Ray-finned fishes exhibit quite a variety of mating systems. The four major types, along with a few examples, are: monogamy - maintains the same partner for an extended period or spawns repeatedly with one partner (Pomacentridae , Cirrhitidae , Blenniidae); polygyny - male has multiple partners over each breeding season (Cottidae , Serranidae , Centrarchidae , Anhingidae); polyandry - female has multiple partners over each breeding season (Amphiprion); and polygynandry or promiscuity - both males and females have multiple partners during the breeding season (Clupeidae , Gasterosteidae , Labridae , Acanthuridae). Polygyny is much more common than polyandry, and usually involves territorial males organized into harems (males breed exclusively with a group of females), as in numerous Cichlidae species and several families of reef fishes (Scaridae , Labridae and Pomacentridae , Malacanthidae , Acanthuridae and Balistidae). (Helfman, Collete, and Facey, 1997; Moyle and Cech, 2004)
There are also "alternative mating systems," which include alternative male strategies, hermaphroditism, and unisexuality (Moyle and Cech 2004:161). Alternative male strategies usually occur in species with large males dominating spawning, such as Salmonidae , Scaridae and Labridae . In this situation, smaller males attempt to 'sneak' fertilize the eggs of females as peak spawning is occurring; the smaller males release gametes simultaneously in the vicinity of the spawning pair. Hermaphroditism in ray-finned fishes involves individuals containing ovarian and testicular tissue (synchronous or simultaneous), as in the Hypoplectrus nigricans, as well as individuals that change from one sex to another (sequential). Sequential hermaphrodites most commonly change from being female to male (protogynous), as in Scaridae , Labridae and Serranidae . A much smaller number of actinopterygians, such as Amphiprion and some Muraenidae , change from being male to female (protandrous). Finally, unisexuality (egg development occurring with or without fertilization) can also occur in a variety of forms, and usually involves some male involvement, although at least ones species (Menidia clarkhubbsi) appears to utilize true parthenogenesis – females produce only female offspring with no participation from males. In most cases, however, there is at least some male involvement, either simply to commence fertilization (gynogenesis) or to produce true female hybrids (hybridogenesis). (Helfman, Collete, and Facey, 1997; Moyle and Cech, 2004)
The mating systems above do not necessarily represent discrete categories and, as with development, the discussion ignores much of the complexity and variety within each system. For instance, one unisexual species, which is actually part of a "species complex" (Poeciliidae), the Poecilia formosa , uses the sperm from two other bisexual species within the complex (Poecilia mexicana and Poecilia latipinna) to activate development of the eggs; only genetic material from the female lineage is retained (Moyle and Cech, 2004:162; Helfman et. al. 1997:352). This means that the unisexual females are actually parasitizing bisexual males of these other species. Also, many species exhibit a combination of major and alternative mating systems. For instance, hermaphroditism is known among some polygynous Labridae and Scaridae (among others). (Helfman, Collete, and Facey, 1997; Moyle and Cech, 2004)
Most ray-finned fishes reproduce continually throughout their lifetime (?20020904145554?), although some (e.g. Oncorhynchus and Petromyzontidae) spawn only once and die shortly thereafter (? 20020904145784?). Fertilization occurs externally in the great majority of species, however in some mouthbrooding species (incubation occurs inside mouth for the purpose of protection, mostly among Cichlidae), fertilization occurs inside the mouth. In a few families, such as Clinidae , Embiotocidae , Scorpaenidae , Poeciliidae , eggs are fertilized internally. (Helfman, Collete, and Facey, 1997; Moyle and Cech, 2004)
During courtship ray-finned fishes exhibit a wide range of complex behaviors, reflecting their evolutionary heritage and the particular environments they inhabit. For instance, pelagic spawners tend to have more elaborate courtship rituals than benthic spawners. Some of the behaviors include sound production, nest building, rapid swimming patterns, the formation of large schools, and many others. In addition, ray-finned fishes frequently change color at specific points in their reproductive cycle, either intensifying or darkening depending on the species, release pheromones, or grow tubercles (tiny bumps of keratin) on the fins, head or body. (Helfman, Collete, and Facey, 1997; Moyle and Cech, 2004)
One of the more peculiar mating behaviors among actinopterygians is found in deepsea anglerfishes (superfamily Ceratioidea). Many female deepsea anglerfishes are essentially "passively floating food traps"; quite a useful adaptation in the dark, barren waters of the deep sea (Bertelson and Pietsch 1998:140). However, this makes it quite difficult to locate a mate. Finding a female, therefore, is the sole purpose of many males, which are dramatically smaller than females (from 3 to 13 times shorter) and unable to feed as they lack teeth and jaws. With good swimming capabilities and olfactory organs, they are guided to females by pheromones (a unique chemical odor). After finding their mate, males attach themselves to females with hooked denticles, and in some species (Haplophryne mollis) the tissue between the two fuses; the males become permanently attached and receive nourishment from the female while the testes develop. (Bertelson and Pietsch, 1998)
While a surprising number of actinopterygian families exhibit parental care, it is not common, occurring only in approximately 22 percent. Unlike Mammalia , most parental care is the responsibility of males (11 percent), with 7 percent the sole responsibility of females and the rest carried out by both sexes. Not surprisingly, virtually no pelagic spawners, which release their gametes into the water column, exhibit parental care. However, among the fishes that do exhibit parental care, there is considerable diversity. (Helfman, Collete, and Facey, 1997; Moyle and Cech, 2004)
Some of the most extensive parental behaviors are found in Cichlidae. Many Cichlidae brood the eggs in the mouth and, although rare, the free-swimming young of some species also rush into the parent’s mouth for protection. Quite an elaborate form of parental care is found in Copella arnoldi. At peak spawning, males and females of this species make simultaneous leaps out of the water, touching and briefly adhering to the underside of overlying vegetation (a leaf). Each time, a fertilized egg is stuck to the underside of the leaf, usually a dozen or so. Then, to keep the leaf moistened, the male, correcting for the refraction of the water surface, sprays the eggs at one- to two-minute intervals by splashing with his tail. After keeping this up for two to three days (!), the newly hatched young fall into the water. Several tidal species utilize similar methods to keep eggs from desiccating as the tide goes out. Two such methods include coiling the body around the eggs (Stichaeidae and Pholidae) and covering the eggs with algae (temperate Cottidae and Labridae). (Helfman, Collete, and Facey, 1997)
- Helfman, G., B. Collete, D. Facey. 1997. The Diversity of Fishes. Malden, Mass.: Blackwell Science.
- Moyle, P., J. Cech. 2004. Fishes: An Introduction to Ichthyology - fifth edition. Upper Saddle River, NJ: Prentice-Hall, Inc..