seahorse changed colour

Dear Chester:

No, sir — it isn’t necessary to procure a mated pair of seahorses in order to assure successful breeding. The urge to reproduce is very strong in Hippocampus — especially captive-bred-and-raised seahorses — and providing you obtain males of the same species, provide your seahorses with good nutrition, a stress-free environment, and conditions to their liking, along with an aquarium that’s tall enough for them to accomplish the copulatory rise, you can expect your seahorses to pair up on their own and breed sooner or later.

Regarding the change in coloration, seahorses do indeed alter their background coloration and pattern in response to a wide range of social and environmental factors, so the fact that yours have brightened up is not that unusual. However, it’s an encouraging sign that they changed from dark-colored seahorses to a bright yellow in coloration, since seahorses will often expand their melanophores (black pigment cells) and a darken in response to stress. It sounds to me like your store-bought seahorses are finding the conditions in your aquarium less stressful and much more to their liking than the conditions at your LFS. That’s a good thing, and it suggests that you did a very good job of creating a comfortable environment for your seahorses.

Here’s some additional information regarding the factors that influence coloration in seahorses, in case you haven’t already seen it, Chester:

Seahorses 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.

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.

The hobbyist should also be aware that there are any number of environmental conditions that can 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.

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 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, Chester, you can expect your seahorses to exhibit a number of different color phases over the coming months and years. All of the different factors mentioned above need to be addressed in order to keep your seahorses looking their best and brightest, Chester, and it sounds like you’re doing a very good job of that.

Best of luck with your seahorses and your efforts to find them suitable mates, sir!

Happy Trails!
Pete Giwojna