Status of conventional and molecular breeding of salinity-tolerant tilapia

Aquaculture is an important sector for ensuring 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 high salinity. Among tilapia species, Oreochromis mossambicus, Oreochromis aureus, Oreochromis spilurus, Oreochromis urolepis hornorum, Sarotherodon galilaeus and Coptodon zillii are the most salinity-tolerant. Hybrids derived from salinity-tolerant tilapia species are tolerant to a certain level of salinity. They have been used in aquaculture production in brackish water and full seawater. Conventional selective breeding has been applied to increase the growth rate of salinity-tolerant tilapias. However, their growth rate is lower than that of the freshwater Oreochromis niloticus. Recently, many genomic resources and tools have been developed for salinity-tolerant tilapia. Quantitative trait locus (QTL) mapping and genome-wide association studies (GWAS) for important economic traits, including salinity tolerance and other desired traits, have been carried out and applied in molecular breeding for superior salinity-tolerant tilapia lines. In this review, we systematically analysed tilapia species that can be cultured in brackish and saltwater. We summarized previous works in conventional breeding and molecular breeding for salinity-tolerant tilapia. We pointed out a few known and potential challenges in the selective breeding and culture of salinity-tolerant tilapia. Due to the rapid advances in molecular and other disruptive technologies, we are optimistic that novel breeding approaches will significantly increase the production salinity-tolerant tilapia.