check for you, http://baike.baidu.com/view/22162.htm
鱼肝油含有维生素D和A,前者可帮助钙的吸收,后者可预防干眼症、维持正常生长。
In China called 鱼肝油, in NL it is Vitamine AD. CB only suggest to supplement vitamine D for the baby if baby doesnot drink enough fomular milk If your baby drinks more than 500 ml fomular, it is even not necessay to supplement vitamine D. I suppose you have already done according to CB's advice.
The polyunsaturated fatty acids exsit also in milk and other food. Overfeed that type of fatty acids can not give more benefit.
The health care for baby is more professional in NL than in China. LZ, no need to worry at all. Your baby does not need 鱼肝油.