When you're feeding seahorses there a few different options depending on what kind of seahorses you have.
Captive bred seahorses will have already been trained to eat frozen foods (once or twice a day) such as mysids (or mysis shrimp) which have been thawed out and rinsed beforehand. Although mysis shrimp form the basis of most captive bred seahorse diets, you should also offer live food once or twice a week.
It is possible to train wild-caught seahorses to eat mysids, but as we explained in the article about buying seahorses, it is better to stick to captive-bred animals since they are easier to keep and do not have a negative impact on the environment. You must be aware if you are determined to keep wild seahorses that they may never adapt to eating frozen foods at all, so you will have to provide live food continually for the duration of their lives. Depending on which species of seahorse you are keeping, you will need to feed them enriched brine shrimp, ghost shrimp or Hawaiian red shrimp.
Brine shrimp have little nutritional value and seahorses fed solely on artemia (brine shrimp) will starve to death over time. Live ghost or glass shrimp have more nutrients than artemia, even if the brine shrimp have been enriched. Glass or ghost shrimp are particularly good for larger seahorses like Hippocampus reidi or Hippocampus erectus and freshwater varieties can be sourced at bait stores - remember that these need to be enriched (see below).
Red shrimp from Hawaii are a great seahorse food - although they're usually only available mail order it's worth trying to track some down - most seahorses will eat them.
Variety is good for all seahorses - for health reasons they are more likely to receive all the nutrients they need if they're fed more than one kind of food.
"Enriching" seahorse food will ensure that your seahorses are receiving the correct nutrients and that if the foods are coming from freshwater sources that they contain the correct fatty acids that their marine counterparts contain (and that seahorses need!).