It really depends how big it is and what conditions its kept in. What type of lights is it under? I dont feed mine at all, its still very young and came on some live rock as a passenger. I would never ever purchase one again as i have strong views about their sustainability in captiviy. However, your nenny will need a feed probably once per week and depending on size i would guess it will take anything fro mnoral frozen food or largfer ones would take frozen cockle (what i fed my atlantic before i returned him)