Yes, one reason brightly colored seahorses may darken in a new aquarium is if the lighting is too intense. In nature, bright light means exposure to harmful ultraviolet radiation, and the seahorses respond by producing excess melanin, just as people will develop a dark tan in the summertime if they spend a lot of time in the sun. For this reason, seahorses that are displayed under metal halide lighting or other high intensity lighting may darken in coloration due to the excessive production of melanin. As Jorge Gomezjurado (Head Curator at the National Aquarium in Baltimore and the owner-operator of the Draco Marine aquaculture facility) reports, “I have exposed yellow seahorses to strong metal halide and they have turned black in few hours.” It would be a terrible shame to display colorful seahorses such as Sunbursts or Fire Reds or Pintos under metal halides or other high-intensity lighting, only to see them darken in coloration and lose their vivid colors…
On the other hand, the proper lighting can often greatly enhance the appearance of colorful seahorses. As one example of how this can work, Grolux fluorescent lighting stimulates dazzling coloration in bright red or orange seahorses (e.g., Mustangs or Sunbursts in their red or orange color phases, the bright red orange color morphs of H. reidi, or perhaps H. barbouri with vivid orange coloration). Osram Gro-lux fluorescent bulbs put out wavelengths of light that are concentrated toward the red and violet regions of the spectrum. They are intended to stimulate better plant growth, but have the added effect of greatly enhancing any red or orange or purple colors they illuminate. When bathed in Gro-lux light, bright red or orange seahorses literally glow!
In fact, when I first discovered this effect — with a Red Philippine Lobster (Enoplometapus sp.) in a specialty tank — I believed I was witnessing actual fluorescence. The seven-inch bulldozer of a crustacean was covered with sensory bristles that made it look almost fuzzy, and under the Gro-lux bulb, the extraordinary excavator was instantly suffused with a fiery radiance that dazzled the eye. At first I thought its exoskeleton was glowing, and I hypothesized that perhaps the chitin was infused with the type of calcite crystals that fluoresce under ultraviolet, and which perhaps could be similarly excited by the wavelengths emitted by the Gro-lux bulb.
I only realized the truth when I added the same type of bulb to an aquarium containing, among other choice specimens, a gorgeous purple-and-yellow Royal Gramma and a rare red-orange Hippocampus erectus. Now, that seahorse was very colorful under any kind of lighting, but as soon as that Gro-lux lamp switched on, the erectus was ablaze with a shade of brilliant Day-Glo orange ordinarily only seen from neon signs, nuclear meltdowns, and psychedelic posters displayed under UV. The stunning steed shone with a luminous aura, awash with glorious orange glow that made it look like it was swathed with liquid fire. Suddenly, it was the color of red-hot lava, aflame with a blinding orange incandescent, and the result was truly spectacular. Then my shy Royal Gramma emerged from its sleeping cave to keep the seahorse company, and its magenta end was immediately suffused with a dazzling hot-pinkish purple glow that ended abruptly where its yellow half began. That made it obvious that the new bulb was accenting colors at the red and violet regions of the spectrum, which are precisely the wavelengths of light chlorophyll absorbs best.
The reflected Gro-lux light was responsible for the breathtakingly beautiful effect, and it will produce the same scintillating display in your aquariums. It would certainly set red and orange Brazileros (Hippocampus reidi) aglow, as well as Mustangs or Sunbursts (H. erectus) in their red to orange color phases. Pink to purple seahorses should be similarly enhanced under Gro-lux lighting. Fire Reds that approach true scarlet or crimson would no doubt blaze brilliantly, but I’m less certain what effect it would have on specimens that tend more toward auburn or which display that rich mahogany luster instead. And it would have no effect whatsoever on black or brown or yellow or green seahorses, which would absorb the light rather than reflecting it. Suffice it to say if we’ll be including any red, orange, or purple seahorses in your exhibit, you should use Gro-lux bulbs in order to display them in all their glory!
Otherwise, Paul Groves, curator at Underwater World in Perth, recommends combining a triphosphor (6500k) fluorescent tube with a Phillips TL Blue fluorescent tube to produce the best overall lighting and colors for a seahorse exhibit. After much experimentation, he found the above combination of lights really encouraged the coloration of the seahorses as well as being aesthetically pleasing to the eye. He reports that the diversity in colors displayed by Hippocampus subelongatus was much less under any other lighting. So if you want to accent the colors of red, orange, or purple seahorses, Osram Gro-lux fluorescents are ideal; on the other hand, bright yellow seahorses display best under ordinary white (daylight) florescent light, and for other seahorses, try a 6500k triphosphor fluorescent in conjunction with a Phillips TL Blue fluorescent to keep them looking their best. And avoid metal halide lighting for your seahorse exhibit.
In your case, D, if your light fixture is adjustable, I would tone down the “cool” end of the visible spectrum (i.e., blue/violet) and turn up the “warm” end of the visible spectrum (i.e., yellow/red) in order to accentuate the coloration of bright yellow or orange seahorses. As for the overall light level, the settings that are appropriate for live gorgonians, tree sponges, and colorful macroalgae will suit seahorses perfectly as well.
If you contact me off list ([email protected]), I will be happy to send you some more suggestions for keeping your ponies looking their best and brightest at all times.
Best wishes with all your fishes, D!
Pete Giwojna, Ocean Rider Tech Support