It sounds like you’ve got a pretty good grasp of the relationship between Mustangs and Sunbursts, and Leslie has summed up the differences between the two types very nicely.
Mustangs and Sunbursts are indeed different color morphs of the same species (Hippocampus erectus). As such, they have identical aquarium requirements, interbreed freely, and are equally hardy. Sunbursts are a bit smaller than Mustangs on average, topping out at around 5-6 inches, whereas the ‘stangs can reach well in excess of 6 inches in length.
But they differ primarily in their coloration: Mustangs tend to be darker colored, displaying the dominant dark brown to black coloration that is so typical of wild erectus, whereas the Sunbursts tend to be more brightly colored, and typically display the much less common yellow to orange color pattern.
But it’s important to note that the Sunbursts are not genetic mutations that are locked into specific colors. Colorful Ocean Riders are not homozygous recessives nor or they mutations that are unable to manufacture certain pigments altogether. In other words, they are not like albinos that are always white because they lack the ability to produce melanin (black pigment), nor are they like lutino mutations that are always yellow because they lack the ability to manufacture any pigments other than yellow. But they do exhibit differential proliferation of chromatophores and this gives each type a predisposition to display certain colors.
Mustangs, for example, have a preponderance of melanophores (black pigment cells) 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.
Although yellow and orange pigments tend to predominate in Sunbursts, they are equipped with a full range of chromatophores and can display a wide range of colors. This means they are predisposed towards the sunset colors (yellow, gold, peach and orange) when conditions are to their liking. However, they have a complement of melanophores in addition to their bright pigment cells and are able to change their coloration to reflect changing circumstances and conditions. So yellow and orange are the most commonly seen colors in Sunbursts, but you also find them in white, pearly, tan or even brown color phases from time to time.
In short, Mustangs exhibit the normal coloration for wild H. erectus and tend to be darker colored as a rule, but will show brighter color phases from time to time. Likewise, Sunbursts tend to exhibit the sunset colors when conditions are favorable, but they also display darker color phases on occasion.
You can expect both Mustangs and Sunbursts to go through quite a range of color phases from month to month. For example, I have watched my pair of Mustangs go through a number of color changes over the years. One has settled on a dark grayish -green as its base coloration for the moment, and the other ranges between rust, chocolate brown and russet-brown, but always with contrasting beige bands. Last season, the male adopted a deep burnt umber as his everyday attire (still with the same beige saddles, 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.
Sunbursts exhibit equally variable coloration from month to month and are just as hardy as the Mustangs. Of course, the two types make great tankmates for one another. Most Sunbursts are bright yellow to orange in coloration when they arrive from Ocean Rider, but there’s no guarantee they will retain those colors indefinitely in the home aquarium because conditions are different in small closed-system hobby tanks and the vast aquaculture facility, and especially because all seahorses can alter their coloration in response to so many factors.
See the following URL for an excellent discussion of the various things that affect your seahorses’ coloration and tips on how to keep your seahorses looking their best and brightest in the aquarium:
Click here: Seahorse.com – Seahorse, Sea Life, Marine Life, Aquafarm Sales, Feeds and Accessories – Re:how to get color back..
Best wishes with all your fishes, tizyou!