Re:Reidi Fry

Pete Giwojna

Dear Haynes:

Yes, sir, Brazilian seahorses (Hippocampus reidi) and Sunbursts (H. erectus) have compatible temperature and feeding requirements and can be safely kept together. And three pairs of large seahorses such as erectus and/or reidi is certainly a reasonable stocking density for a tall 45-gallon tank.

However, H. reidi are notoriously difficult to raise because the fry are so numerous, so small, and go through an extended pelagic period. They are very challenging for even professional aquaculturists to raise with a satisfactory survival rate.

The first brood of young produced by a virgin male is often inordinately small in number, but mature H. reidi males that are experienced breeders often produce broods ranging anywhere from several hundred up to 1600 fry. A tiny percentage of these fry may be able to accept newly-hatched brine shrimp (Artemia nauplii) right from birth, but the vast majority of the newborns will need to be started on rotifers or larval copepods for several days at least until they have grown sufficiently to accept baby brine shrimp instead.

It may be possible to use plankton rich seawater obtained from a clean source to help get the newborns through those critical first few days of life when they are too small to eat baby brine shrimp, so you could always give that a try, Haynes, but I suspect mortalities will be very high nonetheless. at least, that’s the basic concept behind greenwater nursery tanks, as discussed below:

The Greenwater "Starter" Nursery.

Basically, this system involves giving small numbers of handpicked fry a head start by raising them in a tank with a well-established greenwater culture for the crucial first week or two of their lives. A tank of greenwater is set up in a well-lit area and once the microalgae culture has taken off, it is seeded with copepods or rotifers. The microalgae acts as the filtration, utilizing nitrogenous wastes for growth. The idea is to provide a balanced system in microcosm with a self-sustaining food chain: the phytoplankton (microalgae culture) utilizes sunlight and nitrogenous wastes for growth and helps maintain water quality, while zooplankton (copepods or rotifers) feed on the microalgae and larger predators (seahorse fry) keep the ‘pod population in check. Additional greenwater and/or copepods or rotifers may be added periodically as needed to keep the nursery going.

In actual practice, it is difficult to for the home hobbyist to maintain the proper balance for any length of time before the greenwater culture or the population of copepods (or both) crashes. As a result, greenwater nurseries have limited applications and are useful primarily for the short-term rearing of small numbers of pelagic fry.

However, they can be quite helpful in giving pelagic seahorse fry a badly needed headstart. For example, once the hobbyist has culled a large brood of Hippocampus reidi fry down to a manageable number of the hardiest newborns, they can be introduced to a greenwater nursery where they can fatten up on tiny copepods or rotifers. This can help get the newborns through the first week or two of their lives until they are able to accept first-instar Artemia nauplii and can be transferred to a conventional nursery for further rearing.

The turbidity provided by the greenwater helps keep the phototactic fry evenly dispersed throughout the water column and away from the surface. Jorge Gomezjurado has been very successful rearing Hippocampus reidi and H. ingens fry at the National Aquarium in Baltimore using kreisel nurseries with the proper density of microalgae (i.e., greenwater). Jorge has found that turbidity is an important factor in the juvenile rearing environment for these species and he achieves the proper level of murkiness for optimum results by using algae (Nannochloropsis and Isochrysis) at a concentration of about 100 cells per ml (Bull and Mitchell 2002).

However, in my opinion, the best way to reduce the huge broods of H. reidi to manageable proportions is by culling the newborns:

Culling Newborn Seahorses.

Start the culling process by eliminating any stillborn young (up to 1/3 of the entire spawn are born dead in some cases; Bellomy, 1969). Other newborns will be alive but still attached to their yolk sacs, and some of the fry may have obvious deformities (Giwojna, Jan. 1997). Such pug-nosed ”preemies” and crippled specimens must also be weeded out since their chances for long-term survival are very poor (Giwojna, Jan. 1997).

Next remove all of the undersized individuals. You will notice that the fry in every brood exhibit a range of sizes (Giwojna, Jan. 1997). The largest individuals may be almost twice the length of the smallest of the fry. Such "runts" are at a serious disadvantage compared to their larger siblings primarily because their bigger brethren benefit from increased feeding opportunities (Giwojna, Jan. 1997). Not only can they swallow larger prey, they can swim further with less expenditure of energy (Giwojna, Jan. 1997). This allows them to feed on a greater range of potential prey and to capture food more efficiently than the small fry.

Continue the process of elimination with the goal of selecting only the healthiest, most vigorous young for further rearing (Giwojna, Jan. 1997). The idea is to decide how many fry you can reasonably hope to care for, and then cull mercilessly until you reach that number. It sounds cruel, but the colossal task ahead is going to stretch your time, equipment and patience to the breaking point, and your limited resources must be reserved for the fry that can benefit from them the most (Giwojna, Jan. 1997). The harsh truth is that if you try to save the entire spawn, you will markedly reduce your chances of raising any of them. It’s far better to keep a few well-fed babies in pristine water and perfect health than it is to keep a few hundred malnourished fry under crowded conditions, in water of rapidly deteriorating quality, that are certain to languish and die (Giwojna, Jan. 1997).

Bear in mind that if you do not cull out the weaklings, Mother Nature will be happy to do it for you. The disadvantaged fry will still be weeded out and die during the rearing process, but they will jeopardize the healthy fry in the interim by consuming your precious resources, polluting the nurseries, and increasing the chances of disease spreading throughout the nursery. Culling will occur, one way or another, and it’s best for the hobbyist to do it immediately rather than to prolong the suffering and put the healthy young at risk while the less fit fry are slowly eliminated nature’s way.

And there is another important factor favoring culling that most home hobbyist never stop to consider. Even if you beat the odds and manage to raise one or two undersized fry to the juvenile stage with a little luck and a lot of TLC, you do not want to perpetuate their inferior genes in future generations.

Once the reidi fry are finally eating first-instar Artemia nauplii, they must remain on that diet for several weeks before you can consider weeding them onto conventional foods. 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.

However, reidi fry grow slower than the young of most seahorse species, and may require longer than that before they can be successfully weaned onto minced Mysis, Cyclop-Eze, or other frozen foods.

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.

Best of luck with your efforts to rear these challenging pelagic seahorse fry, Haynes!

Pete Giwojna

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