Hello friends:
Since I moved the fries into my warmed garage for about 3 months ago I have not paid so much attention to them. Half of them have been doing very well, while the other half have died mysteriously. The most usual way to die is that they became thinner and thinner, and then one day they were floating around dead.
I have not cared to ask why. Please correct me if I am wrong, but I think that the most individual fish fries have poor genes, as no fish species need so many fries with perfect genes to survive. They produce so many fries, and it is sufficient that some pro cent of them have good genes. Nature does not give any species the luxury of many off-springs with perfect genes. Those of my fries that died must have weak genes. That is true even for H. sapiens, therefore we have so many natural miscarriages.
The surviving fries have been doing very well in the last 1 month. Until for about 10 days ago one of the fries started to float with belly up. My intuition is that it has got constipation, because it had not been eating for some days, and its belly was swollen. I did not mind if it would die, so I just let it be and waited for its death.
Today I realized that I had not seen it for some days. I worried that it had been dead and rotting somewhere in the aquarium, so I made a huge water change. To my surprise it is still alive, with a bent body and unbalanced way to swim. It had a nice body before.
And I also noticed that my biggest fry which I after all somehow appreciate seems to have the same problem the above-mentioned fry had for some 10 days ago: Swollen belly, havenīt had food for 2-3 days, and much less agile as it used to be, though not yet floating with belly up.
All other fries are just fine.
They have been in an aquarium, and the water is from the tank I have for my bigger koi (not fresh water due to the position of the water outlet). The water is changed every 1-2 days, 50-80% each time.
I checked the water parameters which have been similar every time I do the checking:
Ammonia: 0, nitrite: 0.2 ppm (the water contains 0.1 % NaCl), nitrate: 40 ppm, pH: 8.0, temperature: 18 centigrade.
The biofilter consists of a sponge filter, a lot of plastic plants and gravels on the bottom.
When I change water I siphon out the most debris among the gravel.
I have been feeding them with sinking pellets for sturgeon and flakes for tropic fish.
I just wonder if someone could explain what disease the latest 2 fries have got. Thank you!
The video shows the first fry today when I have found it: