Congratulations on your four-week old juveniles! Getting 18 of the youngsters past their first month is an excellent way to begin your attempts at rearing! You are obviously doing a lot of things right, Carrie. Keep up the good work!
The current thinking is that the fry can remain on a steady diet of newly hatched Artemia until you are ready to begin weaning them onto a diet of frozen foods (usually minced Mysids and/or Cyclop-eeze). Aquaculturists are now converting the fry to frozen foods earlier than ever, often beginning around 3-4 weeks old. Jeff Mitchell reports that the fry are healthier and grow faster the sooner they make the transition to enriched frozen foods, and he expects the young seahorses to have made the transition to frozen foods by the age of 4-1/2 weeks.
The best way to prepare the Mysis for this is to mince the frozen Mysis coarsely rather than putting it through a blender. How fine or coarse you need to chop it depends on the size of your fry, since you want to wind up with bite-size pieces of Mysis. Initially, many breeders prefer to shave small pieces of Mysis off of a cube while it’s still frozen.
When the fry have grown a little larger and can accommodate bigger pieces of Mysis, I find it convenient to carefully thaw whole Mysis individually and then carefully chop them into several pieces.
Either way, it is very important to be extra diligent about vacuuming up leftovers (and any fecal pellets) while the fry are making the transition to frozen Mysis. Otherwise, the minced Mysis that doesn’t get eaten right away while it’s still suspended in the water column or shortly after it has settled on the bottom will begin to degrade the water quality in your nursery tank.
It’s important to overlap the fry food when they are making the transition. Offer them shaved or minced Mysis along with the newly hatched brine shrimp they are accustomed to eating. (Many times it’s better to offer the minced Mysis first, while the fry is still the hungriest, and then add the baby brine shrimp.) Once they begin eating the bits of frozen Mysis well, gradually increase the amount of minced Mysis and decreased the amount of baby brine shrimp you offer at every feeding until they are finally eating the shaved Mysis almost entirely.
Overlapping the feedings this way, offering newly-hatched brine shrimp as usual along with just a little frozen Mysis at first, assures that there is familiar food available to the fry while they are making the transition and makes sure that the slow learners still get enough to eat.
Some hobbyists find it helpful to begin soaking the newly hatched brine shrimp in Mysis juice for a week or two before they actually began offering the bits of minced Mysis along with the bbs. That way, the juveniles get used to the scent of the frozen Mysis and associate it with food before you start to add the bits of frozen Mysis.
Here’s a previous post from Patti that describes how she weaned her erectus fry onto frozen to Kari Mysis:
I’m wondering if nutrition is your problem.
Could you train them onto frozen mysis? My 4 week old erectus are
eating shaved Hikari frozen mysis already. They started not eating
much of the BBS and looking around the bottom of the bowl. I
enriched the shaved mysis w/Vibrance & put it in the bowl. It goes
to the bottom and they’re on the hunt. They’ll look at it a good
while and then snick. It only took 1 day to train them. I swish it
around a little at first to get them interested.
I think the mysis is better for them nutritionally and they don’t
have to spend so much energy eating all those tiny BBS. Give it a
try. It may take a few days. I gave mine the mysis 1st – before
adding the BBS. That way they were pretty hungry. Then I gave them
some BBS for desert to make sure each one got something to eat if
they weren’t eating enough mysis yet.
Patti [close quote]
Notice that Patti’s erectus fry were all hitching and beginning to look around on the bottom for things to eat, indicating that they were ready to give up their planktonic existence (the high-risk pelagic phase) and make the transition from live brine shrimp suspended in the water column to frozen foods.
When the newborns are the right age, don’t hesitate to try them on frozen Cyclop-Eze first if you aren’t having any luck with the frozen Mysis.
Bonus tip: adding one or two older juveniles that are already eating the frozen Mysis well to the nursery tank along with with the inexperienced fry in order to act as their mentors can hasten the transition. Many hobbyists report that fry learn to take frozen minced mysids much faster and easier when they are provided with teachers to show them the way. These teachers are usually a few of the older fry from a previous brood, which have already become proficient at feeding on the frozen mysids (Liisa Coit, pers. com.). The younger fry are quick to copy them, learning from their example.
With regard to the air bubbles you have noticed in some of the youngsters when the light was right, I agree with Seagazer that it may actually be the silvery swimbladder or gas bladder that you are seeing. As in many other bony fishes, the seahorse’s gas bladder functions as a swim bladder, providing the lift needed to give them neutral buoyancy. In essence, the swim bladder is a gas-filled bag used to regulate buoyancy. Because the seahorse’s armor-plated body is quite heavy, this organ is large in Hippocampus and extends from the neck well down into the body cavity along the dorsal boundary.
When the swim bladder is inflated with just the right amount of gas, the seahorse achieves neutral buoyancy, which just means that if neither tends to rise or sink. It is thus weightless in the water, with the buoyancy from its gas bladder exactly canceling out the pull of gravity. This facilitates swimming and makes holding its body upright effortless. So if your juveniles are now over a month old, Carrie, and are not having problems with positive buoyancy, I suspect it is just the silvery gas bladder you are seeing and not excess air the fry have accidentally ingested.
Best of luck keeping up with the endless appetites of your voracious fry and weaning them onto frozen foods, Carrie!