
As most aquarists (and herpers)I raised many kinds of "live food"for my pets,and many times I had more fun breeding the prey animals than the predators!

Now that it is clear that I don´t hate harps and that I like raising them,I must be honest and say that I don´t think they are useful as larval or fish food.
This is my personal opinion and I welcome any different thoughts to be debated here.Let´s get deeper into this.
Harps are present in virtually any aquarium,especially those with rocks,gravel and plants.They can be seen crawling on all substrates and ocasionally swimming fast across the water.Here they help as micro scavengers,eating small left-over particles that otherwise would increase the burden of our skimmer and WQ treatment system.
But they are not taken as food by fish,other than by mandarins.Let me know if somebody observed any other fish definitely feeding on them.
They are hatched as nauplii that are also substrate dwellers.These look like microscopic roaches,very different to calanoid/cyclopoid nauplii in appearance and behaviour.Therefore they are not larval food.
Summarizing,harps and their naups are benthic,crawl on substrates,feed on detritus,and hide from the light.Few fish and no larva feeds on them.
Calanoids and their naups are pelagic,filter feeding on algae,swimming in open water.They are the preferred and natural food of fish and larvae,and are atracted to light.
That being said,and as nothing is absolute in biology,there are exceptions.
Among the thousands of harps species,there is one very atypical and interesting for aquaculturists:Euterpina acutifrons.
This harp is planktonic and filter feeder of algae,like calanoids.Same are their naups,which are very small.This species is raised like calanoids and said to be much more harder and productive.Though this harp is found in many areas of the world,it was only in Hawai that it was cultured and used in aquaculture(Syd K.,Waikiki Aquarium).
Some harps are said to be "partly pelagic"or that they being benthic,their nauplii are pelagic,and good larval food.Most of the times this didn´t stand true.Again with one exception;there is a scientific work that shows that the benthic Tisbe holothuriae has planktonic,atracted to light naups that could be collected and given to larvae.It would be interesting to find if these naups were accepted by our fastidious ornamental fish larvae...
Again,please submit any personal experience or serious work showing how other harps could be useful.It would be great,given that as a group,they are so prolific,hardy and easy to culture.