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Does anybody have a scientific answer to why, in the morning, my rasabora hets are a dull tan and their scales do not reflect light. After a few minetes they slowly regain their color and brightness. I thought it might be a natural adaptation to avoid predation a night, but I do not know.

probably because they are sleeping

My guess it is to avoid being preyed upon during the night hours, so their neon colors don't refelect any light! Also, they are sleeping, its just a natural part with most fish, I have ever seen

72 gallon bowfront:Tanganyikan Lake set up
75 gallon: A. Baenschi trio,Cyanotilapia Afra Cobwe(4), copadichromis trewavase, protomelas sp. tangerine tiger(breeding pair)

Quite a few fishes undergo significant colour changes betwsen sleeping and waking.

My Cardinal Tetras turn purple during the night, then return to being the more usual blue once they've woken up. Additionally, much of the red colouration darkens during the night.

Beckford's Pencil Fishes (which I had last year) are another fish species that undergo marked colour changes. During the daytime, they're horizontally striped. During the night, the acquire oblique vertical stripes that disappear once they've been awake for about 30 minutes. In fact most species of Pencil Fish (Nannostomus species) will exhibit a dramatic colour change from night to day and back again.

A more remarkable example of colour change is exhibited by the Characin Hemigramus coeruleus. In life, this fish is blue (as might be inferred from the scientific name - coeruleus means 'blue'). However, the fish turns red shortly before it dies! Likewise, when Herbert Axelrod was told of the existence of a black Cichlid in the Amazon, and offered $1,000 for a pair, people rushed to find the "Black Cichlid" ... however, when the fish was found (originally named Chuco axelrodi by Fernandez-Yepez), it was an undistinguished brown fish. It only turns black when dying! Details of this can be found in the November 1977 issue of TFH (page 62).

Move into the world of marine fishes and colour changes take on a whole new dfmension. Large Pomacanthus and Euxiphipops Angelfishes from the reefs undergo dramatic colour changes between juvenile and adult (a feature also manifested by certain Wrasses of the Genus Coris, and the Dragon Wrasse, Novaculichthys taeniourus, which also undergoes dramatic finnage changes), so that the blue and white juvenile Emperor Angelfish purchased three years ago becomes, upon changing to adult colours, a spectacular rainbow-hued fish whose stripes change from vertical to horizontal. then, of course, you have colour changes taking place in some marine fishes because, hey presto, they change sex - some change from female to male, others change in the opposite direction. When that happens, a colour change accompanies the sex change in many instances. Then, of course, you have certain flatfishes such as the Flounders, that can change their colouration, chameleon like, to match the substrate upon which they are resting.

However, if you want the real virtuoso colour changers, you have to look outside the world of fishes, and look at the Cephalopods (Octopi, Squid and Cuttlefishes). Octopi and Cuttlefishes in particular can change not only their colour, but their surface texture, at will, and can perform startling 'disappearing acts', blending into the background with a degree of apparent ease and finesse that astonishes everyone who witnesses it for the fist time. Then, you have the bizarre manner in which the Cuttlefishes generate pulsating waves of colour as they hover over crustaceans, poised to strike - during the course of approaching a crab or lobster and preying upon it, a Cuttlefish stops looking like a living creature and starts resembling an alien spaceship!

I suspect that if more people observed their fishes at night, they would witness a host of other colour changes too.


Panda Catfish fan and keeper/breeder since Christmas 2002