Agreed. Try and get him feeding on frozen foods as soon as you have the chance. This decreases the risk of poor nutrition from one staple food. If he is a small lion, they do eat brine shrimp or bloodworm when they are alive/swiming in the water coloum. You could try baby mollies, as they can be addapted/kept in brakish water, they last longer than normal feeders. (Feed them some marine flake before feeding them to the lion, this way they have more nutritional value).