I observed the video you provided closely, and your seahorse has a very healthy appetite and no difficulty whatsoever feeding on frozen Mysis. He literally eats like a horse!
After examining the video, my best guess is that the white substance protruding from one of its gills is a bit of the frozen Mysis he has been eating. I suspect that it became lodged in this unusual location as a result of the seahorse’s powerful suctorial feeding mechanism.
You see, the distinctive head bob when your stallion snicks up its food is actually just the outward manifestation of a surprisingly sophisticated feeding mechanism. This is how I usually describe the seahorse’s unusual feeding apparatus and breakdown the complex actions that result in that powerful “snick!,” sir:
Seahorses suck! That’s a fact. Our amazing aquatic equines are supremely well adapted for suctorial feeding, which just means that their tubular snouts are designed for generating a powerful suction and slurping up small prey whole (Giwojna, Feb. 2004). Basically, their tubular mouths operate like slurp guns, a method of feeding that is often adopted by fish accustomed to taking prey from the bottom or plucking small crustaceans and larvae from the leaves of underwater plants (Evans, 1998). The anatomy of the seahorse’s head has evolved to accommodate this method of feeding (Giwojna, Feb. 2004).
For example, a tubular mouth is an advantage for suctorial feeding because it acts like a pipette and the narrow opening accelerates the inrush of water via the Venturi effect, thus maximizing the suction generated by the powerful head muscles (Giwojna, Feb. 2004). The seahorse’s oral or buccal cavity and gill chambers (opercular cavities) act as dual suction pumps that draw the water inwards with considerable force (Evans, 1998). Expansion of the buccal and opercular cavities causes a sudden drop in pressure within the mouth (Evans, 1998). The suction thus created allows the seahorse to suck up food through its slurp-gun snout faster than the eye can follow. In essence, the seahorse inhales its food in the blink of an eye, and cavitation caused by the sudden inrush of water traveling at tremendous velocity through the narrow snout and characteristic movements of its head and skull bones produce the distinctly audible “snick!” which announces the demise of its prey (Giwojna, Feb. 2004).
Every seahorse keeper is familiar with the seahorse’s “trigger,” located at the underside of its jaws at the base of its throat, which moves downward sharply when the seahorse strikes, thereby expanding its oral (buccal) cavity and generating the suction to draw its prey inwards. This trigger is actually the seahorse’s hyoid bone, and it is pulled downward by contraction of the powerful sternohyoideus muscle that runs from the hyoid bone to the cleithrum (one of the bones of the pectoral girdle), which forms part of the seahorse’s bony exoskeleton (the cleithral ring) just behind its head (Evans, 1998).
The suction generated by the sudden downward contraction of the hyoid bone when a feeding seahorse “pulls the trigger” on its intended prey is greatly enhanced by the nearly simultaneous expansion of its gill chambers or opercular cavities (Giwojna, Feb. 2004). The additional suction thus created by the seahorse’s opercular pump is produced by contractions of the hyohyoideus muscles and dilator operculi muscles (Evans, 1998). The water pulled into the gill chambers this way is then expelled from the opercular cavity through a small pore. (This narrow opening accelerates the stream of water passing through it in the same way as its narrow tubular snout does.) The seahorse’s bony coronet evolved atop its head in part to provide solid anchorage and attachment points for the large muscles that operate its buccal suction pump and twin opercular suction pumps, which enable it to feed so efficiently (Giwojna, Feb. 2004). This is the perfect feeding mechanism for an ambush predator, ideal for extracting small prey items from heavy cover or sucking up suspended prey neatly from the water column, and the seahorse is perfectly adapted for its role as the sniper of the seagrass jungle (Giwojna, Feb. 2004).
Of course, the seahorse’s turreted, independently operating eyes are the perfect targeting system for this sophisticated feeding apparatus (Giwojna, Feb. 2004). Side-mounted, hemispherical eye turrets provide nearly 360 degrees of vision and allow the seahorse to look upwards and downwards (or forward and backwards) simultaneously in search of potential prey or possible predators (Giwojna, Feb. 2004). As soon as it detects a likely prey item, both eyes lock on it simultaneously and track it intently, thus providing excellent depth perception. This allows the seahorse to judge distances with remarkable accuracy as it draws a bead on its intended victim (Giwojna, Feb. 2004).
The hyoid bone is the trigger which fires the seahorse’s slurp-gun snout, and the moment its prey closes within striking distance, the powerful sternohyoideus muscle contracts and pull the trigger (Giwojna, Feb. 2004). The buccal cavity expands, followed by the almost instantaneous contraction of the hyohyoideus muscles and dilator operculi muscles, which likewise expand the opercular cavities (Evans, 1998). The resulting drop in pressure creates a sharp inrush of water, which draws the prey irresistibly into the seahorse’s mouth (Evans, 1998). Once the prey has been sucked in, the mouth is closed. At this point, the buccal and opercular cavities are contracted and the excess water is forced out in a strong stream via the tiny opercular pores (Evans, 1998).
All this happens in an instant, faster than the eye can follow, and the powerful suction that is generated often macerates large prey (Giwojna, Feb. 2004). When the resulting debris is expelled from the gill chambers, it looks remarkably as if the seahorse is shooting smoke out of its ears, thus giving a feeding seahorse an uncanny resemblance to the legendary fire-breathing dragon (Giwojna, Feb. 2004).
In this case, I suspect that the debris expelled after slurping up one of the frozen Mysis included a fairly substantial bit of macerated Mysis that was large enough to partially occlude the gill pore. It doesn’t appear to be causing your stallion any distress, so I don’t think you need to be overly concerned about this development.
However, I would like to suggest a change in the way you are feeding the frozen Mysis to your seahorse, sir. You don’t want your seahorse eating the frozen Mysis from the bottom of your tank. That’s a very unsanitary practice, since the substrate is where all of the fecal pellets and detritus accumulate in your aquarium. Unfortunate things can happen if a seahorse is feeding on frozen Mysis that have become contaminated with bacteria after laying on the substrate.
And any uneaten frozen Mysis may begin to decay and degrade your water quality following a heavy feeding.
Therefore, I would suggest that you train your seahorse to eat from a feeding dish or feeding tray, which contains the frozen Mysis in a clean, sanitary receptacle until it is eaten. It’s a very simple process to train your pony to use a feeding station and it’s a lot of fun, too.
I wrote an article in Conscientious Aquarist explaining exactly how to set up a feeding station and train your seahorses to use a feeder in some detail that you may find to be of interest, munmachi. It discusses all the different kinds of feeding stations, including natural feeding stations. It’s available online free of charge at the following URL:
Click here: Seahorse Feeders
Best wishes with all your fishes, sir!
Pete Giwojna, Ocean Rider Tech Support