Question: why some fry bigger than others

Continuing question/answer time, here's another follow up.

> why are some of my fry is bigger than others, and some are too small.
> It seems the smallest fry wont grow at all.they also show slower growing rate.
> is there any related to the food?

If you've done spawning a number of times, you notice that the above problem seems to reoccur frequently. There are a number reasons for it, but it boils down to 2 things:

1. genetic - you never know what the history of your fish. This is hardly likely, since if it was genetic, you would expect most if not all of the fry to be small
2. environment - the most likely cause

Genetic can play a role in making stunt fish, however we dont have much knowledge in this field as yet to say anything conclusive. One thing that we notice though, many extreme feathertail/rosetail will have smaller body compared to their siblings. It seems that the gene that produces excessive branching on the rays also affect other cells on the body, making them slightly smaller.

Let's discuss the 2nd reasoning. Basically, your fry develop on slightly different pace. Assuming you always provide ample food for all of them, there will always be some slow learners in the pool. (note that if you don't provide enough food for the fry, it is pretty obvious that some of them will starve and grow slow).

Feeding experience is important to the fry. Getting them used to the competition of fighting for the food and eating vigorously will ensure that most of your fry develop fast and large. The negative effect of that would be some "shy" fry will be stunt when they see others being too aggressive. If this is continued for longer period, there is no way for you to help those stunt fry to grow any larger.

It is therefore important for you to monitor the fry and separate the big ones to another tank as soon as possible. Usually this happens on 3rd week or earlier (or otherwise you're too late!) Removal of the big ones from the rest of the brood will relieve the pressure for those possible-to-be-stunt fry. If you do this early, the rest of the normal-sized-not-so-big fry will grow and prevent/reduce the number of your possible stunt fry.

What we noticed is that stunt fry will result in a number of conditions:

• tank is too big, fry scattered everywhere, difficult to find food
• tank is too small, fry bumping to each other, some bumps harder than others
• wrong food for wrong stomach - vinegar eels or microworms are not as nutritious and can't be the regular food
• dirty/smelly tank full of gunk
• extreme tank temperature (too cold/hot) rendering your fry to be inactive

As you noted, once they are stunt, it is very difficult to get them un-stunt. You can feed them lots of food, they wont grow any bigger! In fact, we have been experimenting with some of these dwarf to see if there is genetic involved - similar to the theory of giant gene being unstable we suspect dwarf gene exists too and producing semi-random occurrences. We would like to see the outcome of crossing 2 stunt fish (provided we can identify if they are male or female to begin with!)

The rate of stunt-ness varies. Sometimes you get an extreme rate where majority of your fry to be small. Again, assuming genetic is not playing any role, we would suggest you change the way you feed your fry :) In our case, we have around 3 to 10 fry stunt in a 100+ fry, and this is totally acceptable in our dictionary anyway... Most of the time, you wont care about the stunts, just let them be :) So long they're happy...