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Breeding halfbeaks This diary follows one particular brood of halfbeaks; I've had subsequent broods since beginning this diary, and for the most part mixing fry of different ages doesn't seem to be a problem. They all coexist without any obvious aggression or cannibalism. Freshwater halfbeaks are typically ovoviviparous or viviparous, though some brackish water species are oviparous like marine halfbeaks. Nomorhamphus are viviparous. Males perform a fluttering display in front of females before mating, and the females carry the embryos for at least six weeks before producing a clutch of relatively large fry. My experience is that the fry are durable and agile, and appear to be well able to escape predation in a moderately stocked community tank provided there is plenty of cover, specifically floating plants. Because I seem to have had at least two species of Nomorhamphus in my tank, it's possible that hybridsation could have occured between species. Regardless of the exact species involved, at some point in mid-July, a female Nomorhamphus became pregnant. Over the next couple of months she became visibly much fatter, and in the days leading up to the birth of her brood, it was pretty obvious she was pregnant. A large, dark ‘gravid spot’ appeared just in front of the anal fin during the last 2-3 weeks of gestation; after she gave birth to the fry, the spot became much less obvious. September 3rd 2005 - 14 fry, length ~13 mm Fourteen babies suddenly appeared amongst the floating Ceratophyllum demersum. These were gathered into a clip-on breeding trap. The main problem was finding foods they would eat; the books all suggested baby brine shrimp and powdered flake, but neither of these were accepted. Pond water full of Daphnia and other small creatures was appreciated though, as were frozen black mosquito larvae and frozen lobster eggs. Large Daphnia were spat out though, and only the very small ones seem to be swallowed. Tiny crustaceans like Cyclops would probably be a better bet. September 8th 2005 - 11 fry, length ~15 mm The baby fish are transferred to their own aquarium, a 50 cm tank with an air-powered bubble-up box filter. My original idea was to move them after a couple of weeks, but after one of my plecs, probably the Ancistrus, had abraded a hole in the netting, removing the halfbeak fry became a priority. Several baby fish escaped, and while I rescued most of them, three vanished without trace, presumably getting eaten by one of the other fish in the aquarium. September 9th 2005 - 13 fry (it seems I miscounted!), length ~17 mm By the seventh day, the fry are large enough to tackle all but the largest Daphnia. Some fish were also snapping at live midge larvae, but midge pupae were too big for them to handle. No signs of sexual dimorphism are apparent yet, both sexes seemingly having identical anal fins. Red spots are present on the beaks of several fish, but these may be bruises from swimming into the glass. The aquarium is placed alongside a window so that it gets illuminated naturally with sunlight instead of an aquarium light; this should prevent the fish being surprised by an aquarium light suddenly being switched on or off. September 10th 2005 - 13 fry, length ~18 mm Now a week old, the fry are readily taking Daphnia, lobster eggs, and small midge larvae. They are also starting to exhibit a certain amount of personality, coming to the front of the tank when they think they are about to be fed. As the close-up picture below shows, they really are nicely formed miniatures of their parents. September 12th 2005 - 13 fry, length ~20 mm The baby halfbeaks are now much more adaptable as far as food goes. They are happily eating Daphnia of all sizes, as well as frozen marine plankton, frozen bloodworms, and tiny pieces of flake food. September 13th 2005 - 13 fry, length ~22 mm Halfbeaks still doing well. One appears to have a swim bladder problem and is not able to hold its position in the water properly, but otherwise appears to be healthy. No signs of sexual differentiation yet. They are now feeding mostly on frozen foods, but as yet show no interest in flake food. September 14th 2005 - 14 fry, length ~23 mm While feeding the fish in my main aquarium, I found another baby halfbeak, presumably the one I lost a few days earlier. It has grown a bit, but is quite a bit smaller than the ones I've been raising separately. This suggests that while halfbeak fry are pretty good at escaping predation in a community tank, they do much better if fed on live foods in their own tank. Still, I'm amazed it has managed to survive in a tank containing six adult halfbeaks, a South American puffer, and numerous other, much larger fish. For the first time, traces of red are starting to become apparent on the fins of the fry, similar to those of adult Nomorhamphus ebrardtii. September 23rd 2005 - 14 fry, length ~29 mm All the fish continue to feed and grow well, and some individuals are very obviously beginning to develop a beak. Daphnia is still a favourite food, with lobster eggs and marine plankton being less popular but still accepted. Flake food is only grudgingly taken. September 29th 2005 - 14 fry, length ~30 mm Many of the fry are not obviously males or females. The andropodium (or modified anal fin) of the males are clearly developed, and red and black markings are starting to appear on the dorsal and anal fins. The tip of the beaks of some fish are also turning red. October 15th 2005 - 14 fry, length ~35 mm The fry continue to grow well, and now readily take frozen foods such as whole bloodworms. There is no real aggression between males, but sometimes fish will chase one another for a few moments. October 22nd 2005 - 13 fry, length ~35-40 mm Most of the young fish are now large enough to be moved from the breeding tank to the main tank. I lost one in the process, and found its body the next morning, but all the others seem to have adapted to their new home successfully. The adult halfbeaks don't show any ill-intentioned interest in their offspring, and in fact usually school with them quite peacefully. There are some obvious signs of fighting though, suggesting that the young fish are now building up the 'pecking order' within their group rather more forecefully than before. In conclusion, it seems to take about a month and a half for halfbeaks to grow to a size where they are suitable for inclusion in a community tank. At around 35 to 40 mm in length, they're comparable in size to adult neon tetras, if a bit more slender. November 6th 2005 - 11 fry, length ~42 mm Having lost a couple of the young halfbeaks, presumably through aggression from the adults, I returned the fish to the small aquarium. They continue to do grow well. The males are colouring up very nicely, with obvious blue patches on their fins and the distinctive curly beak typical of Nomorhamphus liemi liemi. November 25th 2005 - 11 fry, length ~45 mm Returned the juvenile halfbeaks to the main aquarium, and this time no problems. Quite the reverse in fact: all the fish are schooling nicely, and aggression between the adult males has been reduced somewhat, presumably by some crowding effect. It seems quite likely that if you have the space, the larger the school of halfbeaks, the more peaceful they will be. Summary
Growth rate Below is a plot of total length against age, showing the growth rate of the halfbeaks. What is interesting that at about the time when the fry become able to feed on Daphnia rather than really tiny live foods, their growth rate increases considerably. Once they are 45-50 mm in length, they can be returned to the community tank.
(Click to enlarge) |
Male Nomorhamphus liemi displaying in front of a female
Fry about one week old
Fry aged about six weeks
Dermogenys fry about a week old tackling a defrosted bloodworm
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