I’m very sorry you lost your pregnant male and the young that he was carrying! All my condolences on your losses, Cathi!
A widowed seahorse certainly can be traumatized by the loss of its mate. But although it can be stressful for a pair-bonded seahorse to lose its partner, and they may go off their feed for a while as a result, a widowed seahorses doesn’t normally go on a hunger strike and starve itself to death, or die of a broken heart or loneliness, or anything of that nature.
So there is no need to rush right out and obtain another male in order to keep your female company. I cannot even venture to guess what may have befallen your pregnant male when he was so frisky and flirtatious and eating well the night before, but it’s possible that some sort of disease process may have been involved. Right now you should just concentrate on maintaining optimum water quality and keeping a close eye on your female for any symptoms that might indicate a possible problem.
If you are concerned about your solo seahorse becoming lonely by herself, you might consider taping a mirror up against the aquarium glass where she can get a good look at herself. Seahorses will often interact with their own reflections in the aquarium glass, so having a mirror-image seahorse that moves in response to his own actions can be very reassuring for a single seahorse and perk up the isolated individual dramatically. It’s an effective technique for a situation like yours and can fool the lonely seahorse into thinking he or she is still in the presence of other seahorses.
In short, I think I would give the old mirror trick a try before I introduced in another seahorse to your aquarium at this time. Let’s make sure that your female is 100% healthy and is not going to be affected by what ever affliction or accident may have befallen your male before you replace her mate.
If you read through my responses to the post on this page titled "New seahorse owner crisis," you will find a good discussion of the sort of things that can stress a seahorse and make it susceptible to disease. Please read through that discussion thread and make sure that none of those stressors are at work at this time in your seahorse tank.
Once assured that your female is going to remain healthy and that there is nothing amiss in your seahorse tank that might be stressful to your seahorses, Cathi, you can start thinking about obtaining another male to pair with your lonely female.
Pete Giwojna, Ocean Rider Tech Support