Raising these valuable species is made considerably more difficult by their propensity to change sexes as they mature. For example, red porgy are female until they reach 20 kgs, when they become males.
以黑鯛為例，一生下來沒有明顯性別，長大後是母的，更大一點又變公的。石斑魚初出娘胎是母的，非長到廿公斤後才能變成「男生」，但是能長到廿公斤以上的石斑魚很少。