Nuptial tubercles or breeding tubercles (also called pearl organs or nuptial efflorescence) are noticeable skin roughness or horny nodules that form on male fish during breeding. They are made of keratin, the same material as hair, hooves, and fingernails.
These tubercles are dermal structures present in 15 families of fish belonging to 4 orders of Actinopterygii – Salmoniformes, Gonorhynchiformes, Cypriniformes and Perciformes [1] [2] are used in the courtship and reproduction process. They consist of partially or fully keratinised cells that form in certain regions, used to stimulate females during courtship. [3] Their development is stimulated by hormones secreted by the pituitary and adrenal glands, and is induced shortly before the breeding season and discarded after. In some species, at least, there is a correlation between the level of androgens present in the endocrine system and the volume and complexity of tubercle growth. [4] [5]
They normally form on the heads of male fish, often covering the whole of the top part of the snout, but may also occur on fins, or anywhere else on the scaled integumentary system. The actual purpose of nuptial tubercles is not definitively known. There are many theories about their function, which include: use to stimulate females during courtship, in aggressive rituals performed by males during mate selection, to maintain contact between individuals during reproduction, [3] or in defence of the nest from predators. There is definite proof that they grow mainly on areas with greater mechanical stress, [4] which means that those species that head-butt females to stimulate them to release eggs will have more on the head, whereas those that dig nests in gravel substrates will develop them more on their fins. Nuptial tubercles occasionally develop on female fish also, but this is rare, and they are often barely visible to the naked eye. [6]
Nuptial tubercles have been described as an honest signal of the general health of the male bearer, in common with other biological ornaments. [7] Indeed, research has proven a correlation between tubercle density and parasite resistance, [8] though it is not always a positive correlation. [9]
In species that use lek mating, the females choose the males with the roughest skin, but were not confused by males that had papillomatosis (a skin disease resulting in rough skin). [4]
The presence of nuptial tubercles has been used to distinguish speciation. The genus Leucos was described from similar Rutilus species in Europe as they do not develop them. [10] Similarly, the description of Messinobarbus (now a synonym of Luciobarbus ) in 1994 was an attempt to distinguish those species with them from Barbus that do not have them. [11]
Visually similar structures to nuptial tubercles are produced by male loricariid catfishes during the mating season, in similar places to nuptial tubercles (snout and fins). These are actually hypertrophied odontodes, which are therefore dermal teeth, rather than keratin, and are covered by flesh containing taste buds. It has been proposed that these ornaments may assist breeding success by mimicking fry, tempting females to lay their eggs in the nest cave of a successful male, already guarding his own offspring. [12]
Instead of tubercles, cichlid males produce nuchal humps (koks), where additional fat is laid under the skin over the skull forming a hump on the head. [13] This trait has been developed to an extreme in the hybrid Flowerhorn cichlid, by selective breeding in the aquarist hobby.
Nuptial pad - a similar ornament of frogs
A secondary sex characteristic is a physical characteristic of an organism that is related to or derived from its sex, but not directly part of its reproductive system. In humans, these characteristics typically start to appear during puberty. In animals, they can start to appear at sexual maturity. In humans, secondary sex characteristics include enlarged breasts and widened hips of females, facial hair and Adam's apples on males, and pubic hair on both. In non-human animals, secondary sex characteristics include, for example, the manes of male lions, the bright facial and rump coloration of male mandrills, and horns in many goats and antelopes.
Cichlids are fish from the family Cichlidae in the order Cichliformes. Traditionally Cichlids were classed in a suborder, the Labroidei, along with the wrasses (Labridae), in the order Perciformes, but molecular studies have contradicted this grouping. On the basis of fossil evidence, it first appeared in Argentina during the Early Eocene epoch, about 48.6 million years ago; however, molecular clock estimates have placed the family's origin as far back as 67 million years ago, during the late Cretaceous period. The closest living relative of cichlids is probably the convict blenny, and both families are classified in the 5th edition of Fishes of the World as the two families in the Cichliformes, part of the subseries Ovalentaria. This family is large, diverse, and widely dispersed. At least 1,650 species have been scientifically described, making it one of the largest vertebrate families. New species are discovered annually, and many species remain undescribed. The actual number of species is therefore unknown, with estimates varying between 2,000 and 3,000.
A seahorse is any of 46 species of small marine bony fish in the genus Hippocampus. "Hippocampus" comes from the Ancient Greek hippókampos (ἱππόκαμπος), itself from híppos (ἵππος) meaning "horse" and kámpos (κάμπος) meaning "sea monster" or "sea animal". Having a head and neck suggestive of a horse, seahorses also feature segmented bony armour, an upright posture and a curled prehensile tail. Along with the pipefishes and seadragons they form the family Syngnathidae.
Pipefishes or pipe-fishes (Syngnathinae) are a subfamily of small fishes, which, together with the seahorses and seadragons, form the family Syngnathidae.
The roach, or rutilus roach, also known as the common roach, is a fresh- and brackish-water fish of the family Cyprinidae, native to most of Europe and western Asia. Fish called roach can be any species of the genera Rutilus, Leucos and Hesperoleucus, depending on locality. The plural of the term is also roach.
Pelvicachromis pulcher is a freshwater fish of the cichlid family, endemic to Nigeria and Cameroon. It is popular amongst aquarium hobbyists, and is most commonly sold under the name kribensis, although it has other common names, including various derivatives and color morphs of the kribensis: krib, common krib, red krib, super-red krib and rainbow krib, along with rainbow cichlid and purple cichlid.
Pelvicachromis taeniatus is a species of cichlid from Benin and Nigeria that is occasionally kept as an aquarium fish. It is native to the soft-water rivers. This species can reach a length of 7.1 centimetres (2.8 in) SL. It is known to exist in a variety of geographically restricted varieties distinguished by differences in coloration. These are often given names such as "Nigerian red" or "Moliwe" that refer to the places where each variety is collected.
The Mozambique tilapia is an oreochromine cichlid fish native to southeastern Africa. Dull colored, the Mozambique tilapia often lives up to a decade in its native habitats. It is a popular fish for aquaculture. Due to human introductions, it is now found in many tropical and subtropical habitats around the globe, where it can become an invasive species because of its robust nature. These same features make it a good species for aquaculture because it readily adapts to new situations. It is known as black tilapia in Colombia and as blue kurper in South Africa.
Rutilus meidingeri is a species of freshwater fish in the family Cyprinidae. It is only found in three subalpine lakes in Austria and probably in few lakes of Slovakia. Since the 1980s, it has been extirpated from the German Lake Chiemsee and Austrian Traunsee.
Astatotilapia burtoni is a species of fish in the family Cichlidae.
Neolamprologus pulcher is a species of cichlid endemic to Lake Tanganyika where it prefers locations with plenty of sedimentation. The common names for N. pulcher include daffodil cichlid, fairy cichlid, princess of Zambia and lyretail cichlid. This species can reach a length of 10 centimetres (3.9 in) TL. It can also be found in the aquarium trade.
The streber, also known as the Danube streber, is a species of freshwater ray-finned fish in the family Percidae. It is found in strongly flowing waters in the Danube and Dniester drainages of Austria, Bosnia and Herzegovina, Bulgaria, Croatia, the Czech Republic, Germany, Greece, Hungary, Italy, Moldova, Serbia, Slovakia, Slovenia, Switzerland, and Ukraine.
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), vocalizations, mechanical sound production, or displays of beauty, strength, or agonistic ability.
Apistogramma agassizii, commonly known as Agassiz's dwarf cichlid, is a species of cichlid found in the Marañón and Ucayali River in Peru, some tributaries of the Amazon River, as well as downstream to the estuary in the Atlantic. It is named after the Swiss-American zoologist and geologist Louis Agassiz (1807–1873).
A biological ornament is a characteristic of an animal that appears to serve a decorative function rather than a utilitarian function. Many are secondary sexual characteristics, and others appear on young birds during the period when they are dependent on being fed by their parents. Ornaments are used in displays to attract mates, which may lead to the evolutionary process known as sexual selection. An animal may shake, lengthen, or spread out its ornament in order to get the attention of the opposite sex, which will in turn choose the most attractive one with which to mate. Ornaments are most often observed in males, and choosing an extravagantly ornamented male benefits females as the genes that produce the ornament will be passed on to her offspring, increasing their own reproductive fitness. As Ronald Fisher noted, the male offspring will inherit the ornament while the female offspring will inherit the preference for said ornament, which can lead to a positive feedback loop known as a Fisherian runaway. These structures serve as cues to animal sexual behaviour, that is, they are sensory signals that affect mating responses. Therefore, ornamental traits are often selected by mate choice.
The pugnose minnow is a species of cyprinid fish found in the eastern North America. There are two recognized subspecies with the subspecies from Florida recognized as race peninsularis.
The cactus roach is a species of fish in the family Cyprinidae, native to the basin of the Danube River upstream of the Iron Gate, very numerous in the Sava basin. It is also recorded in the Ukrainian Zakarpattian region. This freshwater fish is up to 55 cm (22 in) long, averaging 40 cm (16 in).
The Caspian roach is a species of roach fish living in the Caspian Sea. The Caspian roach can be distinguished from other roaches by its laterally compressed body, silvery grey iris, rounded snout and grey pectoral pelvic and anal fins with dark margins. The Caspian roach is semi-anadromous and inhabits mostly shallow coastal waters. It enters Volga, Ural, Emba, Terek and Kura drainages for spawning.
Leucos is a genus of fishes in the family Cyprinidae, from Southern Europe. They are carp close to the genus Rutilus, and were only recently taxonomically distinguished from that genus.
Rutilus stoumboudae is a species of freshwater fish in the family Cyprinidae. It is found only in Greece, in Lake Volvi and is a lacustrine species adapted to still water. It is named for Maria Stoumboudi, in honour of her research on the ecology and conservation of the freshwater fishes of Greece.
Stephanie C. McMillan; Zhe T. Xu; Jing Zhang; Cathleen Teh; Vladimir Korzh; Vance L. Trudeau; Marie-Andrée Akimenko (2013). "Regeneration of breeding tubercles on zebrafish pectoral fins requires androgens and two waves of revascularization". Development. 140 (21): 4323–4334. doi:10.1242/dev.095992. hdl: 10393/31649 . PMID 24089472.
