If your fry are reidi hybrids, I am not surprised that they are proving to be quite challenging to raise. The good news is that H. reidi are incredibly prolific and are sure to provide you with many more broods to come. The bad news is that they produce enormous broods of tiny fry that go through an extended pelagic phase of development, making them among the most difficult of all seahorses to rear. But it can be done, and the factors you need to address to achieve success are well-known, so I will happy to discuss some reidi rearing tips with you.
Two main factors determine how easy or hard seahorse fry are to raise: (1) their size at birth and (2) whether or not they undergo a prolonged pelagic phase. The bigger and better developed the newborns are, the easier they are to raise. Seahorse fry whose average length at birth is 10 mm (0.4 inches) or more are able to take enriched Artemia as their first foods and are relatively easy to rear. Seahorse fry that are significantly smaller than 10 mm (0.4 inches) at birth need to be started on smaller foods that are more difficult to provide in copious amounts on a daily basis, such as rotifers, copepods, and larval Mysis, making them more difficult to raise. Likewise, seahorse fry that undergo an extended pelagic phase, during which they drift freely with the plankton, are much more troublesome to raise than benthic seahorse fry, which orient to the substrate and seek out hitching posts straightaway. The pelagic fry are difficult because the surface huggers tend to gulp air and suffer fatal buoyancy problems, and may even become entrapped by surface tension. As a result, most hobbyists find that mortality is very high during the pelagic phase.
The easiest seahorse fry to rear are therefore benthic fry that are large and well developed at birth. Dwarf seahorses or Pixies (Hippocampus zosterae) fall into this category, and indeed many hobbyists have closed the life cycle with zosterae. The most difficult seahorse fry to raise are relatively small and underdeveloped at birth, and must pass through a lengthy pelagic stage. Brazilian seahorse fry (Hippocampus reidi) are a good example of this category, and are notoriously difficult to raise.
In short, Doug, your hybrid seahorse fry are going to be tough for a home hobbyist to raise. For best results, they will need rotifers as their first foods. I think that part of your problem may be that the food you are offering them is too large for the newborns to handle. For example, newborn reidi often cannot swallow newly-hatched brine shrimp (Artemia nauplii) as their first food, and must therefore be started on rotifers or larval copepods for the first three or four days of their lives. If they don’t receive adequate nutrition during this crucial period, they will die. I suggest feeding your newborns rotifers for several days before you switch them over to newly-hatched brine shrimp. The link below will take you to an article that discusses how to culture suitable live foods for pelagic fry like yours:
Click here: Seahorse Nutrition Part IV: Feeding & Rearing the Fry
Hippocampus reidi are famous among seahorse keepers for two things: brilliant colors and making babies. The Brazilian breeding machine is the most prolific of all the seahorses. They have a well-deserved reputation for churning out brood after brood every two weeks with relentless regularity, and hold the world record for delivering ~1600 young in a single brood (anecdotal reports of broods up to 2000 fry are not uncommon)! Not bad for a livebearer. But with that many fetal fry crammed into one incubator pouch, the inevitable tradeoff is that the young are born at a considerably smaller size than most seahorses. They also go through a lengthy pelagic phase, drifting freely with the plankton for up to 1-2 months.
As you know, Doug, Hippocampus reidi fry are notoriously difficult to rear because they go through a prolonged pelagic period before they settle down to the bottom and seek out hitching posts, and no doubt this is also causing some of the rearing problems you have experienced. Special precautions must be taken to circumvent the surface-hugging behavior of pelagic fry and the problems this presents, and above all, to prevent them from accidentally ingesting air. The planktonic seahorse fry feed at the surface where their prey tends to congregate, drawn to the light, and all too often the newborns take in air along with their food and cannot expel this air. When this happens, it upsets the fry’s equilibrium, and they will float sideways on the surface of the water. Upon close examination of these floaters, a bubble of trapped air can be spotted just below the head (Tracy Warland, pers. com.).
Sadly, such fry are doomed. Once air has been ingested, there is nothing the aquarist can do to save the delicate babies. Therefore, once the newborns have had an initial opportunity to fill their swim bladders, pelagic fry must be kept away from the surface.
Three factors have been found to increase the survivorship of reidi fry during their pelagic phase: (1) the use of kreisel or pseudokreisel nurseries, (2) hyposalinity, and (3) the use of greenwater to maintain the proper level of turbidity in the nurseries and help keep the phototropic fry away from the surface.
Kreisel and Pseudokreisel Nurseries.
Kreisel/pseudokreisel nursery tanks rely on gentle, carefully directed currents to keep pelagic fry — and their food (rotifers, Artemia nauplii, copepods, etc.) — suspended evenly in a circular flow until the young seahorses are ready to settle down on the bottom. Centripetal force draws the fry and their food gently towards the center of this vortex and keeps them suspended in midwater. This has several beneficial effects. Most importantly, it keeps the fry off the surface and prevents them from gulping air. Secondly, it keeps the newborns from swimming into the side glass (in the vastness of the ocean, pelagic fry NEVER encounter such obstacles, and the baffled newborns can injure or exhaust themselves trying to swim through these invisible barriers in an aquarium). And it has the added advantage of concentrating the newborns’ food supply exactly where the hungry fry are drifting.
The kreisel-effect can be accomplished any number of ways, and is generally much easier to achieve than you might imagine. Many different pseudokreisel designs are suitable for use by the home hobbyist, but Liisa Coit’s in-tank nurseries featuring drum-style goldfish bowls as the inner rearing chambers are among the very best. If you are unfamiliar with kriesels, Doug, just let me know and I would be happy to discuss how to set up a suitable kriesel are pseudokreisel system of nurseries for your hybrid fry.
Hyposalinity for Pelagic Nurseries.
Regardless of the type of nursery tank you use, there is one simple measure you can take to counteract the surface-hugging tendency of pelagic fry and increase survivorship during their pelagic phase: raise them at reduced salinity. Keeping the nurseries at a specific gravity of 1.016 (23 ppt salinity) makes the fry less buoyant and thereby reduces problems with surface huggers, entrapment in surface tension and accidentally ingesting air while feeding at the surface.
As an added benefit, reduced salinity also helps prevent parasite problems. Marine parasites need high osmotic pressure externally in order to maintain a normal water balance within their bodies (Kollman, 1998). Reduce the salinity of the surrounding saltwater sufficiently, and water moves via osmosis into the parasites’ bodies until they literally explode (Kollman, 1998). A specific gravity of 1.016 is low enough to provide the fry with a significant measure of protection from parasites in this way.
Hyposalinity is compatible with all types of nurseries. It can be safely employed with shaded or side-lit nurseries, kreisels and pseudokreisels, or divided nurseries and in-tank nurseries. Hippocampus reidi breeders report that reducing the salinity in their fry tanks can reduce mortalities by up to 50% during the high-risk pelagic period (Nicola Strawbridge, pers. com.).
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.
The turbidity provided by the greenwater helps keep the phototropic 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).
The following recommendations for nursery and rearing tanks, as well as diet and nutrition, are again based on Jorge Gomezjurado’s successful breeding and rearing program for H. reidi at the National Aquarium in Baltimore.
Jorge notes that the best way to rear reidi fry is by using circular black pseudokreisel nurseries with the flows being established by positioning a bubble curtain or a water jet at one end of the tank (Bull and Mitchell, 2002, p51). He cautions that the stocking density should be limited to no more than 80 fry per gallon (20 fry per liter) for the first two months (Bull and Mitchell, 2002, p51). After the second month, the juveniles will have passed through their pelagic phase and can be transferred to a regular rectangular rearing tank without turbulence or a circular kreisel flow for further growth and development (Bull and Mitchell, 2002, p51).
Water quality and photoperiod should be maintained by using 10% daily water changes and 150-200 Lux as the optimal light level (Bull and Mitchell, 2002, p51). Jorge advises that turbidity is an important factor in the fry’s rearing environment. He uses a technique similar to greenwater nurseries to maintain the proper level of turbidity by adding algae (Nannochloropsis and Isochrysis) at a concentration of about 100 cells per ml (Bull and Mitchell, 2002, p51).
Jorge finds that the optimal water flow for rearing reidi fry is10 mm/sec, and he notes that feeding decreases at lower or higher flow rates (Bull and Mitchell, 2002, p51). At the proper level of flow (10mm/sec), the water movement also generates enough turbulence to break the surface tension of the water, allowing the newborn fry access to the surface where they will gulp enough air to inflate their swim bladders initially and achieve neutral buoyancy (Bull and Mitchell, 2002, p51).
Diet, Nutrition, and Feeding Techniques:
Gomezjurado stresses that high standards of hygiene must be maintained during food preparation and the maintenance of live food cultures. He points that the quality and quantity of the food you provide are important regulators of seahorse growth and survival (Bull and Mitchell, 2002, p51).
Adult H. reidi at the National Aquarium in Baltimore receive a staple diet of frozen mysid shrimp (Mysis relicta) coated with essential vitamins and amino acids, Astaxanthin Natu-Rose, and Canthaxanthin (Bull and Mitchell, 2002, p51). They receive 3 feedings of day of the enriched frozen Mysis relicta, and this highly nutritious diet is one of the keys to their successful breeding and rearing program for H. reidi (Bull and Mitchell, 2002, p51). Jorge Gomezjurado finds that providing his broodstock with a well rounded, nutritious diet increases the size of the fry they produce (Bull and Mitchell, 2002, p51). Consequently, his reidi fry are closer to 10mm in length than the usual 6-7mm (Bull and Mitchell, 2002, p51). The larger reidi are able to feed more efficiently and can ingest larger prey items, including Artemia franciscana Instar I nauplii, thus giving them a considerable advantage over the smaller fry (Bull and Mitchell, 2002, p51).
As with all seahorse fry, Gomezjurado finds that providing H. reidi fry with proper nutrition during the crucial first weeks of life is one of the greatest challenges in seahorse husbandry. He meets that challenge by providing the developing fry with a natural food chain of living prey (Bull and Mitchell, 2002, p51). This live food chain consists of phytoplankton (species such as Nannochloropsis aculata and Isocchrysis galvana), brine shrimp nauplii (Artemia franciscana), copepods (Acartia tonsa), and juvenile Mysis shrimp (Americomysis bahia) (Bull and Mitchell, 2002, p51). The microalgae (phytoplankton) serve as a source of food and nutrition for the various zooplankton in the chain, and the progressively larger prey items are introduced to the fry and juveniles as they grow (Bull and Mitchell, 2002, p51).
The feeding levels provided at NAIB depend on the stocking densities of the nurseries and rearing tanks, which Jorge cautions should not exceed 80 fry per gallon or 20 fry per liter in the case of H. reidi (Bull and Mitchell, 2002, p51). Recommended feeding densities for reidi fry are 10 rotifers/ml, 15 nauplii/ml, and 3 copepods/ml to start with, with the amounts increased accordingly as the fry grow to keep up with demand (Bull and Mitchell, 2002, p51). The water intakes in the rearing tanks are closed or markedly reduced during feeding times. Jorge finds that the gradual transfer from one live food organism to another is easily achieved simply by overlapping feedings at the different weaning stages (Bull and Mitchell, 2002, p51).
The zooplankton that comprise the live food chain at NAIB are enriched with essential vitamins, commercial Highly Unsaturated Fatty Acids (HUFA) rich in docosahexaenoic acid (DHA), and carotenoids such as Astaxanthene biological pigment Natu-Rose (Bull and Mitchell, 2002, p51). Special precautions are taken at NAIB in order to assure that the enriched brine shrimp nauplii (platinum-grade Artemia franciscana cysts) the Aquarium uses are germ free. The decapsulated brine nauplii are kept at high salinity (55-60 ppt) after hatching and the culture water is changed every day in order to prevent bacterial proliferation (Bull and Mitchell, 2002, p51).
Juvenile H. reidi are ready to be weaned onto frozen mysids by the age of 8 weeks. Jorge finds it helpful to leave the frozen mysids unenriched during this initial training period. He feels the juveniles can better recognize the frozen mysids as prey if it free of any enrichment coating (Bull and Mitchell, 2002, p52).
In summation, the ultimate nursery design for home breeders rearing Hippocampus reidi may thus be Liisa Coit’s in-tank nursery setup (or a variation thereof), with the inner drum-style goldfish bowls adjusted to maintain the circular kreisel flow and the optimal turbulence at a rate of 10mm/sec, and the specific gravity adjusted to 1.016 to provide moderate hyposalinity, a 12:12 photoperiod at 150-200 Lux, and greenwater added as necessary to maintain the necessary turbidity (i.e., 100 cells/microliter).
Best of luck rearing your hybrid seahorse fry, Doug! Don’t be discouraged if you have poor results with your first few attempts at rearing. Now that they have begun breeding, you can expect your broodstock to churn out a new brood about every 14 days with clockwork regularity, so you’ll have plenty of opportunities to refine your rearing techniques, and as you gain experience, your results will improve. Let me know if you want to try a kriesel or pseudokreisel nursery at some point, and I will be happy to go over some of the options in that regard with you.