Parse as 亚 (short for 亚马逊 Amazon) + 河豚 (river dolphin, literally 'river pig'). So 亚河豚 is 'Amazon-river-pig' — the pink boto.
mistakes
Despite sharing the character, 河豚 in most contexts means 'pufferfish' (Takifugu). Only in the compound 亚河豚 (and related dolphin names like 江豚) does 豚 refer to an aquatic mammal.
