Acrobrycon Argopleura Chrysobrycon Corynopoma Diapoma Gephyrocharax Glandulocauda Hysteronotus Iotabrycon Landonia Lophiobrycon Mimagoniates Phenacobrycon Planaltina Pseudocorynopoma Pterobrycon Ptychocharax Scopaeocharax Tyttocharax Xenurobrycon Glandulocaudinae are a subfamily of tropical freshwater characin fish from Central and South America.
In all species of this subfamily, a gland on their caudal fin is found almost exclusively in the males, which allows the release and pumping of pheromones; also, members of this subfamily have complex courtship behaviors which lead to insemination.
[1] Glandulocaudinae consists of twenty genera divided among seven monophyletic, morphologically differing tribes.
[3][5] These fishes are found in every South American country, including Trinidad and excluding Chile; they inhabit streams that are tributaries to larger rivers such as the Amazon, Orinoco, and Paraguay Rivers in tropical species, or coastal streams tributary to the Atlantic and Pacific Oceans and the Caribbean Sea in the few subtropical species.
[5] All males have some form of modified caudal gland used to release pheromones as part of courtship.
[2] The females produce fewer eggs per unit body weight than externally fertilizing species; this is possibly because insemination increases the efficiency of fertilization, so fewer eggs are necessary.
[3] After insemination, the female may retain the live sperm for many months in her ovaries.
[5][6] Hooks on the anal fin of males may play a role, although these are also found in characins that exhibit external fertilization.
In the tribe Diapomini, the genus Planaltina expresses only round sperm (like that of externally fertilizing characins) and the genera Diapoma and Acrobrycon only express slightly elongated sperm; this may indicate a possible plesiomorphy.
The spermatozeugmata are situated in the posterior end of the testes, which serves as a storage area for sperm.
[6] Many of the genera also have a gland situated in the gill cavity called a "gill gland", a secondary sex characteristic found in sexually mature male glandulocaudines that is apparently suited to release chemical signals.
In Corynopoma riisei, the males have extended finnage (giving it the common name "swordtailed characin") as well as paddle-like extensions of the operculum.
[3] Like other ostariophysans, glandulocaudines show a reaction to chemical signals in the water.
As the male hovers, he will quickly swim to the surface and take a gulp of air and return, expelling the gas and making continuous, rhythmic pulses of croaking sounds, interrupted only by the male returning to the surface for more air.
[1] Herbert R. Axelrod has discussed the care of a number of species, including Corynopoma riisei, Gephyrocharax caucanus, Mimagoniates microlepis, M. lateralis, M. inequalis, Pseudocorynopoma doriae, and Tyttocharax madeirae.
Like most tetras, they prefer to swim in schools; some species may be nippy, and should be kept in groups to divide aggression.