Home | Ocean Watch | Books | About Susan | Search | Email Susan

I recently had the opportunity to visit the zoo in Dhaka, the capital of Bangladesh. That may not sound too appealing, and I admit I was worried about the conditions I might find there, but the trip turned out to be a pleasant experience. The animals' homes were clean and spacious, and the nine Bangladeshi kids I took with me were a joy to be around.

One of the children's favorite places was the zoo's aquarium where the kids exuberantly admired the fish.

Interestingly, the fish there were all freshwater species, likely an economical choice in this developing country. I recognized swordtails, mollies and other species common in Hawaii's home aquariums. These fish seemed healthy and well tended, but the usual bright colors of several species were drab compared to the same pet fish here.

Later, when we spotted a flock of flamingos whose white feathers showed only a trace of their past pink glory, I knew what was happening here: The fish and flamingos were lacking carotenoids in their diet.

Carotenoids are natural pigments in plant tissues that give them color. Although the word carotenoid usually invokes images of orange, yellow and red colors (the word carrot comes from carotenoids), these substances are responsible for a wide range of colors in the natural world. That's because when carotenoid pigments attach themselves to proteins or fats, they can turn blue, green, purple or brown.

Plants and seaweeds can make carotenoids, but animals cannot. Therefore, if an animal's skin or feather color comes from carotenoids, and the creature doesn't get it in its food, some or all of the color fades.

Flamingos are famous for this phenomenon, but carotenoids affect the color of other animals, too, including some fish.

University of Hawaii researchers illustrated this recently when they added carotenoids to the food of some aqua-cultured clown anemone fish. Within a week, the yellow and maroon colors of the fish brightened noticeably. Just as striking was the darkening of the black stripes on one type of anemonefish.

The researchers conducted a similar experiment with freshwater aquarium fish and found a similar result. The scientists used two kinds of carotenoid-rich algae grown at Cyanotech Corp., a company on the Big Island's Kona coast. When these algae were added to fish food, the colors of swordtails, rainbow fish, mollies, and cichlids, among others, were significantly enhanced within one week. When the additives were stopped, the colors faded.

BECAUSE only two additives produced a variety of colors, researchers know that different species metabolize carotenoid pigments in different ways. Exactly how the fish create the hues they need is yet to be learned. But this research shows that if ornamental fish growers and keepers want their fish to show their best colors, they should add carotenoids to their fishes' food.

The same goes for flamingos. These big birds sift mud through their upside-down beaks, eating everything from bacteria and algae to shelled animals and fish. Because in their natural habitat some of these foods contain carotenoids, flamingos' feathers are usually pink. When given food without these "pinkening" agents, however, the birds quickly turn white.

Did my young Bangladeshi friends care that the fish were pale and the flamingos white at the Dhaka Zoo? Not in the least. Like kids everywhere in the world, simply going there made them happy. And I was happy to share their joy.