Captive Care Notes: Riffle Daces (Rhinichthys, Family Cyprinidae)
Because of their abundance and wide distribution, Longnose Dace (Rhinichthys cataractae) and Blacknose Dace (R. atratulus) are popular aquarium residents. They're peaceful, active, easy to feed, and in the case of the Blacknose Dace, tolerant of poor water quality conditions.
In the aquarium, Longnose Dace require cool, clean water and plenty of swimming room. Surprisingly, this benthic, riffle-loving species doesn't require swiftly moving water, nor food that reaches the bottom. Given a week or so to find their "balance" in standing water, wild-caught Longnose Dace acclimatize to feeding in mid-water and even from the surface, the latter of which requires the dace to almost completely invert its body in order to point its downward-facing mouth upwards. As with most minnows, all manner of prepared, frozen and live foods are taken. Aquarists who like to create realistic simulations of stream habitats may wish to submerge a powerhead to create current; just be sure to provide "pool" areas where the dace can seek refuge and rest.
Blacknose Dace and Longnose Dace will spawn in the aquarium if they are given a simulated winter cooling period followed by a simulated springtime rise in light and temperature. Blacknose Dace are probably the easiest Rhinichthys to spawn. Maintain a group of five males and five females in a well-aerated aquarium, 30 gallons or larger, with moderate current (25 cm/sec) over sand or fine gravel. Situate plants, logs, and rockwork to the sides and backs of the aquarium to create an open spawning area in the middle. Condition with heavy feedings of live or frozen foods. As temperature rises, watch for males to establish a territory over a section of gravel. Once spawning occurs, either remove the eggs or the adults immediately, as the adults will eat the eggs. Eggs hatch in 5-8 days. The fry, after their yolk sacs disappear, require small live foods such as rotifers, copepodites, and newly hatched brine shrimp, but may accept Tetramin paste and flakes. For spawning Longnose Dace, increase the current speed to 50 cm/sec and create an irregular bottom consisting of various sized rocks and coarse gravel.
Speckled Dace (R. osculus) are also easy to spawn. Valerie Burtson, writing in the NANFA publication American Currents, was surprised to find Speckled Dace fry feeding on algae growing on the leaves of plants in a densely planted 55-gallon, hexagonally shaped aquarium. Apparently, the five Speckled Dace she kept in the tank (presumably collected near Burtson's home in South Lake Tahoe, California) spawned without her knowledge. Water conditions at the time were as follows: 23-24C (74-76F), soft, pH 7.0, with one teaspoon of rock salt added per gallon. Indirect sunlight and 12 hours of fluorescent light contributed to plant and algae growth. The fry grew rapidly on microworms, baby brine shrimp, and liquid fry food. The fry were removed when the adults, which usually stayed at the bottom of the tank while the fry gathered near the top, began nipping the fry tails.
Details from Burtson's fortuitous spawning are consistent with those used by a biologist raising Speckled Dace in the laboratory. Apparently, the dace do not need live or frozen foods to reach spawning condition. Calvin Kaya, working out of Montana State University, fed his Speckled Dace broodstock commercial trout chow and flake food. He kept them in aquaria 130 l (43 gal) and larger with 14 hours of light per day, and induced them to spawn by gradually raising the temperature from 15C (59F) to 24C (75F) -- roughly the same temperature at which Burtson noticed her dace had spawned. Fortunately, Kaya observed the spawning act: A single female was chased by one or more males. Adhesive eggs were scattered in tank corners and crevices in the gravel around undergravel filter standpipes. Since both sexes foraged on the spawned eggs, Kaya placed a woven mat in the tank through which the eggs could sink to safety. The fry were free-swimming 8-10 days later and fed on powdered flake food, liquid fry food, and baby brine shrimp. The first generation matured and spawned at almost two years of age.
The federally threatened Loach Minnow (R. cobitis) has been raised at Alchesay-Williams Creek National Fish Hatchery in Whiteriver, Arizona, as part of the species' recovery effort. Nonspawning adults (8-10 per tank) were kept in 75 liter (20 gal) aquariums at 15C (59F) with gravel bottoms and broken clay pots to provide cover. Natural illumination from a single southern exposure window provided primary light and natural light cycles throughout the year. The fish were fed 3-4 times daily a varied diet of frozen foods consisting of bloodworms, mosquito larvae, brine shrimp, and krill. Although initially reluctant to accept flake or freeze-dried foods, Loach Minnow can be trained to feed on flakes and pellets after all other foods have been withheld for several days. The Loach Minnow usually spent daylight hours hidden under the clay potsherds, but darted in and out to retrieve food. The species is highly susceptible to parasites, particularly Ichthyophthirius.
To induce spawning among captive Loach Minnow, aquarium conditions were patterned after in the fish's natural habitat. Beginning in early October, temperatures were incrementally lowered from 15C (59F) to 7.2C (45F) by mid-November. This temperature was maintained throughout the winter until mid-March when, in response to increasing stream temperatures, it was slowly raised to 10C (50F) by mid-April. At this temperature Loach Minnow began feeding more, females appeared slightly gravid, and males displayed a gradual increase in reddish breeding hues. Two males and one female were transferred to each of two 19-liter spawning aquariums. Temperature was slowly increased to 17.2C (63F) by mid-June. Spawning began in late April when temperature reached 12.2C (54F). Eggs were deposited in an adhesive mass on the underside of the potsherd, usually where the shard came in contact with the gravel. Egg masses, often still connected to a portion of shard, were moved to a special incubator tank in which a rigid sheet of PVC, containing three circular cutouts each mounted with a stainless steel screen sieve, was placed just above the water surface. Many eggs were lost to fungus, requiring frequent treatments of malachite green. A spray bar was placed under the sieves to aerate the eggs and create a gentle upwelling effect. Eggs hatched 12-16 days later. Fry were moved to small plastic nursery tanks which were suspended in larger supporting aquariums to maintain temperature. The fry began feeding on algae and rotifers 9-18 days after hatching. Older, larger fry could take newly hatched brine shrimp supplemented with small portions of krill shaved from frozen cubes. Approximately 60% of the nursery tank water was siphoned off every 2-3 days and replaced with water from the supporting aquarium. Fry were then moved to the supporting tanks 29 days after hatching, where they began feeding on the same diet as their parents.