Yeah, if your nursery tank is still swarming with newly-hatched brine shrimp (Artemia nauplii) five hours after your last feeding, then you offered them quite a bit too much for their last feeding. That’s all right — you’ll soon learn the right amount for each feeding through trial and error. When you’ve got it right, the fry will clean up most of the newly hatched brine shrimp within about a half hour, and you should then allow them to our three hours to clean up the rest of the Artemia and digest what they have eaten before you give them another feeding.
When feeding baby brine shrimp (bbs) or Artemia nauplii to seahorse fry, you want to avoid overfeeding (feeding them too much at a single feeding) as well as feeding them newly hatched bbs which have depleted their yolk supply and are nutritionally barren. The best way to do that is provide the fry with many small feedings throughout the course of the day, each of which they can clean up fairly quickly, rather than one or two massive feedings.
I suggest feeding the fry 3-5 times daily, at least 2-3 hours apart. When you are feeding the right amount, the fry should consume most of the nauplii within the first 20-30 minutes, but give them 3 hours to finish the rest and digest it fully before you feed them again. Ideally some brine shrimp will remain throughout each 3-hour feeding session, albeit at a greatly reduced feeding density after the first half-hour.
In other words, your ideal fry feeding schedule should go something like this: 8 AM feed, 11 AM feed, 2 PM feed, 5 PM feed, 8 PM feed, lights out at 11 PM. Harvest the baby brine shrimp for each feeding session in succession from each of the jars you started hatching at 3-hour intervals. This will assure that the Artemia nauplii you are feeding to the fry are no more than 3 hours old and thus at the peak of their nutritional value.
Like all babies, seahorse fry exist only to eat and poop. To say they are voracious is a gross understatement — at this stage of their development, the newborns have but one mission in life: to eat and thus to grow. Researchers have found that a single seahorse only a few weeks old can consume 3000-4000 newly hatched brine shrimp in a single day! Milligram for milligram, a great white sharks feeding habits appear downright dainty and positively anorexic compared to a baby seahorse on the prowl for live prey. And as you can imagine, when well-fed fry eat that much, defecation is amazingly rapid, with each newborn producing an average of one fecal pellet every 25-30 minutes.
One of the many quirks of seahorse anatomy is that they lack a true stomach like ours with the capacity to store food between meals (Bellomy, 1969). Rather, they are endowed with a rudimentary "stomach" that is little more than a pouchlike expansion of their intestine with no distinct separation between it and the rest of their digestive tract (Tamaru, Aug. 2001). Food passes continuously through this simple stomach instead of being stored therein. This is an adaptation to a sedentary lifestyle in which seahorses feed while at rest (as ambush predators that wait for their prey to come to them) more or less continuously throughout the daylight hours, rather than storing food or stockpiling energy in fat reserves (Tamaru, Aug. 2001). And like other carnivorous fishes, their intestinal tract is also relatively short (Tamaru, Aug. 2001).
Therefore, think of their digestive tract as a short continuous tube. When a seahorse is full, nothing more can be taken in at one end of its digestive tract without something being passed out of the other end. Seahorse fry don’t stop eating once they are full — the feeding instinct of these seagoing gluttons is so strong it compels them to keep eating as long as suitable prey is present. Baby seahorses, not sharks, are the ocean’s "remorseless eating machines!"
When they are overfed, particularly on hard-to-process Artemia nauplii, food passes through their system too fast to be digested properly. Because they swallow their prey whole and intact, this can actually reach the absurd point where they are passing live Artemia in their fecal pellets (Warland, 2003)! When that happens they are getting virtually no nourishment from their food and are literally starving in the midst of plenty. Here’s how Tracy Warland, a commercial seahorse farmer in Port Lincoln, Australia, describes this feeding dilemma and how to deal with it:
"We feed by looking closely at the ponies feces under a microscope, (a cheap dissecting microscope is ample); we breed 5 different species and all the ponies are the same, in as much as they are total gluttons. Baby seahorses (ponies) will eat so much instar 2 Artemia that they will pass out live Artemia in their feces, and they will of course not get any nutritional value from any feeds, so by over feeding you will starve them to death. We have done this. So if you feed them too much you will just love them to death as they will starve due to inability to digest. We look at the feces to determine the level of digestion and feed accordingly. Usually a feed is what the biomass of the tank can clean up in a 20-minute session, after which we leave them alone for about 2 hours and then feed them again. As soon as they defecate, we use a pipette to gather up the droppings and examine them under the microscope to check digestion levels and adjust our feeding accordingly. This is not necessary for every feed as you can soon learn the quantity required for each feeding; just make sure that the Artemia is digested fully (Warland, 2003)."
So if you have a microscope, you can easily verify that you are feeding enough but not too much at any given feeding by visual examination of the fry’s fecal pellets. Otherwise, you will eventually learn the right amount to feed and how often to feed from experience. The right feeding regimen varies according to species, the size of the brood and the size of your nursery tanks, as well as the type of food you are providing, so it is difficult to make generalizations in that regard. But Tracy Warland recommends the following:
You need to add enough food for your fry to eat for about 15-20 minutes (75%
of the food should have been consumed within that time). If it is not, then you have added too much. The fry then should have some time to digest this food, about 2 – 3 hours is plenty. Provide at least 3-5 feedings daily. Only feed during daylight hours and turn off lights at night (Warland, 2003)."
Tracy’s feeding regimen may not be the best option for the home hobbyist, however. The average hobbyist has his hands full just trying to keep up with the demands of a brood of fry, doesn’t have access to a microscope to monitor the fecal pellets of the fry, and generally needs to be far more concerned about underfeeding than overfeeding. The salient point is that when rearing fry, many small feedings daily are vastly preferable to one or two large feedings. Most hobbyists are more successful at rearing when their goal is to assure that the fry have access to at least some food throughout the day. Many breeders accomplish this by adding small amounts of newly hatched Artemia to their nurseries whenever they walk by. For the sake of hygiene and water quality, its important to siphon off the bottom of the nursery tanks between feedings, whether or not you are able to do a microscopic examination of the fecal pellets.
It’s imperative that you work out the most efficient feeding regimen one way or another, since overfeeding is not only bad for the seahorse’s digestion, it also debilitates the fry because it is very energetically demanding for them to pursue prey and eat nonstop all day long (Warland, 2003). With a little experience, you will soon work out the feeding regimen that works best for you.
Many home hobbyists find an alternating 2-hour feeding schedule works well during the day. The fry are allowed to feed for 2 hours, then fasted for 2 hours, then given another feeding and fasted for 2 hours, and so on. The nursery is then darkened overnight and the seahorses are rested.
Best of luck keeping up with the endless appetites of your Mustang babies, Carrie!