Re:Seahorse Breathing Question

Pete Giwojna

Dear Grant:

It’s good to hear that your new female is making the transition to frozen foods so well.

Can you refresh my memory regarding the size of your Biocube, sir? Is your setup a 12-gallon nano tank, a 24-gallon Biocube, or what? I need to know how big your Biocube is in order to give you a good answer regarding the proper stocking density for the tank.

But offhand I would say that adding any more than one new seahorse would probably be pushing things, considering the amount of invertebrates that are already in the tank.

Yes, sir, you are quite correct in assuming that seahorses will breed more readily in a small, closed-system aquarium than clownfish or angelfish will. However, reproductive success with seahorses often depends largely on whether they are wild-caught specimens or cultured seahorses. Allow me to elaborate.

Environmental triggers, such as changes in salinity, and other seasonal changes often have a strong influence on breeding in the aquarium, particularly for wild seahorses. Wild-caught seahorses may have a difficult time adjusting to captive conditions, don’t tolerate crowding at all, and most importantly of all, in the aquarium they lack the type of seasonal or cyclical environmental cues (falling water temperature, changes in day length, reduced salinity from monsoon rains, moon phases and high tides, etc.) they normally experience in the wild that regulate the breeding season. These environmental stimuli trigger the secretion of gonadotropin and other key hormones that prepare them for breeding and govern their reproductive activity. Without these environmental cues and the hormonally induced changes they trigger, many times wild-caught seahorses simply do not breed in captivity. (For instance, studies by fish endocrinologists show that it takes at least two years for wild fish just to adjust to a reverse photoperiod in the aquarium if they are from the southern seas and are now being kept in the northern hemisphere.)

The point is that breeding may not occur without the proper environmental stimuli to trigger the secretion of pituitary hormones. This often presents a problem in the aquarium, especially for wild-caught seahorses. Artificial lighting eliminates daylight as a cue, heaters prevent temperature fluctuations, and hobbyists take pains to keep the salinity rock solid. Such stability in aquarium conditions is generally a good thing — the goal that all conscientious aquarists are taught to strive for, but it is not necessarily the best thing to promote breeding (Indiviglio, 2002). With no seasonal changes in day length, water temperature, or salinity to trigger a surge in gonadotropin and get the ball rolling, reproductive activity in wild-caught seahorses can grind to halt. This problem was often exasperated in the past by the fact that hobbyists often kept wild ponies in aquariums that were too shallow for them to mate successfully.

In short, breeding in Hippocampus is often seasonal, regulated by cyclical changes in water temperature, day length, and salinity (monsoons). In the wild, both temperate and tropical seahorses breed best during the summer months and typically take a break from breeding during the offseason. Although domesticated seahorses that have been born and bred for aquarium life for generation after generation are no longer as strongly dependent on such environmental cues and will often breed year-round in captivity, even captive-bred seahorses sometimes experience a lull in the festivities at this time of year. That’s just their natural breeding cycle, the rhythm of life built into their genes.

Breeding is another area where wild seahorses simply cannot compete with their captive-bred counterparts. In the olden days, greater seahorses removed from the wild rarely bred in captivity. There were a number of reasons for this ranging from traumatic capture techniques and mishandling by dealers to difficulty adjusting to a captive environment to the sort of feeding problems we’ve been discussing above. But one big factor was that in the aquarium they lacked the type of seasonal or cyclical environmental cues (falling water temperature, changes in day length, reduced salinity from monsoon rains, moon phases and high tides, etc.) they normally experience in the wild that regulate the breeding season. These environmental stimuli trigger the secretion of gonadotropin and other key hormones that prepare them for breeding and govern their reproductive activity. Without these environmental cues and the hormonally induced changes they trigger, many times they simply ceased to breed in captivity. Researchers dealt with such setbacks through wild procurement of gravid males. In other words, loaded or pregnant males removed from the wild provided the fry needed for rearing projects and laboratory study in those days. Those were truly the Dark Ages of seahorse keeping.

Nowadays, captive-bred seahorses normally experience no such difficulties in the boudoir. They are highly domesticated and very well adapted to the aquarium environment. Unlike wild seahorses, they are not subject to traumatic capture methods or mishandling and abuse en route to the hobbyist. Born and bred for captivity generation after generation, for them the aquarium is their natural habitat. As a result, for the most part, they have lost their dependence on seasonal cues and external stimuli when it comes to mating. Rather than external environmental cues, for farm-raised seahorses, which have been raised at far greater population densities than seahorses ever experience in the wild, it is the presence of other seahorses — potential mates — that appears to get their hormones flowing and triggers courtship. (Pheromones or sex hormones almost certainly play a role in this.) In other words, living amidst a group of potential partners at all times seems to be what turns on captive-bred seahorses, and breeding appears to be their number one mission in life. Compared to their wild conspecifics, farm-raised seahorses seem to court constantly, breed like bunnies, and change partners often.

In fact,nowadays, the primary concern of many new seahorse keepers who are not prepared for rearing the young is how to prevent their prolific CB ponies from settling down and breeding. Some aquarists will keep their seahorses in a unisex environment in order to avoid breeding so they don’t have to deal with brood after brood of young.

If you have a compatible pair of captive bred and raised seahorses and you provide them with optimum water quality, good nutrition, and the stress-free environment, the chances are excellent that they will produce offspring at some point, Grant.

No, sir, the newborn seahorses cannot be kept in your Biocube or in a refugium. Either of those options would rapidly result in an aquarium that was being overrun by hydroids, which would quickly get out of hand when you began adding copious amounts of newly hatched brine shrimp to your nano reef or refugium on a daily basis in order to feed to seahorse fry. And the dreaded hydroids would then quickly take a grievous toll on the newborns.

Realistically, you would need to set up separate nursery and rearing tanks to have any kind of chance at raising the seahorse fry. When that time comes, I would be happy to help you set up suitable nurseries for the newborns.

Yes, sir — you did it right when you set up your mini reef using primarily mushrooms and polyps, while avoiding SPS corals and LPS corals. Soft corals have very little stinging ability and generally make good choices for a modified mini reef that will include seahorses (Delbeek, Oct. 2001). This includes most mushroom anemones (corallimorpharians). However, as Charles Delbeek cautions, "One notable exception is the elephant ear mushroom anemone (Amplexidiscus fenestrafer). This animal is an active feeder on small fish and will envelope them whole with its mantle then slowly digest them by extruding its digestive filaments into the space created. No small fish are safe with these animals in the tank (Delbeek, Oct. 2001).".

Hippocampus also does very well with zooanthids and colonial polyps in general. But the hobbyist must be sure to observe a couple of precautions when handling the zoanthids and placing them in your aquarium.

First and foremost, many of the commonly available Zooanthus (button polyps) and Palythoa (sea mats) species contain a very toxic substance in their mucous coat known as palytoxin, which is one of the most poisonous marine toxins ever discovered (Fatherree, 2004). Palytoxin can affect the heart, muscles, and nerves, resulting in paralysis or possibly even death, and many hobbyists have reported numbness, nausea and/or hallucinations after merely touching these corals (Fatherree, 2004). When you handle zoanthids and palythoans, you cannot help picking up some of their protective slime on your fingers, and so much as rubbing your eye, picking your nose, or a small cut on your finger can be enough to land you in the hospital. When handling Zooanthus are Palythoa species, it’s very important to wear disposable latex gloves, avoid touching your mouth or eyes, and carefully dispose of the gloves immediately afterwards (Fatherree, 2004).

Secondly, zoanthids and other soft corals such as mushrooms may wage border battles if you place them in close proximity to each other (and the zoanthids almost always lose out to the mushrooms in these skirmishes). So be sure to allow adequate space between the colonies. Some rapidly growing Zooanthus colonies can be aggressive to soft and stony corals alike as they rapidly spread over the rockwork, but in general they are quite peaceful, and you can always slow down their rate of growth by reducing the nutrient loading in the aquarium.

Other low light corals that should be suitable for a seahorse reef include genera such as Cynarina, Scolymia and Trachyphyllia, as well as non-photosynthetic gorgonians such as Subergorgia and Didogorgia, and perhaps wire corals such as Cirripathes spp. (Delbeek, Nov. 2001).. However, supplemental feedings of zooplankton may be required to maintain these corals in good health.

The hard or stony corals fall into two categories depending on the size of their polyps. The small polyped stony (SPS) corals have tiny polyps that extend out of minute openings in the stony skeleton, and generally have weak stings that should not pose a threat to seahorses. Depending on conditions in the tank, SPS corals such as Acropora, Montipora, Pocillipora, Porities, Seriatopora and Stylophora can be tried freely at your discretion (Delbeek, Oct. 2001).

The large polyped stony (LPS) corals, however, are generally best avoided altogether. These include genera such as Catalaphyllia, Cynarina, Euphyllia and Trachyphyllia that have large fleshy polyps which often have tentacles equipped with powerful stinging cells. The Euphyllia and Catalaphyllia have the most powerful nematocysts among the LPS corals, and can deliver stings that are stronger than most anemones (Delbeek, Oct. 2001).

Some of the soft corals and stony corals that generally do well with seahorses in a modified reef tank are listed below. (By no means is this intended to be a comprehensive list, but rather just a few examples of suitable corals to serve as general guidelines when stocking a reef tank that will house seahorses):

Finger Leather Coral (Lobophyton sp.)
Flower Tree Coral – Red / Orange, (Scleronephthya spp.)
aka: Scleronephthya Strawberry Coral, or Pink or Orange Cauliflower Coral
Christmas Tree Coral (Sphaerella spp.)
aka: the Medusa Coral, Snake Locks Coral, or French Tickler
Cauliflower Colt Coral (Cladiella sp.)
aka: Colt Coral, Soft Finger Leather Coral, Seaman’s Hands or Blushing Coral.
Toadstool Mushroom Leather Coral (Sarcophyton sp.)
aka: Sarcophyton Coral, Mushroom, Leather, or Trough Corals.
Bullseye Mushroom Coral (Rhodactis inchoata)
aka: Tonga Blue Mushroom, Small Elephant Ear Mushroom (rarely)
Clove Polyps (Clavularia sp.)
Stick Polyp (Parazoanthus swiftii)
Green Daisy Polyps (Clavularia sp.), Indonesia
Orange & Green Colony Button Polyps (Zooanthus sp.), Fiji
Pulsing Corals (Xenia spp.)
Red Ricordea (Ricordea sp.), Indonesia, occasionally Solomon Islands
Lavender Hairy Mushroom (Actinodiscus sp.), Tonga
Pimpled Mushroom (Discosoma sp.), Indonesia
Purple Gorgonians

For additional information regarding seahorse-safe corals and invertebrates, please see Will Wooten’s guide to tankmates for seahorses at the following URL:

Best wishes with all your fishes (and invertebrates), Grant!

Pete Giwojna

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