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So if I can see an air bubble in a baby seahorse, does this mean that it will eventually die? My fry are 15 days old now, I have 22 left out of the 43. There is only one out of the 22 that is looking rather thin, but I can see air bubbles in a LOT of them when all the lights in the room are out except the aquarium lights. Are they doomed?
Dear Carrie:
Congratulations on your 15-day old juveniles!
The risk depends on the size of the air bubble. If the internal air bubble (or overinflated gas bladder) is so large that it results in positive buoyancy, the survival rate of the affected fry is a very poor. Floaters and surface huggers suffer a high mortality rate during the first few weeks of life.
Your 15-day old fry will begin settling out, orienting to the substrate, and seeking out hitching posts more and more very shortly now, if they have not already done so. Fry with internal "air bubbles" that hamper them when swimming and have difficultly descending as a result will have to expand greater energy in order to maneuver as well as in pursuit of prey and are at a serious disadvantage compared to fry with neutral buoyancy.
However, the time of greatest danger for gulping air and developing fatal buoyancy problems has already come and gone for your fry, so the prospects for any fry with internal air bubbles/overinflated gas bladders are now improving day by day.
The reason exposure to the air is a serious problem for newborn seahorses but of no concern at all for older seahorses is due to the presence or absence of the pneumatic duct. Allow me to elaborate.
In seahorses as in other fish, the gas bladder arises as a simple pouch or outgrowth from the foregut (Evans, 1998). In newborn seahorses, this connection with the gut is retained as an open tube, called the pneumatic duct, and seahorse fry gulp air at the surface to fill their gas bladder initially. There is only a short window of opportunity to do this, since the fry lose this open connection very early in life. As a result, the air bladder is often completely closed off (physoclistous) in fry that are more than a few days old, and they can no longer inflate their gas bladders this way.
Newborn seahorses are therefore physosymotous, and their gas bladders open into their esophagus via the pneumatic duct. If they are exposed to the air for any length of time in this condition, chances are great that they will swallow too much air and overinflate their gas bladders. When that happens, the fry develop fatal buoyancy problems and become the infamous "floaters" that bob helplessly at the surface until they starve to death. If you examine a floater carefully, you can actually see its overinflated swim bladder, which appears as a silvery bubble in its neck at the base of the throat.
In seahorses, the pneumatic duct closes off after a few days of development, and this open connection to the esophagus is lost. At that point, exposure to the air is no longer a threat to the physoclistous fry since they can no longer overinflate their gas bladders by gulping air. So your 15-week old fry are no longer in danger from exposure to the air and how well they will fare now depends on how much air they may have ingested when they were newborns. If they are not severely hampered by positive buoyancy, they may have a good chance to develop normally at this stage of their life.
Best of luck with your 15-day old youngsters, Carrie!
Respectfully,
Pete Giwojna
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