Hybrid tilapias are crosses between different species of Oreochromis tilapias developed for aquaculture, either through natural hybridization, or more often artificially, in an effort to improve yields through improving various qualities of the fish, such as growth and hardiness. Hybrids are often divided into two varieties: gray tilapia and red tilapia, which are assigned variable binomial names based on the author, though the red hybrid is more often distinguished due to its distinct coloration. Tilapia is an extremely important aquacultured resource; in 2022, worldwide production of tilapia (reported as Oreochromis niloticus) reached five million t (4,900,000 long tons; 5,500,000 short tons) produced from aquaculture and three hundred thousand t (300,000 long tons; 330,000 short tons) captured, ranking 5th among all aquacultured species produced behind whiteleg shrimp, cupped oysters, grass carp, and silver carp.
Genetics Hybrid tilapia are most often created through crossing Nile tilapia (Oreochromis niloticus), Mozambique tilapia (O. mossambicus), blue tilapia (O. aureus), and/or the Wami tilapia (O. hornorum), though pure Wami tilapia is considered to have poorer growth rates. The Nile tilapia is often considered the best overall in tropical aquaculture for its tolerance of dense stocking, Mozambique tilapias (and hybrids) tolerate salinities from brackish water conditions, and blue tilapias are the most cold tolerant. Hybridization is done intentionally to try achieve superior qualities in the resultant offspring (hybrid vigor); in nature, tilapias hybridize readily between species and even genera, and there are no reports of sterility in hybrids (which is often the case in hybrids of other forms of animals, such as the mule). Crossing stocks of the same species doesn't produce significant hybrid vigor, though it is useful in creating higher genetic variability for future breeding.
Red hybrid tilapia (reported as Oreochromis mossambicus × O. niloticus, O. niloticus × O. mossambicus, O. aureus × O. mossambicus, O. spp., O. sp., or simply not given a scientific name at all) possess multiple strains; among them are Taiwanese red tilapia (reddish-orange O. mossambicus ♀ × WT O. niloticus ♂), Florida red tilapia (WT O. hornorum ♀ × red-gold O. mossambicus ♂), Israel red tilapia (red/pink Nile tilapia × WT blue tilapia), Malay red tilapia (Oreochromis niloticus × O. mossambicus), and other unknown strains originating from undocumented crosses between these "original" strains and wild type fish. Their color arises from a mutation in either or both parent, which may (F1) or may not be hybrids themselves. Taiwanese red tilapia presumably originated from an "albino" (or leucistic) O. mossambicus; these color mutations were first noticed in 1968, 22 years after the species was first introduced in Taiwan, which started with a founding population of 12 adult fish. This strain was "fixed" by crossing O. mossambicus possessing mutant coloration with O. niloticus, which resulted in an increase of the mutant coloration in produced fry (from 30% in 1969 to 80% in 1974) along with a marked increase in yield. The strain was commercialized in 1979.
Gray hybrid tilapia (reported as Oreochromis niloticus x O. aureus) are often reported as one of their parent species or not reported to be hybrids at all, as their coloration conforms more closely to the wild type, so are less distinct than the red fish. Molobicus strain tilapias, developed in the Philippines, were developed by crossing GIFT tilapia with feral O. mossambicus. The different strains of hybrids may be distinguished based on their morphometric characters; their genotypical difference is reflected in their phenotype. Sexual dimorphism is observed even in F2 hybrids, the expression of which is regulated by the amh gene. The dusp2, rtn4r, bhmt1, adamts12, and s100p genes are linked to growth.
YY male tilapias (sometimes referred to as "supermale tilapia") were developed in an effort to improve growth in tilapia cultures; these are produced through crossing estrogen-treated males (which become phenotypically female) with normal males, producing offspring which are phenotypically 75% male and 25% YY. Subsequent crossing of YY males with XX females produce offspring which were 99.6% males.
Production
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