Adult male Celebes Rainbowfish (also known as a Celebes Sailfish), Telmatherina ladigesi.
As most of my readers know, I am an evolutionary biologist and ornithologist by training, and an aviculturist and birder by experience, so imagine my surprise when I was recently asked to write a guest blog essay about fishkeeping for an aquarium hobbyist blog site, The Reef Tank. How the heck did they know I am an avid aquarist? I wondered. But the truth is that before I started keeping and breeding birds, I kept and bred fish (I still keep fish now), and I even was a manager of the fish department for a very well-respected Seattle-area pet shop before I managed to earn enough money to finish my university education. In fact, fish were wonderful teachers for developing and honing my sharp eye for detail and my disciplined husbandry techniques that were extremely useful later when I started keeping and breeding rare parrots. But like most aquarists, after keeping a variety of freshwater tropical fishes for five or six years, I began looking around for a group of fishes to devote my energies to. Because I worried about the environmental ethics of keeping wild-caught marine coral reef fishes, I instead chose to specialize in two distinct fishy groups, one of which were the brackish water rainbowfishes from the South Pacific Islands (where, not surprisingly, my research birds also originate).
The rainbowfishes are a beautiful but challenging group of fish to work with, so it is difficult to choose a favorite. However, that said, perhaps one of my favorite rainbowfish species is the Celebes Rainbowfish, also known as the Celebes Sailfish, Telmatherina ladigesi, which was the first species in this group that I learned how to keep and breed. This medium-sized, large-eyed species is a lively but peaceful schooling fish that possesses a subtle, elegant beauty. They have a slender, laterally compressed and streamlined body, adorned with two dorsal fins; the first being very small and thus, is often overlooked. The miniscule first dorsal fin is a rich amber color while the other, larger, fins are a delicate lemon yellow. The first rays of the larger dorsal and anal fins are black, and the edges of the caudal fin are yellow with bright white tips. The delicately colored tail and back half of the body is translucent, so you can easily see the gas bladder (“air bladder” or “swim bladder”) through this portion of the fish’s body when the light is strong. The belly, which is not translucent, is a dark silvery-yellow covered with shiny scales that impart a brilliant silver flash when the light is just right — which no doubt acts as a visual signal for these fish’s companions. The entire body have an iridescent overlay that ranges between green and blue and lateral line is likewise adorned with a rich iridescent stripe that ranges from a dark green to blue in color. Gender can be visually identified, and adult males are especially gorgeous with their elongated, filamentous fins and characteristically deep blue-green iridescent body that shimmers over their base body color during courtship.
Adult female Celebes Rainbowfish, Telmatherina ladigesi.
Image: Scott Craig, Tropical Fish Gallery [larger view].
Celebes Rainbowfish reach lengths of up to three inches (7.5 cm) as adults. They are slow-growing fish, and take at least seven or eight months to attain full size. If you decide to breed these fish, you should set up a separate breeding aquarium filled with many salt-tolerant fine-leafed plants such as Cabomba, Milfoil, Riccia and Java Moss. The parents will scatter roughly 50-70 relatively large eggs throughout the plant leaves — and will then begin enthusiastically eating them if not removed quickly. The eggs hatch within seven days and the surprisingly tiny fry (considering the relatively large egg size) hang around and eat from the water’s surface. The young fish usually are large enough to add to the main school by the time they are five months old.
While the Celebes Rainbowfish fry and young live near the water surface, the adults typically spend most of their time zipping around with their friends in the middle two-thirds of the water column, so I kept them with other brackish fishes that utilized either the top or bottom regions of the aquarium; Celebes halfbeaks, Nomorhamphus celebensis — which only tolerate brackish water — and another truly brackish water species, bumblebee gobies, Brachygobius xanthozona — both of which are fascinating species in their own right. (NOTE: Halfbeaks tolerate cooler brackish waters but prefer softer, warmer water for breeding. Additionally, you should be aware that there are two very similarly marked bumblebee gobies — make sure you are getting the brackish water specialist and not the species that prefers freshwater).
Celebes Rainbowfishes are omnivorous in the wild, but they eagerly accept a large variety of foods in captivity, especially live and floating prepared foods. I varied their diet daily between floating flaked foods, live or flash-frozen Tubifex worms, bloodworms, and brine shrimps. Brine shrimps were particular favorites, so I ended up feeding this as the main part of the rainbowfishes’ diet (roughly half of the feedings consisted of live or frozen brine shrimps). I never fed insect larvae to my rainbowfish, but I’ve heard they accept these eagerly — but be sure that the source is pesticide-free.
I kept my rainbowfish in a 55-gallon aquarium, which is larger than the “minimum recommended size” for this species. Because rainbowfish always used that “extra” space and appeared to be so much more comfortable in large areas, I argue that it is best to always keep active fishes such as this species in the largest space possible. Certainly, if I had not moved across the country to NYC, my plan was to increase their numbers in my collection and provide them with a 100 gallon aquarium.
The most challenging aspect to keeping this species in captivity is its extreme sensitivity to its water conditions, so they can be extremely challenging to keep in certain regions of the country. However, I was lucky that most of my fishkeeping occurred in Seattle, Washington, where the water was naturally clean and soft, and its chemistry was easily altered. Perhaps the most crucial help for maintaining and buffering water pH and hardness was my choice of coarse crushed coral as the aquarium sand. Despite frequent water changes, this medium maintained water hardness between 16-18 dGH and pH between 7.6-7.8. I changed the water twice or thrice per week (this is the bare minimum, in my experience); removing between one-tenth and one-fifth of the water volume during the week and replacing with fresh water, and replacing one-half of the total water volume on weekends, and adding either rock salt or sea salt (7.5 teaspoons salt per 10 gallons (1 g/L) of added water) to re-establish salinity levels. Overall, the water salinity hovered around 1%, but dipped to 0.8-0.9% after the midweek water changes.
Recommended water temperatures for this species range between 70-80 degrees, so I opted to keep my fish at 74 degrees (23 C) to balance their needs with those of the other residents of the aquarium (bumblebee gobies and Celebes halfbeaks), which preferred slightly warmer water temperatures (it is interesting to note that fish kept at the cooler temperatures within their recommended range tend to live longer, all other things being equal). Additionally, Celebes Rainbowfish tend to spawn more readily at cooler temperatures, preferring temperatures between 70-73 degrees (21-23 C). During the summer months, when ambient temperatures soared, I would drop ice cubes into the aquarium to prevent water temperatures from exceeding 80 degrees, to prevent the fish from becoming distressed. Even though the rainbowfish (and halfbeaks) actively investigated these ice cubes, they never experienced any ill effects from the temperature differential and the overall cooling effect was to their benefit.
Because the Celebes Rainbowfishes originated in the slow-moving estuarine waters in the foothills of the South Pacific island of Sulawesi (Celebes), Indonesia, I tried to mimic those conditions by creating a moderately fast current in my aquarium. To do this, I used a variety of commercially available electric pumps and filters as well as a water jet attached to an undergravel filter bed that I constructed specifically for this aquarium. The resulting water current was considerably slowed by traveling through the leaves of many large live plants that I cultivated (Hornwort, Water Wisteria and Java Moss).
Even though it is recommended that these fish are kept in groups numbering at least five individuals, my experience has been that six is the minimum number for this and every other schooling species. I typically kept groups of 24-36 rainbowfish — always in even numbers so everyone had a special friend. I also found that keeping larger groups provided the fish with the opportunity to engage in natural behaviors that they might otherwise not display, and further, they also appeared to be more comfortable in larger groups. However, due to their expense and limited availability, it can be difficult to find Celebes rainbowfish at all. So when first establishing this species in your aquarium, I recommend that you wait to do so until you manage to find at least six healthy individuals to start with, and later, more individuals, pairs or trios can be added to that initial group.
When adding new rainbowfish to your aquarium, I strongly recommend that you exercise caution because, as I previously mentioned, this species is quite sensitive to water conditions. To add new fish, I rigorously followed this protocol: first, allow the water temperatures to equalize across the walls of the transport container (usually a plastic bag). Only after temperature equalization has occurred (after 20 minutes or so) should you begin mixing aquarium water into the water that the new fish arrived in. To do this, add small volumes of aquarium water to the new arrivals’ container every fifteen minutes or so. After the aquarium water volume has exceeded the total volume of the new arrival’s water, gently remove the new arrivals from their container and release them into the aquarium (do not pour their water into their new home because this can introduce parasites or diseases into your resident fish population).
Despite the challenges involved, there are many rewarding aspects about keeping these lovely fish, but there is one special attribute of the Celebes Rainbowfish that you are probably not aware of: they love sunlight. So my secret tip for successfully keeping this species is to place their aquarium so that it is exposed to morning sunlight. I spent many early mornings sitting in front of their aquarium in my pajamas, drinking coffee or hot chocolate, enthralled by their intense courtship displays where both sexes were transformed from their delicate silvers and yellows into deep vivid greens, blues, and purples, and zooming through their home, demonstrating what seemed to be a general joie de vivre that was highlighted by a glowing Seattle sunrise.
Adult male Celebes Rainbowfish, Telmatherina ladigesi.
Image: Orphaned. Please contact me so I can provide proper attribution.
NOTE: this essay was written at the request of The Reef Tank, where it was originally published one month ago. This is a rewritten and edited version of the original piece.