The respiration rate of seahorses 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. Their breathing rate will increase temporarily anytime they are excited, which includes courtship and mating, of course. Let’s discuss how these factors affect the respiration of Hippocampus in more detail below.
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.
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.
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, Nova, 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 – 1.025
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, Nova. 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 in healthy, which will vary somewhat with water temperature and their activity level or degree of arousal/excitement as we have been discussing, and subsequent changes in their normal breathing pattern can alert you to a possible problem.
In short, sir, heavy or labored breathing is not normally associated with courtship behavior, but an increase in the seahorses’ respiratory rate is typical for seahorses that are actively courting. As you might expect, a pregnant male’s breathing rate increases to 70-80 breaths per minute when he is experiencing labor pains and preparing to deliver his brood, but that happens late in his pregnancy and there isn’t much effect on respiration shortly after a male becomes pregnant.
One male is pregnant, its brood pouch will become distended as his pregnancy advances, but the abdomen of a pregnant male is unaffected. The brood pouch at the base of the tail, slung underneath the abdomen will become quite rotund as the pregnancy progresses, but there should be no swelling of the seahorse’s abdomen itself.
There are a couple of tip offs that indicate mating has occurred you should keep in mind.
First of all, when a female ripens a clutch of eggs in preparation for mating, her lower abdomen becomes noticeably swollen, particularly around the area of the vent. When she subsequently mates and passes her eggs along to the male, she may then lose up to 30% of her body weight as a result. So if you notice that one of your females has slimmed down dramatically at the same time one of the male’s pouches has become enlarged, that could be an indication of a successful egg transfer.
The other rule of thumb to keep in mind is that if a stallion’s pouch remains enlarged for more than three or four days in a row, there is a good chance that an egg transfer may have taken place rather than that the male is simply showing off for the females by pumping up his brood pouch.
Gravid males also behave somewhat differently; as their pregnancy progresses, they are less mobile and become real home bodies, since they cannot expose their developing brood to any unnecessary risks. They tend to hole up and may even go into hiding; they may go off to feed and miss a meal or two or fail to show up at the feeding station now and then.
So it’s very difficult to say at this point if your H. reidi stallion may be pregnant or is out of sorts due to the onset of an illness. Keep a close eye on him and adjust your water chemistry as we previously discussed, and concentrate on maintaining optimum water quality. Install a protein skimmer at your earliest opportunity.
Best of luck with your seahorses, sir!