Status of conventional and molecular breeding of salt-tolerant tilapia

Aquaculture is an important sector to ensure global food security. Due to the scarcity of freshwater available for expanding aquaculture, the development of omnivorous fish species and varieties that can tolerate high salinity will enhance fish production. Some tilapia species are good candidates for aquaculture in brackish and seawater because they can grow in a high salinity. Among tilapia species, Oreochromis mossambicus, O. aureus, O. spilurus, O. urolepis hornorum, Sarotherodon galilaeus and Coptodon zillii are the most salt-tolerant. Hybrids derived from salt-tolerant tilapia species are tolerant to a certain level of salinity. They have been used in aquaculture production in blackish water and in full seawater. Conventional breeding has been applied to increase the growth of saline-tolerant tilapia. However, their growth is lower than that of the freshwater O. niloticus. Recently, many genomic resources and tools have been developed for saline-tolerant tilapia. Quantitative trait locus (QTL) mapping and genome-wide association studies (GWAS) for important economic traits, including salt tolerance and other desired traits, have been carried out and applied in molecular breeding for superior saline-tolerant tilapia lines. In this review, we systematically analysed tilapia species that can be cultured in blackish and salt water. We summarized previous works in conventional breeding and molecular breeding for saline-tolerant tilapia. We pointed out a few known and potential challenges in the aquaculture of saline-tolerant tilapia. Due to the rapid advances in molecular and other disruptive technologies, we are optimistic that the production of saline-tolerant tilapia will increase in the coming years.