Select Aquatics of Erie, CO

         Breeding Alfaro cultratus - The Knife Livebearer




      This is a show tank of the Alfaro cultratus, the Knife
      Livebearer. These are a peaceful schooling fish that
      generally feed at the surface. Here, they are over a
      bed of Bolbitis Fern and Java Fern in a barebottom 55
      gallon. Though the plants are thick and lush, and you
      would expect it to be great for fry, few if any fry
      survive to adulthood in this tank because of the way
      it is set up.


       Over the last few years, the Alfaro cultratus has been one of the best selling fish offered, but also the one that generates
      the most questions regarding its breeding. The young are particularly small when compared to other livebearers- thin,
      translucent and about 6mm long. They are eagerly eaten by other fish, and often are preyed upon by adults of their own

      As a result, some consider these to be tricky to breed, and they are not. Like most fish, they will breed easily enough when
      healthy and well fed with good water quality, but without following a few practices, your efforts to save and raise up the fry
      may be met without success.

      When breeding livebearers, so that no fry are lost or eaten, how to set up the tank and manage the harvesting of fry will have
      the greatest odds of success when using the methods described here. The process explained will work for any livebearers that
      are prone to eat their fry, or with species where the fry are known to be fragile due to small size or water quality

      By using this process, you will not only be able to breed the Alfaros, but any other livebearer species prone to eating their
      fry, such as the Gambusias, Brachyrhaphis, poeciliids, goodeids, etc..

      Separating the female by placing her in a net breeder will not work for the Alfaros, as with many other livebearer species,
      as the females are too large, while the fry are too small and numerous to survive long in a confined space with a potentially
      hungry adult.

      Fry are often lost, females do not do well in small breeders, and neither the fry or the adults do well in the temporary
      crowded conditions we create in an effort to save the fry. Also, the females of the cultratus are not marked as clearly
      gravid as with many other species- their gravid spot is not as pronounced, and what may appear to be a female about to
      drop any time may go for weeks before the fry are born.

      The Alfaro cultratus gestation period is similar to other commonly kept poeciliid livebearers, at about 4-5 weeks, and the
      females will become very plump. However, they do not possess the dark gravid spot we are used to seeing in Guppies, Swordtails
      and Platies. A dark outlining of the abdominal cavity may appear, and it is possible to identify gravid females easily enough,
      but the signs you are looking for are more subtle than they are with other livebearers.


    These females are about to pop, what you
  see here is as dark a gravid spot as this species
  will show.


     A slightly more gravid female. The dark spot
      behind her abdomen is not yet clearly seen.

   A. cultratus pair. Note the male's stick like
   gonopodium. This female may be slightly gravid.

       Because the fry are so small and the batches can be fairly large, I use only 10, 15 or 20 gallon breeder tanks to breed the
      alfaros. I have tried larger homemade breeders that hang inside a tank, with some success, but assume a few of the fry were
      eaten, and more importantly, the adult females did not do well confined as they were. They are a schooling fish accustomed to
      skimming the tank just below the surface looking for food. Being held nearly stationary for up to 2-3 weeks, in a container
      with gradually deteriorating water quality, as uneaten food accumulated, was not ideal for the females or the fragile fry.

      Using water from the home tank that the female had come from to season the new tank, a bare bottom 10 gallon tank is filled with
      Java Moss or Java Fern. Najas grass (Guppy grass) will also work, even the fake plastic home décor stuff that looks like Java
      moss should work, but I try to avoid harder plastic stuff in crowded conditions as the adult fish could scrape and harm
      themselves. A firm fitting top should be used with low to moderate light for 12-14 hrs per day. Alfaro adults, when in a new
      environment, are jumpers, but this is not a problem with the new fry. Once there are no adults in the breeding tank it is not
      necessary to keep the tank covered.

   The breeder tank setup, using Java Fern. The
   bottom is open enough that the female can
   navigate the tank, but plants are at the top
   to protect fry after they first hatch and go to
   the surface. The female at the left produced
   62 fry in this setup. The female needs to be
   removed within a couple hours of when she
   gives birth.
              Newly born A. cultratus fry.
         Gravid female used for this drop of fry.

       A sponge filter that will not suck up fry should be used, run with moderate aeration, and a dependable heater should maintain
      the temperature at 74-77 degrees. The tank should be placed in a quiet location where disturbances are minimal.

      The female Alfaro, when in a tank by herself will tend to hide and stay near the bottom of the tank, positioning herself as
      best she can within the Java moss so she cannot be seen.

      How you place the Java moss or fern in the tank is important. You want there to be enough plant material in the tank such that 
      the female can get around, throughout most of the tank, swimming fairly easily from one side to the other. At the same time, 
      you want the Java moss to rest within the lower portion of the tank so that there is a space of at least a half inch of open 
      space at the surface.

      The way I feed the female at this time is to sink some flake food into a little water, and squirt the water/ food mix with a
      turkey baster in front of her. I make an effort to feed only high quality flake at this time. I assume – and I may be mistaken-
      that getting the female into the habit of eating live food, or even frozen brine shrimp or bloodworms could encourage the female
      to eat her young when they appear. So to be “better safe than sorry”, I try not to feed anything similar in size or movement to
      the new fry at this time.

      Females of most livebearers will give birth in the morning, generally just as the sun comes up, and are usually done by noon.
      When the new cultratus fry are born, the fry will go immediately to the surface for the first few hours, hovering above the
      Java Moss. Fortunately, the females rarely venture to those parts of the tank when by themselves in the heavily planted tank.
      Each day that the female is in the breeding tank I will look for fry at about 8-9 am, then again just before noon. If even a
      single fry is seen, the fry are all already born or will be so within an hour, and the female will need to be pulled. When the
      birthing starts, it doesn’t stop until all young are born. There are a few exceptions to this – the Heterandria Formosa, for
      example, will drop a couple young per day for up to a week-but most of the livebearers we keep will release all of their young
      within about an hour to 90 minutes,including the cultratus.

      Using this method you can actually breed more than one female at a time- I will often put up to 4 females at a time into this
      10 gallon tank. If there are other females in the tank, and fry are seen swimming at the surface, I will net them out into a
      tank of their own as soon as they are seen. Once all fry are removed, I will then remove the females that appear to have dropped
      their brood. Some fry are lost with this method, but enough are saved to make the effort worthwhile.

      One practice mentioned in other articles that works exceptionally well for many of the livebearers is to have a female drop her
      brood, pull her, then let the fry age for a week or two, and then put a number of gravid females into the tank. The previous batch
      will serve as dither fish to keep the new batch from being eaten as the majority of the fry seen will be larger than what the
      female wants to ingest, but the older fry are too small to be interested in eating the new fry themselves.


    This is the tank after the female was removed,
    and the fry were grown out for about a month
    before being split up into other tanks to grow
    grow out into adulthood.

           Once the female is pulled, gently remove the majority of the plants, leaving the fry so they can be easily seen. They can be
          fed vinegar eels or microworms, but will take newly hatched brine shrimp or even finely ground dry food right away. I recommend
          hatching a few batches of brine shrimp ahead of time, filtering out the shrimp and putting them into freshwater. The
          shrimp are then frozen into ice cube trays, and the new fry will take the frozen BBS from the melting ice cube dropped into the
          tank. When frozen soon after hatching, the nutritional difference from live is negligible, and the fry are guaranteed fresh
          shrimp with each feeding. When fed 2x per day they will grow quickly with water changes of about 20% done 3-4x weekly, for
          the first 2-3 weeks. As well, quick 50% water changes may be necessary if any cloudiness is witnessed from the deteriorating
          brine shrimp feedings. At about a month to 6 weeks old the young will be large enough to combine with the adults, and will
          sex out relatively early at 3-4 months. In the the lower body profile of the males, gonopodium development can start to be
          seen at 2-3 months.

          The fry do grow out fairly uniformly, and there is no concern that the faster growing, larger fry will pick on any small
          broodmates. The Alfaro is a very peaceful, good community fish that generally does well with its own kind and other species.
          As also occurs with some species, the Alfaros when first bred in new water conditions will sometimes produce batches that
          are skewed toward one sex or the other. I have kept, removed and reintroduced the Alfaros to my fishroom, and have had this
          sex ratio issue come up on 3 separate occasions. Twice I was producing mostly females, once I was producing mostly males. In
          all 3 cases, by the 2nd generation the sex ratios evened out to close to a 50/50 ratio into the second generation.

          Speculation exists as to what causes this, and papers have been written pointing to temperature in some species pushing the
          sex ratio to one direction or another. Warmer temperatures are generally considered to produce more females, cooler temps in
          the species studied produced more males. pH is also an issue with some species, and with at least one swordtail (The Xiph.
          helleri Rio Otapas), a sex ratio of more males than females issue was corrected by feeding a finely powdered food to the fry
          during their first month. The reason that works is not clear, but may point to a slight difference in mouth structure that
          keeps the females from being able to eat a larger flake normally, as the male fry do.

          Complicating matters is that the temperature of the current generation may influence future sex ratios. The Xiph. Helleri,
          for example, is routinely kept warmer in home aquariums that the species experiences in the wild. This is because
          temperatures recommended by pet stores and hobbyist information often recommend temperatures in the upper 70s to low 80s.
          Yet in the wild they are better accustomed to temperatures that are much cooler – 68 – 75 degrees, with 72-74 being about
          their ideal temperature. Just as pet shop swords kept in the high 70s temps will likely become ill with ich when abruptly
          kept at 72 degrees, a line of fish reproducing at near 50/50 sex ratios at 78 degrees may produce an overabundance of males
          at first when kept closer to their natural temperatures.

          In that case, just as the gradual acclimation over 2 generations would return the Alfaros to a normal 50/50 sex ratio,
          the swords may take a generation or two to return to normal sex ratios when exposed to routine cooler temperatures that
          can initially skew the sex ratio.

          Reasons such as this explains advice or criticism from some looking for a quick explanation to a problem, who often blame
          the fishkeeper’s inexperience. In fact, the understanding of acclimation issues over many generations is not fully understood.
          Even today much is still being learned, lending an air of both uncertainty and surprise to the keeping of these fish.

          When raising the fry, a few issues need to be considered. The Alfaros being bred in 10 gallon aquariums producing
          30-50 fry will need to be split up into smaller groups and raised separately, or moved into a larger tank as soon as
          one is available. Without doing this, the growth of any particular fry will be stunted as they will not have appropriate
          access to the food, water quality and simple space needed to grow. Until they are large enough to move to other tanks easily,
          the beneficial effects of proper access to food, water quality and to some extent, space, can be duplicated through frequent
          smaller feedings, and large – 40%+ routine water changes. However, you are just buying time, and getting them into an
          appropriate sized tank given the tank density is essential if they are to grow into fish that are healthy and full sized.

          If you are looking to develop the line or exploit the occasional mutation, raising every fry up is essential. New fry
          carrying a genetic anomaly you may be interested in will likely be undersized, weaker or not as fit to compete with its
          bretheren for food and other resources. Watching the fry closely is important, and when an albino or leucistic fish is spotted,
          you must move it to a net breeder or smaller container of its own to raise up separately if it is to survive and possibly be
          used to start a new line in the future.

         The Alfaro cultratus line carried here with often throw leucistic fish – a yellow or amber body, with little to no black
          coloration, and eyes that are not blue. With these Alfaros, the leucistic form is an overall amber color (as opposed to the
          all yellow body with a blue sheen), and smaller silver, rather than blue eyes. Not an unattractive fish, attempts to breed
          the leucistics with one another were unsuccessful, as they have not been fertile. I am sure with further attempts, that morph
          of the fish could be developed and bred. I have not had an albino with this species.

          An albino of this fish would be very interesting and attractive, and since they do not seem to be produced spontaneously
          as is the case with many of the swords, finding a fertile pair of leucistic fish may begin to produce albinos – I have
          found that albinos can be produced this way with other species.

          Hopefully if I do not find the tank space, a customer will decide to exploit these leucistic fish that occur fairly regularly.
          Here are some pics of those fish:



   These are the leucistic fish thrown by the line
    kept here. They have colony bred here for over
   10 years and they continue to appear, but are only
    about 1% of fish born. They are almost always
    males. Females have occurred, and multiple
    attempts to breed them did not result in any
    fry. Compare to normal colored fish on lower




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