Retarded Development Of Danio Fry

[cs091]

Hi everyone,

I've just come back from 2 weeks on holiday and found my danio fry have survived being cared for by my mother in law. (What would we do without them? She's great, even if she knows nothing about fish.)

The adults have been out of that tank - which was my only tank up til then - for nearly two months.

There are about 4 fry which are now proper little fish about 1.5cm long.

There are however, about 3 others which are still very small (0.5cm) and 'fry-like'. Are these runts which will never mature, or could they be from eggs which were laid sometime after the bigger ones, just before the adults were moved, or do some fry develop slower than others?

I'm just contemplating moving the bigger ones into the new, large tank with their parents and wondering what to do with the late developers? Give them a few more weeks in the little tank (which I want to use for quarentining some new fish - can't wait ), get a fry net and put them in the main tank in that or just put them in the main tank and let nature take its course? I don't want to condem them to death but if they are not going to survive anyway that may be the kindest thing to do. At least the end would be quick and natural.

Does anyone have any views?

CS

 

[Tokis-Phoenix]

What have you been feeding the fry, what is the temp in the tank and how many gallons is it? Danios prefer cooler tropical temps, particually when they are growing, and having a larger enough tank for raising these fry is important- if the filtration is also not very powerful, the danio fry may also not grow very quickly as they are active fish and need a lot of excercise in tanks to thrive and grow well.
Diet is of course also very important- as the fry grow their needs change as far as diet is concerned, what have you been feeding them during the time you have been raising them? How old are they now?

 

[cs091]

These fry have a strange, if lucky, background. I got a new tank in mid august and moved the adult fish into it with the filter media to clone the new filter. I left the old tank - 10 uk gal, 60x30x30cm - until I had more time to strip it down.

After about two weeks I went to do this and realised there were fry in it. They had been at about 22C as we were having a hot spell. I then started feeding them tetra-baby powder twice a day and restarted the heater at 27C as I read danio fry need warmer water than the adults. There is still no filter in the tank, as I needed it for the adult fish, but the readings have been at ammonia = 0, nitrite = 0 since I started testing - when I realised the fry were there. Would the lack of filter damage the fry permanently?

Mid september I went on holiday for 2 weeks and my mother in law came over twice a week to feed the fish, including these fry with tetra-baby.

I expect the most recent eggs were layed mid august but the larger fry may have avoided adult attention for much longer than that.

I can probably move the filter media back now if necessary, but I would rather mover the fry if the little ones aren't going to thrive anyway. I would think the larger ones would be at a safe size anyway.


Thanks for your help.

CS

 

[millym]

hi
although we've not raised danios we have raised swordie & mollie babies & have found the size difference between once single 'batch' is amazing sometimes. with our last bunch of swordie babies (over 50) some werer still teeny specs whilst others were nearly 1 & 1/2 cm long & males had developed little swords. our lfs owner told me that apparently fry release hormones in a tank which allows the strongest to get bigger & bigger whilst inhibiting the growth of the smaller fry keeping them small if you like - i guess the survival of the biggest & fittest. he said to get fry to develop at a same rate you need to do frequent like daily small water changes to dilute out the hormone or whatever is released by the boss(biggest) fry in a batch. i havent been able to check out the validity of his observations but it makes sense to me . although if your fry are in a big tank this probably isnt so relevant or a factor in the size difference. also i suppose just like humans some folks are just smaller. make sure they get a varied diet like brine shrimp as well as powdered/crushed flake to give them the best chance of getting strong.
good luck

 

[cs091]

Thanks Millym,
This could very well be the answer, as I haven't been able to do many water changes. First 'cause I didn't know the fry were there, then with my hols.

I'll move the 'BIG FOUR' out and do a decent water change and see what happens.

CS