Re:Seahorse Breathing Question

Pete Giwojna

Dear Grant:

Your spiny seahorse is probably Hippocampus barbouri, a species which is commonly known as the prickly or spiny seahorse, zebra-snout seahorse, or simply as "barbs," for short. All seahorse keepers are familiar with these thorny beauties. They are the pretty, prickly, tropical seahorses we all used to know and love as Hippocampus histrix until the histrix complex was revised and taxonomists officially changed their name to H. barbouri (Abbott, 2003). They are readily identified by their sharp, very well developed spines, their prominent five-pointed crown, and their boldly striped snouts (Abbott, 2003). The latter is one of their most attractive features and is responsible for one of their common names — the zebra-snout seahorse. Cultured specimens range from pale yellow to a brilliant red-orange, often further adorned with reddish brown spots and lines.

There is no easy answer to your question regarding the normal breathing rate of seahorses, Grant. Their respiration rate varies according to the levels of oxygen and carbon dioxide in the aquarium, the water temperature, their metabolic rate, their activity level, and their emotional state.

Unlike human beings, which are homeothermic and maintain homeostasis at all times, seahorses are of course cold-blooded creatures, so their metabolic rate is determined largely by the water temperature. The warmer the water temperature, the higher their metabolism and the greater their oxygen demand becomes, and their breathing rate goes up according. At lower water temperatures, the seahorse’s metabolism and oxygen demand are reduced, and their breathing rate slows.

The level of oxygen in the atmosphere that we breathe is quite stable and constant, but that’s not the case with the level of oxygen in an aquarium. For example, the warmer the aquarium water is, the less dissolved oxygen it can hold, and the higher the salinity of the aquarium water, the less dissolved oxygen it can hold. So the amount of oxygen in the water varies with the aquarium temperature and specific gravity.

Likewise, the levels of oxygen and carbon dioxide in an aquarium varies from day to night due to the photosynthesis performed by macroalgae and zooanthellae. When the aquarium reflector is on, providing plenty of light, the algae and plants in the aquarium take in carbon dioxide and release oxygen as a byproduct of photosynthesis. As a result, the pH of the water and the dissolved oxygen levels rise throughout the day, while the level of dissolved carbon dioxide drops.

On the other hand, during the night when the aquarium light is turned off and no photosynthesis takes place, the plants will begin to take in oxygen and give off carbon dioxide. This has exactly the opposite effect — the pH of the aquarium water and the level of dissolved oxygen drop at night, while the amount of dissolved carbon dioxide rises. This can occasionally become a problem in a small, poorly circulated, closed-system aquarium that is very heavily planted if the oxygen levels drop so much during the night and the carbon dioxide levels rise so high that the seahorses have difficulty breathing and getting enough oxygen.

So in an aquarium where they dissolved oxygen levels are low and/or the carbon dioxide levels are high, seahorses will exhibit very rapid respiration. They will often be pale in coloration and perch near the surface of the aquarium, often with their heads directly in the outflow from the filter, where the oxygen levels are highest.

Seahorse setups are often more susceptible to such problems because hobbyists are so conscious of their seahorses’ limited swimming ability that they tend to leave their aquariums undercirculated. Poor circulation and inadequate surface agitation can lead to inefficient oxygenation and insufficient offgassing of carbon dioxide, aggravating the situation.

Seahorses are more vulnerable to the low O2/high CO2 levels than most fishes because of their primitive gills. Unlike most teleost (bony) fishes, which have their gills arranged in sheaves like the pages of a book, seahorses have rudimentary gill arches with small powder-puff type gill filaments. Seahorses are said to have "tufted" gills because they appear to be hemispherical clumps of tissue on stems. Their unique, lobed gill filaments (lophobranchs) are arranged in grape-like clusters and have fewer lamellae than other teleost fishes. Because of the difference in the structure and efficiency of their gills, seahorses are thus especially vulnerable to low oxygen levels and asphyxia.

Warm water temperatures exacerbate such problems in the aquarium. Elevated water temperatures increase the metabolism of seahorses, and therefore their consumption of oxygen, at the same time that the rise in temperature is reducing the amount of dissolved oxygen the water can hold. That double whammy creates a dangerous situation for seahorses and may well result in respiratory distress and rapid, labored breathing.

For best results with your seahorses, Grant, strive to maintain stable water conditions in your Biocube within the following aquarium parameters at all times:

Temperature = optimum 72°F-75°F (22°C-24°C).
Specific Gravity = range 1.022 – 1.026, optimum 1.0245
pH = 8.2 – 8.4
Ammonia = 0
Nitrite = 0
Nitrate = 0-20 ppm; optimum 0-10 ppm

Provide good surface agitation and aeration in order to promote better oxygenation and facilitate better gas exchange at the air/water interface.

Your seahorses’ respiration rate may increase naturally when they are feeding, actively courting, being handled, or excited in general, and then return to their normal resting respiratory rate afterwards, Grant. That’s natural and nothing to be concerned about. Symptoms of respiratory distress are ordinarily pretty obvious and you should have no trouble determining when your seahorse is laboring or struggling to breathe.

For example, seahorses that are stressed or suffering from gill disease or parasites that attack the gills will exhibit rapid respiration, labored breathing, huffing, panting, yawning or coughing behavior, and other indications of respiratory distress. So familiarize yourself with your seahorse’s normal respiration rate when they are comfortable and healthy, which will vary somewhat with water temperature and their activity level or degree of arousal/excitement as we have been discussing, and any subsequent changes in their normal breathing pattern can alert you to a possible problem.

Ocean Rider markets a strain of captive-bred-and-raised Hippocampus barbouri under the trade name of Spikeys, Grant, but they are currently out of stock. You might try Oceans, Reefs and Aquariums (ORA) to see if they have a male zebra-snout seahorse (H. barbouri) available, sir. Otherwise, keep a close eye out wherever you obtained the female to see if a male may become available through them.

Best of luck with your spiny seahorse, Grant!

Pete Giwojna

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