OK a brief intro. I have been keeping coldwater fish with great success for over 20 years (I can breed Koi which live for at least 10 years, will let you know when the die!). I work in the Science department of a school and was asked last year to set up three tanks for the department, two of which are tropical. I read two books (one old, one new) on tropical aquaria to try to get a good start as I was previously only familiar with goldfish and koi.
The problem tank is a 60 litre one, pH of the water is 6.8, no measurable ammonia, nitrates or nitrites. In the lab we have measuring equipment far more sensitive than the shop we bought the fish from. Tank temperature is usually 25 degrees Centirgrade. Originally (April 2008) I introduced three marble mollies (2F, 1M) into the tank and four neon tetras. This month I added two angel fish. Good two inches of gravel, three different species of plant/weed, internal filter which is cleaned every 7-10 days. Half water change performed roughly every 2-3 weeks. Fed on either Aquarian Tropical Fish Flakes or King British Tropical Fish Flakes. They also tend to nip at the plants.
The problem is with the offspring of the mollies. I expect a lot of inbreeding goes on before we even buy our fish, so my original 3 fish may well have been siblings to begin with. All the offspring seem to start off fine. Some later develop what can only be described as a bent tail. They find it impossible to swim in a controlled manner and may spiral about corkscrew fashion. At this point the usually friendly adult fish begin to nip at them, which causes the "sick" fish to dart about like they are mad.
I've tried isolating the "sick" fish into separate smaller tank, where they seem much less stressed but don't seem to eat. The affected fish (about 20% of the total offspring) have all died to date. Just yesterday I separated two more fish from the main tank, and at least they seem to feed. The larger of these only developed this illness when he was already 2/3 the size of the adults, and he bizarrely stands on his tail much of the time. Balance/equilibrium problems seem to affect some of the sick fishes, and two appear to have had one bulbous eye. I recall one with a head too big for its body
The three original adult mollies seem fine, as are the four tetra and (so far) the angel fish. I am theorising genetic defects, but why would they appear some weeks/months after birth?
Has anyone seen this before? Does it ring any bells?
The problem tank is a 60 litre one, pH of the water is 6.8, no measurable ammonia, nitrates or nitrites. In the lab we have measuring equipment far more sensitive than the shop we bought the fish from. Tank temperature is usually 25 degrees Centirgrade. Originally (April 2008) I introduced three marble mollies (2F, 1M) into the tank and four neon tetras. This month I added two angel fish. Good two inches of gravel, three different species of plant/weed, internal filter which is cleaned every 7-10 days. Half water change performed roughly every 2-3 weeks. Fed on either Aquarian Tropical Fish Flakes or King British Tropical Fish Flakes. They also tend to nip at the plants.
The problem is with the offspring of the mollies. I expect a lot of inbreeding goes on before we even buy our fish, so my original 3 fish may well have been siblings to begin with. All the offspring seem to start off fine. Some later develop what can only be described as a bent tail. They find it impossible to swim in a controlled manner and may spiral about corkscrew fashion. At this point the usually friendly adult fish begin to nip at them, which causes the "sick" fish to dart about like they are mad.
I've tried isolating the "sick" fish into separate smaller tank, where they seem much less stressed but don't seem to eat. The affected fish (about 20% of the total offspring) have all died to date. Just yesterday I separated two more fish from the main tank, and at least they seem to feed. The larger of these only developed this illness when he was already 2/3 the size of the adults, and he bizarrely stands on his tail much of the time. Balance/equilibrium problems seem to affect some of the sick fishes, and two appear to have had one bulbous eye. I recall one with a head too big for its body
The three original adult mollies seem fine, as are the four tetra and (so far) the angel fish. I am theorising genetic defects, but why would they appear some weeks/months after birth?
Has anyone seen this before? Does it ring any bells?
