buried in muddy substrates, marshy areas and sandy riverbank areas; thus, throughout the year certain species consume some crustaceans found on the banks of running rivers, The diet of this superfamily may change depending on seasonal variations in rainfall, since while in dry season some species supplement their diet with high amounts of larvae of Trichoptera, in rainy season this includes Ephemeroptera. Reproduction '' specimen in Gabon The breadth of species within the superfamily Mormyridae results in a paucity of information on their reproduction and intergeneric relationships, which is limited in both behavioral and biological terms. However, and in comparison to the electric fishes Gymnotiformes of South America, there is a greater understanding regarding their reproduction: it is known that much of the species reproduces in the rainy season Courtship takes place at the beginning of the rainy season, as the water level within the riverine sectors increases and decreases its conductivity —and the pH-value—; some species migrate towards the flooded areas, and during the mating season produce certain sounds and electrical discharge patterns. Other specimens build nests (as in the case of Pollimyrus and Gymnarchus which make floating nests of plant material) In this regard, there are data for some species such as Hyperopisus bebe, Pollimyrus adspersus, Mormyrus rume proboscirostris, Campylomormyrus tamandua, Hippopotamyrus pictus and Petrocephalus soudanensis, although only in the case of Pollimyrus isidor an analysis on its embryonic and larval development is appreciated. Eggs are variable in size, with a probable maximum size of about 10 millimeters in diameter as occurs in gymnarchids. After laying the eggs, both the male and female guard the nest, while after eighteen days, they hatch and the larvae swim freely. == Classification ==

The first respectable classification for some of the species in this superfamily appeared in Volume I of the tenth edition of Linnaeus's Systema Naturae in 1758 which, based on John Ray's Synopsis methodica Animalium (1693), included the genus Mormyrus within the order Branchiostegui. Since this work, various changes occurred within the international zoological literature, and it was not until the appearance of the International Code of Zoological Nomenclature in 1905 where the subordination of taxa followed a homogeneous pattern. Thus, while in the 1950s the mormyriformes included the families Mormyridae, Notopteridae and Hiodontidae within the Clupeiformes group,'' as early as the 1960s was regarded as an order containing the families Mormyridae and Gymnarchidae. In 1972, Louis Taverne proposed the inclusion as a suborder to the Mormyridae and Gymnarchoidea, which in turn agglutinated the families Mormyridae — with the subfamilies Petrocephalinae and Mormyrinae — and Gymnarchidae and Gymnarchidae respectively. His analysis considered osteological and external morphological characteristics, in addition to proposing a phylogenetic tree and reaffirming its inclusion within the osteoglossomorphs'', Phylogeny There is no consensus regarding the origin and diversification of the species belonging to this superfamily, since while some suggest that it appeared before the separation between Africa and South America, others indicate that it was later. One of the oldest fossils corresponds to a partial dentition of a species of Gymnarchus that lived at the end of the Eocene — about 37 million years ago – in the Faiyum oasis of Egypt, and succeeding remains of the genus Hyperopisus in Pliocene deposits in Wadi El Natrun of Egypt and from the Plio-Pleistocene — more recent than 5 million years ago – in Uganda, Lake Edward, and the Semliki River in Congo. In 1999, it was estimated on the basis of Mitochondrial DNA from thirteen species – two Petrocephalinae, one Gymnarchidae and ten Mormyrinae — that the core group of the mormyriformes could be between 60.69 and 71.98 million years old, In 2009, a new estimate was made with the species Brienomyrus Niger and Gnathonemus petersii, which determined 162 ± 24 million years. The following cladogram shows the relationship between the different families of Mormyriformes outlined by Sébastien Lavoué and colleagues: }} == Threats and protection ==

According to the information available for the 178 species assessed by the IUCN, the conservation status of the species associated with this superfamily is heterogeneous: 118 can be categorized as "least concern (LC or LR/lc)", 15 as "vulnerable (VU)", 3 as "near threatened (NT or LR/nt)" and 4 as "endangered (EN)". The main threats depend on the geographic area, country or river basin: • Several species have economic importance in the areas where they inhabit, including Hyperopisus bebe,' or the Campylomormyrus bredoi, whose overfishing with trawl nets elevated it to vulnerable status. According to estimates by the Fisheries and Aquaculture Department of the FAO, catches as of 2009 worldwide reached 35 685 tons of mormyrids and 13 901 tons of gymnarchids, representing an increase of 183.9% and 52.8% respectively since 2002. • Externalities due to mining activities on the banks of various rivers are also a cause of threat, observable in the case of Ivindomyrus opdenboschi in the Ntem and Ivindo rivers or the Marcusenius cuangoanus in the banks of the Kasai River. • Habitat loss and degradation due to agriculture, urban development, and deforestation is also a source of threat, as in the case of Marcusenius brucii, the Marcusenius abadii in the Black Volta or the Oti/Pendjari River, the Marcusenius furcidens in the Tano River'''''''' or the Mormyrus cyaneus'' in the Bas-Congo. On the other hand, the conservation actions implemented are scarce or non-existent for most species, of low impact, and with unknown results. == Notes ==