It’s difficult to say whether the large size of the jumbo Piscine Energetics frozen Mysis will be problematic for your young seahorses, sir. I have seen small ponies wolf down king-sized Mysis that appeared impossibly large at first glance. Zulu’s (Hippocampus capensis), for instance, are renowned for their aggressive feeding habits and, in an impressive display of voracity, even small specimens will unhesitatingly tackle large frozen Mysis that may take them two or three snicks to successfully swallow. A hungry Cape seahorse will often have more than half of a large mysid protruding from its snout, making it look like a sword swallower in mid-performance as it gradually works its gargantuan meal down with a series of mighty snicks! It is an amazing sight to watch an undersized capensis choke down several oversized frozen Mysis in quick succession and come hurrying back for more like it was starving with the tail of the last shrimp still sticking out of its mouth! They are capable of remarkable feats of sheer piggery, and everyone marvels at how rotund they are when they get their first good look at well-fed, captive-bred capensis.
On the other hand, I have noticed that seahorses can sometimes be very selective when it comes to the size of the prey they prefer. The jumbo PE Mysis relicta are indeed quite large, and in it’s certainly possible that your youngsters may balk at the jumbos simply because of their size.
Fortunately, the Piscine Energetics frozen Mysis relicta is now available graded for size. You can get the usual jumbo Mysis relicta or smaller Mysis and, in your case, Richard, because your seahorses are still fairly young you may have better luck with the smalls since your pony may prefer smaller prey. Some seahorses are very particular in that regard, and tend to reject food items that are significantly larger or smaller than their preferred range of prey. For example, I’ve seen some seahorses that rejected the smaller Hikari Mysis with great disdain, yet which greedily gulped down the jumbo Piscine Energetics Mysis relicta. On the other hand, I’ve had small seahorses turn up their snouts at the jumbo PE frozen Mysis because it’s too large for their liking, and attack the small Hikari frozen Mysis with great gusto.
If that’s the case with your new acquisitions, you might try ordering some of the small Piscine Energetics Mysis relicta and feeding the larger ones to your other fish, or you can pick up a package of the much smaller Hikari frozen Mysis at your LFS for your pony instead. Painstakingly cutting the larger PE Mysis relicta into smaller pieces is more time consuming, but it can also be very effective at times. The Hikari Mysis is the smallest of them all and many pet stores carry the Hikari brand so it should be readily available.
Best of luck with your new arrivals, Richard! Here’s hoping they are soon eating like horses and scarfing down frozen Mysis greedily.