Does egg production/spawning stunt growth? Not that I've ever seen. There would have to be other factors, whether health, nutrition, water quality, etc.
Does egg production/spawning slow growth? In my personal experience, not so much, perhaps somewhat with some fish more than others, but as an end result of eventual size of the fish, not really-- just my experience. Is it possible to start some breeding at such a young age and keep them so unnaturally busy breeding that it can affect their growth to an unnatural extent? I'd say yes, but this doesn't mean breeding automatically or inevitably inhibits a female's growth.
But this is not as simple as the comments I've seen in most discussions on it. In fact, it's not simple at all. Lets start with the fact that there have been at least a few studies done on the effects of gender segregation on growth, with results differing between species. Some species yes (in some studies significantly), some species no. I have no idea how many studies have ever been done in total or on how many species, so I'm just reporting that I've done some reading on this and that I've seen differing conclusions with different fish. So part of the answer would seem to be this can vary between species. Consider just one (simplistic) reason why this could be true. It should be obvious that the energy costs of reproduction differ between species with differing reproduction and parental care strategies. This isn't the only factor, as the biology of different species differs in other ways.
However, let me point out that in nature there would not normally be such long term gender segregation as to virtually eliminate breeding opportunities. So you might consider whether a breeding female allowed a natural breeding cycle would actually reach their natural size at maturity and one that is not allowed to breed and gets larger is actually anomalously large. In other words, which one is normal and which one isn't?
Other factors I rarely, if ever, see mentioned-- Females of most species will begin producing eggs when their species and individual biology and other cues, including available food, water temperature, photo periods, etc. tell them to. In other words, whether you have them paired up and breeding or not they're producing eggs or, in the case of some hobbyists, are spawning unnoticed by their owner. Otherwise they may be scattering the eggs to be eaten by tankmates, reabsorbing the eggs, or whatever the particular strategy of the species and behavior of the individual dictates. In other words, most fish are producing eggs anyway. It's not as simple as if you're breeding them they're using up energy to produce eggs and if you're not breeding them they're not using energy to produce eggs. Obviously, what happens after that-- egg scatterer, substrate layer, mouthbrooder, strip or let hold, etc. etc. etc. are all variables.
Egg production in many species is relative to available nutrition. Studies have been done on some species and say they regulate egg production to balance with growth, dependent on available food energy. Plenty of food energy available-- plenty of eggs without disrupting growth, not enough food energy available-- lower egg production as nature attempts to balance the need for reproduction with individual survival and environmental conditions.
Interaction and relationship of growth hormones with egg production. This gets technical, and I'm not claiming a high level of expertise here-- again, just something I've done some reading on-- but there are a lot of endocrine system things going on (and, again, studies on this) that affect growth, egg production, etc. In other words, all else being equal, it might be as simple as egg production subtracts energy available for growth by a simple, one to one ratio, but all else is not equal and the complexities of hormone production and the endocrine system come into it.
Whether-- or the extent to which-- the fish in a particular breeding setup are breeding on a similar cycle as they would naturally in the wild or are breeding more (or less) often due to various artificial factors.
Females of some species are naturally smaller than males, other species similar size as males, other species females are larger or chunkier than males. At least ime, this holds true in an aquarium, meaning females needn't be growth disadvantaged compared to nature, just because they're reproducing. In some setups, sure, they may well be or maybe some species are more susceptible to this than others, but it's not a given ime.
This is not to mention variables in the things I sometimes do see mentioned-- feed and nutrition, tank size, stocking densities, tankmates, environmental factors (water parameters and mineral/nutrient content, temperature, photo periods, whether your feeding regimen allows females to stock up energy stores as they would in the wild, whether you or your setup allows females a rest period similar to what they'd get naturally, etc. etc. etc.
Bottom line is this is not as simple as some people think and it's no wonder you can see different opinions on it, because there are a lot of variables, including species and your own particular fishkeeping methods. It's really no wonder at all that you'd get differing observations on this.
My conclusion-- or my opinion if you wish-- is there are simply too many variables and complexities to take what you see in your fish room with your particular fish and all the potential variables of care, feeding, and biology and extrapolate an authoritative rule or natural law from it.
Does egg production/spawning slow growth? In my personal experience, not so much, perhaps somewhat with some fish more than others, but as an end result of eventual size of the fish, not really-- just my experience. Is it possible to start some breeding at such a young age and keep them so unnaturally busy breeding that it can affect their growth to an unnatural extent? I'd say yes, but this doesn't mean breeding automatically or inevitably inhibits a female's growth.
But this is not as simple as the comments I've seen in most discussions on it. In fact, it's not simple at all. Lets start with the fact that there have been at least a few studies done on the effects of gender segregation on growth, with results differing between species. Some species yes (in some studies significantly), some species no. I have no idea how many studies have ever been done in total or on how many species, so I'm just reporting that I've done some reading on this and that I've seen differing conclusions with different fish. So part of the answer would seem to be this can vary between species. Consider just one (simplistic) reason why this could be true. It should be obvious that the energy costs of reproduction differ between species with differing reproduction and parental care strategies. This isn't the only factor, as the biology of different species differs in other ways.
However, let me point out that in nature there would not normally be such long term gender segregation as to virtually eliminate breeding opportunities. So you might consider whether a breeding female allowed a natural breeding cycle would actually reach their natural size at maturity and one that is not allowed to breed and gets larger is actually anomalously large. In other words, which one is normal and which one isn't?
Other factors I rarely, if ever, see mentioned-- Females of most species will begin producing eggs when their species and individual biology and other cues, including available food, water temperature, photo periods, etc. tell them to. In other words, whether you have them paired up and breeding or not they're producing eggs or, in the case of some hobbyists, are spawning unnoticed by their owner. Otherwise they may be scattering the eggs to be eaten by tankmates, reabsorbing the eggs, or whatever the particular strategy of the species and behavior of the individual dictates. In other words, most fish are producing eggs anyway. It's not as simple as if you're breeding them they're using up energy to produce eggs and if you're not breeding them they're not using energy to produce eggs. Obviously, what happens after that-- egg scatterer, substrate layer, mouthbrooder, strip or let hold, etc. etc. etc. are all variables.
Egg production in many species is relative to available nutrition. Studies have been done on some species and say they regulate egg production to balance with growth, dependent on available food energy. Plenty of food energy available-- plenty of eggs without disrupting growth, not enough food energy available-- lower egg production as nature attempts to balance the need for reproduction with individual survival and environmental conditions.
Interaction and relationship of growth hormones with egg production. This gets technical, and I'm not claiming a high level of expertise here-- again, just something I've done some reading on-- but there are a lot of endocrine system things going on (and, again, studies on this) that affect growth, egg production, etc. In other words, all else being equal, it might be as simple as egg production subtracts energy available for growth by a simple, one to one ratio, but all else is not equal and the complexities of hormone production and the endocrine system come into it.
Whether-- or the extent to which-- the fish in a particular breeding setup are breeding on a similar cycle as they would naturally in the wild or are breeding more (or less) often due to various artificial factors.
Females of some species are naturally smaller than males, other species similar size as males, other species females are larger or chunkier than males. At least ime, this holds true in an aquarium, meaning females needn't be growth disadvantaged compared to nature, just because they're reproducing. In some setups, sure, they may well be or maybe some species are more susceptible to this than others, but it's not a given ime.
This is not to mention variables in the things I sometimes do see mentioned-- feed and nutrition, tank size, stocking densities, tankmates, environmental factors (water parameters and mineral/nutrient content, temperature, photo periods, whether your feeding regimen allows females to stock up energy stores as they would in the wild, whether you or your setup allows females a rest period similar to what they'd get naturally, etc. etc. etc.
Bottom line is this is not as simple as some people think and it's no wonder you can see different opinions on it, because there are a lot of variables, including species and your own particular fishkeeping methods. It's really no wonder at all that you'd get differing observations on this.
My conclusion-- or my opinion if you wish-- is there are simply too many variables and complexities to take what you see in your fish room with your particular fish and all the potential variables of care, feeding, and biology and extrapolate an authoritative rule or natural law from it.
