Breeding for traits other than colour or shap

[Mattyd123]

Hi There, im pretty novice to fish breeding but ive done my fair share of breeding ricefish, zebra danios, CPD’s and have some other fish growing out for future projects. Im curious if anyone has bred for things such as faster fry growth rates? Especially with my ricefish fry ive noticed there’s a huge disparity in the size and growth rates of fry 

has anyone tried say pulling the top 5 or however many fastest growing fry and then breeding them together and then repeating for a few generations? And if so what were the results? 
I can imagine there could be problems with fish growing faster than they are “meant” too but there is probably also a sweet spot? 
not really planning on experimenting myself as i have limited space currently but the idea is interesting too me. 

[Tlindsey]

On 3/9/2024 at 7:04 PM, Mattyd123 said:

Hi There, im pretty novice to fish breeding but ive done my fair share of breeding ricefish, zebra danios, CPD’s and have some other fish growing out for future projects. Im curious if anyone has bred for things such as faster fry growth rates? Especially with my ricefish fry ive noticed there’s a huge disparity in the size and growth rates of fry 

has anyone tried say pulling the top 5 or however many fastest growing fry and then breeding them together and then repeating for a few generations? And if so what were the results? 
I can imagine there could be problems with fish growing faster than they are “meant” too but there is probably also a sweet spot? 
not really planning on experimenting myself as i have limited space currently but the idea is interesting too me. 

Not experienced with those species but proper foods and water changes to remove growth inhibiting hormones, Nitrate for cichlid fry growth. @Mattyd123

[T. Payne]

When you are raising fish you will always have "runners" which are a term for the few quicker growing fry. If space allows, it is always best to remove them and then you will see another group take off and do the same. I don't believe it is genetic, more of a survival of the fittest from if they were wild.

[Wheelfish]

On 3/10/2024 at 2:49 PM, T. Payne said:

When you are raising fish you will always have "runners" which are a term for the few quicker growing fry. If space allows, it is always best to remove them and then you will see another group take off and do the same. I don't believe it is genetic, more of a survival of the fittest from if they were wild.

Sounds like a good way to strengthen the line

[WhitecloudDynasty]

On 3/9/2024 at 7:04 PM, Mattyd123 said:

Hi There, im pretty novice to fish breeding but ive done my fair share of breeding ricefish, zebra danios, CPD’s and have some other fish growing out for future projects. Im curious if anyone has bred for things such as faster fry growth rates? Especially with my ricefish fry ive noticed there’s a huge disparity in the size and growth rates of fry 

has anyone tried say pulling the top 5 or however many fastest growing fry and then breeding them together and then repeating for a few generations? And if so what were the results? 
I can imagine there could be problems with fish growing faster than they are “meant” too but there is probably also a sweet spot? 
not really planning on experimenting myself as i have limited space currently but the idea is interesting too me. 

Fastest fry growth rate..itll be hard to do if you use judge the runner. Since not all fry hatched the same time and not all fry get the same amount of feed ect... need to make it as fair as possible.

I would Judge their growth rate as a group. I like a group of fry that are consistently the same size. Feeding alot of bbs will cause alot of runner atleast in my experience. I recommend finding a system in waterchange/feeding /food/temperature that work very well, stick to it, then just breed for a bigger fish. 

[TOtrees]

Yes you probably could breed for faster fry growth, on the assumption that there is/may be some genetic component to it. But there are a lot of other things that you'll also breed for at the same time, unintentionally. The challenge in selecting (and then fixing) a trait that you want is avoiding things you don't. Your runners don't just grow faster as fry, they'll keep going faster through all life stages. Ie shorter-lived. Also, accelerated growth likely comes with other costs, eg less energy/calories/resources to put into coloration, immune system, etc. 

Let me make an attempt at a discussion/justification (coming at this with evolutionary biology degree)...

I like the term "runners" used above it's fairly clear what it implies. From a population genetics point of view, a runner would be an individual that grows and matures faster than other individuals. If there was a clear and consistent advantage to this (in the wild), eventually after a number of generations all the individuals would be runners, through natural selection. But in reality being a runner isn't just a benefit, there is also a cost. Most readers here will be familiar with the idea that if you keep a given species fish at the upper end of its temp range, it will "live fast and die young". Being cold-blooded, this causes their biological clock (aka metabolism, over the life-long time range) to run faster, and expire sooner. Runners just have a genetic dial on the growth/aging rate, in addition to the environmental one (it would be more accurate to say their genetic dial has a different setting).

The reason (a reason) runners exist is that sometimes it's an advantage, but not always. It might also be that the trait is a legacy from distant ancestors, that isn't currently a plus or minus, but it's just variability that has continued to exist in the population. What would be the relative advantage of not being a runner, over being a runner? Longer life and larger final size (even if these come with slower growth rate) = greater contribution to the overall number of individuals in successive generations. 

Having runner genes in some progeny could be beneficial in transient or unpredictable climates. It can also be a population-level insurance policy. Let's say you breed in puddles, or seasonally flooded rivers (anyone say killis, or black water tetras?). Most years, say 95 out of a hundred, the standard or typical approach works, because the weather and rainfall and drying times are within expected norms. Most of the fish can condition, breed, lay, hatch, and grow and maybe even breed again within the seasonal window. But what if a 1 in 20 or 1 in 100 year dry event causes your puddle or river or whatever to dry up before the generational cycle is complete? Here killis make a great example, because this literally describes some of their life cycles, eg all the adults die, and the only survivors are eggs. What if the adults didn't have time to lay those eggs? The entire population will die, in one cycle. If each generation has a few runners, even if they don't do as well as their normal siblings under normal conditions, guess who the survivors will be in those short seasons? It's the runners. But those runners won't make 100% runner babies... some of their offspring would be runners and some would be 'normal'. After a year or two when things settle back down, the runners no longer have the reproductive advantage, and the "normies" are the one who again provide the greater contribution to the next generation(s), due to having more time to grow, feed, fatten, breed and make more eggs. 

Back to your question... So,