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The normal development of lens fiber cells plays a critical role in lens morphogenesis and maintaining transparency. Factors involved in the development of lens fiber cells are largely unknown in vertebrates. In this study, we reported that GATA2 is essential for lens morphogenesis in Nile tilapia (<i>Oreochromis niloticus</i>). In this study, Gata2a was detected in the primary and secondary lens fiber cells, with the highest expression in primary fiber cells. <i>gata2a</i> homozygous mutants of tilapia were obtained using CRISPR/Cas9. Different from fetal lethality caused by <i>Gata2</i>/<i>gata2a</i> mutation in mice and zebrafish, some <i>gata2a</i> homozygous mutants of tilapia are viable, which provides a good model for studying the role of <i>gata2</i> in non-hematopoietic organs. Our data showed that <i>gata2a</i> mutation caused extensive degeneration and apoptosis of primary lens fiber cells. The mutants exhibited progressive microphthalmia and blindness in adulthood. Transcriptome analysis of the eyes showed that the expression levels of almost all genes encoding crystallin were significantly down-regulated, while the expression levels of genes involved in visual perception and metal ion binding were significantly up-regulated after <i>gata2a</i> mutation. Altogether, our findings indicate that <i>gata2a</i> is required for the survival of lens fiber cells and provide insights into transcriptional regulation underlying lens morphogenesis in teleost fish.