Unicorn Pouch Emphysema
I found Unicorn the Seahorse floating upside down, at the surface, unable to swim or hitch. He had Pouch Emphysema. Unfortunately this illness happens to a lot of male sea horses, when gas bubbles bloat their pouch (where they carrie the babies).
Having know about this possibility, I recognized the problem. Hopefully it was not too serious, and not too late. It can cause serious problems if it become chronic or is left too long, as the stress can kill the seahorse.
I put my hand in the tank, and he weakly hitched onto my finger. Holding him softly in my fingers, I massaged the pouch, with a soft plastic pipette in hand to use as a catheter. After a few minutes, a few large bubbles burped out of the pouch. Clearly Unicorn was in shock, but he was now upright. He swam weakly down and didn't move for the rest of the night from the corner of the tank. But he has been swimming and eating just fine since... it seems he is okay!!
