Re:Tank and horse questions:

Pete Giwojna

Dear Catherine:

It’s very difficult to say why the yellow Hippocampus erectus you adopted have reverted to drab coloration because so many different factors can influence the coloration that seahorses express at any given moment. But if you are feeding them frozen Mysis enriched with Vibrance, then you can rule out any sort of a dietary deficiency or lack of carotenoids in their diet or anything of that nature. Rather, the factors that I would focus on in your case are the lighting, the coloration of the aquarium background and decor, stress, and the coloration of their tankmates.

The lighting can certainly have a profound influence on the coloration expressed by seahorses, Catherine. For instance, seahorses don’t like excessively bright light and they may go into hiding, seeking shaded areas amidst the rockwork, if the lighting is too intense for their comfort level. And the seahorses won’t look their best and brightest under high-intensity lighting such as metal halides because they will produce excess melanin (black pigment) in order to protect themselves against the harmful ultraviolet radiation they associate with intense light, and darken as a result. For instance, Jorge Gomezjurado reports "…I have exposed yellow seahorses to strong metal halide and they have turned black in few hours." (Jorge served as the head curator at the National Aquarium in Baltimore and operated Draco Marine, an aquaculture facility devoted to captive-bred-and-raised seahorses, so consider him to be an expert on the subject.) Some hobbyists who keep a selection of handpicked live corals with their seahorses like to use metal halides or other high-intensity lighting systems for the sake of the corals, but it would be a shame to display brightly colored seahorses under such strong lighting and cause them to darken.

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 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 bring out the brightest colors in your seahorses, try a 6500k triphosphor fluorescent in conjunction with a Phillips TL Blue fluorescent to keep them looking their best. Avoid metal halide lighting and other high-intensity lighting for your seahorse tank.

So it’s possible that the lighting in your aquarium may have had something to do with why the bright yellow seahorses you adopted have changed to black in your tank, Catherine.

Secondly, if dark colors predominate in your aquarium, it’s certainly possible that the seahorses may have darkened in order to better blend in with their background and make themselves less conspicuous. If you have a black background, dark-colored substrate, and lots of dark-colored live rock in your aquarium, so that black or dark colors predominate, that may have been a factor as well, and you may want to consider adding some brightly colored artificial corals and gorgonians to your tank. Yellow, orange, red and even pink artificial corals may encourage your seahorses to brighten in coloration, especially if they adopt one of the colorful decorations as their favorite hangout.

And, of course, you must also be cognizant of the fact that seahorses typically expand their melanophores (i.e., black pigment cells) and darken when they are stressed out, so it’s important to provide your ponies with a stress-free free environment to keep them healthy and happy and looking their best and brightest.

With this in mind, it’s important to review the most common stressors of captive seahorses. These include poor water quality and the design of the aquarium itself. A poorly designed seahorse setup that lacks adequate cover and shelter, or has too few hitching posts, will be stressful to the occupants (Topps, 1999). Seahorses are shy, secretive animals that rely on camouflage and the ability to conceal themselves for their safety and survival. A sparsely decorated tank that leaves them feeling vulnerable and exposed will be a source of constant stress (Topps, 1999). The seahorse setup should have plenty of secure hiding places so they can conceal themselves from view completely whenever they feel the need for privacy.

Needless to say, rapid fluctuations in temperature, pH, salinity and other aquarium parameters must also be avoided. In general, a large aquarium of 40 gallons or more provides much greater stability in that regard than does a smaller setup. The greater the water volume in the aquarium and sump, the more stable the system will be.

Heat stress is especially debilitating and dangerous for seahorses due to a number of reasons (Olin Feuerbacher, pers. com.). For one thing, elevated temperatures can have a very detrimental effect on the immune system of fishes. This is because many of the enzymes and proteins involved in their immune response are extremely temperature sensitive (Olin Feuerbacher, pers. com.). Some of these protective enzymes can be denatured and inactivated by an increase of just a few degrees in water temperature (Olin Feuerbacher, pers. com.). So when seahorses are kept at temperatures above their comfort zone, not only will they not look their best, but their immune system is compromised and they are unable to fend off diseases they would normally shrug off.

Incompatible tankmates are also stressful for seahorses. This includes not only aggressive, territorial fishes and potential predators but also inoffensive species that are restless, active fishes. Seahorses may be uneasy around fishes that are always on the go, swimming tirelessly back and forth.

Other common stressors for seahorses include overcrowding, overfeeding, stray voltage, and a host of issues related to water quality: ammonia or nitrite spikes, high nitrate levels, inadequate circulation and oxygenation, high CO2 levels and low 02 levels, low pH, etc., etc., etc (Giwojna, Jun. 2002).

Finally, I have often observed that colorful seahorses may undergo a change in coloration when they are added to a herd of normally colored seahorses. In such instances, the newcomers will often subdue their colors or adapt colors that match the rest of the ponies in the herd, in order to make themselves less conspicuous. So if you add a bright yellow or orange seahorse to a herd of brown or blackish H. erectus, the colorful seahorse is apt to adopt a similar brown or blackish coloration so that it doesn’t stick out from the rest of the herd. This works both ways, by the way, Catherine — if you add the drab black or brown H. erectus to a tank full of colorful yellow or orange ponies, the dark-colored newcomer may well brighten up to a nice yellow or orange shade to match his tankmates.

So any of these factors may have played a role in the loss of coloration in the yellow seahorses you adopted. Or it could be a combination of all of the above. Or the change in coloration may be due to entirely different reasons than what we have discussed thus far. This is normally what I advise hobbyists when they ask about changes in coloration or how to keep their seahorses looking their best and brightest, Catherine:

Coloration in Seahorses

When it comes to their color pattern, seahorses are not like most other marine fish — rather, they are truly the chameleons of the sea with a propensity for changing color in response to a wide range of environmental factors, hormonal influences, and behavioral interactions.

It’s important to understand that although Ocean Rider (OR) seahorses have been endowed with a palette of pigments rich in bright hues, they are not like albinos or lutino or melanistic mutants that are "locked" into their white or yellow or black coloration respectively. Such mutants are a certain color because they are genetically unable to manufacture other pigments; ORs are not. Rather, ORs are genetically equipped to express a wide range of vivid colors, and each type has a built-in predisposition towards a wardrobe of certain shades. But they can and will change colors to reflect their mood, environment, and well-being, as well as to interact with other seahorses.

Seahorses accomplish color changes through the contraction or expansion of pigment cells known as chromatophores. Each chromatophore is a contractile cell or vesicle containing liquid pigment and capable of changing its form or size, thus causing changes of color in the skin of the animals that possess them. The chromatophores may be under nervous control and able to change very rapidly or under hormonal control and able to change only relatively slowly.

In seahorses, the chromatophores are branched (dendritic) cells, within which the color pigment can be moved. When a chromatophore contracts, all of its pigment is concentrated in one small spot in the center of the cell, resulting in the loss of color in the fish. When a chromatophore expands, the pigment spreads throughout the entire cell to all its branches, resulting in bright color.

Different types of chromatophores contain different pigments such as melanin (black), xanthin (yellow), lipochrome (orange), erythrin (red) and so on. The different types of chromatophores are named according to the type of pigment they contain (e.g., melanophores, erythrophores and xanthophores). These specialized pigment cells are usually stacked upon each other or clustered in groups. Hippocampus is typically endowed with 3 or 4 different types of chromatophores, and all other colors are derived from these 3 or 4 basic pigments. The exact color the seahorse displays at any given time therefore depends on the concentration of these pigment cells, how close the cells are to the surface of the skin, and which chromatophores are expanded or contracted at the moment.

For example, seahorses have no blue pigment cells, but the color blue can be approximated nonetheless. A low concentration of melanin (black pigment) deep in the dermal layer gives the skin of the fish a bluish cast. Achieving a blue tint in this way while simultaneously expanding xanthophores (yellow pigment cells) produces shades of green, and maintaining a bluish background color while opening erythrophores (red pigment cells) yields shades of purple and violet. Likewise, a seahorse that has no orange pigment cells can still assume a bright orange coloration by simultaneously expanding its xanthophores (yellow pigment cells) and erythrophores (red pigment cells) to the fullest. The exact shade of orange it becomes and its brightness is determined by the proportion of yellow to red cells it opens, how fully they are expanded, and how close to the skin’s surface they are. Obviously, a seahorse that is black has all its melanophores expanded and a seahorse that is white has ALL of its chromatophores contracted so that all the wavelengths of visible light are reflected back to the observer, and so on.

In seahorses, melanophores are the most common of these pigment cell types. They contain the pigment melanin, which gives most seahorses their typical black or dark brown coloration. Essentially melanin absorbs the entire visible light spectrum and looks black because no light is reflected back to the observer. When a melanophore is open and fully expanded, the melanin it contains is dispersed throughout the cell, and when all the melanophores are opened at once, melanin is distributed evenly across the surface of skin, rendering the seahorse black. Seahorses typically respond to stress by expanding their melanophores and darkening this way.

The different types of pigment cells seahorses possess varies from species to species. Hence, not all seahorses have the same palette of colors at their disposal. Some seahorses can never turn red because they lack erythrophores; red is simply not in their wardrobe. In general, tropical seahorses tend to have brighter colors in their repertoire than temperate species. And deep-water seahorses often have more red and orange pigment cells than other seahorses. In order words, different seahorse species have different coloration due to the differential proliferation of chromatophore cell types.

Colorful Ocean Riders, for example, are not homozygous recessives nor or they mutations that are unable to manufacture certain pigments altogether. But they do exhibit differential proliferation of chromatophores and this gives each type a predisposition to display certain colors. Mustangs have a preponderance of melanophores, for instance, and tend to be dark (earth tones) or cryptically colored most of the time. But ‘stangs also have bright pigment cells and they can brighten up when the occasion calls for it, such as during courtship or when competing for mates.

I own a pair of these spirited steeds myself, and have watched them go through a number of color phases from month to month. One has settled on gray-green as its base coloration for the moment, and the other ranges between rust, burnt umber, and orange, but always with contrasting beige bands. Last season, the male adopted a rich ochre yellow as his everyday attire (still with the same beige bands, though), while the female displayed a dark purplish ensemble with definite greenish highlights. When courting, they consistently brighten to a pearly white and a creamy yellow respectively. They make a handsome couple, and I find my Mustangs to be very attractive specimens in all their guises.

As for their coloration, Sunbursts are equipped with a full range of chromatophores (pigment cells) and can display a wide range of colors, but they are predisposed towards the sunset colors (yellow, gold, peach and orange) when conditions are to their liking. They have proportionally fewer melanophores (black pigment cells) than Mustangs, which are typically dark brown or black, so the background or base coloration of the Sunbursts tends to be lighter. Yellow and orange specimens predominate, but they also display whitish, tan, pearly and even brown color phases at times. You can expect your Sunbursts to go through a number of color phases and color changes over the months.

Sunbursts have fully functional melanophores, albeit somewhat fewer of them, in addition to their bright pigment cells and they will darken in response to stress or change their coloration to reflect changing circumstances and conditions. In short, Catherine, there are any number of environmental conditions that can also affect the coloration of seahorses, often by affecting the ability of chromatophores to contract and expand. These include the following factors:

Stress — seahorses often respond to stress by darkening.

Emotional state — when excited, seahorses typically brighten in coloration, reflecting a state of high arousal. On the other hand, fear, anxiety and distress are generally accompanied by dark, somber hues.

Social interactions — seahorses often brighten during their courtship displays; pair-bonded seahorses likewise brighten during their morning greeting rituals, and rivals go through characteristic color changes (see below) during their confrontations and competitions.

Competition for mates — dominant individuals brighten; subordinate seahorses darken in submission.

Hormonal influences — juvenile seahorses may change coloration when they hit sexual maturity in response to a change in their hormonal levels.

Poor water quality — high levels of nitrogenous wastes (e.g., ammonia, nitrite or nitrate) can cause chromatophores to contract and colors to fade.

O2/CO2 — low oxygen levels (or high CO2 levels) can cause colorful seahorses to fade and they will blanch when subjected to hypoxic conditions.

Background colors — seahorses will often change color in order to blend in with their immediate surroundings.

Medications — some antibiotics and malachite-green-based remedies negatively affect color.

Tankmates — seahorses may change their base coloration to blend in with the rest of the herd or to match their mate (or a potential partner). This can work both ways: a dark seahorse may brighten up and assume vivid hues when introduced to an aquarium with bright yellow or orange tankmates, just as a brightly colored seahorse may darken and adopt subdued coloration when placed amidst drab tankmates. Of course, seahorses are not respondsing to peer pressure when they conform in this manner; rather, this is probably instinctive behavior. In nature, it’s not healthy to be too conspicuous and stick out in a crowd since an individual that stands out from the rest of the herd draws the attention of potential predators to itself.

Temperature — chromatophores tend to contract at high temperatures (above the seahorse’s comfort zone), causing colors to fade; cooler temps within their optimal range can make pigment cells expand, keeping colors bright.

Disease — skin infections (bacterial, fungal, or parasitic) can cause localized loss of pigmentation or discoloration of the affected areas.

Diet — seahorses cannot synthesize the pigments used in their chromatophores. It is therefore important to enrich their food with pigments such as carotenoids in a form that’s easy for them to absorb. If color additives are not provided, the chromatophores will gradually lose their pigments and the seahorse’s color can fade. Vibrance, for example, is exceptionally rich in Vitamins A and C as well as natural carotenoids, which are not found in Mysis relicta. This is important because the carotenoids are a class of yellow to red pigments, which include the carotenes and the xanthophylls. Like all cells, individual pigment cells have a limited life expectancy in the body and must be regularly renewed. Marine organisms cannot synthesize carotenoids, so if they do receive adequate amounts in their diet, they will have difficulty replenishing their red and yellow pigments. This means that the colors of bright yellow, orange, and red seahorses will gradually fade over time if their daily diet is lacking in carotenoids. So don’t neglect the enrichment step in your daily feeding regimen! If seahorses are fed a strict diet of Mysis relicta without additional enrichment, they may begin to develop dietary deficiencies over time, and both their health and coloration will eventually suffer.

Lighting — seahorses may darken in response to UV radiation or intense lighting (e.g., metal halides) as a protective measure, whereas bulbs that emit wavelengths of light shifted towards the red end of the visual spectrum (i.e., Grolux fluorescent tubes) can greatly enhance the coloration of red, orange or purplish seahorses to the point that they almost literally glow.

In short, you can expect your seahorses to exhibit a number of different color phases over the coming months and years. Expect them to display brighter colors when they get serious about breeding and courtship, for instance. And if they happen to adopt a colorful hitching post as their favorite perch or hang out, they may gradually change coloration to match their favorite resting spot.

All of the different factors mentioned above need to be addressed in order to keep your seahorses looking their best and brightest, Catherine. There are a number of other things that you can explore to influence their coloration and encourage them to display bright colors. These are discussed in some detail in a two-part article on coloration in seahorses that I recently wrote for Conscientious Aquarist online magazine. The first article explains how seahorses use their amazing color changing ability, while the second article explains how they accomplish their color changes and is loaded with tips for keeping colorful seahorses such as Sunbursts looking their best and brightest. You can read the articles at the following URL’s and enjoy Leslie Leddo’s magnificent photographs. Just copy the following URL’s and paste them into your web browser, and it will take you directly to the articles:

part one:

part two:

When it comes to your new 55-gallon aquarium, I don’t recommend keeping large seahorses such as Mustangs or Sunbursts (H. erectus) in aquariums that are less than 20 inches tall, but your new tank meets that minimum requirements and has sufficient water volume to provide stability and a comfortable margin for error. I should think it would make a fine seahorse setup and the height should not be an overriding issue as long as you include a shallow substrate that is only 1/2 inch to an inch deep. In general, the taller the aquarium, the better it is for seahorses, but you would have to look for a hex tank or column tank or consider a considerably larger aquarium in order to get a tank that is much more than 20 inches tall, Catherine, and an aquarium the size of your 55-gallon tank is certainly more than adequate to allow Hippocampus erectus seahorses to mate comfortably.

I would say to stick with the 55-gallon tank and invest your money in a good filtration system to maintain optimum water quality and colorful aquarium decor that will make your seahorses feel at home and encourage them to look their best and brightest. And I would hold off on ordering the Sunbursts until you can get a better handle on what ever factors may have played a role in causing the beautiful yellow seahorses you adopted to turn black, assuming the change in coloration is not just a transitory color phase they are going through.

Best wishes with all your fishes, Catherine!

Pete Giwojna

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