The three are
鲥鱼 (Reeves shad),
刀鱼 (knife fish) and
河豚 (pufferfish). Knife fish is best before the Qingming festival, pufferfish comes with spring and the shad in early summer. Pufferfish is poisonous unless expertly prepared, hence the saying
拼死吃河豚, 'risk death to eat pufferfish'.