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RIVULUS AGILAE   by Eric Bodrock

I never thought as Rivs as particularly attractive fish until I saw these beauties in a Killifish show in Niagara Falls New York. Once I spotted them I immediately added them to my “Most Wanted List” of fish. There were some for auction at the show, but unfortunately for me, someone with a really fat wallet took them home, NOT ME! My search for them began. Several months later I received my monthly BNL (Business News Letter) from the American Killifish Association (AKA) and in it, under the Fish and Egg List someone had posted Rivulus agilae, “Mont de Maheury”. The Fish and Egg List is where members can list fish and/or eggs that they have for sell or trade. I immediately emailed the fellow AKA member who listed them to order some. His answer was that he had only two pair left and my reply was; they’re mine! By the time he was able to ship them out, a female was lost. He ended up sending me the remaining reverse trio, two males and one female, along with a container of peat that contained eggs he collected from them.

     I set a pair up for breeding in a bare two-gallon tank with a tight fitting glass cover. A sunken mop made of dark green yarn, for them to deposit eggs into, sat on the bottom. An airstone with light air flow was placed in the back, upper corner. Water temperature was in the low 70 degree Fahrenheit range. Knowing that I was going to pick eggs from the mop and place them on damp peat, I assumed that the breeders would do fine in a little lower pH, 6.4-6.6 area. (Assuming that some hobbyist would spawn them directly over peat in their tank). A diet of live black worms, daphnia, mosquito larvae and newly hatched brine shrimp seemed to be eagerly accepted.

     The instructions on the container of eggs that I received provided me with the collection date of the eggs, the correct, full name, with location, so the fish could be properly identified and the date they needed to be added to water for hatching. When they were ready I used a plastic shoebox with aged tap water for the hatching container. Over several days, after wetting the peat, about twenty or so fry could be seen darting about. I added about an ounce of Euglena, also know as “green water”, into the shoebox with the tiny, two-millimeter long fry for their fist meal. As with any tiny, newly hatched fry, I added a clump of Java Moss to provide an additional source of “micro” critters for fry to graze on. Within days a started adding microworms to their diet and baby brine was added to the menu soon after that. The fry grow rather quickly, with the males noticeably faster than the females.

     As for the pair I set up for breeding, nothing happened for several months. Then, out of the clear blue, eggs were found scattered thru out the mop. Checking the mop daily revealed that anywhere from two to eight eggs were laid each day. The eggs are clear and a pretty good size at about a millimeter and a half. I collected eggs for several days and mixed them in with damp peat. The peat was then stored at a temperature around 78 degrees Fahrenheit for eighteen days, which is about when they are ready to hatch. I picked up a second pair of Rivulus agilae “Mont de Maheury” at an auction in Virginia. These were set up the same as the first pair and results were the same.

     One interesting observation with all my hatches was the high ratio of males over females, probably close to six to one! I have spoken to several hobbyist who are working with these Rivs and it is believed that spawning that occurs in a lower pH will produce more males and a higher pH will produce more females. Another point that should be noted about these Rivs is that there is another location, Mount Jolly that is in the hobby. I was informed that these are from the same location as the Mont de Maheury and to use the Mont de Maheury location name. I have also seen a different spelling of the location: Montagne du Mahury. I know that all of this name and location confusion sounds confusing, (and it is) but anyone who is into Killifish should know this is an ongoing problem that will most likely never end. The best that any hobbyist can do is to pass along as much information as they have to others as they distribute the fish.