We marine aquarium hobbyists generally strive to create aquatic environments that are as naturalistic as possible for the animals in our care. We use high-quality salt mixes to replicate natural sea water (assuming we don’t collect salt water directly from the ocean). We aquascape our tanks with live rock to create a naturalistic reef structure. If we keep photosynthetic invertebrates, we even suspend high-intensity lighting over the tank in an effort to replicate the tropical sun.
But no matter how naturalistic we try to make our marine systems, there’s simply no getting around the fact that certain elements and devices we utilize to create an appropriate environment for marine fish and invertebrates are never actually encountered in nature.
The most obvious example of this is the glass/acrylic tank itself. Nowhere in the ocean do fish find themselves running headfirst into an invisible wall. But another, and potentially more significant, example is the submersible powerhead. These pumps, which are very commonly used to create water movement in marine systems, can pose a threat to certain livestock if precautions aren’t taken.
Here are just a few circumstances in which livestock and submerged powerheads can meet with potentially damaging results:
The roaming anemone
Unlike most sessile invertebrates, anemones have the ability and tendency to detach from the substrate and roam around in search of the most advantageous position in the tank with respect to water movement, light exposure, etc. In a crowded reef tank, this wandering behavior can lead to damaging or even deadly encounters between the anemone and any neighboring cnidarians. But it can also get the anemone into serious trouble if it should happen to blunder into the powerful intake of an impeller-style powerhead.
Anytime a powerhead is used in an aquarium containing an anemone, its intake must be covered with mesh, sponge, screening, or some other porous material to prevent the anemone from getting stuck should it decide to go roaming. Some hobbyists even go so far as to build a protective flow-through casing around the powerhead, for example out of eggcrate or a similar material.
Snail meets suction
For some inexplicable reason, snails seem to be drawn to powerhead intakes like moths to a flame. On more than one occasion, I’ve come downstairs in the morning to find as many as four or five of them trapped on a powerhead in my reef tank.
In most cases of such entrapments, the snails simply withdraw into their shells and are essentially unharmed, though unable to escape the powerful suction. Then all you have to do is unplug the powerhead, knock the snails off the intake, and go about your business. But every once in a while, a snail’s soft body may get stuck on the intake so it cannot retract, in which case it will likely die as a result of the trauma.
If your powerhead comes equipped with a tapering intake extension of some sort (most powerhead models come with various attachments), installing it may reduce the strength of the suction at the opening just enough to prevent snails from getting snagged. Of course, you can also cover the intake with any of the materials mentioned above to keep snails safe.
The “cuke nuke”
Sea cucumbers are yet another group of invertebrates that can get caught on powerhead intakes with deadly consequences—not just for the sea cucumber, but potentially for all the other livestock in the tank as well.
How so? Many sea cucumbers, if sufficiently stressed (e.g., if caught on a powerhead intake—which, let’s face it, might as well be the mouth of a predator as far as the cuke is concerned), can eviscerate their internal organs and release the toxin holothurin, which, in the closed system of an aquarium, can prove deadly to all the tank inhabitants.
I don’t know about you, but I can’t think of a better motivator to cover powerhead intakes than the possibility of a deadly toxin release and total tank wipeout!
A fish tail tale
It’s not especially common for healthy fish to get trapped on a powerhead intake (though especially small, weakened, dying, or dead ones certainly can). However, certain powerheads can pose a threat to fish in a manner you might never have considered.
I recently noticed that the long filaments extending from the tail of my Niger triggerfish were missing. Both lobes of the tail were cleanly cut at pretty much the same location. At first, I suspected one of the other fish in the tank might be nipping the trigger’s fins, but then I hadn’t seen any fighting—and then there was the symmetry of the injury to consider. Could a fin-nipping fish snip a tail with such precision?
Soon thereafter, I was watching with amusement as the triggerfish playfully chased bubbles at the water surface. It would pursue them from one end of the tank (where they were produced by the sump return) right up to the overflow box at the opposite end, which is positioned very close to a powerhead—a propeller-style unit with a slotted housing. Each time the trigger got close to the powerhead, I observed that its tail draped over the housing and slipped right through one of the slots. Aha! Mystery solved!
The solution? I simply tie-wrapped nylon window-screening material around the slotted casing so no other fish’s fins can get nipped by the propeller.
What’s your powerhead plight?
Have you ever had a specimen killed or injured as a result of a powerhead encounter? If so, please be sure to share your story in the comment section below!