The name Giant Rivulus is well earned by this fish. When most people think of killifish, they envision racks of tiny tanks and small fish. The Giant Rivulus, on the other hand, grows to nearly four inches in total length, with a robustness and an appetite to match.
Rivulus hartii comes from South America, Trinidad and Tobago and the northern coast of Venezuela to be more specific. The male is a light blue-green in color with longitudinal rows of red spots from the operculum to the caudal peduncle and yellow stripes at the top and bottom of the caudal fin. The female is a more subdued brown in color with a black eyespot high on the caudal peduncle. There is little difference in size between the two sexes.
A pair of young adult fish was acquired and placed in a 20 gallon long tank with a few Corydoras aeneus and a generous portion of floating water sprite to make them feel more secure. The tank bottom was bare and it was tightly covered as these fish were enthusiastic jumpers. The fish settled in quickly and ate any flake, frozen, or live food that was given to them. They did show a marked preference for larger items, as small flakes and baby brine shrimp were eaten reluctantly at best. Tap water was used with a pH of 6.8 and conductivity of 190 micro siemens and the temperature was maintained at 78 degrees Fahrenheit. Forty percent water changes were made on a weekly basis.
The addition of a floating spawning mop after two days resulted in immediate spawning activity. Four to nine eggs were laid each day, usually in midmorning or early afternoon. The eggs were placed within two inches of the top of the mop, most frequently quite close to the knot. The larger spawns generally occurred the day after a heavy feeding of live or frozen foods. The eggs were large at 1/8 inch in diameter and they hatched after 10-14 days. The resulting fry were fully 1/4 inch long at hatching. They had a small yolk sac and were free-swimming the next day. They had no difficulty handling live baby brine shrimp and flake food right away. Growth was rapid with the fry approaching one inch in total length after a month.
It was surprising to find that the older fry did not eat their younger siblings, thus it was not necessary to sort them by size. The fry were extremely hearty and fry mortality was virtually nil. It was interesting to note that the large eggs allowed an easy view of the process of embryonic development. The formation of the primitive streak, brain and spinal chord development (neurulation), etc. were visible to the naked eye. This would make Rivulus hartii an excellent subject for classroom study.
Thus, Rivulus hartii was an interesting and undemanding fish to keep. It would be an excellent choice for both the novice and advanced hobbyist alike.
First publication: Norwalk Aquarium Society
Source: Aquarticles.com (no longer available)
Editors note: The Rivulus genus has been revised, Rivulus hartii has been renamed to Anablepsoides hartii.